Enzymatic preparation of casein hydrolysates with high digestibility and low bitterness studied by peptidomics and random forests analysis

Enzymatic hydrolysis can not only increase the digestibility of casein, but also cause bitterness. This study aimed to investigate the effect of hydrolysis on the digestibility and bitterness of casein hydrolysates and provided a novel strategy for the preparation of high-digestibility and low-bitterness casein hydrolysates based on the release pattern of bitter peptides. Results showed that with the increase of the degree of hydrolysis (DH), the digestibility and bitterness of hydrolysates increased. However, the bitterness of casein trypsin hydrolysates rapidly increased in the low DH range (3%-8%), while the bitterness of casein alcalase hydrolysates rapidly increased in a higher DH range (10.5%-13%), indicating the discrepancy in the release pattern of bitter peptides. Peptidomics and random forests revealed that peptides containing >6 residues with hydrophobic amino acids (HAAs) at the N-terminal and basic amino acids (BAAs) at the C-terminal (HAA-BAA type) obtained from trypsin contributed more to the bitterness of casein hydrolysates than those containing 2-6 residues. On the other hand, peptides containing 2-6 residues with HAAs at both N- and C-terminals (HAA-HAA type) released by alcalase contributed more to the bitterness of casein hydrolysates than those containing >6 residues. Furthermore, a casein hydrolysate with a significantly lower bitter value containing short-chain HAA-BAA type peptides and long-chain HAA-HAA type peptides from the combination of trypsin and alcalase was obtained. The digestibility of the resultant hydrolysate was 79.19% (52.09% higher than casein). This work is of great significance for the preparation of high-digestibility and low-bitterness casein hydrolysates.