Rheological behaviors exhibited by soy protein systems under dynamic aqueous environments

ABSTRACT In this study, rheological behaviors of soy protein and soy flour as powders, pastes, and dispersions are characterized over a range of water contents and temperature to understand their processing in adhesives or paints. At ambient temperature, soy protein samples were characterized by low critical strain values (<0.1%), whereas soy flour samples exhibit linear viscoelastic regions >1% strain with 30–90% water content. On heating, the aqueous soy protein and soy flour compositions have complex rheological behaviors due to plasticization by water and the thermal denaturing and crosslinking of protein and carbohydrate with increasing temperature. Below 100 °C, soy protein rheological behaviors were attributable to the glass transition of the 7S and 11S soy globulin fractions, polymer flow, and plasticization by residual moisture. Above 100 °C, the onset of protein crosslinking was observed with this shifting to higher temperatures for samples still dehydrating. With soy flour samples, the residual moisture present above 100 °C similarly increase protein crosslinking to higher temperatures (125–148 °C) for samples with initial water contents of 30–90%. These results provide a basis for understanding why soy systems undergoing heat processing and rapid dehydration will require higher temperature and longer processing time to attain a cured, crosslinked state. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 45513.