Laboratory-scale extraction and characterization of ice-binding sericin peptides

Sericin peptides (SPs) are a new cryoprotectant with protecting abilities for organisms or biomacromolecule in food stuff from freezing injury in subzero environments. The extraction of ice-binding sericin peptides (I-SPs) by ice affinity extraction adsorption and their cryoprotective effect on Lactobacillus Delbrueckii Subsp. bulgaricus LB340 LYO during frozen storage was studied in this paper. The optimal extraction conditions by application of a new and assembled ice absorption apparatus were identified as temperature of −3 °C, SPs concentration of 5 mg/mL, and extraction time of 3 h. Compared with SPs, I-SPs were found to be increased in the contents of some special amino acid residues, including Ser, Thr, Gly, and Ala, which might be relative with the ice affinity as well as the cryoprotective activity of ice-structuring proteins. Meanwhile, the molecular mass distribution data implied that the free amino acids in the SPs could be excluded from the ice affinity adsorption, and peptides containing 3–6 amino acid residues might be more liable to adsorb to ice surface. Furthermore, with addition of I-SPs at concentrations of more than 0.01 mg/mL, LB340 strain had a higher survival rate after frozen storage compared to the water control as well as SPs (p < 0.05).