The present study pertains to the effect of nutritional factors on the growth and production of antimicrobial substances (AS) by Streptococcus lactis subsp. diacetylactis S1-67/C. Among nine media tested, yeast extract dextrose broth supported good growth and maximum production of AS. Addition of beef extract and yeast extract at 1.0 and 0.6% levels, respectively, increased growth as well as production of AS. Of ten carbohydrates examined, maximum production of AS was achieved with 1% glucose followed by fructose, 4% molasses, lactose, sucrose, galactose, mannitol, maltose and 2% molasses. Xylose inhibited production of AS, although it stimulated growth of the organism. Peptone, tryptone and tryptose (each at the 1.5% level) significantly stimulated production of AS. Other nitrogen sources, including soytone, casein hydrolysate and proteose peptone, retarded production of inhibitory substances. Among the amino acids, L-leucine, DL-methionine and L-glutamic acid were most essential for growth and production of AS, whereas L-lysine, L-proline, DL-serine, DL-asparatic acid, L-arginine-HCl and DL-tryptophan were stimulatory. Other amino acids such as DL-ornithine, L-cysteine-HCl and DL-citrulline slightly stimulated AS production. In the presence of cynocobalmin, niacin, folic acid, calcium pantothenate and riboflavin, S. lactis subsp. diacetylactis S1-67/C produced maximum amounts of inhibitory substances. Omission of individual mineral salts from the basal medium did not affect production of AS by the organism.

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Author notes

1Department of Animal Products Technology, Faculty of Agriculture, Okayama University, Okayama Sh-700, Japan.