New insight into starch-lipid complexes inhibiting the starch gelatinization during sorghum grain steaming

This study investigated starch-lipid complexes formation during sorghum grain steaming and its inhibitory mechanism on starch gelatinization and hydrolysis. Scanning electron microscopy revealed that the remaining ungelatinized starch (RUS) within the white core region of steamed grains retained a granular structure but exhibited surface collapse. ¹³C nuclear magnetic resonance analyses indicated that, compared to native sorghum starch (NS), RUS from grains steamed for 10 min displayed an increased single helix content (from 0.69 % to 1.24 %), confirming starch-lipid complexes formation. Confocal laser scanning microscopy demonstrated that starch-lipid complexes formed a protective barrier on RUS surfaces after 10 min of steaming. This barrier impeded water penetration, thereby delaying subsequent gelatinization and increasing the gelatinization temperature from 74.25 °C to 87.20 °C. It also blocked the action of enzymes, reducing the starch hydrolysis rate from 77.93 % to 68.54 %. This study provides a new research approach for investigating the effect of lipid on starch gelatinization during sorghum grain steaming, and a theoretical basis for precisely controlling sorghum steaming time and improving brewing efficiency.