Effect of Toughening-Enzyme Modification on the Structure and Properties of Sorghum Starch

To investigate the effects of mechanical toughening and toughening-enzymatic modification on the formation, structure, and physicochemical properties of slow-digestible starch content in sorghum starch, a comparative analysis was conducted on the structure and physicochemical characteristics of sorghum starch before and after these modifications. Parameters including slow-digestible starch content, starch granule morphology, crystal structure, solubility, expansion capacity, water extraction rate, and thermal stability were examined. Results showed that, the slow-digestible starch content in modified sorghum starch significantly increased (P<0.05). Specifically, the content after toughening reached 18.68%, and following toughening and enzyme modification, it increased to 38.37%. The surface morphology of enzyme-modified sorghum starch exhibited irregularities and fragmentation, and the internal structure of modified sorghum starch underwent rearrangement. Notably, the relative crystallinity of toughened sorghum starch increased to 21.43%, and that of enzymatically modified toughened sorghum starch increased to 27.53%. Toughened sorghum starch retained an A-type crystalline form, while enzymatically modified toughened sorghum starch transitioned to an A+V type crystalline form. At 90 °C, both solubility and dilatability were significantly lower in modified sorghum starch compared to unmodified samples (P<0.05), while transparency and water precipitation rates were markedly higher (P<0.05). An increase in the initial gelatinization temperature was observed, indicating enhanced thermal stability. In conclusion, compared to toughened modified sorghum starch alone, the combination of toughening and enzyme modification demonstrated a more pronounced impact on the content, structural attributes, and physicochemical properties of slow-digestible starch in starchy sorghum materials.