Amino acids lactic acid bacteria

In more recent times chemically defined basal media have been elaborated, on which the growth of various lactic acid bacteria is luxuriant and acid production is near-optimal. The proportions of the nutrients in the basal media have been determined which induce maximum sensitivity of the organisms for the test substance and minimize the stimulatory or inhibitory action of other nutrilites introduced with the test sample. Assay conditions have been provided which permit the attainment of satisfactory precision and accuracy in the determination of amino acids. Experimental techniques have been provided which facilitate the microbiological determination of amino acids. On the whole, microbiological procedures now available for the determination of all the amino acids except hydroxy-proline are convenient, reasonably accurate, and applicable to the assay of purified proteins, food, blood, urine, plant products, and other types of biological materials. On the other hand, it is improbable that any microbiological procedure approaches perfection and it is to be expected that old methods will be improved and new ones proposed by the many investigators interested in this problem. 

Penicillium caseicolum produces an extracellular aspartyl proteinase and a metalloproteinase with properties very similar to those of the extracellular enzymes produced by P roqueforti (Trieu-Cout and Gripon 1981 Trieu-Cout et al. 1982). Breakdown of casein in mold-ripened cheese results from the synergistic action of rennet and the proteases of lactic streptococci and penicillia (Desmazeaud and Gripon 1977). Peptidases of both lactic acid bacteria and penicillia contribute to formation of free amino acid and nonprotein nitrogen (Gripon et al. 1977). 

Enterobacter aerogenes, B. subtilis, P. fluorescens, and Serratia marces-cens produce acetoin by decarboxylation of a-acetolactate. However, yeasts and E. coli form acetoin from the acetaldehyde-TPP complex and free acetaldehyde (Rodopulo et al 1976). These organisms do not decarboxylate a-acetolactate, but use it to produce valine and pantothenic acid. In lactic acid bacteria, a-acetolactate is not used for valine or pantothenic acid synthesis, since these substances are required for growth (Law et al. 1976B Reiter and Oram 1962). In those microorganisms which can synthesize valine, this amino acid inhibits a-acetolactate synthesis (Rodopulo et al 1976). 

Of all the metabolic activities that lactic acid bacteria can carry out in wine, the most important, or desirable, in winemaking is the breakdown of malic acid, but only when it is intended for this to be removed completely from the wine by malolactic fermentation. Although the breakdown of malic and citric acids has considerable consequences from a winemaking perspective, it is also evident that lactic acid bacteria metabolise other wine substrates to ensure their multiplication, including sugars, tartaric acid, glycerine and also some amino acids. We will now describe some of the metabolic transformations that have received most attention in the literature, or which have important repercussions in winemaking. 

Most studies to screen for biogenic amine-producing lactic acid bacteria use differential media that contain the precursor amino acid and a pH indicator. This indicator, usually purple bromocresol, will change colour when the medium is alkalinized and this colour change will be observed in the medium if the lactic acid bacteria produce amines (Bover-Cid and Holzapfel 1999 Choudhury et al. 1990 Maijala 1993). 

When the diastase of the malt has had time to act the mash is inoculated with a smaller special mash of rye and malt in which a pure culture of lactic acid bacteria (Bacillus delbruckii) is growing. The mash is now incubated for about sixteen hours at the proper temperature (ca. 50° C., 1220 F.). During this time the proteins of the grains are partially hydrolyzed and some lactic acid is formed. The liquor now contains largely sugars, resulting from the action of malt diastase on the starch, lactic acid, amino acids, and other hydrolysis products of the proteins, all in a highly assimilable form for the yeasts, and the cellulose residues from the cereals. 

Although lactic acid bacteria (LAB) are weakly proteolytic they do possess a proteinase and a wide range of peptidases which are principally responsible for the formation of small peptides and amino acids in cheese. The genus most widely used as a cheese starter is Lactococcus, the proteolytic system of which has been studied thoroughly at the molecular, biochemical, and genetic levels. The proteolytic system of Lactobacillus spp. is less well characterized than that of Lactococcus, but the systems of both genera appear to be generally similar. 

Lactacin F was the first non-lantibiotic bacteriocin characterized in lactic acid bacteria for which both DNA and protein sequences were available [77, 203]. This information demonstrated that lactacin F is translated as a 75-amino acid residue precursor which is posttranslationally processed by cleavage of a... 

Contrary to what one sometimes hears or reads. Nature does not favour one particular twist. For example, (+) - and ( — )-quartz are equally common and so are ( +)- and ( —)-lactic acids. Bacteria are as mortally injured by deprivation of D- as of L-alanine (Section 5.3) and, although a mixture ofD- and L-amino acids cannot be fitted into the structure of a protein, they are often found side-by-side... 

Cereal flours Fermentation of sourdough with lactic acid bacteria 25 Peptides (8—57 amino acid residues) Coda et al. (2012)... 

Teramoto K, Sato H, Sun L, Torimura M, Tao H. A simple intact protein analysis by MALDI-MS for characterization of ribosomal proteins of two genome-sequenced lactic acid bacteria and verification of their amino acid sequences. J Proteome Res. 2007 6(10) 3899-907. doi 10.1021/pr0702181. 

Dozens of different peptides have been identified in cheeses. Most of them arise from and -caseins and a few are from aj2-and K-caseins. The proteinases involved in hydrolysis of aj -casein are mainly cathepsin D originating from milk and cell-envelope proteinase from thermophilic starters, while P- and aj2-caseins are mainly hydrolysed by plasmin. Moreover, peptidases from starters are also active throughout the ripening process, presumably similar to those from non-starter lactic acid bacteria. For example, the bitterness of mature Gouda cheese is caused by calcium and magnesium chlorides, some bitter-tasting free amino acids and is modified by peptides, which arise from the hydrolysis of fS-casein (such as decapeptide Tyr-Pro-Phe-Pro-Gly-Pro-Ile-His-Asn-Ser and derived nonanpeptide without the terminal serine) and casein (tetrapeptide Leu-Pro-Gln-Glu). 

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