Ice it as quickly as possible, this prevents lactic acid from building up.
Lactic acid fermentation is a biological process by which glucose, fructose, and sucrose are converted into cellular energy and the metabolite lactate. It is an anaerobic fermentation reaction that occurs in some bacteria and animal cells, such as muscle cells.
If oxygen is present in the cell, many organisms will bypass fermentation and undergo cellular respiration; however, facultative anaerobic organisms will both ferment and undergo respiration in the presence of oxygen. Sometimes even when oxygen is present and aerobic metabolism is happening in the mitochondria, if pyruvate is building up faster than it can be metabolized, the fermentation will happen anyway.
Lactate dehydrogenase catalyzes the interconversion of pyruvate and lactate with concomitant interconversion of NADH and +NAD.
In homolactic fermentation, one molecule of glucose is ultimately converted to two molecules of lactic acid. Heterolactic fermentation, in contrast, yields carbon dioxide and ethanol in addition to lactic acid, in a process called the phosphoketolase pathway.
Lactic acid fermentation is used in many areas of the world to produce foods that cannot be produced through other methods. The most commercially important genus of lactic acid-fermenting bacteria is Lactobacillus, though other bacteria and even yeast are sometimes used. Two of the most common applications of lactic acid fermentation are in the production of yogurt and sauerkraut.
The main method of producing yogurt is through the lactic acid fermentation of milk with harmless bacteria. The primary bacteria used are typically Lactobacillus bulgaricus and Streptococcus thermophilus, and US law requires all yogurts to contain these two cultures (though others may be added as probiotic cultures). These bacteria produce lactic acid in the milk culture, decreasing its pH and causing it to congeal. The bacteria also produce compounds that give yogurt its distinctive flavor. An additional effect of the lowered pH is the incompatibility of the acidic environment with many other types of harmful bacteria.
For a probiotic yogurt, additional types of bacteria such as Lactobacillus acidophilus are also added to the culture.
Lactic acid fermentation is also used in the production of sauerkraut. The main type of bacteria used in the production of sauerkraut is of the genus Leuconostoc.
As in yogurt, when the acidity rises due to lactic acid-fermenting organisms, many other pathogenic microorganisms are killed. The bacteria produce lactic acid, as well as simple alcohols and other hydrocarbons. These may then combine to form esters, contributing to the unique flavor of sauerkraut.
Kimchi also uses lactic acid fermentation.
Glycolysis ⇄ Gluconeogenesis
Glycogenolysis ⇄ Glycogenesis
Pentose phosphate pathway Fructolysis Galactolysis
Photosynthesis Anoxygenic photosynthesis Chemosynthesis Carbon fixation
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)
130 °C, 403 K, 266 °F
is an organic compound with the formula HO2
H. It is a dicarboxylic acid that is made by all living organisms, contributes to the pleasantly sour taste of fruits, and is used as a food additive. Malic acid has two stereoisomeric forms (L
- and D
-enantiomers), though only the L
-isomer exists naturally. The salts and esters of malic acid are known as malates
. The malate anion is an intermediate in the citric acid cycle.
-Malic acid is the naturally occurring form, whereas a mixture of L
- and D
-malic acid is produced synthetically.
Malate plays an important role in biochemistry. In the C4 carbon fixation process, malate is a source of 2
CO in the Calvin cycle. In the citric acid cycle, (S
)-malate is an intermediate, formed by the addition of an -OH group on the si
face of fumarate. It can also be formed from pyruvate via anaplerotic reactions.
Malate is also synthesized by the carboxylation of phosphoenolpyruvate in the guard cells of plant leaves. Malate, as a double anion, often accompanies potassium cations during the uptake of solutes into the guard cells in order to maintain electrical balance in the cell. The accumulation of these solutes within the guard cell decreases the solute potential, allowing water to enter the cell and promote aperture of the stomata.
Malic acid was first isolated from apple juice by Carl Wilhelm Scheele in 1785. Antoine Lavoisier in 1787 proposed the name acide malique
which is derived from the Latin word for apple, mālum
. Malic acid contributes to the sourness of green apples. It is present in grapes and in most wines with concentrations sometimes as high as 5 g/l. It confers a tart taste to wine, although the amount decreases with increasing fruit ripeness. The taste of malic acid is very clear and pure in rhubarb, a plant for which it is the primary flavor.
The process of malolactic fermentation converts malic acid to much milder lactic acid. Malic acid occurs naturally in all fruits and many vegetables, and is generated in fruit metabolism.
Malic acid, when added to food products, is denoted by E number E296. Malic acid is the source of extreme tartness in USA-produced confectionery, the so-called extreme candy
. It is also used with or in place of the less sour citric acid in sour sweets. These sweets are sometimes labeled with a warning stating that excessive consumption can cause irritation of the mouth. It is approved for use as a food additive in the EU, USA and Australia and New Zealand (where it is listed by its INS number 296).
Racemic malic acid is produced industrially by the double hydration of maleic anhydride. In 2000, American production capacity was 5000 tonnes per year. Both enantiomers may be separated by chiral resolution of the racemic mixture, and the (S)- enantiomer may be specifically obtained by fermentation of fumaric acid.
Self-condensation of malic acid with fuming sulfuric acid gives the pyrone coumalic acid
Malic acid was important in the discovery of the Walden inversion and the Walden cycle, in which (-)-malic acid first is converted into (+)-chlorosuccinic acid by action of phosphorus pentachloride. Wet silver oxide then converts the chlorine compound to (+)-malic acid, which then reacts with PCl5
to the (-)-chlorosuccinic acid. The cycle is completed when silver oxide takes this compound back to (-)-malic acid.
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)
Biopreservation is the use of natural or controlled microbiota or antimicrobials as a way of preserving food and extending its shelf life. Beneficial bacteria or the fermentation products produced by these bacteria are used in biopreservation to control spoilage and render pathogens inactive in food. It is a benign ecological approach which is gaining increasing attention.
Of special interest are lactic acid bacteria (LAB). Lactic acid bacteria have antagonistic properties which make them particularly useful as biopreservatives. When LABs compete for nutrients, their metabolites often include active antimicrobials such as lactic and acetic acid, hydrogen peroxide, and peptide bacteriocins. Some LABs produce the antimicrobial nisin which is a particularly effective preservative.
A bacterium that is a suitable candidate for use as a biopreservative does not necessarily have to ferment the food. But if conditions are suitable for microbial growth, then a biopreservative bacterium will compete well for nutrients with the spoilage and pathogenic bacteria in the food. As a product of its metabolism, it should also produce acids and other antimicrobial agents, particularly bacteriocins. Biopreservative bacteria, such as lactic acid bacteria, must be harmless to humans.
These days LAB bacteriocins are used as an integral part of hurdle technology. Using them in combination with other preservative techniques can effectively control spoilage bacteria and other pathogens, and can inhibit the activities of a wide spectrum of organisms, including inherently resistant Gram-negative bacteria."
In fish processing, biopreservation is achieved by adding antimicrobials or by increasing the acidity of the fish muscle. Most bacteria stop multiplying when the pH is less than 4.5. Traditionally, acidity has been increased by fermentation, marination or by directly adding acetic, citric or lactic acid to food products. Other preservatives include nitrites, sulphites, sorbates, benzoates and essential oils.
Lactic acidosis is a physiological condition characterized by low pH in body tissues and blood (acidosis) accompanied by the buildup of lactate, especially D-lactate, and is considered a distinct form of metabolic acidosis. The condition typically occurs when cells receive too little oxygen (hypoxia), for example, during vigorous exercise. In this situation, impaired cellular respiration leads to lower pH levels. Simultaneously, cells are forced to metabolize glucose anaerobically, which leads to lactate formation. Therefore, elevated lactate is indicative of tissue hypoxia, hypoperfusion, and possible damage. Lactic acidosis is characterized by lactate levels >5 mmol/L and serum pH <7.35.
Most cells in the body normally metabolize glucose to form water and carbon dioxide in a two-step process. First, glucose is broken down to pyruvate through glycolysis. Then, mitochondria oxidize the pyruvate into water and carbon dioxide by means of the Krebs cycle and oxidative phosphorylation. This second step requires oxygen. The net result is ATP, the energy carrier used by the cell to drive useful work, such as muscle contraction. When the energy in ATP is used during cell work (ATP hydrolysis), protons are produced. The mitochondria normally incorporate these protons back into ATP, thus preventing buildup of protons and maintaining neutral pH.
If oxygen supply is inadequate (hypoxia), the mitochondria are unable to continue ATP synthesis at a rate sufficient to supply the cell with the required ATP. In this situation, glycolysis is increased to provide additional ATP, and the excess pyruvate produced is converted into lactate and released from the cell into the bloodstream, where it accumulates over time. While increased glycolysis helps compensate for less ATP from oxidative phosphorylation, it cannot bind the protons resulting from ATP hydrolysis. Therefore, proton concentration rises and causes acidosis.
The excess protons in lactic acidosis are widely believed to actually derive from production of lactic acid. This is incorrect, as cells do not produce lactic acid; pyruvate is converted directly into lactate, the anionic form of lactic acid. When excess intracellular lactate is released into the blood, maintenance of electroneutrality requires a cation (e.g. a proton) to be released, as well. This can reduce blood pH. Glycolysis coupled with lactate production is neutral in the sense that it does not produce excess protons. However, pyruvate production does produce protons. Lactate production is buffered intracellularly, e.g. the lactate-producing enzyme lactate dehydrogenase binds one proton per pyruvate molecule converted. When such buffer systems become saturated, cells will transport lactate into the bloodstream. Hypoxia certainly causes both buildup of lactate and acidification, and lactate is therefore a good "marker" of hypoxia, but lactate itself is not the cause of low pH.
Lactic acidosis sometimes occurs without hypoxia, for example, in rare congenital disorders where mitochondria do not function at full capacity. In such cases, when the body needs more energy than usual, for example during exercise or disease, mitochondria cannot match the cells' demand for ATP, and lactic acidosis results. Also, muscle types that have few mitochondria and preferentially use glycolysis for ATP production (fast-twitch or type II fibers) are naturally prone to lactic acidosis.
The signs of lactic acidosis are deep and rapid breathing, vomiting, and abdominal pain—symptoms that may easily be mistaken for other problems.
Lactic acidosis may be caused by diabetic ketoacidosis or liver or kidney disease, as well as some forms of medication (notably the antidiabetic drugs phenformin). Metformin is, however, unlikely to cause lactic acidosis although the belief remains in clinical practice. Some anti-HIV drugs (antiretrovirals) warn doctors in their prescribing information to regularly watch for symptoms of lactic acidosis caused by mitochondrial toxicity. Heavy metal toxicity, including arsenic poisoning, can raise lactate levels and lead to generalized metabolic acidosis as well.
In ruminant livestock, the cause of clinically serious lactic acidosis is different from the causes described above. See the "In animals" section, below.
The list of signs and symptoms of lactic acidosis includes the following:
The Cohen-Woods classification categorizes causes of lactic acidosis as follows:
The several different causes of lactic acidosis include:
Lactic acidosis is an underlying process of rigor mortis. Tissue in the muscles of the deceased carry out anaerobic metabolism in the absence of oxygen, using muscle glycogen as the energy source, and significant amounts of lactic acid are released into the muscle tissue. With depletion of muscle glycogen, the loss of ATP causes the muscles to grow stiff, as the actin-myosin bonds cannot be released. (Rigor is later resolved by enzymatic breakdown of the myofibers.) In meat-producing animals, the post-mortem pH drop in muscle tissue contributes to meat quality (by influencing water retention, cutting color and texture of meat) and also contributes to food safety by inhibiting several acid-intolerant spoilage organisms that otherwise might proliferate, even at refrigerator temperature.
Lactic acidosis may also result from 1vitamin B (thiamine) deficiency.
Reptiles, which rely primarily on anaerobic energy metabolism (glycolysis) for intense movements, can be particularly susceptible to lactic acidosis. In particular, during the capture of large crocodiles, the animals' use of their glycolytic muscles often alter the blood's pH to a point where they are unable to respond to stimuli or move. There are recorded cases in which particularly large crocodiles who put up extreme resistance to capture later died of the resulting pH imbalance.
In domestic ruminants, lactic acidosis may occur as a consequence of ingesting large amounts of grain, especially when the rumen population is poorly adapted to deal with grain. Activity of various rumen organisms results in accumulation of various volatile fatty acids (normally, mostly acetic, propionic and butyric acids), which are partially dissociated. Although some lactate is normally produced in the rumen, it is normally metabolized by such organisms as Megasphaera elsdenii and, to a lesser extent, Selenomonas ruminantium and some other organisms. With high grain consumption, the concentration of dissociated organic acids can become quite high, resulting in rumen pH dropping below 6. Within this lower pH range, Lactobacillus spp. (producing lactate and hydrogen ions) are favored, and M. elsdenii and S. ruminantium are inhibited, tending to result in a considerable rise of lactate and hydrogen ion concentrations in the rumen fluid. The pKa of lactic acid is low, about 3.9, versus, for example, 4.8 for acetic acid; this contributes to the considerable drop in rumen pH which can occur. Because of the high solute concentration of the rumen fluid under such conditions, considerable water is translocated from the blood to the rumen along the osmotic potential gradient, resulting in dehydration which cannot be relieved by drinking, and which can ultimately lead to hypovolemic shock. As more lactate accumulates and rumen pH drops, the ruminal concentration of undissociated lactic acid increases. Undissociated lactic acid can cross the rumen wall to the blood, where it dissociates, lowering blood pH. Both L and D isomers of lactic acid are produced in the rumen; these isomers are metabolized by different metabolic pathways, and activity of the principal enzyme involved in metabolism of the D isomer declines greatly with lower pH, tending to result in an increased ratio of D:L isomers as acidosis progresses. Measures for preventing lactic acidosis in ruminants include avoidance of excessive amounts of grain in the diet, and gradual introduction of grain over a period of several days, to develop a rumen population capable of safely dealing with a relatively high grain intake. Administration of lasalocid or monensin in feed can reduce risk of lactic acidosis in ruminants, inhibiting most of the lactate-producing bacterial species without inhibiting the major lactate fermenters. Also, using a higher feeding frequency to provide the daily grain ration can allow higher grain intake without reducing the pH of the rumen fluid. Treatment of lactic acidosis in ruminants may involve intravenous administration of dilute sodium bicarbonate, oral administration of magnesium hydroxide, and/or repeated removal of rumen fluids and replacement with water (followed by reinoculation with rumen organisms, if necessary).
noco/acba/cong/tumr, sysi/epon, urte
proc/itvp, drug (G4B), blte, urte
: 53 °C
: 53 °C
: 16.8 °C
122 °C @ 12 mmHg
, also known as milk acid
, is a chemical compound that plays a role in various biochemical processes and was first isolated in 1780 by the Swedish chemist Carl Wilhelm Scheele. Lactic acid is a carboxylic acid with the chemical formula C3
. It has a hydroxyl group adjacent to the carboxyl group, making it an alpha hydroxy acid (AHA).
In solution, it can lose a proton from the acidic group, producing the lactate
ion (to be specific, an anion due to being negatively charged with an extra electron) CH3
CH(OH)COO−. Compared to acetic acid, its a
pK is 1 unit less, meaning lactic acid deprotonates ten times as easily as acetic acid does. This higher acidity is the consequence of the intramolecular hydrogen bridge between the α-hydroxyl and the carboxylate group, making the latter less capable of strongly attracting its proton.
Lactic acid is miscible with water or ethanol, and is hygroscopic.
Lactic acid is chiral and has two optical isomers. One is known as L
-(+)-lactic acid or (S
)-lactic acid and the other, its mirror image, is D
-(−)-lactic acid or (R
In animals, L
-lactate is constantly produced from pyruvate via the enzyme lactate dehydrogenase (LDH) in a process of fermentation during normal metabolism and exercise. It does not increase in concentration until the rate of lactate production exceeds the rate of lactate removal, which is governed by a number of factors, including monocarboxylate transporters, concentration and isoform of LDH, and oxidative capacity of tissues. The concentration of blood lactate is usually at rest, but can rise to over 20 mmol/L during intense exertion.]
In industry, lactic acid fermentation is performed by lactic acid bacteria. These bacteria can also grow in the mouth; the acid they produce is responsible for the tooth decay known as caries.
In medicine, lactate is one of the main components of lactated Ringer's solution and Hartmann's solution. These intravenous fluids consist of sodium and potassium cations along with lactate and chloride anions in solution with distilled water, generally in concentrations isotonic with human blood. It is most commonly used for fluid resuscitation after blood loss due to trauma, surgery, or burn injury.
Lactic acid was refined for the first time by the Swedish chemist Carl Wilhelm Scheele in 1780 from sour milk. In 1808 Jöns Jacob Berzelius discovered that lactic acid (actually L-lactate) also is produced in muscles during exertion. Its structure was established by Johannes Wislicenus in 1873.
In 1856, Louis Pasteur discovered Lactobacillus
and its role in the making of lactic acid. Lactic acid started to be produced commercially by the German pharmacy Boehringer Ingelheim in 1895.
In 2006, global production of lactic acid reached 275,000 tonnes with an average annual growth of 10%.
During power exercises such as sprinting, when the rate of demand for energy is high, glucose is broken down and oxidized to pyruvate, and lactate is produced from the pyruvate faster than the tissues can remove it, so lactate concentration begins to rise. The production of lactate is a beneficial process because it regenerates +NAD which is used up in the creation of pyruvate from glucose, and this ensures that energy production is maintained and exercise can continue. The increased lactate produced can be removed in two ways:
Strenuous anaerobic exercise causes a lowering of pH and pain, called acidosis.
The effect of lactate production on acidosis has been the topic of many recent conferences in the field of exercise physiology. Robergs et al
. have discussed the creation of H+ ions that occurs during glycolysis. and claim that the idea that acidosis is caused by the production of lactic acid is a "construct" or myth, pointing out that part of the lowering of pH is due to the reaction ATP−4+H2
−2+H+, and that reducing pyruvate to lactate (pyruvate+NADH+H+=lactate+NAD+) actually consumes H+. However, a response by Lindinger et al
. has been written claiming that Robergs et al
. ignored the causative factors of the increase in concentration of hydrogen ions (denoted [H+]). Specifically, lactate is an anion, and its production causes a reduction in the amount of cations such as Na+ minus anions, and thus causes an increase in [H+] to maintain electroneutrality. Increasing partial pressure of CO2
, also causes an increase in [H+]. During exercise, the intramuscular lactate concentration and PCO2
increase, causing an increase in [H+], and thus a decrease in pH (see Le Chatelier's principle).
During intense exercise, the respiratory chain cannot keep up with the amount of hydrogen atoms that join to form NADH. NAD+ is required to oxidize 3-phosphoglyceraldehyde in order to maintain the production of anaerobic energy during glycolysis. During anaerobic glycolysis, NAD+ is “freed up” when NADH combines with pyruvate to form lactate (as mentioned above). If this did not occur, glycolysis would come to a stop. However, lactate is continually formed even at rest and during moderate exercise. This occurs due to metabolism in red blood cells that lack mitochondria, and limitations resulting from the enzyme activity that occurs in muscle fibers having a high glycolytic capacity.
Contrary to common belief, lactate or lactic acid buildup is not responsible for the muscle soreness felt in the days following strenuous exercise. The production of lactate and other metabolites during extreme exertion results in a burning sensation felt in active muscles. This painful sensation encourages one to stop overworking the body, thus forcing a recovery period in which the body clears the lactate and other metabolites.
Researchers who have examined lactate levels immediately following exercise found little correlation with the level of muscle soreness felt a few days later. This delayed onset muscle soreness (DOMS) is characterized by sometimes severe muscle tenderness as well as loss of strength and range of motion, usually reaching a peak 24 to 72 hours after the extreme exercise event.
The precise cause of DOMS is still unknown, though most research points to actual muscle cell damage and an elevated release of various metabolites into the tissue surrounding the muscle cells. These responses to extreme exercise result in an inflammatory-repair response, leading to swelling and soreness peaking a day or two after the event and resolves a few days later, depending on the severity of the damage. The type of muscle contraction is a key factor in the development of DOMS. When a muscle lengthens against a load the muscle contraction is said to be eccentric. The muscle is actively contracting, attempting to shorten its length, while failing. These eccentric contractions have been shown to result in more muscle cell damage than is seen with typical concentric contractions, in which a muscle successfully shortens during contraction against a load. Exercises that involve many eccentric contractions result in the most severe DOMS, even without any noticeable burning sensations in the muscles during the event.
Although glucose is usually assumed to be the main energy source for living tissues, there are some indications that it is lactate, and not glucose, that is preferentially metabolized by neurons in the brain of several mammals species (the notable ones being mice, rats, and humans). According to the lactate-shuttling hypothesis, glial cells are responsible for transforming glucose into lactate, and for providing lactate to the neurons. Because of this local metabolic activity of glial cells, the extracellular fluid immediately surrounding neurons strongly differs in composition from the blood or cerebro-spinal fluid, being much richer with lactate, as it was found in microdialysis studies.
The role of lactate for brain metabolism seems to be even more important at early stages of development (prenatal and early postnatal), with lactate at these stages having higher concentrations in body liquids, and being utilized by the brain even more preferentially over glucose. It was also hypothesized that lactate may exert a strong action over GABAergic networks in the developing brain, making them more inhibitory than it was previously assumed, acting either through better support of metabolites, or alterations in base intracellular pH levels, or both.
A more recent paper by Zilberter's group looked directly at the energy metabolism features in brain slices of mice and showed that beta-hydroxybutyrate, lactate and pyruvate acted as oxidative energy substrates causing an increase in the NAD(P)H oxidation phase, that glucose was insufficient as an energy carrier during intense synaptic activity and finally, that lactate can be an efficient energy substrate capable of sustaining and enhancing brain aerobic energy metabolism in vitro
. The paper was positively commented by Kasischke: "The study by Ivanov et al. (2011) also provides novel data on biphasic NAD(P)H fluorescence transients, an important physiological response to neural activation that has been reproduced in many studies and that is believed to originate predominately from activity-induced concentration changes to the cellular NADH pools."
Blood tests for lactate are performed to determine the status of the acid base homeostasis in the body. Blood sampling for this purpose is often by arterial blood sampling (even if it is more difficult than venipuncture), because lactate differs substantially between arterial and venous levels, and the arterial level is more representative for this purpose.
During childbirth, lactate levels in the fetus can be quantified by fetal scalp blood testing.
Two molecules of lactic acid can be dehydrated to lactide, a cyclic lactone. A variety of catalysts can polymerize lactide to either heterotactic or syndiotactic polylactide, which as biodegradable polyesters with valuable (inter alia
) medical properties are currently attracting much attention.
Lactic acid is used also as a monomer for producing polylactic acid (PLA), which later has developed application as biodegradable plastic. This kind of plastic is a good option for substituting conventional plastic produced from petroleum oil because of low emission of carbon dioxide. The commonly used process in producing lactic acid is via fermentation, and, later, to obtain the polylactic acid, the polymerization process follows.
Lactic acid is also employed in pharmaceutical technology to produce water-soluble lactates from otherwise insoluble active ingredients. It finds further use in topical preparations and cosmetics to adjust acidity and for its disinfectant and keratolytic properties.
Lactic acid is found primarily in sour milk products, such as koumiss, laban, yogurt, kefir, and some cottage cheeses. The casein in fermented milk is coagulated (curdled) by lactic acid. Lactic acid is also responsible for the sour flavor of sourdough breads. This acid is used in beer brewing to lower the wort pH in order to reduce some undesirable substances such as tannins without giving off-flavors such as citric acid and increase the body of the beer.]
[ Some brewers and breweries will use food grade lactic acid to lower the pH in finished beers.]
In winemaking, a bacterial process, natural or controlled, is often used to convert the naturally present malic acid to lactic acid, to reduce the sharpness and for other flavor-related reasons. This malolactic fermentation is undertaken by the family of lactic acid bacteria.
As a food additive it is approved for use in the EU, USA and Australia and New Zealand; it is listed by its INS number 270 or as E number E270. Lactic acid is used as a food preservative, curing agent, and flavoring agent. It is an ingredient in processed foods and is used as a decontaminant during meat processing. Lactic acid is produced commercially by fermentation of carbohydrates such as glucose, sucrose, or lactose, or by chemical synthesis. Carbohydrate sources include corn, beets, and cane sugar.
Lactic acid has gained importance in the detergent industry the last decade. It is a good descaler, soap-scum remover, and a registered anti-bacterial agent. It is also economically beneficial as well as part of a trend toward environmentally safer and natural ingredients.
M: ♀ FRS
proc/asst, drug (G1/G2B/G3CD)
The lactic acid bacteria (LAB) comprise a clade of Gram-positive, low-GC, acid-tolerant, generally non-sporulating, non-respiring rod or cocci that are associated by their common metabolic and physiological characteristics. These bacteria, usually found in decomposing plants and lactic products, produce lactic acid as the major metabolic end-product of carbohydrate fermentation. This trait has, throughout history, linked LAB with food fermentations, as acidification inhibits the growth of spoilage agents. Proteinaceous bacteriocins are produced by several LAB strains and provide an additional hurdle for spoilage and pathogenic microorganisms. Furthermore, lactic acid and other metabolic products contribute to the organoleptic and textural profile of a food item. The industrial importance of the LAB is further evinced by their generally recognized as safe (GRAS) status, due to their ubiquitous appearance in food and their contribution to the healthy microflora of human mucosal surfaces. The genera that comprise the LAB are at its core Lactobacillus, Leuconostoc, Pediococcus, Lactococcus, and Streptococcus as well as the more peripheral Aerococcus, Carnobacterium, Enterococcus, Oenococcus, Sporolactobacillus, Tetragenococcus, Vagococcus, and Weisella; these belong to the order Lactobacillales.
The lactic acid bacteria (LAB) are rod-shaped bacilli or cocci characterized by an increased tolerance to a lower pH range. This aspect partially enables LAB to outcompete other bacteria in a natural fermentation, as they can withstand the increased acidity from organic acid production (e.g., lactic acid). Laboratory media used for LAB typically include a carbohydrate source, as most species are incapable of respiration. LAB are catalase negative. They consist of the organelles of a simple bacterial structure. LAB are amongst the most important groups of microorganisms used in the food industry.
Two main hexose fermentation pathways are used to classify LAB genera. Under conditions of excess glucose and limited oxygen, homolactic LAB catabolize one mole of glucose in the Embden-Meyerhof-Parnas pathway to yield two moles of pyruvate. Intracellular redox balance is maintained through the oxidation of NADH, concomitant with pyruvate reduction to lactic acid. This process yields two moles of ATP per mole of glucose consumed. Representative homolactic LAB genera include Lactococcus, Enterococcus, Streptococcus, Pediococcus, and group I lactobacilli.
Heterofermentative LAB use the pentose phosphate pathway, alternatively referred to as the pentose phosphoketolase pathway. One mole of glucose-6-phosphate is initially dehydrogenated to 6-phosphogluconate and subsequently decarboxylated to yield one mole of CO2. The resulting pentose-5-phosphate is cleaved into one mole glyceraldehyde phosphate (GAP) and one mole acetyl phosphate. GAP is further metabolized to lactate as in homofermentation, with the acetyl phosphate reduced to ethanol via acetyl-CoA and acetaldehyde intermediates. In theory, end-products (including ATP) are produced in equimolar quantities from the catabolism of one mole of glucose. Obligate heterofermentative LAB include Leuconostoc, Oenococcus, Weissella, and group III lactobacilli.
In 1985, members of the diverse genus Streptococcus were reclassified into Lactococcus, Enterococcus, Vagococcus, and Streptococcus based on biochemical characteristics, as well as molecular features. In practice throughout history, streptococci were segregated primarily based on serology, which has proven to correlate well with the current taxonomic definitions. Lactococci (formerly Lancefield group N streptococci) are used extensively as starter innocula in dairy fermentations, with humans estimated to consume 1018 lactococci annually.][ Partly due to their industrial relevance, both Lactococcus lactis subspecies (lactis and cremoris) are widely used as generic LAB models for research. L. lactis ssp. cremoris, used in the production of hard cheeses, is represented by the laboratory strains LM0230 and MG1363. In similar manner, L. lactis ssp. lactis is employed in soft cheese fermentations, with the workhorse strain IL1403 ubiquitous in LAB research laboratories. In 2001, Bolotin et al. sequenced the genome of IL1403, which coincided with a significant shift of resources to understanding LAB genomics and related applications.
A broad number of food products, commodity chemicals, and biotechnology products are manufactured industrially by large-scale bacterial fermentation of various organic substrates. Because enormous amounts of bacteria are being cultivated each day in large fermentation vats, the risk that bacteriophage contamination rapidly brings fermentations to a halt and cause economical setbacks is a serious threat in these industries. The relationship between bacteriophages and their bacterial hosts is very important in the context of the food fermentation industry. Sources of phage contamination, measures to control their propagation and dissemination, and biotechnological defence strategies developed to restrain phages are of interest. The dairy fermentation industry has openly acknowledged the problem of phage contamination, and has been working with academia and starter culture companies to develop defence strategies and systems to curtail the propagation and evolution of phages for decades.
The first contact between an infecting phage and its bacterial host is the attachment of the phage to the host cell. This attachment is mediated by the phage's receptor binding protein (RBP), which recognizes and binds to a receptor on the bacterial surface. RBPs are also referred to as host-specificity protein, host determinant, and antireceptor. For simplicity, the RBP term will be used here. A variety of molecules have been suggested to act as host receptors for bacteriophages infecting LAB; among those are polysaccharides and (lipo)teichoic acids, as well as a single-membrane protein. A number of RBPs of LAB phages have been identified by the generation of hybrid phages with altered host ranges. These studies, however, also found additional phage proteins to be important for successful a phage infection. Analysis of the crystal structure of several RBPs indicated these proteins share a common tertiary folding, as well as supporting previous indications of the saccharide nature of the host receptor. The Gram-positive LAB have a thick peptidoglycan layer, which must be traversed to inject the phage genome into the bacterial cytoplasm. Peptidoglycan-degrading enzymes are expected to facilitate this penetration, and such enzymes have been found as structural elements of a number of LAB phages.
Probiotics are products aimed at delivering living, potentially beneficial, bacterial cells to the gut ecosystem of humans and other animals, whereas prebiotics are indigestible carbohydrates delivered in food to the large bowel to provide fermentable substrates for selected bacteria. Strains of LAB are the most common microbes employed as probiotics. Two principal kinds of probiotic bacteria, members of the genera Lactobacillus and Bifidobacterium, have been studied in detail.
Most probiotic strains belong to the genus Lactobacillus. Probiotics have been evaluated in research studies in animals and humans with respect to antibiotic-associated diarrhoea, travellers' diarrhoea, pediatric diarrhoea, inflammatory bowel disease, and irritable bowel syndrome. In the future, probiotics possibly will be used for different gastrointestinal diseases, vaginosis, or as delivery systems for vaccines, immunoglobulins, and other therapies.
The quest to find food ingredients with valuable bioactive properties has encouraged interest in exopolysaccharides from LAB. Functional food products that offer health and sensory benefits beyond their nutritional composition are becoming progressively more important to the food industry. The sensory benefits of exopolysaccharides are well established, and there is evidence for the health properties that are attributable to exopolysaccharides from LAB. However there is a wide variation in molecular structures of exopolysaccharides and the complexity of the mechanisms by which physical changes in foods and bioactive effects are elicited.
gr+f/gr+a (t)/gr-p (c)/gr-o
drug (J1p, w, n, m, vacc)
Hydroxypropanoic acid, or alternately hydroxypropionic acid, may refer to either of two isomeric chemical compounds:
The acids in wine are an important component in both winemaking and the finished product of wine. They are present in both grapes and wine, having direct influences on the color, balance and taste of the wine as well as the growth and vitality of yeast during fermentation and protecting the wine from bacteria. The measure of the amount of acidity in wine is known as the “titratable acidity” or “total acidity”, which refers to the test that yields the total of all acids present, while strength of acidity is measured according to pH, with most wines having a pH between 2.9 and 3.9. Generally, the lower the pH, the higher the acidity in the wine. However, there is no direct connection between total acidity and pH (it is possible to find wines with a high pH for wine and high acidity). In wine tasting, the term “acidity” refers to the fresh, tart and sour attributes of the wine which are evaluated in relation to how well the acidity balances out the sweetness and bitter components of the wine such as tannins. Three primary acids are found in wine grapes: tartaric, malic and citric acids. During the course of winemaking and in the finished wines, acetic, butyric, lactic and succinic acids can play significant roles. Most of the acids involved with wine are fixed acids with the notable exception of acetic acid, mostly found in vinegar, which is volatile and can contribute to the wine fault known as volatile acidity. Sometimes, additional acids, such as ascorbic, sorbic and sulfurous acids, are used in winemaking.
Tartaric acid is, from a winemaking perspective, the most important in wine due to the prominent role it plays in maintaining the chemical stability of the wine and its color and finally in influencing the taste of the finished wine. In most plants, this organic acid is rare, but it is found in significant concentrations in grape vines. Along with malic acid, and to a lesser extent citric acid, tartaric is one of the fixed acids found in wine grapes. The concentration varies depending on grape variety and the soil content of the vineyard. Some varieties, such as Palomino, are naturally deposed to having high levels of tartaric acids, while Malbec and Pinot noir generally have lower levels. During flowering, high levels of tartaric acid are concentrated in the grape flowers and then young berries. As the vine progresses through ripening, tartaric does not get metabolized through respiration like malic acid, so the levels of tartaric acid in the grape vines remain relatively consistent throughout the ripening process. Environment
Exercise physiology is the study of the acute responses and chronic adaptations to a wide range of physical exercise conditions. In addition, many exercise physiologists study the effect of exercise on pathology, and the mechanisms by which exercise can reduce or reverse disease progression. Accreditation programs exist with professional bodies in most developed countries, ensuring the quality and consistency of education. In Canada, one may obtain the professional certification title - Certified Exercise Physiologist for those working with clients (both clinical and non clinical) in the health and fitness industry.
An exercise physiologist's area of study may include but is not limited to biochemistry, bioenergetics, cardiopulmonary function, hematology, biomechanics, skeletal muscle physiology, neuroendocrine function, and central and peripheral nervous system function. Furthermore, exercise physiologists range from basic scientists, to clinical researchers, to clinicians, to sports trainers. Muscle
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