Foaming and emulsifying properties of extensively and mildly extracted Bambara groundnut proteins: A comparison of legumin, vicilin and albumin protein

Abstract

Bambara groundnut (BGN) is a novel plant protein source, which has not received much attention in terms of the structure-function relation of its proteins in foaming and emulsifying properties. In this study, these functional properties were evaluated for two BGN protein concentrates that have been extracted using different extraction methods. The first method is based on conventional “extensive” purification, which includes pre-processing (dehulling, defatting and milling), two centrifugation steps and isoelectric point precipitation. The second method is a more sustainable “mild” purification, which does not require pre-processing and uses only one centrifugation step. The three major protein fractions in BGN (vicilin, legumin and albumins) were also purified and included in this study. Both extensively and mildly purified protein concentrates showed comparable emulsion stabilising properties, with emulsions stable against coalescence, flocculation and creaming, for at least seven days. A more pronounced difference was found in the foaming properties, with the mildly purified protein concentrate forming up to 9x more foam, with much higher stability (about 8x higher), compared to the extensively purified protein concentrate. This was attributed to the albumins, which were only present in the mildly purified protein concentrate. These albumins had the ability to form stiff viscoelastic solid-like air-water interfaces, with high dilatational moduli up to 90 mN/m; close to that of whey protein-stabilised interfaces. These strong interfaces largely contributed to the excellent foaming properties of the mildly purified protein extract. We conclude that BGN proteins have promising functional properties, and that mild purification further enhances their potential.