Physicochemical and functional characterization of physically treated commercial corn starches and their mixtures

Corn starches with different physical structures were studied to understand their physico-chemical and functional properties. A novel continuous starch annealing process was developed. An optimum com starch annealing end temperature and heating rate were calculated to be 59°C and 0.67°C/h, respectively; enthalpy (14.2J/g) and onset temperature (69.0°C) were maximized while holding relative percent crystallinity unchanged (52.4%). When these mathematically determined conditions were tested, actual and calculated results for DSC gelatinization enthalpy and onset temperature, and % relative crystallinity were similar. Relationships between the structural properties of raw, swollen, annealed and gelatinized starches and their functionalities were investigated using mixtures of these starch types. Raw, swollen and annealed starches were similar in their water absorption indices, water solubility indexes and percent relative crystallinities. Although the enthalpy values for raw, swollen and annealed starches were similar, gelatinization peaks for swollen and annealed starches were wider and narrower, respectively, than that for raw starch. Gelatinized starch had no DSC peak. Cooked annealed and cooked raw starches made the hardest gels. Gelatinized starch resulted in higher RVA viscosity profiles relative to the other starch structures. When gelatinized starch was mixed with the other starch structures, however, it decreased peak and final viscosities, breakdown, and setback. The relationships between the structural properties of raw and extruders corn starches and their functionalities were also investigated using mixtures of these starch types. The extruded starch sample had higher water absorption and water solubility indices than the raw starch sample (WSI: 24.6% vs. 0.96%, WAI: 4.98 g/g vs. 1.78g/g). There was no DSC endotherm observed for the extruded starch. Cohesiveness and adhesiveness of gels from both raw and extruded starches were similar, while extruded starch made softer gels. Extruded starch produced lower RVA viscosity profiles than raw starch. When extruded and raw starches were mixed, the responses were not always linear. Negative interactions between raw and extruded starches were observed for the viscosity parameters. As extruded starch content increased in the mixture, the mixture viscosity profile decreased, due to starch degradation in the extruded starch