Determination of the essential nutrients required for milk fermentation by Lactobacillus plantarum
Abstract The aim of this study was to investigate the chemically defined nutritional requirements for Lactobacillus plantarum in milk. Twenty amino acids, five nucleotide precursors, ten vitamins, and ten mineral salts were added to skim milk. The selective removal of individual nutrient groups led to the identification of amino acids and nucleotide precursors as essential nutrients for L. plantarum growth. Mineral salts were not essential but had a growth stimulating effect on L. plantarum Further single omission growth experiments revealed six key amino acids (isoleucine, leucine, valine, tyrosine, methionine, and phenylalanine) and at least one purine required as minimal nutrient for L. plantarum growth in milk. L. plantarum grew and propagated well in the fortified milk supplementation with six amino acids and adenine. The pH values of the fortified milk fermented using L. plantarum ST III, WCFS1 and LPHS were 3.93, 3.84 and 4.02 at 72 h, respectively. However, the pH values of the control fermented milk using L. plantarum ST III, WCFS1 and LPHS were only 5.73, 5.61 and 5.84 at 72 h. The identification of the chemically defined requirements for growth of L. plantarum in milk without complex and undefined substances contributes to the understanding of the physiological properties and metabolic pathways of bacteria.