Effects of Chemical Composition and Intramolecular Structural Characteristics of Black Rice Varieties on Glycemic Index and Their Regulation Under Different Processing Conditions

This study explored how the chemical composition and molecular structure of black rice influence its glycemic index (GI), as well as how different processing methods regulate these relationships. Eight black rice varieties were analyzed for their nutritional composition, physicochemical and rheological properties, and protein structural characteristics. Results showed that higher protein and lipid contents were associated with lower GI values, likely due to reduced starch accessibility and slower enzymatic digestion. Varieties with more ordered protein conformations and stronger molecular interactions exhibited lower GI, indicating that protein structural organization plays an important role in starch digestibility. Among the tested varieties, "Huamoxiang" showed the highest GI (68.40 ± 2.04), while "Yanghei No. 3" exhibited the lowest GI (49.27 ± 4.14). Low-GI varieties were further subjected to different processing treatments. Fermentation effectively reduced GI by 8.44% by limiting starch gelatinization and enzymatic susceptibility, while puffing maintained a low GI through molecular rearrangement of starch. In contrast, steaming disrupted ordered starch structures and significantly increased GI. Overall, these findings provide practical guidance for selecting black rice varieties and processing strategies to develop low-GI black rice products, supporting the design of functional foods and dietary management for glycemic control.