Lactic streptococci

Cultured buttermilk is manufactured by fermenting whole milk, reconstituted nonfat dry milk, partly skimmed milk, or skim milk with lactic acid bacteria. Most commercial cultured buttermilk is made from skim milk. Mixed strains of lactic streptococci are used to produce lactic acid and leuconostocs for development of the characteristic diacetyl flavor and aroma. Buttermilk is similar to skim milk in composition, except that it contains about 0.9% total acid expressed as lactic acid. The percentage of lactose normally found in skim milk is reduced in proportion to the percentage of lactic acid in the buttermilk. According to White (1978), the fat content of buttermilk usually varies from 1 to 1.8%, sometimes in the form of small flakes or granules to simulate churned buttermilk, the by-product of butter churning. Usually 0.1% salt is added. 

Kanno, C., Emmons, D. B., Harwalker, V. R. and Elliott, J. A. 1976. Purification and characterization of the agglutinating factor for lactic streptococci from bovine milk IgM immunoglobulin. J. Dairy Sci. 59, 2036-2045. 

The lactic streptococci used in cheese manufacture produce only the l( + ) isomer of lactic acid (Lawrence et al. 1976). However, ripened cheeses contain both d(-) and l( + ) lactate isomers (T irner and Thomas 1980). Nonstarter bacteria (pediococci and lactobacilli) form d( —) lactate from residual lactose or by conversion of l( + ) lactate (Thomas and Crow 1983). 

Vitamins and Minerals. Milk is a rich source of vitamins and other organic substances that stimulate microbial growth. Niacin, biotin, and pantothenic acid are required for growth by lactic streptococci (Reiter and Oram 1962). Thus the presence of an ample quantity of B-complex vitamins makes milk an excellent growth medium for these and other lactic acid bacteria. Milk is also a good source of orotic acid, a metabolic precursor of the pyrimidines required for nucleic acid synthesis. Fermentation can either increase or decrease the vitamin content of milk products (Deeth and Tamime 1981 Reddy et al. 1976). The folic acid and vitamin Bi2 content of cultured milk depends on the species and strain of culture used and the incubation conditions (Rao et al. 1984). When mixed cultures are used, excretion of B-complex vita-... 

The most important fermentative reaction used in dairy processing is the homofermentative conversion of lactose to lactic acid. The efficient manufacture of high-quality cultured products, including most cheese varieties, yogurt, and cultured buttermilk, requires a rapid and consistent rate of lactic acid production. Lactic acid helps to preserve, contributes to the flavor, and modifies the texture of these products. Nearly all starter cultures used to produce acidified dairy products contain one or more strains of lactic streptococci, because these organisms can produce the desired acidity without causing detrimental changes in flavor or texture. Strains of lactic streptococci can be classified as... 

Figure 13.3 Alternative pathways of pyruvate metabolism by homofer-mentative lactic streptococci. CoA = coenzyme A TPP = thiamine pyrophosphate. (Adapted from Thomas et at. 1979.)...

NADH oxidase (Grufferty and Condon 1983). Not all lactic streptococci express these alternative pathways. However, these deficient strains grow poorly under conditions producing low nLDH activity. 

Thomas and Mills (1981) have reviewed the literature on the proteolytic enzymes of lactic streptococci. Lactic streptococci present in... 

During cheese ripening, proteases associated with starter culture organisms are released into cheese after cell lysis (Law et al. 1974). The proteolytic activity associated with lysed lactic streptococci is necessary for proper flavor development in Cheddar and other cheese varieties. The role of streptococcal proteases and peptidases appears to be production of flavor compound precursors such as methionine and other amino acids, rather than direct production of flavor compounds (Law et al. 1976A). Additional discussion of cheese ripening is presented in Chapter 12. 

Lactic streptococci initiate casein degradation through the action of cell wall-associated and cell membrane-associated proteinases and peptidases. Small peptides are taken into the cell and hydrolyzed to their constituent amino acids by intracellular peptidases (Law and Sharpe 1978). Peptides containing four to seven residues can be transported into the cell by S. cremoris (Law et al. 1976B). S. lactis and S. cremoris have surface-bound peptidases and thus are not totally dependent on peptide uptake for protein use (Law 1979B). Some surface peptidases of S. cremoris are located in the cell membrane, whereas others are located at the cell wall-cell membrane interface (Exterkate 1984). Lactic streptococci have at least six different aminopeptidase activities, and can be divided into three groups based on their aminopeptidase profiles (Kaminogawa et al 1984). 

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). 

Cogan, T. M. 1980. Mesophilic lactic streptococci A review. Lait 60, 397-425. (French)... 

Collins, E. B. 1961. Domination among strains of lactic streptococci with attention to antibiotic production. Appl. Microbiol. 9, 200-205. 

Forsen, R. and Haiva, V. 1981. Induction of stable slime-forming and mucoid states by p-fluorophenylalanine in lactic streptococci. FEMS Microbiol. Lett. 12, 409-413. 

Gibson, C. A., Landerkin, G. B. and Morse, P. M. 1966. Effects of additives on the survived of lactic streptococci in frozen storage. Appl Microbiol. 14, 665-669. 

Gilliland, S. E. and Speck, M. L. 1972. Interactions of food starter cultures and food-borne pathogens Lactic streptococci versus staphylococci and salmonellae. J. Milk Food Technol. 35, 307-310. 

Harper, W. J., Carmona de Catril, A. and Chen, J. L. 1980. Esterases of lactic streptococci and their stability in cheese slurry system. Milchwissenschaft 35, 129-132. 

Hogarty, S. L. and Frank, J. F. 1982. Low temperature activity of lactic streptococci isolated from cultured buttermilk. J. Food Prot. 45, 1208-1211. 

Hoyle, M. and Nichols. A. A. 1948. Inhibitory strains of lactic streptococci and then-significance in the selection of cultures for starter. J. Dairy Res. 15, 398-408. 

Keen, A. R. 1972. Growth studies on lactic streptococci. III. Observations on continuous growth behaviour in reconstituted skim-milk. J. Dairy Res. 39, 151-159. 

Macura, D. and Townsley, P. M. 1984. Scandinavian ropy milk—Identification and characterization of endogenous ropy lactic streptococci and their extracellular excretion. 

Mattick, A. T. R. and Hirsch, A. 1947. Further observations on an inhibitory substance (nisin) from lactic streptococci. Lancet 253, 5-7. 

McKay, L. L. 1983. Functional properties of plasmids in lactic streptococci. Antonie van Leuwenhoek 49, 259-274. 

Okamoto, T. and Morichi, T. 1979. Distribution of 0-galactosidase and 0-phosphogalac-tosidase activity among lactic streptococci. Agr. BioL Chem. 43, 2389-2390. 

Thomas, T. D. 1975. Tagatose-1,6-diphosphate activation of lactate dehydrogenase from Streptococcus cremoris. Biochem. Biophys. Res. Commun. 63, 1035-1042. Thomas, T. D. 1976A. Activator specificity of pyruvate kinase from lactic streptococci. J. BacterioL 125, 1240-1242. 

This patent describes a method of processing milk in which bifidus bacteria and lactic streptococci are introduced, along with a citrus vitamin additive and Jerusalem artichoke juice, powder, or syrup. 

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