Functionality of lupin protein-polyphenols conjugates for structuring high internal phase oil-in-water (O/W) emulsion

The development of food products with a reduced fat content is aimed at preventing and reducing the incidence of diseases related to obesity and other chronic illnesses. In this sense, high internal phase oil-in-water (O/W) emulsions (HIPEs) stabilized by proteins have been explored to partially replace saturated and hydrogenated fats, considering their rheological properties that may contribute to the structuring of the final product. However, the functionality of plant proteins is limited, hindering their performance as emulsifiers. The conjugation of plant proteins with phenolic compounds and heating treatment are some strategies that can modify the surface properties of plant proteins, improving their functionality. In this context, the present study evaluated the covalent conjugation of lupin protein isolate (LPI) with grape seed extract (GSE) in different concentrations (0.04-0.12 wt%) and heat treatment (85 °C, 15 min) as sustainable approaches for tuning LPI surface properties and O/W HIPEs rheology. In this context, the characterization of O/W HIPEs was performed by rheology, fluorescence microscopy, kinetic stability, droplet size distribution, and oil loss by centrifugation over 56 days of storage at 25 °C. All samples showed a typical microstructure of HIPEs with packed and deformed droplets into polygonal shapes and multimodal droplet size distribution. Although the emulsions showed high stability at quiescent conditions over 56 days of storage, all samples showed oil release under shear. Based on that, heating and conjugation with GSE promoted increased viscoelastic behavior of HIPEs due to improved viscosity and storage modulus (G’). Given the above, the conjugation of plant protein with GSE combined with heating arises as a potential pathway to improve the viscoelastic properties of O/W HIPEs to replace saturated fats partially.