Combined effect of heat moisture and ultrasound treatment on the physicochemical, thermal and structural properties of new variety of purple rice starch.

ABSTRACT

The advantages of physically modifying starch are evident minimal environmental impact, no by-products, and straightforward control. The impact of dual modification on starch properties is contingent upon modification conditions and starch type. Herein, we subjected purple rice starch (PRS) to heat-moisture treatment (HMT, 110 °C, 4 h) with varying moisture content, ultrasound treatment (UT, 50 Hz, 30 min) with different ultrasonic power, and a combination of HMT and UT. Our findings reveal that UT following HMT dispersed starch granules initially aggregated by HMT and resulted in a rougher granule surface. Rheological analysis showcased a synergistic effect of HMT and UT, enhancing the fluidity of PRS and reinforcing its resistance to deformation in paste form. The absorbance ratio R1047/1015 indicates that increased moisture content during HMT and high ultrasound power for UT reduced the short-range order degree (1.69). However, the combined HMT-UT exhibited an increased R1047/1015 (1.38-1.64) compared to HMT alone (1.29-1.45), likely due to short-chain rearrangement. Notably, the A-type structure of PRS remained unaltered, but overall crystallinity significantly decreased (23.01 %-28.56 %), consistent with DSC results. In summary, physical modifications exerted significant effects on PRS, shedding light on the mechanisms governing the transformation of structural properties during HMT-UT.