Physicochemical and surface property changes induced by polyphenols and heat: Effects on pea protein digestibility

With a growing interest in sustainability, plant-based proteins are viable substitutes for animal-derived proteins. Pea protein isolate (PPI), from Pisum sativum L seeds, is a sustainable plant-based protein due to its affordability and superior nutritional quality, hence the increased attention for its application in developing alternative food products. However, processing methods and ingredient interactions from food-matrix systems can significantly affect its structural and functional properties. This study investigates the effect of thermal treatment and interactions with curcumin, a bioactive polyphenol, on in vitro digestibility of PPI. PPI was combined with curcumin at concentrations ranging from 2 to 100 µM or subjected to heating at temperatures of 25, 50, 75, and 95°C for 15 minutes, followed by cooling. UV-Vis spectral analysis confirmed the formation of PPI-curcumin complexes, characterized by reducing transmittance and surface hydrophobicity along with increased average particle size. In contrast, thermal treatments induced protein aggregation, as shown by ThT fibrillation kinetics, with increased surface hydrophobicity, decreased free sulfhydryl groups, and a reduction in average particle size. Fluorescence and transmission electron microscopy imaging revealed the formation of amorphous aggregates by curcumin complexation, as well as a mixture of aggregates and fibrillar species post-thermal treatment. Non-reducing SDS-PAGE indicated that curcumin interaction did not affect the pea protein profile. Interestingly, curcumin interaction and thermal treatment led to a significant reduction in PPI in vitro digestibility by up to 30.5%, as indicated by the protein digestibility corrected amino acid score (PDCAAS). Taken together, these findings provide comprehensive insights into the interplay between polyphenolic interactions and thermal exposure on pea protein structure and quality as indicated by the in vitro digestibility. This research contributes to the understanding of food matrix interactions and their implications on protein functionality, digestibility, and the development of protein-based nutraceutical delivery systems and plant-based formulated food products.