Growth requirements of Lactobacillus johnsonii in skim and UHT milk

Chemically undefined substances, like yeast extract or peptones, are common ly used as milk supplements in industrial fermentations to allow the growth of bacterial strains unable to grow in pure milk. In order to look for sub stances to replace their positive effects on the bacterial growth, the requ irements of the probiotic strain L. johnsonii NCC 533 (La1) in skim and who le fat UHT milk were investigated. A mixture of 20 amino acids was added to skim milk and the removal of single amino acids identified alanine, serine , isoleucine and cysteine as the most important amino acids for growing L. johnsonii in milk. The requirements of L. johnsonii NCC 533 (La1) for nucle otide precursors were also investigated. Supplementation of milk with the f our identified amino acids, four ribonucleosides and one source of iron was able to support the growth of the tested strain in milk with cell counts a nd final pH as obtained by the addition of yeast extract. The impact of mil k supplementation was also investigated for additional 10 lactobacilli and a positive effect on the growth could be demonstrated for other L. johnsoni i strains, a probiotic L. acidophilus strain and the L, gallinarum type str ain. (C) 1999 Elsevier Science Ltd. All rights reserved.