The Construction Of Model System With Soymilk Volatiles And Influence Of Components On Its Flavor

Soymilk is a kind of healthy vegetable-protein drink with high nutrition value and rich protein content, but its beany smell is difficult to accept for a lot of consumers, which largely limits the soybean milk market. The lipid oxidation reaction catalyzed by LOXs is a principal pathway of the production of volatile flavor compounds in soymilk, so it is necessary to further clarify the reaction mechanism of LOX pathway and its related influence factors, so that we can remove soymik flavor and gain soymilk with higher quality. In this paper, a simulation system with soymilk flavor was successfully constructed based on the components of soy milk, and then the content of each component in the system was adjusted,also, the changes of the flavor substances was identificated by HS-SPME-GC-MS, so that to define the the reaction mechanism and related factors of LOX pathway.Based on the soymilk components and its beany flavor origin, we firstly separated the components with light flavor and closely related with LOX reaction, including SPI, LOXs and polyphenols. After a series of comparative analysis, the lab-made alcohol washing SPI, LOX enzyme and polyphenol and soybean oil, soybean lecithin, linoleic acid purchased would be used to build the simulation system.Afterwards, the condition of HS-SPME on volatile substances of soymilk was optimized, also, the quantitative correction of GC-MS was conducted. It was found that the optimum extraction conditions of HS-SPME was DVB/PDMS/CAR-50/30μm, adsorption of 30 min under 40 °C and desorption of 7 min. The internal standard method and external standard method were used for quantitative correction of results of GC-MS, and a series of quantitative standard curves of different kinds of volatile substances was obtained.Then, the blending ratio and conditions of these components of the mixed system were confirmed, and a model system equipped with volatile flavor similar to soymilk was constructed. The composition of the mixed system based on the soymilk(protein content of 2%) was 2% SPI, 1.11% TAG, 0.038% PL, 0.027% polyphenol and LOX enzyme activity of 2.36×105 U/m L. Then the influence of mixing conditions on flavor was studied, it showed that p H could affect the LOX reactivity of the multicomponent mixture system, while the temperature and time had no significant influence on it, and then 40 °C, p H7.0, 30 min was determined as the mixing conditions. It showed that the emulsion properties of our mixed system were close to soymilk, but its volatile flavors contents were lower than soymilk. According to adding three different forms of lipid and lipase into systems respectively, the contribution rate of material was FFA> TAG> PL,and the content of free fatty acids in the model sytem was improved to 0.0057%, the results of PCA and sensory test showed that its flavor was similar to soymilk.By adjusting the content of each component in the simulation system, the effects of TAG, PL, FFA, LOXs, polyphonel and SPI on LOX pathway and their correlations with volatiles. It showed that:(1) The content of FFA was highly positive correlated with aldehydes, alcohols, ketones, hydrocarbons and furans, and the contents of TAG and PL were highly positive correlated with all kinds of volatile substances except for furans.(2) The activity of LOX was highly positive correlated with all kinds of volatile substance, and LOX3 also participated in the lipid oxidation reaction process besides LOX1 and LOX2.(3) Polyphenols of soybean played dual role of antioxidant and prooxidant effects, and the content of it was not always negatively correlated with volatiles.(4) The adsorption capacity of SPI to different kinds of flavor compounds are different, and there was a dynamic adsorption equilibrium between the model system and volatile flavors, which in a way could weaken the beany smell.