Effects Of Soybean Varieties And Two Coagulants On The Quality Of Tofu

Tofu is a gelled product made from soymilk by adding coagulant.Tofu has a high nutritional value which contains rich in high-quality protein,and it is easily digested and absorbed by the human body.It is known as the “plant meat”.At the same time,soybeans contain nutrients such as unsaturated fatty acids and flavonoids,which play an important role in lowering blood lipids and delaying oxidation of the body.Studies have shown that the quality characteristics of tofu made by different soybean varieties under the action of different coagulants are also different.The higher content of the protein and 11 S component in soybean,the more favorable the formation of tofu gel.the more conducive to the formation of tofu gel.Due to the different protein content,species and protein subunit composition of different soybean varieties,they have an important influence on the formation of tofu gel and the quality of tofu under different coagulants.Thus,different soybean varieties and two coagulants were studied in this paper.Five soybean varieties and two coagulants were selected to prepare tofu,and the effects of processing materials and coagulants on the quality of tofu were discussed.Several works involved in this study included the following three aspects:(1)analysis of main components in different soybeans and selection of varieties;(2)physicochemical properties and digestive characterization of different tofu;(3)evaluation of nutritional function and potential allergenicity of different tofu.The main methods,results and conclusions are addressed as follows.1.After different soybean proteins were obtained by ultrafine pulverization,degreasing in n-hexane and extraction with Tris-HCl,the protein concentration was determined by BCA,and the protein species and their subunits were also analyzed by SDS-PAGE.The Kjeldahl method and Soxhlet extraction were further tested the content of protein and oil in soybean.Five soybeans(Xudou 25,Fudou 234,Dongnong 42,Heinong 84 and Heinong 512)with high protein content and moderate oil content were selected as raw materials for production of tofu in order to provide material guarantee for subsequent research.2.Tofu was prepared from five selected soybeans using glucono-?-lactone and calcium sulfate as coagulants.The texture characteristics of tofu were measured by texture analyzer,and the microstructures of tofu were observed by scanning electron microscopy.The results showed that the hardness,chewiness and adhesiveness of Xudou 25 tofu were the highest among lactone tofu.As far as gypsum tofu is concerned,the hardness,chewiness and adhesiveness of Heinong 84 tofu are generally better than those of other tofu varieties.Comparing two kinds of coagulant tofu,the hardness and viscosity of gypsum tofu are generally higher than those of lactone tofu.Among the lactone tofu,the gel network structure of Fudou 234 tofu is denser,and the gel network structure of Xudou 25 tofu is more looser compared with other tofu varieties.The gel structure of Fudou 234 tofu in the gypsum tofu is more porous than that of other tofu varieties,and the filling property is better.3.Different tofu were digested by simulated gastrointestinal digestive juice,and the changes of protein structure and surface hydrophobicity of different tofu digestion products were characterized by circular dichroism,ultraviolet spectroscopy and fluorescence spectroscopy.The results showed that ?,?,,? subunits of proteins in various tofu were gradually degraded with the prolongation of digestion time in simulated gastric digestion stage,and most of the proteins in tofu have been degraded during the simulated intestinal digestion stage.With the prolongation of intestinal digestion time,the degradation degree increased.The circular dichroism analysis showed that ?-helix,?-sheet and random coils of proteins in tofu were changed except for the ?-turn.Most of the proteins were lower than those before digestion.Ultraviolet spectrum analysis showed that the ultraviolet absorption value of Xudou 25-lactone tofu digested by intestine was significantly higher than that of other tofu varieties,indicating that the degree of protein structure unfolding in Xudou 25-lactone tofu was higher than that of other tofu varieties.Fluorescence spectrum showed that the fluorescence intensity of Xudou 25-lactone tofu digested by stomach was the highest at 525 nm.The greater the fluorescence intensity,the stronger the hydrophobicity of protein.4.Amino acid content in different tofu was measured by amino acid analyzer.Nutritional value of different tofu was evaluated by protein efficacy ratio,amino acid score and essential amino acid index.IgE binding ability of protein in tofu was further evaluated by indirect ELISA.The results showed that the amino acid score,amino acid index and protein efficacy ratio of Fudou 234 tofu were better than other tofu varieties.In terms of potential allergenicity,the OD value of protein binding to IgE in Fudou 234 tofu was 1.44,and its IgE binding capacity was the strongest.The OD value of protein binding to IgE in Heinong 84 tofu was 1.15,and its IgE binding capacity was the weakest.