Study On Quality Improvement And Safety Assessment Of Whole Soybean Curd Based On High-speed Shearing Technology

Whole soybean curd(WSC),a novel protein gel that retains all the nutritional components of soybeans,is rich in dietary fiber and various vitamins.However,due to the presence of insoluble dietary fiber in okara,the cross-linking between proteins is weakened,which significantly reduces the gel strength and palatability of WSC.Moreover,the introduction of okara also brings challenges to the shelf life and edible safety of WSC.In order to provide theoretical reference for the quality improvement and safety evaluation of this new type of whole-soybean product with high dietary fiber content,I used high-speed shearing(HSS)technology to micronize okara fibers and investigated its effect on the physiochemical properties of soybean curd and the corresponding mechanism;Moreover,predictive microbiology was also used to evaluate the shelf life and safety of WSC.The main conclusions are as follows:1.The HSS treatment destroyed the hollow columnar structure of the parenchyma tissue in okara fiber,leading to the fracture of hourglass cells and the separation of hourglass cells from the palisade epidermis.The HSS treatment also degraded the crystalline and amorphous areas of okara fibers,and resulted in the decrease of the dimension and the increase of the crystallinity of okara fiber.The homopolymer fiber connected by ?-1,4 glycoside bond may be partly degraded during HSS process.2.Soy proteins partly denatured during HSS process,thus it showed different thermal aggregation behaviors and could not form specific protein aggregates.The relative content of ?-helix,?-sheet and ?-turns all decreased after HSS,but the random coil and the surface hydrophobicity showed an opposite trend.HSS led to the formation of a loose and lessconnected gel network,leading to the decrease of gel strength and water holding capacity.Correlation analysis shows that separating the okara individually,shearing them at high speed,and then adding them back to the soy milk to prepare WSC can not only micronize the okara,but also avoid the shearing-denaturation of soy proteins.The gel strength of final WSC is higher.3.The introduction of okara fibers exacerbated the initial pollution level of WSC,but pathogenic bacteria were not detected.The main spoilage bacteria were identified as Bacillus subtilis subsp.Inaquosorum and Bacillus cereus,which may originate from soybean raw materials.4.Using the modified Gompertz model,the growth condition of spoilage bacteria in WSC can be well fitted.The maximum relative growth rate of spoilage bacteria in WSC was higher than that in okara-filtered curd(OFC).Moreover,when stored at 10 ? and 35 ?,the predictive shelf life values of WSC were 141.95 h(5.91 days)and 3.28 h,respectively,which were 31.17% and 38.92% lower than OFC.The results of the risk assessment indicated that for young people,the food safety risk of WSC and OFC were the same even if were consumed once a day or weekly.In conclusion,HSS technology can effectively degrade the cellular and crystal structures of okara fibers.But if it is directly used in whole soybean milk,it will lead to the shearing denaturation of soybean proteins.The edible safety of WSC is not significantly different from that of traditional okara-filtered tofu.Although its shelf life is reduced,it is still within the acceptable range.