Role of glassy and crystalline transitions in the responses of corn starches to heat and high pressure treatments: Prediction of solute-induced barostabilty from solute-induced thermostability

The effects of heat and high hydrostatic pressure (HHP) on glassy and crystalline transitions of starches, and the distinctive contributions of amylopectin and amylose, with respect to annealing, gelatinization, pasting, and retrogradation were explored by conducting an experimental design with five factors: type of starch (dent and waxy corn), pressure (atmospheric to 600 MPa), temperature (25–70 °C), time (5–60 min), and type of diluent (water, most efficient plasticizer, lowest Tg; salt-water, non-glass-forming solvent; and sucrose-water, glass-forming plasticizer, high Tg). When 50% w/w starch slurries were HHP-treated for 15 min at 25 °C, treatment at 300 MPa showed no effects on glassy or crystalline transitions, but treatment at 600 MPa showed significant extents of gelatinization and annealing, and smaller extents of subsequent retrogradation, for both starches. Longer treatment time at 600 MPa showed the role of the glass transition. Elevated treatment temperature at 600 MPa showed the roles of both glassy and crystalline transitions. NaCl (2 M, lyotropic concentration) or sucrose (50% w/w, glass-forming concentration) showed thermostabilizing effects against starch gelatinization at atmospheric pressure and baroprotective effects against starch gelatinization during HHP treatment at 600 MPa, 15 min, 25 °C. Both the thermoprotective and baroprotective effects of sucrose were more dramatic than those of salt. In the case of dent and waxy corn starches, solute-induced thermostabilization by both NaCl and sucrose predicted solute-induced barostabilization.