Abstract:  The fractionation of soy peptides by ultrafiltration separation was studied． Soy peptides products（hydrolysis degree of14．5％） can be separated into four components （＞30000u、10000～30000u、5‚000～10000u and ＜5000u） in terms of its molecular weight using fractional ultrafiltration separation system．The molecular weight distribution of each group was determined by filtration chromatography．The result showed that fractional ultrafiltration separation can effectively separate soy peptides．The molecular weight distribution of soy peptides with hydrolysis degree of 14．5％ mainly was below 5000 u．The soy peptides with different
molecular weight have different functional properties‚such as solubility‚viscosity‚foaming property and
emulsifying property．The membrane filtrated flux decreased but the efficiency and selectivity of membrane
increased as the content of soy peptides increased with total reflux operation．It provided a feasible way to purify
soy peptides by fractional ultrafiltration．

Key words: soy peptide, fractionation, ultrafiltration, membrane separation, functional property