Synergistic effect of amyloglucosidase and resveratrol on reducing in vitro starch digestibility

Bread is a major dietary carbohydrate source, but its rapid starch digestion promotes a high glycemic index. Resveratrol (RSV), a plant polyphenol, and amyloglucosidase (AMG) can modify starch structure which could potentially alter the starch digestibility. This study examined whether the individual and combined use of RSV and AMG could lower starch digestibility while preserving bread quality. The pasting and hydrolysis behavior of white and whole-wheat flours enriched with RSV, AMG, or their combination were analyzed by Rapid Visco Analyzer and modeled with Box–Lucas kinetics. Breads were evaluated for texture, color, RSV recovery, and in-vitro starch digestibility. In white flour, AMG reduced peak viscosity, whereas RSV mitigated this effect and increased setback, indicating enhanced retrogradation. The combined RSV-AMG treatment yielded the lowest hydrolysis rate (k = 0.56 min⁻¹), suggesting a denser starch–polyphenol network that restricted enzymatic access. Whole-wheat flours, bran and fiber led to different effects, with RSV increasing starch retrogradation during cooling. The combination of the treatment led to softer white crumbs and reduced the RSV induced firmness of whole-wheat crumbs. In both breads, RSV shifted starch fractions from rapid digestible starch to slowly digestible starch in both matrices, slowing the in vitro starch hydrolysis. Overall, RSV and AMG acted synergistically to modulate starch chain length and matrix structure, reducing starch digestibility without compromising technological performance. These findings highlight a feasible strategy to design lower-glycemic breads through enzyme–polyphenol co-modulation of starch retrogradation and digestibility.