fruit sugar, levulose, D-fructofuranose, D-fructose, D-arabino-hexulose
103 °C, 376 K, 217 °F
, or fruit sugar
, is a simple monosaccharide found in many plants, where it is often linked to glucose forming sucrose. It is one of the three dietary monosaccharides, along with glucose and galactose, that are absorbed directly into the bloodstream during digestion. Fructose was discovered by French chemist Augustin-Pierre Dubrunfaut in 1847. Pure, dry fructose is a very sweet, white, odorless, crystalline solid and is the most water-soluble of all the sugars. From plant sources, fructose is found in honey, tree and vine fruits, flowers, berries, and most root vegetables. In plants, fructose may be present as the monosaccharide or as a molecular component of sucrose, which is a disaccharide.
Commercially, fructose frequently is derived from sugar cane, sugar beets, and corn and there are three commercially important forms. Crystalline fructose is the monosaccharide, dried, ground, and of high purity. The second form, high-fructose corn syrup (HFCS) is a mixture of glucose and fructose as monosaccharides. The third form, sucrose, is a compound with one molecule of glucose covalently linked to one molecule of fructose. All forms of fructose, including fruits and juices, are commonly added to foods and drinks for palatability and taste enhancement, and for browning of some foods, such as baked goods.
About 240,000 tonnes of crystalline fructose are produced annually.
Fructose is a 6-carbon polyhydroxyketone. It is an isomer of glucose; i.e., both have the same molecular formula (C6
) but they differ structurally. Crystalline fructose adopts a cyclic six-membered structure owing to the stability of its hemiketal and internal hydrogen-bonding. This form is formally called D-fructopyranose. In solution, fructose exists as an equilibrium mixture of 70% fructopyranose and about 22% fructofuranose, as well as small amounts of three other forms, including the acyclic structure.
Fructose may be anaerobically fermented by yeast or bacteria. Yeast enzymes convert sugar (glucose, or fructose) to ethanol and carbon dioxide. The carbon dioxide released during fermentation will remain dissolved in water, where it will reach equilibrium with carbonic acid, unless the fermentation chamber is left open to the air. The dissolved carbon dioxide and carbonic acid produce the carbonation in bottle fermented beverages.
Fructose undergoes the Maillard reaction, non-enzymatic browning, with amino acids. Because fructose exists to a greater extent in the open-chain form than does glucose, the initial stages of the Maillard reaction occurs more rapidly than with glucose. Therefore, fructose potentially may contribute to changes in food palatability, as well as other nutritional effects, such as excessive browning, volume and tenderness reduction during cake preparation, and formation of mutagenic compounds.
Fructose readily dehydrates to give hydroxymethylfurfural ("HMF"). This process may in the future be part of a low-cost, carbon-neutral system to produce replacements for petrol and diesel from plants.
The primary reason that fructose is used commercially in foods and beverages, besides its low cost, is its high relative sweetness. It is the sweetest of all naturally occurring carbohydrates. Fructose is generally regarded as being 1.73 times as sweet as sucrose. However, it is the 5-ring form of fructose that is sweeter; the 6-ring form tastes about the same as usual table sugar. Warming fructose leads to formation of the 6-ring form.
The sweetness of fructose is perceived earlier than that of sucrose or glucose, and the taste sensation reaches a peak (higher than that of sucrose) and diminishes more quickly than that of sucrose. Fructose can also enhance other flavors in the system.
Fructose exhibits a sweetness synergy effect when used in combination with other sweeteners. The relative sweetness of fructose blended with sucrose, aspartame, or saccharin is perceived to be greater than the sweetness calculated from individual components.
Fructose has higher solubility than other sugars as well as other sugar alcohols. Fructose is, therefore, difficult to crystallize from an aqueous solution. Sugar mixes containing fructose, such as candies, are softer than those containing other sugars because of the greater solubility of fructose.
Fructose is quicker to absorb moisture and slower to release it to the environment than sucrose, glucose, or other nutritive sweeteners. Fructose is an excellent humectant and retains moisture for a long period of time even at low relative humidity (RH). Therefore, fructose can contribute improved quality, better texture, and longer shelf life to the food products in which it is used.
Fructose has a greater effect on freezing point depression than disaccharides or oligosaccharides, which may protect the integrity of cell walls of fruit by reducing ice crystal formation. However, this characteristic may be undesirable in soft-serve or hard-frozen dairy desserts.
Fructose increases starch viscosity more rapidly and achieves a higher final viscosity than sucrose because fructose lowers the temperature required during gelatinizing of starch, causing a greater final viscosity.
Many artificial sweeteners are not suitable for home-baking, but, with a little adjustment, many traditional recipes can be prepared using fructose.
Natural sources of fructose include fruits, vegetables (including sugar cane), and honey. Fructose is often further concentrated from these sources. The highest dietary sources of fructose, besides pure crystalline fructose, are foods containing table sugar (sucrose), high-fructose corn syrup, agave nectar, honey, molasses, maple syrup, and fruit juices, as these have the highest percentages of fructose (including fructose in sucrose) per serving compared to other common foods and ingredients. Fructose exists in foods either as a free monosaccharide or bound to glucose as sucrose, a disaccharide. Fructose, glucose, and sucrose may all be present in a food; however, different foods will have varying levels of each of these three sugars.
The sugar contents of common fruits and vegetables are presented in Table 1. In general, in foods that contain free fructose, the ratio of fructose to glucose is approximately 1:1; that is, foods with fructose usually contain about an equal amount of free glucose. A value that is above 1 indicates a higher proportion of fructose to glucose, and below 1 a lower proportion. Some fruits have larger proportions of fructose to glucose compared to others. For example, apples and pears contain more than twice as much free fructose as glucose, while for apricots the proportion is less than half as much fructose as glucose.
Apple and pear juices are of particular interest to pediatricians because the high concentrations of free fructose in these juices can cause diarrhea in children. The cells (enterocytes) that line children's small intestines have less affinity for fructose absorption than for glucose and sucrose. Unabsorbed fructose creates higher osmolarity in the small intestine, which draws water into the gastrointestinal tract, resulting in osmotic diarrhea. This phenomenon is discussed in greater detail in the Health Effects section.
Table 1 also shows the amount of sucrose found in common fruits and vegetables. Sugarcane and sugar beet have a high concentration of sucrose, and are used for commercial preparation of pure sucrose. Extracted cane or beet juice is clarified, removing impurities; and concentrated by removing excess water. The end product is 99.9% pure sucrose. Sucrose-containing sugars include common table white granulated sugar and powdered sugar, as well as brown sugar.
All data with a unit of g (gram) are based on 100 g of a food item. The fructose / glucose ratio is calculated by dividing the sum of free fructose plus half sucrose by the sum of free glucose plus half sucrose.
Fructose is also found in the synthetically manufactured sweetener, high-fructose corn syrup (HFCS). Hydrolyzed corn starch is used as the raw material for production of HFCS. Through the enzymatic treatment, glucose molecules are converted into fructose. There are three types of HFCS, each with a different proportion of fructose: HFCS-42, HFCS-55, and HFCS-90. The number for each HFCS corresponds to the percentage of synthesized fructose present in the syrup. HFCS-90 has the highest concentration of fructose, and typically, is used to manufacture HFCS-55; HFCS-55 is used as sweetener in soft drinks, whereas HFCS-42 is used in many processed foods and baked goods.
Data obtained from Kretchmer, N. & Hollenbeck, CB (1991). Sugars and Sweeteners, Boca Raton, FL: CRC Press, Inc. for HFCS, and USDA for fruits and vegetables and the other refined sugars.
Cane and beet sugars have been used as the major sweetener in food manufacturing for centuries. However, with the development of HFCS, a significant shift occurred in the type of sweetener consumption. As seen in Figure 3, this change happened in the 1970s. Contrary to the popular belief, however, with the increase of HFCS consumption, the total fructose intake has not dramatically changed. Granulated sugar is 99.9% pure sucrose, which means that it has equal ratio of fructose to glucose. The most commonly used forms of HFCS, HFCS-42 and HFCS-55, have a roughly equal ratio of fructose to glucose, with minor differences. HFCS has simply replaced sucrose as a sweetener. Therefore, despite the changes in the sweetener consumption, the ratio of glucose to fructose intake has remained relatively constant.
Fructose exists in foods either as a monosaccharide (free fructose) or as a unit of a disaccharide (sucrose). Free fructose is absorbed directly by the intestine. When fructose is consumed in the form of sucrose, it is digested (broken down) and then absorbed as free fructose. As sucrose comes into contact with the membrane of the small intestine, the enzyme sucrase catalyzes the cleavage of sucrose to yield one glucose unit and one fructose unit, which are then each absorbed. After absorption it enters the hepatic portal vein and is directed toward the liver.
The mechanism of fructose absorption in the small intestine is not completely understood. Some evidence suggests active transport, because fructose uptake has been shown to occur against a concentration gradient. However, the majority of research supports the claim that fructose absorption occurs on the mucosal membrane via facilitated transport involving GLUT5 transport proteins. Since the concentration of fructose is higher in the lumen, fructose is able to flow down a concentration gradient into the enterocytes, assisted by transport proteins. Fructose may be transported out of the enterocyte across the basolateral membrane by either GLUT2 or GLUT5, although the GLUT2 transporter has a greater capacity for transporting fructose, and, therefore, the majority of fructose is transported out of the enterocyte through GLUT2.
The absorption capacity for fructose in monosaccharide form ranges from less than 5 g to 50 g (per day?) and adapts with changes in dietary fructose intake.]
[ Studies show the greatest absorption rate occurs when glucose and fructose are administered in equal quantities. When fructose is ingested as part of the disaccharide sucrose, absorption capacity is much higher because fructose exists in a 1:1 ratio with glucose. It appears that the GLUT5 transfer rate may be saturated at low levels, and absorption is increased through joint absorption with glucose. One proposed mechanism for this phenomenon is a glucose-dependent cotransport of fructose. In addition, fructose transfer activity increases with dietary fructose intake. The presence of fructose in the lumen causes increased mRNA transcription of GLUT5, leading to increased transport proteins. High-fructose diets]
[ increase transport proteins within three days of intake.
Several studies have measured the intestinal absorption of fructose using hydrogen breath test. These studies indicate that fructose is not completely absorbed in the small intestine. When fructose is not absorbed in the small intestine, it is transported into the large intestine, where it is fermented by the colonic flora. Hydrogen is produced during the fermentation process and dissolves into the blood of the portal vein. This hydrogen is transported to the lungs, where it is exchanged across the lungs and is measurable by the hydrogen breath test. The colonic flora also produces carbon dioxide, short-chain fatty acids, organic acids, and trace gases in the presence of unabsorbed fructose. The presence of gases and organic acids in the large intestine causes gastrointestinal symptoms such as bloating, diarrhea, flatulence, and gastrointestial pain Exercise immediately after consumption can exacerbate these symptoms by decreasing transit time in the small intestine, resulting in a greater amount of fructose emptied into the large intestine.
All three dietary monosaccharides are transported into the liver by the GLUT2 transporter. Fructose and galactose are phosphorylated in the liver by fructokinase (Km
= 0.5 mM) and galactokinase (Km
= 0.8 mM). By contrast, glucose tends to pass through the liver (Km
of hepatic glucokinase = 10 mM) and can be metabolised anywhere in the body. Uptake of fructose by the liver is not regulated by insulin. However, insulin is capable of increasing the abundance and functional activity of GLUT5 in skeletal muscle cells.
The initial catabolism of fructose is sometimes referred to as fructolysis, in analogy with glycolysis, the catabolism of glucose. In fructolysis, the enzyme fructokinase initially produces fructose 1-phosphate, which is split by aldolase B to produce the trioses dihydroxyacetone phosphate and glyceraldehyde . Unlike glycolysis, in fructolysis the triose glyceraldehyde lacks a phosphate group. A third enzyme, trioskinase, is therefore required to phosphorylate glyceraldehyde, producing glyceraldehyde-3-phosphate. The resulting trioses are identical to those obtained in glycolysis and can enter the gluconeogenic pathway for glucose or glycogen synthesis, or be further catabolized through the lower glycolytic pathway to pyruvate.
The first step in the metabolism of fructose is the phosphorylation of fructose to fructose 1-phosphate by fructokinase, thus trapping fructose for metabolism in the liver. Fructose 1-phosphate then undergoes hydrolysis by aldolase B to form DHAP and glyceraldehydes; DHAP can either be isomerized to glyceraldehyde 3-phosphate by triosephosphate isomerase or undergo reduction to glycerol 3-phosphate by glycerol 3-phosphate dehydrogenase. The glyceraldehyde produced may also be converted to glyceraldehyde 3-phosphate by glyceraldehyde kinase or converted to glycerol 3-phosphate by glyceraldehyde 3-phosphate dehydrogenase. The metabolism of fructose at this point yields intermediates in the gluconeogenic and fructolytic pathways leading to glycogen synthesis as well as fatty acid and triglyceride synthesis.
The resultant glyceraldehyde formed by aldolase B then undergoes phosphorylation to glyceraldehyde 3-phosphate. Increased concentrations of DHAP and glyceraldehyde 3-phosphate in the liver drive the gluconeogenic pathway toward glucose and subsequent glycogen synthesis. It appears that fructose is a better substrate for glycogen synthesis than glucose and that glycogen replenishment takes precedence over triglyceride formation.]
[ Once liver glycogen is replenished, the intermediates of fructose metabolism are primarily directed toward triglyceride synthesis.]
Carbons from dietary fructose are found in both the free fatty acid and glycerol moieties of plasma triglycerides. High fructose consumption can lead to excess pyruvate production, causing a buildup of Krebs cycle intermediates. Accumulated citrate can be transported from the mitochondria into the cytosol of hepatocytes, converted to acetyl CoA by citrate lyase and directed toward fatty acid synthesis. Additionally, DHAP can be converted to glycerol 3-phosphate as previously mentioned, providing the glycerol backbone for the triglyceride molecule. Triglycerides are incorporated into very low density lipoproteins (VLDL), which are released from the liver destined toward peripheral tissues for storage in both fat and muscle cells.
Fructose absorption occurs in the small intestine via the GLUT-5 (fructose only) transporter, and the GLUT2 transporter, for which it competes with glucose and galactose. Over-consumption of fructose, inhibition of GLUT2 by other phytochemicals, such as flavonoids, or other issues, may result in unabsorbed fructose being carried into the large intestine, where, like any sugar, it may provide nutrients for the existing gut flora.
Excess fructose consumption has been hypothesized to be a cause of insulin resistance, obesity, elevated LDL cholesterol and triglycerides, leading to metabolic syndrome. In preliminary research, fructose consumption was correlated with obesity. A study in mice showed that a high fructose intake may increase adiposity.
Although all simple sugars have nearly identical chemical formulae, each has distinct chemical properties. This can be illustrated with pure fructose. A journal article reports that, "...fructose given alone increased the blood glucose almost as much as a similar amount of glucose (78% of the glucose-alone area)".
In Wistar fatty rats, a laboratory model of diabetes, 10% fructose feeding as opposed to 10% glucose feeding was found to increase blood triglyceride levels by 86%, whereas the same amount of glucose had no effect on triglycerides. Neither glucose nor fructose influenced insulin or blood sugar in this model. The authors concluded "These results show that in genetically obese, diabetic rats feeding fructose and glucose is associated with an increase in hepatic lipogenic enzyme activities and triglyceride production, and suggest that fructose stimulates triglyceride production but impairs triglyceride removal, whereas glucose stimulates both of them."
Another study in humans concluded that fructose and sucrose are metabolized similarly, whereas a different analysis "produced significantly higher fasting plasma triglyceride values than did the glucose diet in men" and "...if plasma triacylglycerols are a risk factor for cardiovascular disease, then diets high in fructose may be undesirable".
In a meta-analysis of clinical trials with controlled feeding—where test subjects were fed a fixed amount of energy rather than being allowed to choose the amount they ate—fructose was not an independent factor for weight gain. In one study of a diet with excessive calories, fructose consumption was associated with weight gain.
Fructose is a reducing sugar, as are all monosaccharides. The spontaneous chemical reaction of simple sugar molecules binding to proteins is known as glycation. Showing potential cause of skin and bone damage in a rat model of diabetes, investigators suggested "that long-term fructose consumption negatively affects the aging process." From the context, it is clear that the authors meant that long-term fructose consumption accelerates ageing, rather than inhibiting it. Another study using human proteins showed that the glycation caused by fructose appears to be equivalent to glucose and so does not seem to be a better answer for diabetes for this reason alone, save for the smaller quantities required to achieve equivalent sweetness in some foods. It also found evidence for glycation of human lens proteins caused by fructose.
Fructose is often recommended for diabetics because it does not trigger the production of insulin by pancreatic β cells, probably because β cells have low levels of GLUT5, although the net effect for both diabetics and non-diabetics is debated. Fructose has a very low glycemic index of 19 ± 2, compared with 100 for glucose and 68 ± 5 for sucrose. Fructose is also seventy-three percent sweeter than sucrose (see relative sweetness) at room temperature, so diabetics can use less of it. Studies show that fructose consumed before a meal may even lessen the glycemic response of the meal.
Studies that have compared high-fructose corn syrup (an ingredient in nearly all soft drinks sold in the US) to sucrose (common table sugar) find that most measured short term physiological effects are equivalent for blood glucose, insulin, leptin, and ghrelin levels. This is not surprising since sucrose is a disaccharide that digests to 50% fructose and 50% glucose, whereas the high-fructose corn syrup most commonly used in soft drinks is 55% fructose and 41% glucose (4% other sugars). The difference between the two lies in the fact that HFCS contains little sucrose, the fructose and glucose being independent moieties. Studies that compare the long term effects between sucrose and fructose have yet to be conducted.
While a few other tissues (e.g., sperm cells and some intestinal cells) do use fructose directly, fructose is metabolized primarily in the liver.
Compared with consumption of high glucose beverages, drinking high fructose beverages with meals results in lower circulating insulin and leptin levels, and higher ghrelin levels after the meal. Since leptin and insulin decrease appetite and ghrelin increases appetite, some researchers suspect that eating large amounts of fructose increases the likelihood of weight gain.
Excessive fructose consumption may contribute to the development of non-alcoholic fatty liver disease.
A 2008 study found a substantial risk of incident gout associated with the consumption of fructose- or fructose-rich foods. Cases of gout have risen in recent years, despite commonly being thought of as a disease of the Victorian era, and it is suspected that the fructose found in soft drinks (e.g., carbonated beverages) and other sweetened drinks is the reason for this.
Fructose has the lowest glycemic index (GI = 19) of all the natural sugars. In comparison, ordinary table sugar (sucrose, which is half fructose) has a GI of 65 and honey (usually about 50% fructose content) has a GI of 55. Because excessive consumption of fructose may be a factor in some diseases, including metabolic syndrome and insulin resistance, consumption of products containing large amounts of fructose may be discouraged.
A preliminary human study indicated that fructose may not influence metabolic activity or blood flow in brain regions regulating satiety, and so may promote overeating.
Galactose-1-phosphate → Glucose 1-phosphate → Glucose 6-phosphate → Fructose 6-phosphate
Uridine diphosphate galactose Uridine diphosphate glucose
mt, k, c/g/r/p/y/i, f/h/s/l/o/e, a/u, n, m
k, cgrp/y/i, f/h/s/l/o/e, au, n, m, epon
m (A16/C10), i (k, c/g/r/p/y/i, f/h/s/o/e, a/u, n, m)
mt, k, c/g/r/p/y/i, f/h/s/l/o/e, a/u, n, m
k, cgrp/y/i, f/h/s/l/o/e, au, n, m, epon
m (A16/C10), i (k, c/g/r/p/y/i, f/h/s/o/e, a/u, n, m)
mt, k, c/g/r/p/y/i, f/h/s/l/o/e, a/u, n, m
k, cgrp/y/i, f/h/s/l/o/e, au, n, m, epon
m (A16/C10), i (k, c/g/r/p/y/i, f/h/s/o/e, a/u, n, m)
Honey is a sweet food made by bees using nectar from flowers. The variety produced by honey bees (the genus Apis) is the one most commonly referred to, as it is the type of honey collected by beekeepers and consumed by humans. Honey produced by other bees and insects has distinctly different properties.
Honey bees transform nectar into honey by a process of regurgitation and evaporation. They store it as a primary food source in wax honeycombs inside the beehive.
Honey gets its sweetness from the monosaccharides fructose and glucose, and has approximately the same relative sweetness as that of granulated sugar. It has attractive chemical properties for baking and a distinctive flavor that leads some people to prefer it over sugar and other sweeteners. Most microorganisms do not grow in honey because of its low water activity of 0.6. However, honey sometimes contains dormant endospores of the bacterium Clostridium botulinum, which can be dangerous to infants, as the endospores can transform into toxin-producing bacteria in infants' immature intestinal tracts, leading to illness and even death.
Honey has a long history of human consumption, and is used in various foods and beverages as a sweetener and flavoring. It also has a role in religion and symbolism. Flavors of honey vary based on the nectar source, and various types and grades of honey are available. It is also used in various medicinal traditions to treat ailments. The study of pollens and spores in raw honey (melissopalynology) can determine floral sources of honey. Bees carry an electrostatic charge whereby they attract other particles in addition to pollen, which become incorporated into their honey; the honey can be analysed by the techniques of melissopalynology in area environmental studies of radioactive particles, dust and particulate pollution.
Honey's natural sugars are dehydrated, which prevents fermentation, with added enzymes to modify and transform their chemical composition and pH. Invertases and digestive acids hydrolyze sucrose to give the monosaccharides glucose and fructose. The invertase is one of these enzymes synthesized by the body of the insect.
Honey bees transform saccharides into honey by a process of regurgitation, a number of times, until it is partially digested. The bees do the regurgitation and digestion as a group. After the last regurgitation, the aqueous solution is still high in water, so the process continues by evaporation of much of the water and enzymatic transformation.
Honey is produced by bees as a food source. In cold weather or when fresh food sources are scarce, bees use their stored honey as their source of energy. By contriving for bee swarms to nest in artificial hives, people have been able to semidomesticate the insects, and harvest excess honey. In the hive (or in a wild nest), there are three types of bees:
The worker bees raise larvae and collect the nectar that will become honey in the hive. Leaving the hive, they collect sugar-rich flower nectar and return.
In the hive, the bees use their "honey stomachs" to ingest and regurgitate the nectar a number of times until it is partially digested. Invertase synthesized by the bees and digestive acids hydrolyze sucrose to give the same mixture of glucose and fructose. The bees work together as a group with the regurgitation and digestion until the product reaches a desired quality. It is then stored in honeycomb cells. After the final regurgitation, the honeycomb is left unsealed. However, the nectar is still high in both water content and natural yeasts, which, unchecked, would cause the sugars in the nectar to ferment. The process continues as bees inside the hive fan their wings, creating a strong draft across the honeycomb, which enhances evaporation of much of the water from the nectar. This reduction in water content raises the sugar concentration and prevents fermentation. Ripe honey, as removed from the hive by a beekeeper, has a long shelf life, and will not ferment if properly sealed.
The physical properties of honey vary, depending on water content, the type of flora used to produce it (pasturage), temperature, and the proportion of the specific sugars it contains. Fresh honey is a supersaturated liquid, containing more sugar than the water can typically dissolve at ambient temperatures. At room temperature, honey is a supercooled liquid, in which the glucose will precipitate into solid granules. This forms a semisolid solution of precipitated glucose crystals in a solution of fructose and other ingredients.
The melting point of crystallized honey is between 40 and 50 °C (104 and 122 °F), depending on its composition. Below this temperature, honey can be either in a metastable state, meaning that it will not crystallize until a seed crystal is added, or, more often, it is in a "labile" state, being saturated with enough sugars to crystallize spontaneously. The rate of crystallization is affected by many factors, but the primary factor is the ratio of the main sugars: fructose to glucose. Honeys that are supersaturated with a very high percentage of glucose, such as brassica honey, will crystallize almost immediately after harvesting, while honeys with a low percentage of glucose, such as chestnut or tupelo honey, do not crystallize. Some types of honey may produce very large but few crystals, while others will produce many small crystals.
Crystallization is also affected by water content, because a high percentage of water will inhibit crystallization, as will a high dextrin content. Temperature also affects the rate of crystallization, with the fastest growth occurring between 13 and 17 °C (55 and 63 °F). Crystal nuclei (seeds) tend to form more readily if the honey is disturbed, by stirring, shaking or agitating, rather than if left at rest. However, the nucleation of microscopic seed-crystals is greatest between 5 and 8 °C (41 and 46 °F). Therefore, larger but fewer crystals tend to form at higher temperatures, while smaller but more-numerous crystals usually form at lower temperatures. Below 5 °C, the honey will not crystallize and, thus, the original texture and flavor can be preserved indefinitely.
Since honey normally exists below its melting point, it is a supercooled liquid. At very low temperatures, honey will not freeze solid. Instead, as the temperatures become colder, the viscosity of honey increases. Like most viscous liquids, the honey will become thick and sluggish with decreasing temperature. At , honey may appear or even feel solid, but it will continue to flow at very slow rates. Honey has a glass transition between -42 and -51 °C (-44 and -60 °F). Below this temperature, honey enters a glassy state and will become an amorphous solid (noncrystalline).
The viscosity of honey is affected greatly by both temperature and water content. The higher the humidity, the easier honey will flow. Above its melting point, however, water has little effect on viscosity. Aside from water content, the composition of honey also has little effect on viscosity, with the exception of a few types. At , honey with 14% humidity will generally have a viscosity of around 400 poise, while a honey containing 20% humidity will have a viscosity of around 20 poise. Viscosity increase due to temperature occurs very slowly at first. A honey containing 16% humidity, at , will have a viscosity of around 2 poise, while at , the viscosity will be around 70 poise. As cooling progresses, honey will become more viscous at an increasingly rapid rate, reaching 600 poise around . However, while honey is very viscous, it has rather low surface tension.
A few types of honey have unusual viscous properties. Honey from heather or manuka display thixotropic properties. These types of honey enter a gel-like state when motionless, but then liquify when stirred.
Since honey contains electrolytes, in the form of acids and minerals, it exhibits varying degrees of electrical conductivity. Measurements of the electrical conductivity are used to determine the quality of honey in terms of ash content.
The effect honey has on light is useful for determining the type and quality. Variations in the water content alter the refractive index of honey. Water content can easily be measured with a refractometer. Typically, the refractive index for honey will range from 1.504 at 13% humidity, to 1.474 at 25%. Honey also has an effect on polarized light, in that it will rotate the polarization plane. The fructose will give a negative rotation, while the glucose will give a positive one. The overall rotation can be used to measure the ratio of the mixture.
Honey has the ability to absorb moisture directly from the air, a phenomenon called hygroscopy. The amount of water the honey will absorb is dependent on the relative humidity of the air. Because honey contains yeast, this hygroscopic nature requires that honey be stored in sealed containers to prevent fermentation, which usually begins if the honey's humidity rises much above 25%. Honey will tend to absorb more water in this manner than the individual sugars would allow on their own, which may be due to other ingredients it contains.
Fermentation of honey will usually occur after crystallization because, without the glucose, the liquid portion of the honey primarily consists of a concentrated mixture of the fructose, acids, and water, providing the yeast with enough of an increase in the water percentage for growth. Honey that is to be stored at room temperature for long periods of time is often pasteurized, to kill any yeast, by heating it above .
Like all sugar compounds, honey will caramelize if heated sufficiently, becoming darker in color and eventually burning. However, honey contains fructose, which caramelizes at lower temperatures than the glucose. The temperature at which caramelization begins varies, depending on the composition, but is typically between and . Honey also contains acids, which act as catalysts, decreasing the caramelization temperature even more. Of these acids, the amino acids, which occur in very small amounts, play an important role in the darkening of honey. The amino acids form darkened compounds called melanoidins, during a Maillard reaction. The Maillard reaction will occur slowly at room temperature, taking from a few to several months to show visible darkening, but will speed-up dramatically with increasing temperatures. However, the reaction can also be slowed by storing the honey at colder temperatures.
Unlike many other liquids, honey has very poor thermal conductivity, taking a long time to reach thermal equilibrium. Melting crystallized honey can easily result in localized caramelization if the heat source is too hot, or if it is not evenly distributed. However, honey will take substantially longer to liquify when just above the melting point than it will at elevated temperatures. Melting 20 kilograms of crystallized honey, at , can take up to 24 hours, while 50 kilograms may take twice as long. These times can be cut nearly in half by heating at . However, many of the minor substances in honey can be affected greatly by heating, changing the flavor, aroma, or other properties, so heating is usually done at the lowest temperature possible for the shortest amount of time.
The average pH of honey is 3.9, but can range from 3.4 to 6.1. Honey contains many kinds of acids, both organic and amino. However, the different types and their amounts vary considerably, depending on the type of honey. These acids may be aromatic or aliphatic (non-aromatic). The aliphatic acids contribute greatly to the flavor of honey by interacting with the flavors of other ingredients. Gluconic acid, for instance, is a flavor enhancer.
Honey can contain up to 18 of the 20 amino acids. However, amino acid content is almost negligible in honey, accounting for only 0.05–0.1% of the composition. The main amino acid is proline. Amino acids are derived almost solely from the bodies of the bees.
Organic acids comprise most of the acids in honey, accounting for 0.17–1.17% of the mixture. Gluconic acid is the most prevalent. Gluconic acid is formed by the actions of an enzyme called glucose oxidase. Other organic acids are minor, consisting of formic, acetic, butyric, citric, lactic, malic, pyroglutamic, propionic, valeric, capronic, palmitic, and succinic, among many others.
Honey use and production has a long and varied history. In many cultures, honey has associations that go beyond its use as a food. Honey is frequently used as a talisman and symbol of sweetness.][
Honey collection is an ancient activity. Humans apparently began hunting for honey at least 8,000 years ago, as evidenced by a cave painting in Valencia, Spain. The painting is a Mesolithic rock painting, showing two honey-hunters collecting honey and honeycomb from a wild bee nest. The figures are depicted carrying baskets or gourds, and using a ladder or series of ropes to reach the wild nest.
The Greater Honeyguide bird guides humans to wild bee hives and this behavior may have evolved with early hominids
So far, the oldest remains of honey have been found in Georgia. Archaeologists have found honey remains on the inner surface of clay vessels unearthed an ancient tomb, dating back to some 4,700–5,500 years ago. In ancient Georgia, honey was packed for people's journeys into the afterlife. And more than one type, too – along for the trip were linden, berry, and a meadow-flower variety.
In ancient Egypt, honey was used to sweeten cakes and biscuits, and was used in many other dishes. Ancient Egyptian and Middle Eastern peoples also used honey for embalming the dead. The fertility god of Egypt, Min, was offered honey.
Pliny the Elder devotes considerable space in his book Naturalis Historia to the bee and honey, and its many uses. In the absence of sugar, Honey was an integral sweetening ingredient in Roman recipes, and references to its use in food can be found in the work of many Roman authors including Athenaeus, Cato and Bassus][. Some of these are collected in the book Roman cookery.
The art of beekeeping in ancient China has existed since time immemorial and appears to be untraceable to its origin. In the book "Golden Rules of Business Success" written by Fan Li (or Tao Zhu Gong) during the Spring and Autumn Period, there are some parts mentioning the art of beekeeping and the importance of the quality of the wooden box for bee keeping that can affect the quality of its honey.
Honey was also cultivated in ancient Mesoamerica. The Maya used honey from the stingless bee for culinary purposes, and continue to do so today. The Maya also regard the bee as sacred (see Mayan stingless bees of Central America).
Some cultures believed honey had many practical health uses. It was used as an ointment for rashes and burns, and to help soothe sore throats when no other practices were available.
In Hinduism, honey (Madhu) is one of the five elixirs of immortality (Panchamrita). In temples, honey is poured over the deities in a ritual called Madhu abhisheka. The Vedas and other ancient literature mention the use of honey as a great medicinal and health food.][
In Jewish tradition, honey is a symbol for the new year, Rosh Hashanah. At the traditional meal for that holiday, apple slices are dipped in honey and eaten to bring a sweet new year. Some Rosh Hashanah greetings show honey and an apple, symbolizing the feast. In some congregations, small straws of honey are given out to usher in the new year.][
The Hebrew Bible contains many references to honey. In the Book of Judges, Samson found a swarm of bees and honey in the carcass of a lion (14:8). In Old Testament law, offerings were made in the temple to God. The Book of Leviticus says that “Every grain offering you bring to the Lord must be made without yeast, for you are not to burn any yeast or honey in a food offering presented to the Lord” (2:11). In the Books of Samuel Jonathan is forced into a confrontation with his father King Saul after eating honey in violation of a rash oath Saul made (14:24-47). The Book of Exodus famously describes the Promised Land as a "land flowing with milk and honey" (33:3). However, the claim has been advanced that the original Hebrew (דבש devash) actually refers to the sweet syrup produced from the juice of dates. Pure honey is considered kosher even though it is produced by a flying insect, a nonkosher creature; other products of nonkosher animals are not kosher.
In Buddhism, honey plays an important role in the festival of Madhu Purnima, celebrated in India and Bangladesh. The day commemorates Buddha's making peace among his disciples by retreating into the wilderness. The legend has it that while he was there, a monkey brought him honey to eat. On Madhu Purnima, Buddhists remember this act by giving honey to monks. The monkey's gift is frequently depicted in Buddhist art.][
In the Christian New Testament, Matthew 3:4, John the Baptist is said to have lived for a long period of time in the wilderness on a diet consisting of locusts and wild honey.
In Islam, there is an entire Surah in the Qur'an called al-Nahl (the Bee). According to hadith, Prophet Muhammad strongly recommended honey for healing purposes. The Qur'an promotes honey as a nutritious and healthy food. Below is the English translation of those specific verses.
"And thy Lord taught the Bee to build its cells in hills, on trees, and in (men's) habitations; Then to eat of all the produce (of the earth), and find with skill the spacious paths of its Lord: there issues from within their bodies a drink of varying colours, wherein is healing for men: verily in this is a Sign for those who give thought" [Al-Quran 16:68-69].
Honey is collected from wild bee colonies, or from domesticated beehives. Wild bee nests are sometimes located by following a honeyguide bird.
Collecting honey is typically achieved by using smoke from a bee smoker to pacify the bees; this causes the bees to attempt to save the resources of the hive from a possible forest fire, and makes them far less aggressive. The honeycomb is removed from the hive and the honey is extracted from that, often using a honey extractor. The honey is then filtered.
The main uses of honey are in cooking, baking, as a spread on bread, and as an addition to various beverages, such as tea, and as a sweetener in some commercial beverages. According to the The National Honey Board (a USDA-overseen organization), "honey stipulates a pure product that does not allow for the addition of any other substance...this includes, but is not limited to, water or other sweeteners". Honey barbecue and honey mustard are common and popular sauce flavors.
Honey is the main ingredient in the alcoholic beverage mead, which is also known as "honey wine" or "honey beer". Historically, the ferment for mead was honey's naturally occurring yeast. Honey is also used as an adjunct in some beers.
Honey wine, or mead, is typically (modern era) made with a honey and water mixture with a pack of yeast added for fermentation. Primary fermentation usually takes 40 days, after which the must needs to be racked into a secondary fermentation vessel and left to sit about 35–40 more days. If done properly, fermentation will be finished by this point (though if a sparkling mead is desired, fermentation can be restarted after bottling by the addition of a small amount of sugar), but most meads require aging for 6–9 months or more in order to be palatable.
Honey is a mixture of sugars and other compounds. With respect to carbohydrates, honey is mainly fructose (about 38.5%) and glucose (about 31.0%), making it similar to the synthetically produced inverted sugar syrup, which is approximately 48% fructose, 47% glucose, and 5% sucrose. Honey's remaining carbohydrates include maltose, sucrose, and other complex carbohydrates. As with all nutritive sweeteners, honey is mostly sugars and contains only trace amounts of vitamins or minerals. Honey also contains tiny amounts of several compounds thought to function as antioxidants, including chrysin, pinobanksin, vitamin C, catalase, and pinocembrin.][ The specific composition of any batch of honey depends on the flowers available to the bees that produced the honey.
Typical honey analysis:
Its glycemic index ranges from 31 to 78, depending on the variety.
Honey has a density of about 1.36 kilograms per litre (36% denser than water).
Isotope ratio mass spectrometry can be used to detect addition of corn syrup and cane sugar by the carbon isotopic signature. Addition of sugars originating from corn or sugar cane (C4 plants, unlike the plants used by bees, and also sugar beet, which are predominantly C3 plants) skews the isotopic ratio of sugars present in honey, but does not influence the isotopic ratio of proteins; in an unadulterated honey, the carbon isotopic ratios of sugars and proteins should match. As low as 7% level of addition can be detected.
Honey is classified by its floral source, and there are also divisions according to the packaging and processing used. There are also regional honeys. Honey is also graded on its color and optical density by USDA standards, graded on a scale called the Pfund scale, which ranges from 0 for "water white" honey to more than 114 for "dark amber" honey.
Generally, honey is classified by the floral source of the nectar from which it was made. Honeys can be from specific types of flower nectars or can be blended after collection. The pollen in honey is traceable to floral source and therefore region of origin. The rheological & mellisopalynological properties of honey can be used to identify the major plant nectar source used in its production.
Most commercially available honey is blended, meaning it is a mixture of two or more honeys differing in floral source, color, flavor, density or geographic origin.
Polyfloral honey, also known as wildflower honey, is derived from the nectar of many types of flowers.
The taste may vary from year to year, and the aroma and the flavor can be more or less intense, depending on which bloomings are prevalent.
Monofloral honey is made primarily from the nectar of one type of flower. Different monofloral honeys have a distinctive flavor and color because of differences between their principal nectar sources. To produce monofloral honey, beekeepers keep beehives in an area where the bees have access to only one type of flower. In practice, because of the difficulties in containing bees, a small proportion of any honey will be from additional nectar from other flower types.][ Typical examples of North American monofloral honeys are clover, orange blossom, blueberry, sage, tupelo, buckwheat, fireweed, mesquite and sourwood. Some typical European examples include thyme, thistle, heather, acacia, dandelion, sunflower, honeysuckle, and varieties from lime and chestnut trees.][ In North Africa (e.g. Egypt) examples include clover, cotton, and citrus (mainly orange blossoms).][
Instead of taking nectar, bees can take honeydew, the sweet secretions of aphids or other plant sap-sucking insects. Honeydew honey is very dark brown in color, with a rich fragrance of stewed fruit or fig jam, and is not as sweet as nectar honeys. Germany's Black Forest is a well known source of honeydew-based honeys, as well as some regions in Bulgaria, Tara (mountain) in Serbia and Northern California in the United States. In Greece, pine honey (a type of honeydew honey) constitutes 60–65% of the annual honey production. Honeydew honey is popular in some areas, but in other areas beekeepers have difficulty selling the stronger flavored product.
The production of honeydew honey has some complications and dangers. The honey has a much larger proportion of indigestibles than light floral honeys, thus causing dysentery to the bees, resulting in the death of colonies in areas with cold winters. Good beekeeping management requires the removal of honeydew prior to winter in colder areas. Bees collecting this resource also have to be fed protein supplements, as honeydew lacks the protein-rich pollen accompaniment gathered from flowers.
Generally, honey is bottled in its familiar liquid form. However, honey is sold in other forms, and can be subjected to a variety of processing methods.
Because of its unique composition and chemical properties, honey is suitable for long-term storage, and is easily assimilated even after long preservation. Honey, and objects immersed in honey, have been preserved for decades and even centuries. The key to preservation is limiting access to humidity. In its cured state, honey has a sufficiently high sugar content to inhibit fermentation. If exposed to moist air, its hydrophilic properties will pull moisture into the honey, eventually diluting it to the point that fermentation can begin. Honey sealed in honeycomb cells by the bees is considered by many to be the ideal form for preservation.][
Honey should also be protected from oxidation and temperature degradation. It generally should not be preserved in metal containers because the acids in the honey may promote oxidation of the vessel. Traditionally, honey was stored in ceramic or wooden containers; however, glass and plastic are now the favored materials. Honey stored in wooden containers may be discolored or take on flavors imparted from the vessel. Likewise, honey stored uncovered near other foods may absorb other smells.][
Excessive heat can have detrimental effects on the nutritional value of honey. Heating up to causes loss of nearly 200 components, some of which are antibacterial. Heating up to destroys invertase, an important enzyme. At , the honey sugars caramelize. Generally, any large temperature fluctuation causes decay.][
Regardless of preservation, honey may crystallize over time. Crystallization does not affect the flavor, quality or nutritional content of the honey, though it does affect color and texture. The rate is a function of storage temperature, availability of "seed" crystals and the specific mix of sugars and trace compounds in the honey. Tupelo and acacia honeys, for example, are exceptionally slow to crystallize, while goldenrod will often crystallize still in the comb. Most honeys crystallize fastest between about 50 and 70 °F (10 and 21 °C). The crystals can be dissolved by heating the honey.][
In the US, honey grading is performed voluntarily (USDA does offer inspection and grading "as on-line (in-plant) or lot inspection...upon application, on a fee-for-service basis.") based upon USDA standards. Honey is graded based upon a number of factors, including water content, flavor and aroma, absence of defects and clarity. Honey is also classified by color though it is not a factor in the grading scale. The honey grade scale is:
Other countries may have differing standards on the grading of honey. India, for example, certifies honey grades based on additional factors, such as the Fiehe's test, and other empirical measurements.
High-quality honey can be distinguished by fragrance, taste, and consistency. Ripe, freshly collected, high-quality honey at should flow from a knife in a straight stream, without breaking into separate drops. After falling down, the honey should form a bead. The honey, when poured, should form small, temporary layers that disappear fairly quickly, indicating high viscosity. If not, it indicates excessive water content (over 20%) of the product. Honey with excessive water content is not suitable for long-term preservation.
In jars, fresh honey should appear as a pure, consistent fluid, and should not set in layers. Within a few weeks to a few months of extraction, many varieties of honey crystallize into a cream-colored solid. Some varieties of honey, including tupelo, acacia, and sage, crystallize less regularly. Honey may be heated during bottling at temperatures of 40–49°C (104–120°F) to delay or inhibit crystallization. Overheating is indicated by change in enzyme levels, for instance, diastase activity, which can be determined with the Schade or the Phadebas methods. A fluffy film on the surface of the honey (like a white foam), or marble-colored or white-spotted crystallization on a containers sides, is formed by air bubbles trapped during the bottling process.
A 2008 Italian study determined nuclear magnetic resonance spectroscopy can be used to distinguish between different honey types, and can be used to pinpoint the area where it was produced. Researchers were able to identify differences in acacia and polyfloral honeys by the differing proportions of fructose and sucrose, as well as differing levels of aromatic amino acids phenylalanine and tyrosine. This ability allows greater ease of selecting compatible stocks.
Historically, honey has been used by humans to treat a variety of ailments, from gastric disturbances to ulcers, wounds and burns, through ingestion or topical application, but only recently have the antiseptic and antibacterial properties of honey been chemically explained. Different honeys have different properties, which was known since ancient times. Much scientific research has been done, with emphasis of late on fighting infections in wounds. The antibacterial mechanisms known to date are 2O2H, methylglyoxal(MGO), bee defensin-1, the osmotic effect and the pH.
In Ayurveda, a 4000-year-old treatise on medicine originating from India, honey is considered to positively affect all three primitive material imbalances of the body. "Vaatalam guru sheetam cha raktapittakaphapaham| Sandhatru cchedanam ruksham kashayam madhuram madhu|| "It has sweetness with added astringent as end taste. It is heavy, dry and cold. Its effect on doshas (imbalances) is that it aggravates vata (air / moving forces), scrapes kapha (mucus / holding forces) and normalizes pitta (catabolic fire) and rakta (blood). It promotes the healing process." Some wound gels which contain antibacterial raw honey and have regulatory approval are now available to help treat drug-resistant strains of bacteria (MRSA). One New Zealand researcher says a particular type of honey (manuka honey) may be useful in treating MRSA infections.
As an antimicrobial agent honey is useful in treating a variety of ailments. Antibacterial properties of honey are the result of the low water activity causing osmosis, chelation of free iron, its slow release of hydrogen peroxide, high acidity, and the antibacterial activity of methylglyoxal.
Honey appears to be effective in killing drug-resistant biofilms which are implicated in chronic rhinosinusitis.
Honey has an osmotic effect. Honey is primarily a saturated mixture of two monosaccharides, with a low water activity; most of the water molecules are associated with the sugars and few remain available for microorganisms, so it is a poor environment for their growth. If water is mixed with honey, it loses its low water activity, and therefore no longer possesses this antimicrobial property.
Hydrogen peroxide is formed in a slow-release manner by the enzyme glucose oxidase present in honey. It becomes active only when honey is diluted, requires oxygen to be available for the reaction (thus it may not work under wound dressings, in wound cavities or in the gut), is active only when the acidity of honey is neutralized by body fluids, can be destroyed by the protein-digesting enzymes present in wound fluids, and is destroyed when honey is exposed to heat and light. Honey chelates and deactivates free iron, which would otherwise catalyze the formation of oxygen free radicals from hydrogen peroxide, leading to inflammation. Also, the antioxidant constituents in honey help clean up oxygen free radicals present.
When honey is used topically (as, for example, a wound dressing), hydrogen peroxide is produced by dilution of the honey with body fluids. As a result, hydrogen peroxide is released slowly and acts as an antibacterial.
Topical honey has been used successfully in a comprehensive treatment of diabetic ulcers when the patient cannot use topical antibiotics.
The pH of honey is commonly between 3.2 and 4.5. This relatively acidic pH level prevents the growth of many bacteria.
The nonperoxide antibiotic activity is due to methylglyoxal (MGO) and bee defensin-1. Most honeys contain very low levels of MGO, but manuka honey contains very high levels. The presence of the synergist in manuka honey more than doubles MGO antibacterial activity.
Antioxidants in honey have even been associated with reducing the damage done to the colon in colitis in a study involving administering honey enemas to rats. Such claims are consistent with its use in many traditions of folk medicine.
Honey has also been used for centuries as a treatment for sore throats and coughs and, according to recent research, may be an effective soothing agent for coughs.
Unfiltered, pasteurized honey is widely believed to alleviate allergies, though neither commercially filtered nor raw honey was shown to be more effective than placebo in a controlled study of 36 participants with ocular allergies. Nearly 1 in 3 of the volunteers dropped out of the study because they couldn't tolerate eating one tablespoon of honey every day due to the overly sweet taste. The official conclusion: "This study does not confirm the widely held belief that honey relieves the symptoms of allergic rhinoconjunctivitis." A more recent study has shown pollen collected by bees to exert an antiallergenic effect, mediated by an inhibition of IgE immunoglobulin binding to mast cells. This inhibited mast cell degranulation and thus reduced allergic reaction. The risk of experiencing anaphylaxis as an immune system reaction may outweigh any potential allergy relief.
A review in the Cochrane Library suggests honey could reduce the time it takes for a mild burn to heal — up to four days sooner in some cases. The review included 19 studies with 2,554 participants. Although the honey treatment healed mild burns faster than traditional dressings did, the author recommends viewing the findings with caution, since a single research centre performed all of the burn studies.
Because of the natural presence of botulinum endospores in honey, children under one year of age should not be given honey. The more-developed digestive system of older children and adults generally destroys the spores. Infants, however, can contract botulism from honey. Medical grade honey can be treated with gamma radiation to reduce the risk of botulinum spores being present. Gamma radiation evidently does not affect honey's antibacterial activity, whether or not the particular honey's antibacterial activity is dependent upon peroxide generation.
Infantile botulism shows geographical variation. In the UK, only six cases have been reported between 1976 and 2006, yet the U.S. has much higher rates: 1.9 per 100,000 live births, 47.2% of which are in California. While the risk honey poses to infant health is small, it is recommended not to take the risk.
Honey produced from flowers of oleanders, rhododendrons, mountain laurels, sheep laurel, and azaleas may cause honey intoxication. Symptoms include dizziness, weakness, excessive perspiration, nausea, and vomiting. Less commonly, low blood pressure, shock, heart rhythm irregularities, and convulsions may occur, with rare cases resulting in death. Honey intoxication is more likely when using "natural" unprocessed honey and honey from farmers who may have a small number of hives. Commercial processing, with pooling of honey from numerous sources, is thought to dilute any toxins.
Toxic honey may also result when bees are proximate to tutu bushes (Coriaria arborea) and the vine hopper insect (Scolypopa australis). Both are found throughout New Zealand. Bees gather honeydew produced by the vine hopper insects feeding on the tutu plant. This introduces the poison tutin into honey. Only a few areas in New Zealand (Coromandel Peninsula, Eastern Bay of Plenty and the Marlborough Sound) frequently produce toxic honey. Symptoms of tutin poisoning include vomiting, delirium, giddiness, increased excitability, stupor, coma, and violent convulsions. To reduce the risk of tutin poisoning, humans should not eat honey taken from feral hives in the risk areas of New Zealand. Since December 2001, New Zealand beekeepers have been required to reduce the risk of producing toxic honey by closely monitoring tutu, vine hopper, and foraging conditions within 3 km of their apiary.
In 2012, China, Turkey, and Ukraine were the top producers of natural honey.
Significant regional producers of honey include United States of America (ranked fourth worldwide) and Russia (ranked fifth worldwide).
Mexico is also an important producer of honey, providing more than 4% of the world's supply. Much of this (about one-third) comes from the Yucatán Peninsula. Honey production began there when the Apis mellifera and the A. mellifera ligustica were introduced there early in the 20th century. Most of Mexico's Yucatán producers are small, family operations who use original traditional techniques, moving hives to take advantage of the various tropical and subtropical flowers.
Honey is also one of the gourmet products of the French island of Corsica. Corsican honey is certified as to its origin (Appellation d'origine contrôlée) just as are French wines, like Champagne.
Honey consumption per capita per year exceeds one kilogram in some countries like Austria, Germany and Switzerland.
Smoking the hive
Using a blower to remove bees from honey prior to removal to honey house
A beekeeper removing frames from the hive
A capped honey super frame
Opening the cells: Uncapping
An uncapping fork
Uncapping the cells by hand using an uncapping knife
Extracting the honey
Filtering the honey
Pouring in pots
View Honey Al Jabal Alkhdar near the city of Bayda, Libya
A hangover (medical terminology: veisalgia) is the experience of various unpleasant physiological effects following heavy consumption of alcoholic beverages. The most commonly reported characteristics of a hangover include headache, nausea, sensitivity to light and noise, lethargy, dysphoria, diarrhea and thirst, typically after the intoxicating effect of the alcohol begins to wear off. While a hangover can be experienced at any time, generally a hangover is experienced the morning after a night of heavy drinking. In addition to the physical symptoms, a hangover may also induce psychological symptoms including heightened feelings of depression and anxiety.
Hypoglycemia, dehydration, acetaldehyde intoxication, and glutamine rebound are all theorized causes of hangover symptoms. Hangover symptoms may persist for several days after alcohol was last consumed. Some aspects of a hangover are viewed as symptoms of acute ethanol withdrawal, similar to the longer-duration effects of withdrawal from alcoholism, as determined by studying the increases in brain reward thresholds in rats (the amount of current required to receive from two electrodes implanted in the lateral hypothalamus) following ethanol injection.
Hangovers are caused by several factors. First, the body has to metabolize the active ingredient in alcoholic beverages: ethanol. This process requires cellular energy, distracting the body from normal activities like making glucose for the brain. Even after all the ethanol is metabolized, the by-products of this process can cause additional problems. Likewise, other substances in certain alcoholic beverages can make a hangover worse. Lastly, ethanol is a diuretic and can lead to dehydration.
After being ingested, ethanol is first converted to acetaldehyde by the enzyme alcohol dehydrogenase and then to acetic acid by the enzyme acetaldehyde dehydrogenase. These reactions also convert +NAD to NADH. However, by causing a shortage of NAD+ and an excess of NADH, alcoholic beverages make normal bodily functions more difficult. For example, excess NADH causes the important citric acid cycle to shut down by inhibiting three important enzymes (citrate synthase, isocitrate dehydrogenase, and alpha-ketoglutarate dehydrogenase).
To correct this imbalance the body uses pyruvate and lactate dehydrogenase to convert the excess NADH back into NAD+. In the process, however, the body diverts pyruvate from other important pathways such as gluconeogenesis. This impairs the ability of the liver to compensate for a drop in blood glucose levels, especially for the brain. Because glucose is the primary energy source of the brain, this lack of glucose (hypoglycemia) contributes to symptoms such as fatigue, weakness, mood disturbances, and decreased attention and concentration.][
Alcohol consumption can result in depletion of the liver's supply of glutathione and other reductive detoxification agents, reducing its ability to effectively remove acetaldehyde and other toxins from the bloodstream. Additionally, alcohol induces the CYP2E1 enzyme, which itself can produce additional toxins and free radicals.
Acetaldehyde, the first by-product of ethanol, is between 10 and 30 times more toxic than alcohol itself. In addition, certain genetic factors can amplify the negative effects of acetaldehyde. For example, East Asian people have a mutation in their alcohol dehydrogenase gene that makes this enzyme unusually fast at converting ethanol to acetaldehyde. In addition, about half of all East Asians convert acetaldehyde to acetic acid more slowly (via acetaldehyde dehydrogenase), causing a higher build up of acetaldehyde than normally seen in other groups. The high concentration of acetaldehyde causes the alcohol flush reaction, colloquially known as the "Asian Glow". Since the alcohol flush reaction is highly uncomfortable and the possibility of hangovers is immediate and severe, East Asians are less likely to become alcoholics.
Although not scientifically documented, there are reports that consuming certain antacids or Brewer's yeast before drinking can decrease in the alcohol flush reaction.
Likewise, acetic acid (or the acetate ion) can cause additional problems. One study found that injecting sodium acetate into rats caused them to have nociceptive behavior (headaches). In addition, there is a biochemical explanation for this finding. High acetate levels cause adenosine to accumulate in many parts of the brain. But when the rats were given caffeine, which blocks the action of adenosine, they no longer experienced headaches.
In addition to ethanol and water, most alcoholic drinks also contain congeners, either as flavoring or as a by-product of fermentation. However, different types of alcohol contain different amounts of congeners. In general, dark liquors have a higher concentration while clear liquors have a lower concentration.
Several studies have examined whether certain types of alcohol cause worse hangovers. All four studies concluded that darker liquors, which have higher congeners, produced worse hangovers. One even showed that hangover were worse and more frequent with darker liquors. In a 2006 study, an average of 14 standard drinks (330 ml) of beer was needed to produce a hangover, but only 7 to 8 drinks was required for wine or liquor. Another study ranked several drinks by their ability to cause a hangover (from low to high): distilled ethanol diluted with fruit juice, beer, vodka, gin, white wine, whisky, rum, red wine, and brandy. While congeners do cause hangovers, they do not affect how drunk the person becomes.
One potent congener is methanol. It is naturally formed in small quantities during fermentation and it can be accidentally concentrated by improper distillation techniques. Metabolism of methanol produces an extremely toxic compound, formaldehyde; however, its metabolism is suppressed when ethanol is present in the bloodstream. Therefore, methanol is a likely cause of hangovers that begin when the person's blood alcohol level approaches zero. Incidentally, these hangovers can be "cured" by consuming more ethanol.
Ethanol has a dehydrating effect by causing increased urine production (diuresis), which causes headaches, dry mouth, and lethargy. Dehydration also causes fluids in the brain to be less plentiful. This can be mitigated by drinking water before, during and after consumption of alcohol. Alcohol's effect on the stomach lining can account for nausea.][ In addition, it is often said that hangovers grow worse as one ages; this is thought to be caused by declining supplies of alcohol dehydrogenase, the enzyme involved in metabolizing alcohol.
An alcohol hangover is associated with a variety of symptoms that may include dehydration, fatigue, headache, body aches, vomiting, diarrhea, flatulence, weakness, elevated body temperature and heart rate, hypersalivation, difficulty concentrating, sweating, anxiety, dysphoria, irritability, sensitivity to light and noise, erratic motor functions (including tremor), trouble sleeping, severe hunger, halitosis, and lack of depth perception. Many people will also be repulsed by the thought, taste or smell of alcohol during a hangover. The symptoms vary significantly from person to person, and it is not clear whether hangovers directly affect cognitive abilities.
Psychological research of alcohol hangover is growing rapidly. The Alcohol Hangover Research Group had its inaugural meeting in June 2010 as part of the Research Society on Alcoholism (RSA) 33rd Annual Scientific Meeting in San Antonio, Texas.
In 2010, researchers from the Centre for Alcohol and Drug Research at the University of Aarhus in Copenhagen charted how hangovers progress over time in the face of continued drinking. They found no evidence of hangover tolerance. Instead, they found that hangover symptoms became steadily worse over the course of one week.
In 2012, Éduc'alcool, a Quebec-based non-profit organization that aims to educate the public on the responsible use of alcohol, published a report noting hangovers have long-lasting effects that inhibit the drinker's capabilities a full 24 hours after heavy drinking.
Hangovers are poorly understood from a medical point of view. Health care professionals prefer to study alcohol abuse from a standpoint of treatment and prevention, and there is a view that the hangover provides a useful, natural and intrinsic disincentive to excessive drinking.
Within the limited amount of serious study on the subject, there is debate about whether a hangover may be prevented or at least mitigated; additionally, there is a vast body of folk medicine and simple quackery. There is currently no empirically proven mechanism for prevention except reducing the amount of ethanol consumed, or for making oneself sober other than waiting for the body to metabolize ingested alcohol, which occurs via oxidation through the liver before alcohol leaves the body. A four-page literature review in the British Medical Journal concludes: "No compelling evidence exists to suggest that any conventional or complementary intervention is effective for preventing or treating alcohol hangover. The most effective way to avoid the symptoms of alcohol induced hangover is to avoid drinking."
Recommendations for foods, drinks and activities to relieve hangover symptoms abound. The ancient Romans, on the authority of Pliny the Elder, favored raw owl's eggs or fried canary, while the "Prairie Oyster" restorative, introduced at the 1878 Paris World Exposition, calls for raw egg yolk mixed with Worcestershire sauce, Tabasco sauce, salt and pepper. By 1938, the Ritz-Carlton Hotel provided a hangover remedy in the form of a mixture of Coca-Cola and milk (Coca-Cola itself having been invented, by some accounts, as a hangover remedy). Alcoholic writer Ernest Hemingway relied on tomato juice and beer. Certain mixtures were developed specifically for the purpose. The "Black Velvet" consists of equal parts champagne and flat Guinness Stout, A 1957 survey by a Wayne State University folklorist found widespread belief in the efficacy of heavy fried foods, tomato juice and sexual activity.
Activities said to be restorative include a shower—alternating very hot and very cold water, exercise,][ and steambath or sauna (although medical opinion holds this to be very dangerous, as the combination of alcohol and hyperthermia increases the likelihood of dangerous cardiac arrhythmias).
Other untested or discredited treatments include:
dsrd (o, p, m, p, a, d, s), sysi/epon, spvo
proc (eval/thrp), drug (N5A/5B/5C/6A/6B/6D)
noco (m/d/e/h/v/s)/cong/tumr, sysi/epon, injr
proc, drug (N1A/2AB/C/3/4/7A/B/C/D)
-glucose: 146 °C
-glucose: 150 °C
( or ; C6
, also known as D-glucose
, or grape sugar
) is a simple monosaccharide found in plants. It is one of the three dietary monosaccharides, along with fructose and galactose, that are absorbed directly into the bloodstream during digestion. An important carbohydrate in biology, cells use it as the primary source of energy and a metabolic intermediate. Glucose is one of the main products of photosynthesis and fuels for cellular respiration. Glucose exists in several different molecular structures, but all of these structures can be divided into two families of mirror-images (stereoisomers). Only one set of these isomers exists in nature, those derived from the "particular chiral form" of glucose, denoted D
-glucose, or D
The chemical D
-glucose is sometimes referred to as dextrose, a historical name that derives from dextrorotatory glucose
because a solution of D
-glucose in water rotates the plane of polarized light to the right (dextro). However, the D
- in D
-glucose refers to a chiral chemical similarity
property in sugars, not the property of rotating light (for example, D
-fructose rotates light to the left). For this reason, the D
- and L
- designations in sugars do not perfectly predict optical rotation, and do not refer to this property.
Starch and cellulose are polymers derived from the dehydration of D
-glucose. The other stereoisomer, called -glucoseL
, is hardly ever found in nature.
The name "glucose" comes from the Greek word glukus
(), meaning "sweet". The suffix "-ose" denotes a sugar.
Why glucose—and not another monosaccharide such as fructose—is so widely used in organisms is not clearly understood. One reason might be that glucose has a lower tendency, relative to other hexose sugars, to react non-specifically with the amino groups of proteins. This reaction (glycation) reduces or destroys the function of many enzymes. The low rate of glycation is due to glucose's preference for the less reactive cyclic isomer. Nevertheless, many of the long-term complications of diabetes (e.g., blindness, renal failure, and peripheral neuropathy) are probably due to the glycation of proteins or lipids. In contrast, enzyme-regulated addition of glucose to proteins by glycosylation is often essential to their function.]
[ Another reason as to why glucose is the most common sugar is that it is the most conformationally stable among other possibilities.
Glucose is a common medical analyte measured in blood samples. Eating or fasting prior to taking a blood sample has an effect on the result. A high fasting glucose blood sugar level may be a sign of prediabetes or diabetes mellitus.
Glucose is a ubiquitous fuel in biology. It is used as an energy source in most organisms, from bacteria to humans. Use of glucose may be by either aerobic respiration, anaerobic respiration, or fermentation. Glucose is the human body's key source of energy, through aerobic respiration, providing approximately 3.75 kilocalories (16 kilojoules) of food energy per gram. Breakdown of carbohydrates (e.g. starch) yields mono- and disaccharides, most of which is glucose. Through glycolysis and later in the reactions of the citric acid cycle (TCAC), glucose is oxidized to eventually form 2
CO and water, yielding energy sources, mostly in the form of ATP. The insulin reaction, and other mechanisms, regulate the concentration of glucose in the blood.
Glucose is a primary source of energy for the brain, and hence its availability influences psychological processes. When glucose is low, psychological processes requiring mental effort (e.g., self-control, effortful decision-making) are impaired.
Use of glucose as an energy source in cells is via aerobic or anaerobic respiration. Both of these start with the early steps of the glycolysis metabolic pathway. The first step of this is the phosphorylation of glucose by hexokinase to prepare it for later breakdown to provide energy. The major reason for the immediate phosphorylation of glucose by a hexokinase is to prevent diffusion out of the cell. The phosphorylation adds a charged phosphate group so the glucose 6-phosphate cannot easily cross the cell membrane. Irreversible first steps of a metabolic pathway are common for regulatory purposes.
In anaerobic respiration one glucose molecule produces a net gain of two ATP molecules (four ATP molecules are produced during glycolysis but two are required by enzymes used during the process). In aerobic respiration a molecule of glucose is much more profitable in that a net worth of 32 ATP molecules is generated (34 gross with two being required in the process).
Click on genes, proteins and metabolites below to link to respective articles.
Organisms use glucose as a precursor for the synthesis of several important substances. Starch, cellulose, and glycogen ("animal starch") are common glucose polymers (polysaccharides). Some of these polymers like starch or glycogen serve as energy stores while others like cellulose and chitin (which is made from a derivative of glucose) have structural roles. Oligosaccharides of glucose combined with other sugars serve as important energy stores. These include lactose, the predominant sugar in milk which a glucose-galactose disaccharide and sucrose, another disaccharide of glucose and fructose. Glucose is also added onto certain proteins and lipids in a process called glycosylation. This is often critical for their functioning. The enzymes that join glucose to other molecules usually use phosphorylated glucose to power the formation of the new bond by breaking the glucose-phosphate bond.
Other than its direct use as a monomer, glucose can be broken down to synthesize a wide variety of other biomolecules. This is important as glucose serves both as a primary store of energy but also as a source of organic carbon. Glucose can be broken down and converted into lipids. It is also a precursor for the synthesis of other important molecules like vitamin C (ascorbic acid). Though plants and some microbes can create all the compounds they need from glucose given the necessary minerals, all animals and many microbes cannot synthesize some or all of the necessary compounds and thus need to obtain them from an external source such as diet.
Glucose is a monosaccharide with formula C6
-H, whose five hydroxyl (OH) groups are arranged in a specific way along its six-carbon backbone.
In its fleeting open-chain form, the glucose molecule has an open (as opposed to cyclic) and unbranched backbone of six carbon atoms, C-1 through C-6; where C-1 is part of an aldehyde group H(C=O)-, and each of the other five carbons bears one hydroxyl group -OH. The remaining bonds of the backbone carbons are satisfied by hydrogen atoms -H. Therefore glucose is a hexose and an aldose, or an aldohexose.
Each of the four carbons C-2 through C-5 is a stereocenter, meaning that its four bonds connect to four different substitutents. (Carbon C-2, for example, connects to -(C=O)H, -OH, -H, and -(CHOH)4
H.) In D
-glucose, these four parts must be in a specific three-dimensional arrangement. Namely, when the molecule is drawn in the Fischer projection, the hydroxyls on C-2, C-4, and C-5 must be on the right side, while that on C-3 must be on the left side.
The positions of those four hydroxyls are exactly reversed in the Fischer diagram of -glucoseL
- and L
-glucose are two of the 16 possible aldohexoses; the other 14 are allose, altrose, mannose, gulose, idose, galactose, and talose, each with two enantiomers, "D
-" and "L
In solutions, the open-chain form of glucose (either "D
-" or "L
-") exists in equilibrium with several cyclic isomers, each containing a ring of carbons closed by one oxygen atom. In aqueous solution however, more than 99% of glucose molecules, at any given time, exist as pyranose. The open-chain form is limited to about 0.25% and furanose exists in negligible amounts. The terms "glucose" and "D
-glucose" are generally used for these cyclic forms as well. The ring arises from the open-chain form by a nucleophilic addition reaction between the aldehyde group -(C=O)H at C-1 and the hydroxyl group -OH at C-4 or C-5, yielding a hemiacetal group -C(OH)H-O-.
The reaction between C-1 and C-5 creates a molecule with a six-membered ring, called pyranose, after the cyclic ether pyran, the simplest molecule with the same carbon-oxygen ring. The (much rarer) reaction between C-1 and C-4 creates a molecule with a five-membered ring, called furanose, after the cyclic ether furan. In either case, each carbon in the ring has one hydrogen and one hydroxyl attached, except for the last carbon (C-4 or C-5) where the hydroxyl is replaced by the remainder of the open molecule (which is -(C(CH2
OH)HOH)-H or -(CHOH)-H, respectively).
The ring-closing reaction makes carbon C-1 chiral, too, since its four bonds lead to -H, to -OH, to carbon C-2, and to the ring oxygen. These four parts of the molecule may be arranged around C-1 (the anomeric carbon) in two distinct ways, designated by the prefixes "α-" and "β-". When a glucopyranose molecule is drawn in the Haworth projection, the designation "α-" means that the hydroxyl group attached to C-1 and the -CH2
OH group at C-5 lies on opposite sides of the ring's plane (a trans
arrangement), while "β-" means that they are on the same side of the plane (a cis
Therefore, the open-chain isomer D
-glucose gives rise to four distinct cyclic isomers: α-D
-glucofuranose, and β-D
-glucofuranose; which are all chiral.
The other open-chain isomer L
-glucose similarly gives rise to four distinct cyclic forms of L
-glucose, each the mirror image of the corresponding D
The rings are not planar but twisted in three dimensions. The glucopyranose ring (α or β) can assume several non-planar shapes, analogous to the "chair" and "boat" conformations of cyclohexane. Similarly, the glucofuranose ring may assume several shapes, analogous to the "envelope" conformations of cyclopentane.
The glucopyranose forms of glucose predominate in solution, and are the only forms observed in the solid state. They are crystalline colorless solids, highly soluble in water and acetic acid, poorly soluble in methanol and ethanol. They melt at (α) and (β), and decompose at higher temperatures into carbon and water.
Each glucose isomer is subject to rotational isomerism. Within the cyclic form of glucose, rotation may occur around the O6-C6-C5-O5 torsion angle, termed the ω
-angle, to form three staggered rotamer conformations called gauche
(gt) and trans
(tg). For methyl α-D
-glucopyranose at equilibrium the ratio of molecules in each rotamer conformation is reported as 57:38:5 gg:gt:tg. This tendency for the ω
-angle to prefer to adopt a gauche
conformation is attributed to the gauche effect.
All forms of glucose are colorless and easily soluble in water, acetic acid, and several other solvents. They are only sparingly soluble in methanol and ethanol.
The open-chain form is thermodynamically unstable, and it spontaneously isomerizes to the cyclic forms. (Although the ring closure reaction could in theory create four- or three-atom rings, these would be highly strained and are not observed.) In solutions at room temperature, the four cyclic isomers interconvert over a time scale of hours, in a process called mutarotation. Starting from any proportions, the mixture converges stable ratio of α:β 36:64. The ratio would be α:β 11:89 if it were not for the influence of the anomeric effect. Mutarotation is considerably slower at temperatures close to 0 °C.
Mutarotation consists of a temporary reversal of the ring-forming reaction, resulting in the open-chain form, followed by a re-forming of the ring. The ring closure step may use a different -OH group than the one recreated by the opening step (thus switching between pyranose and furanose forms), and/or the new hemiacetal group created on C-1 may have the same or opposite handedness as the original one (thus switching between the α and β forms). Thus, even though the open-chain form is barely detectable in solution, it is an essential component of the equilibrium.
Depending on conditions, three major solid forms of glucose can be crystallised from water solutions: α-glucopyranose, β-glucopyranose, and β-glucopyranose hydrate.
Whether in water
or in the solid form, D
-glucose is dextrorotatory, meaning that it will rotate the direction of polarized light clockwise. The effect is due to the chirality of the molecules, and indeed the mirror-image isomer, L
-glucose, is levorotatory (rotates polarized light counterclockwise) by the same amount. The strength of the effect is different for each of the five tautomers.
Note that the D
- prefix does not refer directly to the optical properties of the compound. It indicates that the C-2 chiral center has the same handedness as that of D
-glyceraldehyde (which was so labeled because it
is dextrorotatory). The fact that D
-glucose is dextrorotatory is a combined effect of its four chiral centers, not just of C-2; and indeed some of the other D
-aldohexoses are levorotatory.
In plants and some prokaryotes, glucose is a product of photosynthesis. In animals and fungi, glucose results from the breakdown of glycogen, a process known as glycogenolysis. In plants the breakdown substrate is starch.
In animals, glucose is synthesized in the liver and kidneys from non-carbohydrate intermediates, such as pyruvate, lactate and glycerol, by a process known as gluconeogenesis.
In some deep-sea bacteria, glucose is produced by chemosynthesis.
Glucose is produced commercially via the enzymatic hydrolysis of starch. Many crops can be used as the source of starch. Maize, rice, wheat, cassava, corn husk and sago are all used in various parts of the world. In the United States, cornstarch (from maize) is used almost exclusively. Most commercial glucose occurs as a component of invert sugar, an approximately 1:1 mixture of glucose and fructose. In principle, cellulose could be hydrolysed to glucose, but this process is not yet commercially practical.
Most dietary carbohydrates contain glucose, either as their only building block, as in starch and glycogen, or together with another monosaccharide, as in sucrose and lactose.
In the lumen of the duodenum and small intestine, the glucose oligo- and polysaccharides are broken down to monosaccharides by the pancreatic and intestinal glycosidases. Other polysaccharides cannot be processed by the human intestine and require assistance by intestinal flora if they are to be broken down; the most notable exceptions are sucrose (fructose-glucose) and lactose (galactose-glucose). Glucose is then transported across the apical membrane of the enterocytes by SLC5A1, and later across their basal membrane by SLC2A2. Some of the glucose is converted to lactic acid by astrocytes, which is then utilized as an energy source by brain cells, some of the glucose is used by intestinal cells and red blood cells, while the rest reaches the liver, adipose tissue and muscle cells, where it is absorbed and stored as glycogen (under the influence of insulin). Liver cell glycogen can be converted to glucose and returned to the blood when insulin is low or absent; muscle cell glycogen is not returned to the blood because of a lack of enzymes. In fat cells, glucose is used to power reactions that synthesize some fat types and have other purposes. Glycogen is the body's "glucose energy storage" mechanism, because it is much more "space efficient" and less reactive than glucose itself.
Because glucose is a basic necessity of many organisms, a correct understanding of its chemical makeup and structure contributed greatly to a general advancement in organic chemistry. This understanding occurred largely as a result of the investigations of Emil Fischer, a German chemist who received the 1902 Nobel Prize in Chemistry as a result of his findings. The synthesis of glucose established the structure of organic material and consequently formed the first definitive validation of Jacobus Henricus van't Hoff's theories of chemical kinetics and the arrangements of chemical bonds in carbon-bearing molecules. Between 1891 and 1894, Fischer established the stereochemical configuration of all the known sugars and correctly predicted the possible isomers, applying van't Hoff's theory of asymmetrical carbon atoms.
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