Abstract: In this study, the structure and antifreeze activity of surimi by-product protein hydrolysate (SBPH) were investigated, and the cryoprotective effect and mechanism on Streptococcus thermophilus were explored by measuring its growth performance, malondialdehyde (MDA) content, protease activity, metabolic activity and membrane potential after freezing treatment. The results showed that the molecular mass range of SBPH was 260–2 550 Da, and a total of 78 peptides with 8–18 amino residues were identified from SBPH, some of which had the characteristic structure of tripeptide repeat sequences imparting high antifreeze activity to SBPH (thermal hysteresis activity of 1.76 ℃). Compared with other antifreeze agents (sucrose, skim milk and glycerol), SBPH (2 mg/mL) enhanced the cell viability, growth activity and acid production of S. thermophilus after freezing treatment, attenuated oxidative stress damage to cells caused by low temperature, significantly inhibited the decrease in the relevant protease activity (P < 0.05), increased the metabolic activity of cells, and attenuated the hyperpolarization of the cell membrane thereby contributing to maintaining the integrity and fluidity of the cell membrane. SBPH could maintain the interaction between phospholipid bilayers to some extent and protect the structure of the cell membrane. In conclusion, SBPH can protect the function and integrity of cells, and reduce cryogenic damage to cells to a certain extent.

Key words: surimi by-product; protein hydrolysate; Streptococcus thermophiles; anti-freezing activity; action mechanism