3-hydroxypropanoic Acid Can Be Produced Microbiologically From Sugars In Corn

[Milan Skidmore]

Inindustry, lactic acid fermentation is performed by lactic acid bacteria, which convert simple carbohydrates such as glucose, sucrose, or galactose to lactic acid. These bacteria can also grow in the mouth; the acid they produce is responsible for the tooth decay known as cavities.[12][13][14][15] 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 burns.

Lactic acid is produced in human tissues when the demand for oxygen is limited by the supply. This occurs during tissue ischemia when the flow of blood is limited. It may also occur more generally when demand is high such as with intense exercise.

Swedish chemist Carl Wilhelm Scheele was the first person to isolate lactic acid in 1780 from sour milk.[16] The name reflects the lact- combining form derived from the Latin word lac, meaning "milk". In 1808, Jns Jacob Berzelius discovered that lactic acid (actually L-lactate) also is produced in muscles during exertion.[17] Its structure was established by Johannes Wislicenus in 1873.

In 1856, the role of Lactobacillus in the synthesis of lactic acid was discovered by Louis Pasteur. This pathway was used commercially by the German pharmacy Boehringer Ingelheim in 1895.[citation needed]

As a starting material for industrial production of lactic acid, almost any carbohydrate source containing C

5 (Pentose sugar) and C

6 (Hexose sugar) can be used. Pure sucrose, glucose from starch, raw sugar, and beet juice are frequently used.[21] Lactic acid producing bacteria can be divided in two classes: homofermentative bacteria like Lactobacillus casei and Lactococcus lactis, producing two moles of lactate from one mole of glucose, and heterofermentative species producing one mole of lactate from one mole of glucose as well as carbon dioxide and acetic acid/ethanol.[22]

Racemic lactic acid is synthesized industrially by reacting acetaldehyde with hydrogen cyanide and hydrolysing the resultant lactonitrile. When hydrolysis is performed by hydrochloric acid, ammonium chloride forms as a by-product; the Japanese company Musashino is one of the last big manufacturers of lactic acid by this route.[23] Synthesis of both racemic and enantiopure lactic acids is also possible from other starting materials (vinyl acetate, glycerol, etc.) by application of catalytic procedures.[24]

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 then produced from the pyruvate faster than the body can process it, causing lactate concentrations to rise. The production of lactate is beneficial for NAD+ regeneration (pyruvate is reduced to lactate while NADH is oxidized to NAD+), which is used up in oxidation of glyceraldehyde 3-phosphate during production of pyruvate from glucose, and this ensures that energy production is maintained and exercise can continue. During intense exercise, the respiratory chain cannot keep up with the amount of hydrogen ions that join to form NADH, and cannot regenerate NAD+ quickly enough, so pyruvate is converted to lactate to allow energy production by glycolysis to continue.[25]

Lactate is continually formed at rest and during all exercise intensities. Lactate serves as a metabolic fuel being produced and oxidatively disposed in resting and exercising muscle and other tissues.[25] Some sources of excess lactate production are metabolism in red blood cells, which lack mitochondria that perform aerobic respiration, and limitations in the rates of enzyme activity in muscle fibers during intense exertion.[26] Lactic acidosis is a physiological condition characterized by accumulation of lactate (especially L-lactate), with formation of an excessively high proton concentration [H+] and correspondingly low pH in the tissues, a form of metabolic acidosis.[25]

Although glucose is usually assumed to be the main energy source for living tissues, there is evidence that lactate, in preference to glucose, is preferentially metabolized by neurons in the brains of several mammalian species that include mice, rats, and humans.[28][29][25] According to the lactate-shuttle hypothesis, glial cells are responsible for transforming glucose into lactate, and for providing lactate to the neurons.[30][31] Because of this local metabolic activity of glial cells, the extracellular fluid immediately surrounding neurons strongly differs in composition from the blood or cerebrospinal fluid, being much richer with lactate, as was found in microdialysis studies.[28]

Some evidence suggests that lactate is important at early stages of development for brain metabolism in prenatal and early postnatal subjects, with lactate at these stages having higher concentrations in body liquids, and being utilized by the brain preferentially over glucose.[28] 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,[32] acting either through better support of metabolites,[28] or alterations in base intracellular pH levels,[33][34] or both.[35]

Studies of brain slices of mice show that β-hydroxybutyrate, lactate, and pyruvate act 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.[36] The study "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 predominantly from activity-induced concentration changes to the cellular NADH pools."[37]

Lactate can also serve as an important source of energy for other organs, including the heart and liver. During physical activity, up to 60% of the heart muscle's energy turnover rate derives from lactate oxidation.[16]

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 arterial (even if it is more difficult than venipuncture), because lactate levels differ substantially between arterial and venous, and the arterial level is more representative for this purpose.

Two molecules of lactic acid can be dehydrated to the lactone lactide. In the presence of catalysts lactide polymerize to either atactic or syndiotactic polylactide (PLA), which are biodegradable polyesters. PLA is an example of a plastic that is not derived from petrochemicals.

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 kumis, 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 bread.

In lists of nutritional information lactic acid might be included under the term "carbohydrate" (or "carbohydrate by difference") because this often includes everything other than water, protein, fat, ash, and ethanol.[41] If this is the case then the calculated food energy may use the standard 4 kilocalories (17 kJ) per gram that is often used for all carbohydrates. But in some cases lactic acid is ignored in the calculation.[42] The energy density of lactic acid is 362 kilocalories (1,510 kJ) per 100 g.[43]

Some beers (sour beer) purposely contain lactic acid, one such type being Belgian lambics. Most commonly, this is produced naturally by various strains of bacteria. These bacteria ferment sugars into acids, unlike the yeast that ferment sugar into ethanol. After cooling the wort, yeast and bacteria are allowed to "fall" into the open fermenters. Brewers of more common beer styles would ensure that no such bacteria are allowed to enter the fermenter. Other sour styles of beer include Berliner weisse, Flanders red and American wild ale.[44][45]

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 lactic acid bacteria.

As a food additive it is approved for use in the EU,[47] United States[48] and Australia and New Zealand;[49] 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.[50] It is an ingredient in processed foods and is used as a decontaminant during meat processing.[51] Lactic acid is produced commercially by fermentation of carbohydrates such as glucose, sucrose, or lactose, or by chemical synthesis.[50] Carbohydrate sources include corn, beets, and cane sugar.[52]

Quantifying Ecosystem Processes in Feedstock Cropping Systems. Researchers sample soil respiration in a Miscanthus field to measure litter carbon respired by microbial decomposers. [Courtesy CABBI]

Sustainability: Improving the Environmental and Economic Bottom Line. CABBI is providing a holistic and systems-based approach to assess the economic and ecological sustainability of feedstocks, biofuels, and bioproducts developed in the Feedstock Production and Conversion research focus areas, at scales ranging from field to biorefinery to bioeconomy. Over the last 5 years, CABBI has improved fundamental understanding of ecosystem carbon, nitrogen, water, and energy fluxes in sorghum, Miscanthus, and Saccharum cropping systems and the effects of management practices and plant-microbe interactions on these ecosystem processes (Dracup et al. 2021; Tejera et al. 2019; Studt et al. 2021; Schetter et al. 2021; Hartman et al. 2022; Burnham et al. 2022; Yang, J., et al. 2022). Experimental results have been incorporated into a suite of ecosystem models: FUN-BioCROP, DayCent, and Agro-IBIS (Juice et al. 2022; Kent et al. 2020; Moore, C. E., et al. 2020; Ferin et al. 2021; Edmonds et al. 2021). The resulting improvements in cropping system representation have enabled model simulations that researchers used to generate mechanistic hypotheses for experimental testing (Hartman et al. 2022) and to assess ecosystem services production by CABBI crops across the rainfed United States.

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