Valorisation of starch-rich pea byproduct into cold-extruded rice analogues: effects of processing temperature on physicochemical, functional, cooking, and in vitro digestibility properties

Abstract

The starch-rich fraction (SRF) from pea protein fractionation is a major underutilized byproduct, and its valorisation is critical for sustainable pulse processing. This study aimed to upcycle SRF into rice analogues using cold extrusion at 25 and 50 °C. Uniformly kneaded SRF (35% added water) was extruded through a rice-shaped die, cut, and dried. The developed analogues were analyzed for nutritional, physicochemical, structural, thermal, cooking, and in vitro digestibility properties. Conventional rice was used as the control. The rice analogues exhibited acceptable physical properties and superior nutritional quality with significantly higher protein content (9.4–11%) than the control (3%). Both extrusion conditions produced analogues with reduced crystallinity (25–27%), lower gelatinization temperatures, and shorter cooking times (2–13 min), although they exhibited slightly higher solid loss during cooking (3.3–3.7%). The extruded products also contained a higher amount of resistant starch (11–15%), resulting in a lower expected glycemic index (76–79) compared to the control (85). Among the treatments, extrusion at 50 °C produced the most pronounced effects. Therefore, RAs developed from SRF provide a potential solution for starch-rich byproduct utilization, yielding rice with enhanced nutritional quality, shorter cooking time, and acceptable cooking stability. Processing at moderate temperatures (25 °C) preserves nutritional quality and results in a lower eGI, whereas higher extrusion temperatures (50 °C) enhance convenience through rapid gelatinization and reduced cooking time but compromise nutritional quality and cooking stability.