| The soy protein isolates (SPI) have high nutritional values. Soy oligo-peptides, which are the products of SPI hydrolysis by enzyme, are kinds of functional food-bases. The metal-chelate complex of soy oligo-peptides can increase the soy oligo-peptide application scopes on food and feed. In this paper, the main study is to found a method to preparie soy oligo-peptide from SPI with papain and bromelain.The enzyme hydrolysis process conditions, including the in vitro ACE (Angiotensin-converting enzyme) inhibitory activity of hydrolysate are the research contents . Seperation of the high activie components and preparation of soy oligo-peptides'metal-chelate complex are included in this paper. The results of the experiments were as follows:a)Through the preliminary enzyme hydrolysis experiments, the enzyme hydrolysis products of SPI were analyzed by SDS-PAGE, HPLC and mass spectrometry, the results showed that the majority molecular weight of oligo-peptides of the two enzymes hydrolysis are about 1000Da. Among the relationship of the enzyme concentration, the substrate concentration, the reaction temperature and the hydrolysis degree of SPI,the hydrolysis products and the reaction substrates could inhibit the reaction rates during the initial reaction times. However the reaction temperature could increase the reaction rate at the same time. The Km of hydrolyzing SPI by Papain is 0.1404g/L and the Vmax is 7.51 g·L-1·min-1.The Km of hydrolyzing SPI by Bromelain is 0.1173g/L and the Vmax is 4.95 g·L-1·min-1.b) The impact of the main factors on the enzyme reaction of SPI: enzymolysis time, hydrolysis temperature, enzyme concentration, pH, substrate concentration was studied according to the single-factor and two-factor experiment. The best process for papain were that recation time was 3h, hydrolysis temperature was 60℃, the amount of enzyme was 0.35g, pH was 7.5, substrate concentration was 5g/100mL. The best enzyme technology for bromelain were that enzymolysis time was 10h, digestion temperature was 40℃, the amount of enzyme was 0.35g, pH was 7.5, substrate concentration was 5g/100mL.c)The study on related factors of impacting ACE inhibitory activity had shown that the proteinase hydrolysis time did not affect the ACE inhibitory activity of soy oligo-peptides deeply by papain and reached the peak at 72 hours, but the soy oligo-peptides by bromelain reducing the ACE inhibitory activity with increasing time. the small molecule carbohydrates would decreased ACE inhibitory activity. In addition, through the study of soy oligo-peptides prapared by papain and bromelain, the IC50 of hydrolysate were around 70μg/mL. Through separated soy oligo-peptide by HPLC and SphadexG-25 and study of inhibitory activity, A kind of high ACE inhibitory activity components was separated from the soy oligo-peptides by HPLC and SphadexG-25. The high active component was at 29.527min of HPLC. d)The preparation of copper chelate and zinc chelate of soy oligo-peptides were studied. For copper chelate of soy oligo-peptides, the optimum reaction conditions were that the copper ion concentration was 0.67×10-4mol/L, the reactin time was 10min, the reaction temperature was 50℃, the pH was 4.0, the precipitation agent (ethanol) ratio was 1:2. The recovery ratio is 76.06%. For chelate zinc of soy oligo-peptides, the optimum reaction conditions were that the zinc ion concentration was 0.67×10-4mol/L, the reaction time was 10min, the reaction temperature was 50℃, the pH was 6.0, the precipitation agent (ethanol) ratio was 1:1.75, the recovery ratio was 74.83%.The copper chelate of Oligo-peptides shew that it had a certain degree of resistance to acid. The compound could exist in the form of chelate when the solvent pH was between 3 ~ 4.
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