Germination time shapes digestibility, functionality, and structure of lupin–corn extrudates

This study evaluated the impact of germination (3, 5, and 7 days) of lupin (Lupinus angustifolius L.) flour on the nutritional quality and antidiabetic potential of corn starch-based extruded formulations. Germination enhanced protein content (15.23 % in 7-day germinated flour vs. 13.64 % in control) and maintained essential amino acid adequacy. Microscopy revealed structural changes related to improved digestibility and bioactivity. Germinated samples, particularly GLE5 and GLE7, promoted the release of peptides <10 kDa and increased bioaccessibility of peptides <0.2 kDa after simulated intestinal digestion. GLE5 exhibited the lowest starch hydrolysis (12.66) and glycaemic indices (46.66), classifying it as a medium-glycaemic food. Although α-amylase inhibition was comparable among samples (IC₅₀: 26.54-29.96 mg/mL), DPP-IV inhibitory activity improved with germinated flour (IC₅₀: 8.35-8.51 mg/mL). Seven digestion-resistant peptides showed high predicted DPP-IV inhibition. These findings support the use of germinated lupin flour in the formulation of functional extruded foods with enhanced nutritional and antidiabetic properties.