Kinetics of dissolution and Transglutaminase (TGase)-catalyzed polymerization of soy proteins from the soy meal suspension

Abstract

It is important to understand the kinetics of dissolution and transglutaminase(TGase)-catalyzed polymerization process of soy proteins from the soy meal either for their extraction or utilization in the food industry. Nevertheless, it is yet still unknown that how the specie concentration, degree of denaturation, subunit composition, and aggregation state evolve with kinetics time (t). This work combines ultraviolet–visible spectroscopy (UV–vis), Fourier infrared transform spectrum (FTIR), sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and size exclusion chromatography (SEC) to explore the above questions by using the soy proteins from the defatted soy meal as the model system. Our main findings include: 1) under the condition of soy meal with varied mass fraction/solid content (wtsoy meal% = 5%, 10%, 15%, and 20%) in pure water and buffer with pH = 6.4 at T = 25 °C, the dual exponential equation is found to illustrate the dissolution kinetics which is contributed by two different dissolution modes, i.e., C = − B1e−k1t − B2e−k2t + B1+ B2, where B1 and B2 denote the final concentration of protein, and k1 and k2 represent the dissolution rate for each dissolution mode, respectively; 2) the analysis of the secondary structure of soy proteins shows that the proteins keep undenatured state during the dissolution process; 3) the analysis of relative content of different subunits indicates that the relative concentration of 7S and 11S is almost constant during the dissolution process; 4) SEC results unambiguously support that the dissolution species at most of time are composed of protein aggregates with different sizes; 5) a semi-empirical equation is proposed to well describe the TGase-catalyzed polymerization kinetics, i.e., dnp/dtp = 0.5wtsoy meal%0.8±0.1wtTGase%1.5±0.1, where dnp/dtp is the generation ratio of insoluble protein particle, and wtTGase% is the concentration of TGase. We believe that the knowledge from present study is beneficial for the optimization of extraction and polymerization processes in real applications.