Study On The Enzymatic Hydrolysis Of Soy Protein And Antioxidative Activity Of Its Hydrolysate

Previous data showed that many chronic diseases and senile phenomenon of human being were all relevant to radical level unbalance in the body. Excessive radicals cause oxidation damage in the body. If the damage could not be repaired timely and be collected to some degree, it would result in some diseases. Bio-antioxidant can help people hold radical balance in the body. It is possible to develop potent antioxidant drugs and functional foods through studying and modifying some natural foods having antioxidative activity. Due to high output and low cost of soy, it has been one of the important foods. Hence, there is important social significance and economic value to study and develop soy peptides with antioxidative activity. In this research each important parameter of enzyme hydrolysis of soy protein, molecular weight distribution and antioxidative activity of soy peptides were analyzed. The aim was to find important factors affecting antioxidative activity of soy peptides and to offer theoretical guidance and technological parameters for the production of antioxidative soy peptides. Single factor experiment was adopted to hydrolyzing soy protein by alcalase, protamex and Papain. Better conditions of soy protein hydrolyzed by each enzyme were obtained. Under these conditions the hydrolysis curves for each enzyme was simulated by mathematical analysis, it is useful for controlling accurately the degree of hydrolysis(DH) of soy protein. Furthermore the value of Km of soy protein hydrolysis by each enzyme was calculated respectively. Deep hydrolysis research was operated in step multi-enzyme. The results showed that the hydrolysis in step multi-enzyme could increase DH of soy protein significantly, and that there was not obvious relation between final total DH of soy protein and the order of adding enzymes or whether the first enzyme had been inactivated. When the soy protein hydrolysate continued to be hydrolyzed by Flavourzyme, The hydrolysate pH value had no significant variation. But the concentration of amino-nitrogen increased gradually and at the same time the bitterness of the hydrolysate decreased. When hydrolyzing soy protein by different enzymes, variation curve of the concentration of amino-nitrogen, Soluble nitrogen content in trichloroacetic acid (TCA), the bitterness of soy peptides with DH were determined. The resulted showed that DH increased with hydrolysis time prolonged, and the total variation trend was that the concentration of amino nitrogen, Soluble nitrogen content in TCA, the bitterness of soy peptides increased with hydrolysis time prolonged. Under the same DH, the concentration of amino-nitrogen increased gradually in sequence of Alcalase,Protamex,Papain. The hydrolysate prepared by Papain and Alcalase had stronger bitterness than hydrolysate by Protamex. In addition, because hydrolysis rate and efficiency of Alcalase is far higher than those of Papain, under the same hydrolysis time the bitterness of Alcalase hydrolysate was higher than that of Papain hydrolysate. Anti-linoleic acid peroxidation capacity and radical scavenging activity of soy protein hydrolysate obtained by single enzyme reaction and step multi-enzyme reaction were determined using linoleic acid-KSCN method and pyrogallol method. Comprehensive results of two experiments indicated that antioxidative activity of soy protein hydrolysate varied with DH in following laws. For the same enzyme (endopeptidases), the DH increased and the bitterness and antioxidative activity of the hydrolysate were enhanced with hydrolysis time prolonged; For the same DH, the hydrolysate prepared by alcalase and Papain had stronger bitterness and their antioxidative activity were also higher than that of Protamex. Of all hydrolysate obtained by single enzyme the soy protein hydrolysate prepared by Alcalase for 5h had the highest antioxidative activity. The soy protein hydrolysate prepared by Alcalase for 5h continued to be hydrolyzed by Papain, Protamex and Flavourzyme. The results indicated that its antioxidative activity could be improved by P...