Abstract:Walnut polypeptides were prepared by liquid fermentation using walnut meal as raw material and Lɑctobɑcillus plɑntɑrum as fermenting strain. The walnut polypeptides were divided into three groups by ultrafiltration method based on their molecular weight:<3 kDa,3-10 kDa,and >10 kDa. Their antioxidant activity and amino acid composition were determined. With polypeptide yield as the index,the fermentation time,inoculation amount and substrate concentration were examined by single factor and orthogonal tests in order to determine the optimal technological conditions for the preparation of polypeptides from walnut meal fermented by Lɑctobɑcillus plɑntɑrum. The results showed that highest peptide yield（0.263 0 g/g）was achieved under the following conditions:fermentation time of 48 h,inoculation amount of 11% and substrate concentration of 7%. In vitro antioxidant results showed that the antioxidant activity of polypeptides increased as the molecular weight of the peptides decreased.When the concentration of polypeptide was 3.0 mg/mL,the scavenging capacity of DPPH free radical,ABTS+ free radical,superoxide anion free radical and total reducing capacity of polypeptide<3 kDa reached the maximum,which were 94.79%,97.42%,20.74% and 23.45%,respectively.The results of amino acid analysis showed that all four groups of peptides had a complete range of amino acids. The polypeptides with molecular weight<3 kDa had a relatively high antioxidant amino acid content,which contributed to their enhanced antioxidant activity.