Effect of degree of cross linking on physicochemical, rheological and morphological properties of Sorghum starch

Abstract

Sorghum starch was cross-linked (CL) with epiclorohydrin (EPI) at different concentrations (0.1–1.0%). Degree of cross-linking (DC) ranged between 49.5-89.7% (for 0.5–1.0% CL starch); the highest value was observed for 1.0% CL starch. Amylose content, swelling power, and solubility ranged between 5.1–18.5%, 6.9–10.5 g/g, 6–11%, respectively. As compared to native starch, peak viscosity increased for 0.1 and 0.3% CL starches, further increase in cross-linking levels resulted in decrease. Temperature sweep testing showed lower G′ values for 0.3–1.0% CL starches in comparison to native starch. Frequency sweep testing of CL starches showed G′ and G′′ values between 365–2010 Pa and 67–113 Pa, respectively.The flow behaviour index (n) ranged between 0.14–0.34, indicating shear thinning behaviour of CL starch pastes. Consistency index (K) value varied from 20.23–119.2 (Pa.s), the highest and the lowest values were observed for 0.1 and 1.0% CL starches, respectively. Crosslinking resulted in pronounced effect on starch morphology. CL starches showed rough surface, cavities and cracks on their surface. For stabilized granular structure and restricted swelling, CL starch is most commonly used in food industry.