Effects Of The Specific Mechanical Energy On The Physicochemical Properties Of Soy Protein Isolate During High-moisture Extrusion Cooking

Specific mechanical energy (SME) is one of the major system parameters affecting the extent ofcooking reaction, and the properties of final products during extrusion cooking process. It could help toperfect the theory of protein texturization to conduct a research on the relationship between extrusionSME and physicochemical changes of protein. In addition, it is helpful to reveal the functionmechanism of mechanical energy affecting protein molecular structure, and improve the energyefficiency in extrusion cooking. Moreover, it is also useful to reveal the formation mechanism oftexturized protein conducting a research on the relationship between SME and physicochemical changesof protein.In this paper, soy protein isolate (SPI) was extruded at high moisture conditions, using DSE-25twin screw extruder of Germany Brabender. Differential SME was obtained by changing screwconfigurations, and the corresponding extrudates in different SME condition were collected. Theneffects of SME on the on-line viscosity, color, texture, texturization degree and solubility of SPI, wereanalyzed. Besides, effects of SME on the molecular weight and molecular weight distribution of SPIwere analyzed using the methord of sodium dodecyl sulfate polyacrylamide gel electrophoresis(SDS-PAGE) and size exclusion chromatography coupled with multi-angle laser light scattering(SEC-MALLS). The main conclusions were as following:(1) SME had a significant effect on the quality properties of SPI extrudates. A higher SME resultedin extrudates with lower L*but higher a*and; Besides, the higher the SME, the higher the tensilestrength, hardness and chewiness.(2) After extrusion process, SPI cross-linked and aggregated into macromolecule polymers,resulted in weight-average molecular weight (Mw) of SPI increasing by101.23%and solubility inphosphate buffer solution decreasing by60.42%. During extrusion cooking process, protein wasdisassociated/depolymerized by mechanical shear, and increasing SME decreased the Mw of SPI.However, increasing SME gradually inceased the SPI solubility in phosphate buffer solution. Thereexisted vital factors contributing to the aggregation of proteins in extrusion cooking. The vital factorswere most likely to be thermal energy and pressure.(3) Extraction sequence exerted a significant effect on the solubility of extruded SPI in SDS,2-MEand their mixed solution. With the sequence of P-S-M-S+M, the extraction rate of extruded SPI by2-Mewas higher than that by SDS; while with the sequence of P-M-S-M+S, the extraction rate of extrudedSPI by SDS was higher than that by2-Me. Meanwhile, extraction sequence also exerted a significanteffect on the Mw of SPI components extracted by different solutions. With the sequence of P-S-M-S+M,the Mw of the component of extruded SPI extracted by2-Me was higher than that by SDS; while withthe sequence of P-M-S-M+S, the Mw of the component of extruded SPI extracted by SDS was higherthan that by2-Me. Only by SDS plus2-Me, could the large Mw component of extruded SPI bedissolved indicating the structure of large Mw component of was hold collectively by non-covalent bond and disulfided linkage.