Lactic acid acidification

Lactic acidosis A condition caused by build-up of lactic acid in the body. It leads to acidification of the blood (acidosis), and is a form of metabolic acidosis. 

Simultaneous and continuous measurements of extracellular pH, potassium K+, and lactate in an ischemic heart were carried out to study lactic acid production, intracellular acidification, and cellular K+ loss and their quantitative relationships [6, 7], The pH sensor was fabricated on a flexible kapton substrate and the pH sensitive iridium oxide layer was electrodeposited on a planar platinum electrode. Antimony-based pH electrodes have also been used for the measurement of myocardial pH in addition to their application in esophageal acid reflux detection. 

These new fermentation processes often require high costs for recovering the product from the fermentation broth. For instance, the production of lactic acid requires the neutralization of the product during the fermentation, to avoid acidification of the medium, and the subsequent re-acidification of the lactate [65]. Similarly, the recovery of 1-butanol implies the distillation of large amounts of water. Alternative recovery processes are therefore the subject of intensive research. 

An improvement of the productivity of the NF-based process to 7.1gl h is obtained by running the process semi-continuously [64]. Final lactic acid concentrations in the permeate can reach values between 10 and 60 g 1 . The higher values are at the lower limit of concentrations found in UF- and MF-based processes [60]. Based on these data, a three-step repetitive process has been proposed [64]. The first step is the cell multiplication step during which pH can be controlled, the second step is an acid production step, followed by NF. In this approach a constant pH is assumed during each separate process step. However, other strategies in the acidification stage, which make use of natural acidification by the lactic acid bacteria are also possible. 

For laboratory-scale production of casein, HC1 is usually used for acidification acetic or lactic acids are used less frequently. Industrially, HC1 is also usually used H2S04 is used occasionally but the resulting whey is not suitable for animal feeding (MgS04 is a laxative). Lactic acid produced in situ by a culture of lactic acid bacteria is also widely used, especially in New Zealand, the principal producer of casein. 

Acid production is a key feature in the manufacture of all cheese varieties -the pH decreases to about 5 ( 0.3, depending on variety) within 5-20h, at a rate depending on the variety (Figure 10.11). Acidification is normally achieved via the bacterial fermentation of lactose to lactic acid, although an acidogen, usually gluconic acid-<5-lactone, alone or in combination with acid, may be used in some cases, e.g. Mozzarella. 

The contribution of these agents, individually or in various combinations, has been assessed in model cheese systems from which one or more of the agents was excluded or eliminated, e.g. by using an acidogen rather than starter for acidification or manufacturing cheese in a sterile environment to eliminate non-starter lactic acid bacteria (NSLAB). Such model systems have given very useful information on the biochemistry of ripening. 

The lactate formed by active skeletal muscles (or by erythrocytes) can be recycled it is carried in the blood to the liver, where it is converted to glucose during the recovery from strenuous muscular activity. When lactate is produced in large quantities during vigorous muscle contraction (during a sprint, for example), the acidification that results from ionization of lactic acid in muscle and blood limits the period of vigorous activity. The best-conditioned athletes can sprint at top speed for no more than a minute (Box 14-1). 

Commercial casein is usually manufactured from skim milk by precipitating the casein through acidification or rennet coagulation. Casein exists in milk as a calcium caseinate-calcium phosphate complex. When acid is added, the complex is dissociated, and at pH 4.6, the isoelectric point of casein, maximum precipitation occurs. Relatively little commercial casein is produced in the United States, but imports amounted to well over 150 million lb in 1981 (USDA 1981C). Casein is widely used in food products as a protein supplement. Industrial uses include paper coatings, glues, plastics and artificial fibers. Casein is typed according to the process used to precipitate it from milk, such as hydrochloric acid casein, sulfuric acid casein, lactic acid casein, coprecipitated casein, rennet casein, and low-viscosity casein. Differences... 

Acidification to the isolectric pH of casein using lactic acid bacteria or food-grade acids/acidogens, at 20 40 C. and resultant slow quiescent aggregation of the sensitized casein micelles e.g., for cream cheese. [A combination of acidification and rennet-hydrolysis (a smaller quantity of rennet than for rennet-curd cheeses, e.g., 5-100 versus 900-1000 chymosin units per 100 L milk) is normally used for low-fat acid-curd cheeses such as Quark and related varieties (Schulz-Collins and Senge, 2004)]... 

Whey is the liquid obtained by separating the coagulum from milk, cream, and/or skim milk in cheese making. Whey obtained from the process in which a significant amount of lactose is converted to lactic acid or obtained from the curd formed by direct acidification of milk is known as acid-type Whey. Whey obtained from the process in which there is insignificant conversion of lactose to lactic acid is known as sweet-type Whey. The acidity of Whey may be adjusted by the addition of safe and suitable pH-adjusting ingredients. The final product is pasteurized and is available as a liquid or dry product. 

Acidification of the culture supernatant, filtration, treatment with active charcoal and concentration usually result in food-grade lactic acid, if the feedstock was pure glucose. Otherwise, more extensive purification may be required. 

J )-l-phen ielhylamine to give the R,R salt, and (5)-lactic acid reacts w ith the R aiiiine to give the S,R salt. The two salts are diastereomers they are ditl erent compounds, with different chemical and physical properties. It may therefore be possible to sepeuate them by crystallization or some other means. Once separated, acidification of the two diastereomeric salts with a strong acid then allow s us to isolate the two pure enantiomers of lactic acid and to recover the chiral amine for reuse. 

Hyperventilation in lactic acidosis is more intense than in other forms of metaboHc acidosis. It is believed that this is because of the participation of the respiratory center in lactic acid production and the resulting greater local acidification of the respiratory center. During exercise, lactate levels may increase significantly, from an average normal concentration of -0.9 mmol/L to 12 mmol/L. However, under normal conditions, the lactate is rapidly metabolized so that the "acidosis is only transient. 

Fruit juices prepared from the pulp contain relatively large amounts of citric acid (Hayakawa, Linko, and Linko, 1999). In most juices citrate is omnipresent, and malic acid is present in high concentrations, with minute concentrations of other organic acids such as lactic acid (Arellano et al., 1997). Lemon juice is often used as an alternative to acidification with citric acid (Valero et al., 2000). 

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