Plant-based oat peptides as cryoprotectants mitigate freezing damage to Lactobacillus bulgaricus CICC 22163

The freezing process leads to the death of lactic acid bacteria (LAB), making cryoprotection a significant research focus. In this study, plant-derived oat peptides demonstrated effective cryoprotective effects against Lactobacillus bulgaricus. First, the oat peptide extraction process was optimized with cell viability as the indicator: the yield was found to be 59.51 %. After freezing, it was identified that a 40 mg/mL oat peptide solution provided the best protective effect. The oat peptides enhanced fermentation vigor and reduced cell membrane damage. The mechanisms of action were explored. The oat peptides preserved the intact morphology of cells and significantly improved the viability of lactic dehydrogenase and β-galactosidase. Additionally, the peptides lowered the freezing point to -2.1 °C, which mitigated ice crystal edge formation and reduced both ice crystal diameter and area. The oat peptides physically absorbed onto the surface of the bacteria, exerting an antifreeze effect. Finally, based on amino acid evaluation, three peptide fragments (LSCDKYCFME, FDGCFMEN, and QHCWLGGK) were synthesized, and these synthesized peptides effectively increased the survival rate of L. bulgaricus, with QHCWLGGK also exhibiting protective effects. Therefore, plant-based oat peptides can be utilized as cryoprotectants for freezing LAB.