Microwave-assisted extraction enhances wet-heating Maillard glycation of lupin protein with galacto-oligosaccharides: structural basis for improved interfacial functionality and gut fermentability.

Lupin protein isolate (LPI) is limited in food use by poor solubility and weak interfacial behavior. This study tested whether the extraction route conditions LPI for subsequent glycation. LPI was recovered by microwave-assisted extraction, applied only during extraction, and conjugated with galacto-oligosaccharides (GOS) by wet heating at 90 °C for 15 min. Spectroscopic, electrophoretic, thermal and microscopic analyses confirmed GOS attachment and partial unfolding. The conjugate from microwave-extracted LPI reached the highest apparent degree of grafting (22%), reduced particle size from 1775.1 to 89.7 nm and surface hydrophobicity from 443.3 to 62.5 arbitrary units, and lowered β-sheet content. Foaming (64%/36%), emulsifying activity (74.2 m2/g) and DPPH scavenging (79.6%) improved accordingly. In fecal fermentation it retained more acetate at 24 h (420.8 versus 212.1 μmol/L for the control) and gave the highest gas volume (13.9 mL) and microbial evenness. Extraction history therefore governs conjugate functionality.