Deamidation of soybean proteins with glutaminase to improve their rheological properties

Glutaminase (EC 3.5.1.2) was applied to treat soybean protein isolates (SPI), and some reaction conditions were selected. Three deamidated SPI products with degree of deamidation of 3.5, 5.6 and 6.6%, were prepared with reaction conditions as following: SPI concentration of 5% (w/v), glutaminase addition level of 400 U/kg SPI, reaction temperature of 37°C, and reaction time of 12, 24 and 36 h, respectively. The results from rheological assay revealed that the suspensions prepared by three deamidated SPI products showed higher apparent viscosity, which depended on the degree of deamidation and addition level of Ca²⁺. The storage modulus G´ and viscous modulus G´´ of the prepared suspensions gave a similar behavior as apparent viscosity did.