Insights into the digestibility differences of thermostable starches under boiling treatment

Boiling treatment can increase starch digestibility and postprandial glycemic response, prompting efforts to enhance starch thermal-processed stability. This study examined boiling-treatment on structural, physicochemical, and digestive properties of thermostable starches: high-amylose corn starch and debranched long/short-chain glucan. Polarized microscopy, XRD, and DSC confirmed that crystalline structures persisted after boiling-treatment, with peak gelatinization temperatures above 100 °C (117 °C ∼ 121 °C), except for high-amylose corn starch (92.5 °C). However, the boiling-treatment did induce some structural changes in the thermostable starches, which then increased their digestibility. Recrystallized short-chain glucan (58 % crystallinity) showed the largest shift: rapidly digestible starch content rose from 26.9 % to 78.2 %, while resistant starch content dropped from 63.1 % to 10.0 %. In contrast, the other samples retained more resistant starch content (43.9 % ∼ 47.2 %), showing greater digestive resistance. Despite resisting boiling-treatment conditions, recrystallized short-chain glucan remains vulnerable to enzymatic degradation. Due to the compact structure of the remained starch after boiling-treatment, high-amylose corn starch and long-chain glucan retained higher resistant starch levels, offering an effective route for thermostable resistant starches. This study identifies starch sources capable of withstanding boiling processing while maintaining high resistant starch content, supporting the development of low-glycemic index foods for diabetes prevention and obesity mitigation.