# Unveiling the Effects of Roasting Pre-Treatment on the Structural and Functional Properties of Lupinus angustifolius Protein Isolates and Their Impact on In Vitro Digestibility

## TL;DR

Roasting lupin seeds before extracting protein improves its solubility, emulsifying ability, and digestibility, making it a better plant-based protein for food use.

## Contribution

The study reveals how roasting alters lupin protein structure and function, enabling controlled modulation for optimized food applications.

## Key findings

- Roasting increases solubility, emulsifying activity, and in vitro digestibility of lupin protein isolates.
- SDS-PAGE shows roasting induces oligomer and aggregate formation, affecting emulsion stability.
- Prolonged roasting maximizes antioxidant capacity but reduces amino acid content.

## Abstract

This study investigates the effects of roasting pre-treatment on Lupinus angustifolius protein isolate (LPI) and the resulting structure–function relationships relevant to food applications. Lupin seeds were roasted for 0, 10, 20, and 30 min prior to protein extraction, and the resulting LPI was characterized using circular dichroism (CD), Fourier-transform infrared (FT-IR) spectroscopy, intrinsic fluorescence spectroscopy, and SDS-PAGE. Unroasted LPI exhibited compact native conglutin structures with low solubility (58.64%), surface hydrophobicity (43.34 μg BPB), emulsifying activity (30.71 m2/g), and in vitro protein digestibility (IVPD, 82.84%). Roasting pre-treatment induced a biphasic structural response. Partial conformational changes increased solubility (up to 97.84%), exposed hydrophobic sites (peak 55.79 μg BPB), enhanced emulsifying activity (45.37 m2/g), doubled foaming capacity (210%), and improved IVPD (90.85%), likely due to structural changes that facilitated digestion. CD analysis showed a modest increase in α-helical content (3.43 → 6.74%) with minor fluctuations in β-sheet content, while fluorescence quenching indicated conformational loosening and partial reorganization. SDS-PAGE revealed the formation of soluble oligomers and high-molecular-weight aggregates, consistent with heat-induced association. Prolonged roasting reduced emulsion and foam stability because of aggregation, but maximized antioxidant capacity, likely associated with Maillard reaction products despite the observed depletion of amino acids. Overall, controlled roasting pre-treatment systematically modulates lupin protein structure and functionality, highlighting LPI as a competitive high-performance plant protein ingredient for food applications.