Texture analysis and physicochemical characteristics of fermented soymilk gel by different lactic acid bacteria

The high hardness and low water holding capacity (WHC) characteristics of fermented soymilk limit the consumer acceptance of its products. In this study, 4 strains were screened from 126 strains of lactic acid bacteria (LAB) for the fermentation of pure soymilk. The soymilk fermented by the 4 strains had different hardness and WHC levels but similar springiness and kinetic viscosity. Effect of the LAB hydrolyzing protein subunits (75 and 115) on the particle size, zeta potential, microstructure and intermolecular force of fermented soymilk gel was studied. The results showed that the different degree of protein subunit hydrolysis would affect the particle distribution, zeta potential and intermolecular force in gel, resulting in the difference of microstructure and texture. Hydrophobic protein subunit (7S beta subunit, 115 basic subunit) degraded by the LAB enhanced the electrostatic repulsion in the gel, resulting in uneven particle distribution and rough microstructure, which reduced WHC of the gel. When the contribution of hydrophobic force in gel was far greater than that of hydrogen bond, it was unfavorable to the WHC of gel. Hydrolysis of 115 subunit increased the cross-linking sites to raise the content of 20 mu m particles and increased the large clusters in the microstructure of gel thus improving the hardness of gel. This study has explained the difference in hardness and WHC of soymilk gel fermented by LAB from a new perspective of protein subunit hydrolysis, and it will help to screen out LAB through protease characteristics to ferment soymilk with low hardness and high WHC.