Lactic acid lactis

Poly(L-lactic acid) Lacty Shimadzu Environmental, biomedical b... 

Cultured buttermilk is that which is produced by the fermentation (qv) of skimmed milk often with some cream added. The principal fermentation organisms used are l ctococcus lactis suhsp. cremoris l ctococcus lactis suhsp. lactis and l euconostoc citrovorum. The effect of the high processing temperature and the lactic acid provide an easily digestible product. 

Fermentations in larger vessels and the final trade fermentation are conducted under quasi-stetile conditions, and yeast growth is accompanied by some growth of contaminant bacteria. These are generally lactic acid-producing organisms but are sometimes coHform bacteria the occurrence of Salmonella in fermentor Hquids has not been reported. Massive contamination with Oidium lactis or wild yeasts has been reported. 

Lactic acid bacteria are common contaminants of distillers fermentations. E. lactis may produce excessive amounts of volatile acids. Some species convert glycerol to fdpropionaldehyde which may break down to acrolein during distillation, producing an acrid odor. 

Addition of acetic or mineral acid to skimmed milk to reduce the pH value to 4.6, the isoelectric point, will cause the casein to precipitate. As calcium salts have a buffer action on the pH, somewhat more than the theoretical amount of acid must be used. Lactic acid produced in the process of milk souring by fermentation of the lactoses present by the bacterium Streptococcus lactis will lead to a similar precipitation. 

The inability to obtain complete protein sequence analysis of purified bacteriocins has been reason to suspect the presence of N-blocked peptide sequences (34) or lantibiotic residues (14). Recently, Piard et al. (14) have shown from partial sequencing and composition analysis that lacticin 481, a broad spectrum bacteriocin produced by L. lactis 481, also contains lanthionine residues. The early widespread interest in nisin and nisin-producing strains had given the impression that lantibiotics may be characteristic of bacteriocins of lactic acid bacteria. However, recent studies with other LAB bacteriocins suggest that simple peptide bacteriocins may prevail among the LAB. 

Fruity flavor in Cheddar cheese is also associated with high levels of ethyl butyrate and ethyl hexanoate (Bills et al. 1965). However, this defect is usually caused by esterase activity from lactic acid bacteria, especially S. lactis and S. lactis subsp. diacetylactis (Vedamuthu et al. 1966). Fruity-flavored cheeses tend to have abnormally high levels of ethanol, which is available for esterification (Bills et al. 1965). Streptococcal esterase activity in cheese is affected by the level of glutathione, which suggests a dependence on free sulfhydral groups for activity (Harper et al. 1980). 

Reiter et al. (1964) showed that growth of S. aureus in raw, steamed, and pasteurized milk was inhibited by a lactic starter culture. When they neutralized the lactic acid as it was produced, inhibition of the staphylococcus was still evident. Jezeski et al. (1967) also observed that growth of S. aureus in steamed or sterile reconstituted nonfat dry milk was inhibited by an actively growing S. lactis culture. Enter-otoxin was detected in S. aureus-S. lactis mixed cultures when S. lactis was inactivated by bacteriophage but not when the lactic streptococcus grew normally. Further information on S. aureus has been summarized by Minor and Marth (1976). 

Cousin, M. A. and Marth, E. H. 1977C. Lactic acid production by Streptococcus lactis and Streptococcus cremoris in milk precultured with psychrotrophic bacteria. J. Food Prot. 40, 406-410. 

Galesloot, T. E. 1956. Lactic acid bacteria which destroy the antibioticum (nisin) of S. lactis. Ned. Melk. Zuiveltijdschr. 10, 143-154. (Dutch)... 

Mellerick, D. and Cogan, T. M. 1981. Induction of some enzymes of citrate metabolism in Leuconostoc lactis and other heterofermentative lactic acid bacteria. J. Dairy Res. 48, 497-502. 

Peeirce, L. E., Skipper, N. A. and Jeirvis, B. D. W. 1974. Proteinase activity in slow lactic acid producing veiriants of Streptococcus lactis. Appl. Microbiol 27, 933-937. 

In the current industrial process, nisin is manufactured by fermentation of L. lactis subsp. lactis in a milk-based medium. Biosynthesis of nisin is coupled with the growth of lactic acid bacteria and the production of a significant amount of lactic acid (7). Lactic acid is an important chemical for food processing. It can also be used as a raw material in the production of the biodegradable polymer poly(lactic) acid (12). Unfortunately, lactic acid is not recovered in the current nisin process. 

Table 4 gives the seven variables chosen as candidate factors with their assigned low and high levels. Table 1 provides the 12-run PB design used to identify which variables have significant effects on nisin and lactic acid production by L. lactis. Table 5 shows the resulting effects of the variables on the responses and the associated Lvalues and significant levels. 

The significance of yeast extract and KH2P04 for lactic acid formation indicates the important role of protein and inorganic phosphate in the metabolism of L. lactis. The lesser influence of polypeptone compared with yeast extract proves that yeast extract is a good nitrogen source for nisin and lactic acid production. The influences of pH and temperature were not significant in this screening experiment, because this test was carried out close to the optimal conditions of these two variables (16). 

Lactic acid (2-hydroxypropionic acid, CH3CH0HC02H, boiling point 122°C, melting point 18°C, density 1.2060) is one of the oldest known organic acids. It is the primary acid constituent of sour milk and is formed by the fermentation of milk sugar (lactose) by Streptococcus lactis. 

Hofvendahl, K., Akerberg, C., Zacchi, G. and Hahn-Hagerdal, B. 1999. Simultaneous Enzymatic Wheat Starch Saccharification and Fermentation to Lactic Acid by Lactococcus Lactis. Appl. 

Kleerebezemab, M., Hols, P., and Hugenholtz, J. 2000. Lactic acid bacteria as a cell factory rerouting of carbon metabolism in Lactococcus lactis by metabolic engineering. Enz. Microbial Technol., 26, 840-848. 

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