Thermal, structural and morphological characterisation of organic rice starch after physical treatment

Rice (Oryza sativa L.) is a cereal of great economic and nutritional importance due to its expressive consumption. To achieve new properties or improve the characteristics presented by native starch, modifications are carried out, catching the attention of many researchers. Therefore, this study aimed to analyse the effects of ultrasound on the thermal, structural and morphological properties of organic rice starch. The starch was extracted by the aqueous method, followed by alcalase treatment for protein removal. Colourimetry, thermogravimetry, differential scanning calorimetry, X-ray powder diffractometry and microscopy were analysed. After treatment of the native starch with the alcalase, a reduction in the thermal stability temperature was observed, as well as a reduction in the gelatinisation transition temperatures and an increase in the gelatinisation enthalpy. When modified by ultrasound, under greater amplitude of vibration, shorter time and lower concentration, an increase in the thermal stability of the starch was achieved. In addition, an increase in peak temperature (Tp) was observed and there was no significant difference for enthalpy in most treatments. The concentration influenced the gelatinisation enthalpy (ΔHgel) only of the treatments under the lowest amplitude of vibration (75%). Changes in relative crystallinity were also found. Through microscopy, it was identified that the alcalase treatment was efficient because no proteins were observed in the images. The use of the physically modified organic rice starch may be an alternative for use as an excipient in the pharmaceutical industry and encapsulating agent in the food industry.