Physicochemical and structural characteristics of sorghum starch as affected by acid‐ethanol hydrolysis

Acid alcohol hydrolysis of starch is a sustainable chemical method and versatile tool to control molecular weight. Sorghum starch was acid hydrolyzed in ethanol for durations ranging from 24 to 240 h. The native and acid ethanol treated (AET) starches were investigated for their physicochemical, thermal, structural and pasting characteristics. Native starch showed degree of polymerization of 2624 anhydrous glucose units (AGU), amylose content of 26%, swelling power and solubility of 12.2 g/g and 5%, respectively. AET starches showed significantly (p < 0.05) higher solubility (19.8–58.4%) whereas lower values for swelling power (4.3–11 g/g), were observed. The chain length profiles of debranched native and AET sorghum starches, as obtained from high-performance size-exclusion chromatography (HPSEC), indicated preferential degradation of amylose and amylopectin long chains. This led to decrease in intrinsic and pasting viscosities for AET starches. Comparison of X-ray diffractograms (XRD) of native and AET treated sorghum starches showed that there is no change in the diffraction pattern (‘A’ type) upon treatment however the relative crystallinity was observed to decrease upon hydrolysis. Granule structure remained intact however, with AET birefringence loss in some granules was observed, which indicated change in radial orientation of double helices and chain mobility at granule centre. The results indicated that sorghum starch can be tailored by AET and could be used in the food industry for various food formulations.