Synergistic modification of chestnut powder via Lactobacillus plantarum and pullulanase: Promotion of resistant starch formation and structural-functional enhancement.

Chestnut (Castanea mollissima Blume) is a nutritionally dense food, notably rich in starch, making it an important natural source of carbohydrates and energy for human diets. However, its high content of rapidly digestible starch (RDS) limits its use in low-glycemic-index (GI) food products. This study developed a synergistic bioprocess combining Lactobacillus plantarum fermentation and pullulanase-catalyzed debranching to enhance the nutritional and structural characteristics of chestnut powder. The optimized conditions involved a 10:1 (v/w) liquid-to-solid ratio, 18 h of fermentation at 37 °C with 8 % inoculum, followed by 7 h of enzymatic hydrolysis at 55 °C with 40 U/g pullulanase. RDS content decreased from 73.51 to 20.65, while resistant starch (RS) increased to 34.16 %. Microstructural analysis revealed denser granule aggregation, reduced particle size, and increased surface area. Structural evaluations (XRD, H NMR, chain-length distribution) confirmed the degradation of α-1,6-glycosidic bonds and formation of linear chains. Thermal and rheological analyses indicated enhanced gelatinization stability (T = 28.88 °C, ΔH = 1.27 J/g) and viscoelasticity. Pearson correlation analysis revealed that amylose content, molecular ordering, and long-chain fractions were strongly associated with RS formation. Overall, this mild, sustainable strategy enables structural remodeling of starch and offers potential for formulating low-GI, functional foods.