Study On Formation Mechanism Of Volatile Components In Soymilk Based On Multiple Simulation System

Soymilk is favored by consumers for its excellent nutritional value and health functions,but its overall acceptability is reduced by its unpleasant flavor.The lipid oxidation reaction catalyzed by lipoxygenase（Lox）is a principal pathway of the formation of volatile flavor components in soymilk.The composition of soymilk emulsification system is complex and the formation of volatile flavor is closely related to the interaction of its ingredients.In order to reduce the undesirable flavor of soymilk products,most of the existing studies focused on the influence of heating soymilk to inactivate enzymes or isolating air processing on flavor formation.However,the key stage of soymilk flavor formation,that is,the mechanism of soymilk flavor formation in the grinding process before heating,has not been systematically studied.In order to better remove the beany flavor and prepare high-quality soymilk,it is necessary to further clarify the reaction mechanism of Lox pathway and related influencing factors in the soymilk system.This paper focuses on the formation mechanism of volatile flavor of raw soymilk during grinding process by constructing a multiple simulation system.Based on the lipoxygenase oxidation pathway of the formation of volatile flavor components of soymilk,the components with very weak flavor which are closely related to the formation of volatile flavor components of soymilk were firstly isolated and extracted from soybean,including lipoxygenase,soybean protein,oil bodies（OBs）and polyphenols.Triacylglyceride（TAG）was purified by refined soybean oil.Soybean phospholipids,linoleic acid,protease,lipase and phospholipase were purchased.The addition amount and enzyme activity of the simulated system components were equivalent to those of raw soymilk.Headspace solid phase microextraction-gas-mass spectrometry was used to detect volatile flavor components.In the binary simulation system of lipids and lipoxygenase,using TAG,PL,and LA as substrates,respectively,the flavor characteristics and content of volatile components generated by Lox oxidation were investigated.The total volatile components generated by the TAG-Lox,PL-Lox and LA-Lox systems are 4.48%,6.07%and 61.20%of those of soymilk,respectively.The results show that the flavor characteristics and content of the volatile components generated in the simulation system with LA as the substrate are most similar to those of soymilk.Through the lipid-Lox binary simulation system,it is found that the contribution rates of the three different forms of lipids to the volatile components of soymilk are LA,PL,and TAG in order.This indicates that LA is the best substrate for enzymatic oxidation in the Lox pathway of the formation of volatile substances in soymilk.In addition,increasing the activity of Lox in the simulated system would also increase the content of volatile components.Lox isoenzymes have different catalytic properties for different forms of lipid substrates.Lox-1 mainly catalyzes the oxidation of free unsaturated fatty acids.Lox-2,3can not only catalyze the oxidation of free unsaturated fatty acids,but also catalyze the oxidation of esterified unsaturated fatty acids in triacylglyceride and phospholipid.In the TAG/PL,lipase and Lox multiple simulation system,the effect of lipase hydrolysis on the volatile components generated by Lox oxidation pathway was studied.The total volatile components generated by TAG-Lip-Lox and PL-Lip-Lox ternary simulation systems are 10.18 times and 3.94 times of the corresponding binary simulation systems,respectively.The lipase hydrolysis of esterified fatty acids can significantly increase the types and contents of volatile components in the simulated system.The total volatile components generated by the TAG-Lip-Lox and PL-Lip-Lox ternary simulation systems are 10.18 times and 3.94 times that of the corresponding binary simulation systems,respectively.The hydrolysis of esterified fatty acids by lipase can significantly increase the type and content of volatile components in the simulated system.The total volatile components generated by the TAG-Lip-Lox,PL-Lip-Lox and TAG-PL-Lip-Lox systems are 45.57%,23.94%and 57.98%of the those of soymilk,respectively.Compared with the binary simulation system,the composition of the volatile components generated by the multiple simulation system has better similarity with the volatile components in soymilk.Among them,the volatile component composition and sensory flavor characteristics of the TAG-PL-Lip-Lox simulation system both have good similarities with soymilk.In the simulation system of soybean oil bodies and complex enzyme,by monitoring the changes of oil bodies characteristics and analyzing the oxidation products generated by the system,it was found that the endogenous oleosins of soybean oil bodies can be hydrolyzed into small peptides by trypsase,and the combined action of trypsase and phospholipase had an effect on the morphology of oil bodies.The intact soybean oil bodies cannot be hydrolyzed by lipase and oxidized by lipoxygenase,but it can be hydrolyzed by phospholipase.When the oleosins were hydrolyzed,it could promote the hydrolysis or oxidation to produce a large number of volatile components.The total volatile components generated by the OBs-Ps-Lip-Lox,OBs-PLA2-Lox,OBs-Ps-PLA2-Lox and OBs-PLA2-Lip-Lox simulation systems are 41.67%,29.71%,40.04%and 65.12%of those of soymilk,respectively.Among them,the composition of volatile components produced by OBs-Ps-Lip-Lox is similar to that of soymilk.In the binary simulation system of lipoxygenase and triacylglyceride hydrolysate,under the condition of certain lipoxygenase activity,increasing the triacylglyceride hydrolysate substrate would increase the amount of volatile components generated by the system.All of the co-oxidants could increase the production of volatile components in the system,but the degree was different.For example,riboflavin and catalase had significant synergistic effect,with an increase of 0.38 times and 0.35 times,respectively.While Fe³⁺and peroxidase had slightly significant synergistic effect,with an increase of 0.19 times and 0.14 times,respectively.Antioxidants reduced the volatile component of the system by inhibiting the oxidation reaction in the system.