Abstract:

Streptococcus thermophilus is regarded as a multi-functional probiotic bacterium. Five protein hydrolysates from
grass carp skin were prepared using Neutrase 0.8L, Protease P “Amano” 6, ProteAX, Alcalase 2.4L FG and Flavourzyme,
respectively, for use as nitrogen sources to culture Streptococcus thermophilus. Among the five proteases, Neutrase 0.8L was
found to be the best enzyme to produce the optimal nitrogen source for the growth of Streptococcus thermophilus. In further
investigations, we optimized hydrolysis conditions using orthogonal array experiments. The results showed that the optimal
hydrolysis conditions were as follows: enzyme dosage, 1%; hydrolysis time, 80 min; initial pH, 6.5; and ratio between fresh
skin and water, 1:2 (m/V). The hydrolysate obtained under these conditions was rich in collagen-derived peptides as a new
optimum nitrogen source for Streptococcus thermophilus incubation.

Key words: grass carp skin, protease, hydrolysis, collagen-derived peptide, Streptococcus thermophilus