Establishment of a Refractive Index Approach for Assessing Starch Digestibility and Estimated Glycemic Index

Traditional starch digestibility methods involving the detection of glucose by spectrophotometric analysis are time‐consuming. Thus, this study is aimed at developing and evaluating a refractive index (RI) method as a faster alternative. Starch samples from wheat, corn, pea, tapioca, and potato were characterized using scanning electron microscopy (SEM) to determine starch morphology, rapid visco analyzer (RVA) to determine pasting properties, and differential scanning calorimetry (DSC) to determine thermal properties. Finally, the hydrolysis index (HI) and expected glycemic index (eGI) were determined using the RI and spectrophotometric methods. SEM revealed varying starch sizes, shapes, and surface structures across starch sources. For example, corn starch granules were small and polyhedral in shape with evidence of surface pores, while potato starch granules were generally larger and had a smooth, compact surface. Thermal properties revealed lower crystallinity of wheat and corn starch granules based on enthalpy, compared to pea, potato, and tapioca starch. Pasting properties revealed distinct behaviors among the starches. For example, potato starch showed rapid swelling and the highest peak viscosity, along with extensive breakdown. Pea starch exhibited the highest setback value and final viscosity. Based on digestibility tests, both the spectrophotometric method and the RI method yielded the same order of starch digestibility (i.e., wheat > corn > tapioca > pea > potato). However, the absolute HI and eGI values differed between the two methods. The spectrophotometric method was able to distinguish the digestibility of corn from that of pea and tapioca, whereas the RI method grouped the three starches together without significant differences. Nevertheless, a strong positive correlation ( r = 0.973, p < 0.01) between the two methods suggests that the RI method could serve as a rapid screening tool for ranking starch samples based on digestibility. This could be essential for guiding early formulation decisions in product development and prioritizing samples for further analysis.