Characterisation of the stimulants produced by Lactobacillus helveticus in milk for Propionibacterium freudenreichii

Growth of P. freudenreichii DPC 3801 in whey was stimulated by peptone, tryptone, pre-growth of Lactobacillus helveticus DPC 4571 in milk and by sodium caseinate hydrolysed with the crude proteinase of Lb. helveticus DPC 4571. Addition of vitamins (riboflavin, thiamine, PABA, Ca panthothenate, biotin and nicotinic acid) and minerals (MgSO₄ and MnCl₂) to control whey did not improve the growth of P. freudenreichii. CoCl₂ and CuSO₄ inhibited growth. Growth of the lactobacillus in milk resulted in significant increases in peptide and amino acid production but the amino acids produced did not stimulate the growth of the PAB. Several chromatographic procedures, including ion-exchange, gel permeation and reverse-phase, high-pressure liquid chromatography failed to categorically identify the peptide(s) responsible for the stimulation of the PAB. In some of these chromatographic systems, the stimulatory activity was shown to be present in several peaks implying that different peptides were involved. Several tetra-, penta- and hexa-peptides produced by other strains of Lb. helveticus from α_s- and β-casein had a small but significant effect on growth of P. freudenreichii DPC 3801. Based on these results it was concluded that stimulation of P. freudenreichii was due to production of peptides by Lb. helveticus from casein.