AbstractBACKGROUND: Immunomodulatory peptides can enhance body immunity. There have been few systematic investigations on preparing immunomodulatory peptides from Alaska pollock frame. The aim of this study was to obtain such peptides from Alaska pollock frame and determine their properties.RESULTS: Trypsin protein hydrolysate (TPH) significantly enhanced the proliferation of spleen lymphocytes, T cells and peritoneal macrophages (P < 0.05). Compared with TPH with molecular weight (MW) > 2 kDa, TPH with MW < 2 kDa showed higher lymphocyte proliferation activity at 10, 50 and 500 µg ml−1. The optimised hydrolysis conditions were a temperature of 50 °C, an enzyme dose of 24 U mg−1 and a time of 290 min. The proliferation rate and degree of hydrolysis were 28.45 ± 1.79% and 16.87 ± 0.15% respectively. The main amino acids in TPH were proline, aspartate, glutamic acid and leucine. TPH had high solubility and low viscosity. TPH showed high stability under both acid and alkaline conditions or when digested by trypsin and/or pepsin.CONCLUSION: TPH showed high immunomodulatory activity, with molecular weight and amino acid composition being the important factors affecting this activity. TPH had high solubility, low viscosity and high stability. As a good immunomodulator, TPH may therefore have wide application. Copyright © 2012 Society of Chemical Industry