| Popis: |
Gelatinization properties of organic and conventional rice and spelt starches were evaluated. Commercial organic and conventional rice starches were obtained from a supplier. Organic and conventional spelt was planted side by side in six replicated plots in Wooster, OH and the starch was extracted using protease digestion method. Differential scanning calorimetry (DSC) was used to analyze starch gelatinization temperature range. Dynamic rheological measurement was applied to study the changes in complex viscosity and loss tangent during heating. High-performance size exclusion chromatography (HPSEC) was performed to elucidate the starch molecular composition. DSC showed that the organic rice starch had a significantly lower gelatinization temperature range than the conventional rice starch (56-66°C for organic, 60-72°C for conventional rice starch). Rheological analysis displayed similar onset temperatures for both organic and conventional rice starches, but a higher peak temperature for the organic rice starch (65°C and 93°C for organic, 64°C and 91°C for conventional starch). The peak complex viscosity was lower for the conventional (2.8 Pa.s) than for the organic rice starch (5.1 Pa.s), suggesting varying structural properties, such as molecular composition, as confirmed by the HPSEC. HPSEC showed that the organic rice starch contained a lower amylose level and a significantly higher molecular weight of amylopectin.For the spelt starch, DSC showed that the gelatinization temperature range was 57°C - 69°C with a peak temperature of 62°C on average. There was no statistical difference in gelatinization properties between organic and conventional spelt starches. Plot locations were found to be the driving factor of some of the observed differences. Rheologically, no significant difference was observed in the onset and peak temperatures of increase in complex viscosity. Variation in the rheological behavior among different plot locations were more pronounced than that between the two growing conditions. The percent mass fraction of amylose in the spelt starch was in the range of 35.7-54.5%. There was no significant difference in the molecular weight of amylose and amylopectin irrespective of the plot locations. Significant difference was found between the amylopectin Mw of organic and conventional spelt starches when analyzed collectively, which also correlated positively with the gelatinization enthalpy. Therefore, the organic rice starches studied may be used to substitute for the conventional counterpart only along with suitable adjustment in formulation or processing parameters to achieve equivalent products. The organic spelt starches may replace the conventional one when gelatinization behavior is considered. |
