Study on the Ability of Lactobacillus delbrueckii subsp. bulgaricus to Hydrolyze Casein and Analysis of the Hydrolysate
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Abstract:
In order to carry out an in-depth study on casein hydrolysis by Lactobacillus bulgaricus, Lactobacillus delbrueckii subsp. bulgaricus strain ATCC 11842 was used, with Lactobacillus delbrueckii subsp. bulgaricus strains KLDS 08007, KLDS 08009, KLDS 08010，KLDS 08014, and KLDS 08018 as controls. The degree of casein hydrolysis and peptide content of the fermentation broths from different strains were measured, and the casein hydrolysate of ATCC 11842 was further analyzed by sodium dodecyl-sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and liquid chromatography-mass spectrometry (LC-MS). The results showed that ATCC 11842 had the strongest hydrolytic ability with the degree of hydrolysis as 13.89%, and the peptide content 0.63 mg/mL. The activities of cell envelope proteinases (CEPs) of the six strains were measured and compared with their hydrolytic abilities, and the results showed that their proteinase activity was positively related to their hydrolytic ability. ATCC 11842 exhibited the highest enzyme activity (up to 15.52 U/mL), and its specific enzyme activity was 6.73 U/mg. It can be seen from the electrophoretogram that the casein was hydrolyzed gradually with a prolonged fermentation time and 3.4~21.0 ku polypeptides were produced. As shown from the LC-MS analysis of the casein hydrolysate, 77 types of peptide fragments containing 6~25 residues were produced after casein hydrolysis, and the peptides containing 6~7 residues and 8~14 residues accounted for 9% and 77% of the total types of polypeptides, respectively.
