Texture Characteristics Of Soymilk Gels Formed By Lactic Fermentation:a Comparison Of Soymilk Prepared By Blanching Soybeans Under Different Temperatures

Soymilk is a kind of complex colloidal system that mainly consists of soy protein and lipids. The stability and gelation property of soymilk are affected by the heat-induced soymilk protein denaturation and the change in particle surface characteristics. Soy yogurt is an innovative gel-like soy food that is produced through lactic acid fermentation of soymilk. However, the beany flavor of traditional soymilk and the rigid as well as friable texture of its gel are not favorable, which prevents the improvement of soy yogurt quality. The Cornell method, that blanches soybeans using hot water, can inactivate the lipoxygenase and thus decrease the beany flavor of soymilk. This method shows potential in produing soy yogurt. However, studies on this soymilk preparation method and its effect on soymilk particle formation and the gel characteristics are quite limited. In this study, we firstly compared the size distribution, composition and content variation of soymilk particles prepared by blanching and traditional treatment, and then determined the protein denaturaion, protein and lipid distribution in the two soymilks. We also fractionated the soymilk into three fractions that contains different soy particles, studied on the changes of their surface charge during acidification, and discussed the effect of electrostatic repulsion on the intermolecular interactions between protein and lipid in acidified soymilk. At last, we obtained soymilk gel with different texture characteristics through blanching soybeans at different temperatures, and studied on the realtion between the texture and microstructure of soymilk gels.Results showed that blanching soybeans at≥60℃could lead to the denaturation of7S globulin in a compressed and dehydtrated form within soybean seeds and the damage on the natural structure of oil body. The balnching treatment also decreased protein aggregation and increased the protein surface hydrophobicity as well as the lipid content in particulate soymilk fraction, which made the whole soymilk subject to form precipitation. Further studies revealed that blanching soybeans at80℃could alter the aggregation behavior of soymilk particles,which prevent them to form the "string of beads" polymeric structure and thus led to the textural change of soymilk gel. An yogurt-like texture could be obtained by soymilks prepared by blanching soybeans≥70℃. Results showed that in the temperature range of60-80℃, the yield stress, hardness, stringiness of soymilk gel could be decreased with the increase of blanching temperature, while the smoothness and softness of soymilk gel could be improved. With the increase in blanching temperature, the microstructure of the soymilk gel transformed from a three-dimensional stranded network with dense crosslinks of "string of beads" protein polymers to a thick honeycomb, lamellar structure of stacked protein particles and areatus aggregated around the stranded networks.