Influence of casein hydrolysates on the growth and lactic acid production of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus

P>The growth performance of Lactobacillus delbrueckii subsp. bulgaricus (L. bulgaricus) and Streptococcus thermophilus (S. thermophilus) was determined in the presence of casein hydrolysates produced by the action of five proteolytic enzymes (Alcalase, Flavorzyme, Neutrase, Papain and Trypsin) with various degrees of hydrolysis (DH). In addition, these five kinds of casein hydrolysates were fractionated by ultrafiltration and the influence of the amino acid composition of the peptides on the growth and lactic acid yield of yoghurt lactic acid bacteria (LAB) was studied. The results showed that the ultrafiltered fraction (< 3000 Da) was the determinant stimulator in crude hydrolysates. Furthermore, the hydrophilic amino acid residua including His, Lys, Glu and Ser were beneficial for bacterial growth. Compared with control, the cell growth and lactic acid yield of yoghurt LAB were increased with the supplementation of the peptides fraction (< 3000 Da) produced with papain by 65.1% and 49.6%, respectively.