Preparation Of Kidney Bean Antioxidant Peptide And Influence On The Thermal Oxidative Stability Of Soybean Oil

The British Red kidney beans are rich in nutrition,vitamins,soluble fibre,protein and antioxidant,however,the fat content of it is low.It has been regarded as an important source of health food.This study provided theoretical basis for the antioxidant effect of antioxidant peptides in vegetable oil.Firstly,the protein of British red kidney bean was extracted by the method of alkali extraction and acid precipitation.Secondly the hydrolysis condition for the preparation of antioxidant peptide using British red kidney bean protein was studied by the enzyme hydrolysis method.Thirdly,the antioxidant peptides of red kidney bean protein with different molecular weights were separated by the method of ultrafiltration.Then,three groups of purified antioxidant peptides with different molecular weights(MW<1000 Da,1000~3000 Da,3000~5000 Da)were added into the soybean oil with a certain percentage.The POV value was detected and analyzed by iodimetry method.Finally,the kinetic parameters of the oxidation process of soybean oil were determined by the DSC analysis and the technique of isothermal and non-isothermal analysis.The three groups of oxidation resistance of antioxidant peptides in thermal induced oxidation in soybean oil was evaluated respectively.The main conclusions are as follows:1.The extraction total protein of British red kidney beanThe optimal extraction parameters were determined by single factor and orthogonal test.The result showed that the extraction rate of the British red kidney bean protein was least affected by extracting time,while most affected by the ratio of material to liquid.The highest extraction rate of the British red kidney bean protein is 82.83% when it was extracted by the solution with PH of 10 for 2 hours under the temperature of 50 ?.2.Preparation and separation of the British Red kidney bean protein antioxidant peptideThe effect of British red kidney bean protein antioxidant peptide on the thermal induced oxidation of soybean oil is evaluated.The degree of hydrolysis and oxidation resistance were used as evaluation index.The alkaline peotease,flavourzyme,trypsin,pepsase and chymotrpsin produced by Bacillus subtilis were filtrated,on the other hand,single factor orthogonal experimental method was used to design the enzymolysis technology.The result indicated that,the protein hydrolyzed by alkaline peotease had the strongest oxidation resistance.The optimal hydrolysis condition was with PH value of 10,time of 2 hours,temperature of 55 ?,enzyme amount of 4000 u/m L.A certain concentration of British red kidney bean protein antioxidant peptide solution is separated and purified by the ultrafiltration membranes with cutoff molecular weights of 5000 Da,3000 Da and 1000 Da,and three kinds of antioxidant peptides of British red kidney bean protein with molecular weights of 3000~5000 Da,1000~3000 Da and less than 1000 Da are obtained.The ultrafiltration components are frozen and dried separately for future use.3.Study of the effect of British red kidney bean protein antioxidant peptide on the thermos-oxidative stability of soybean oilThe analysis of soybean oil POV showed that different molecular weight British Red antioxidant peptides had different antioxidant effects in soybean oil.Result of this research indicated that the antioxidant peptide of British red kidney bean protein with molecular weight of 1000~3000 Da had the strongest antioxidant properties in soybean oil.Also,it demonstrated the existence of interaction between plant protein hydrolysate and vitamin E in vegetable oil.The activation energy of oxidation reaction of the soybean oil(with VE)without adding the antioxidant peptide of red kidney bean protein was calculated with the Arrhenius formula to be 62.24 KJ/mol.While the activation energy of oxidation reaction of the soybean oil(with VE)with the antioxidant peptide of red kidney bean protein was up to 80.88 KJ/mol,demonstrating that the antioxidant peptide of red kidney bean protein with molecular weight of 1000~3000 Da possesses the strongest antioxidant effect in soybean oil.In conclusion,the extraction conditions of red kidney bean protein by single factor orthogonal test to optimize,in order to get the optimal process of British Red kidney bean antioxidant peptide.The different molecular weight of British Red kidney bean antioxidant peptides had different antioxidant effect in soybean oil during thermal oxidation.