Nutritional trade-off in instant buckwheat noodle sheets during boiling and drying: Structural basis of starch digestibility and bioactive stability

Abstract

Instant buckwheat noodle sheets (IBNS) represent a promising functional food. However, the structural evolution during moderate-temperature drying and its nutritional implications remain unclear. This study investigated the effects of buckwheat flour addition (BFA) (0–30%) and drying temperature (60°C and 70°C) on the structural, digestive, and bioactive properties of IBNS. Microstructural and spectroscopic analyses revealed that increasing BFA disrupted the gluten network, reduced starch molecular order, and increased cooking loss to 3.32% and 3.15% at 30% BFA under 60°C and 70°C drying, respectively. Conversely, BFA enhanced resistant starch (RS) and bioactive retention; for instance, RS increased from 65.02% to 77.33% at 60°C and from 63.61% to 87.81% at 70°C as BFA rose from 0% to 30%. Notably, drying at 70°C promoted protein aggregation and matrix densification, which was associated with lower starch digestibility, higher RS content, and greater losses of phenolic compounds and antioxidant activity than drying at 60°C. This effect was reflected in the 0%-BFA IBNS, where total phenolic content retention decreased to 32.46% after drying and further to 24.28% after rehydration under 70°C. These findings reveal a process-induced structure-function trade-off between starch digestibility and bioactive stability in IBNS. A BFA of 20–30% with 60°C drying was proposed as an optimal strategy to balance these competing nutritional benefits. These findings provide a scientific basis for designing nutritious, low-glycemic-index instant noodles through targeted optimization of composition and drying conditions.