Abstract
Plant proteins, and specifically those from legume crops, are increasingly recognised as sustainable and functional food ingredients. In this study, we expand on the knowledge of Bambara groundnut (Vigna subterranea (L.) Verdc.) [BGN] proteins, by characterising the composition, microstructure and rheological properties of BGN protein isolates obtained via wet extraction and protein-enriched fractions obtained via dry fractionation. The BGN protein isolates were compared in the context of the major storage protein, vicilin, as previously identified. Molecular weight analysis performed with gel electrophoresis and size-exclusion chromatography coupled to light-scattering, revealed some major bands (190 kDa) and elution patterns with molecular weights (205.6–274.1 kDa) corresponding to that of BGN vicilin, whilst the thermal denaturation temperature (Tp 91.1 °C, pH 7) of BGN protein isolates also coincided to that of the vicilin fraction. Furthermore, the concentration dependence of the elastic modulus G’ of the BGN protein isolates, closely resembled that of BGN vicilin (both upon NaCl addition); suggesting that vicilin is the main component responsible for gelation. Confocal laser scanning and scanning electron micrographs revealed inhomogeneous aggregate structures, which implies that fractal scaling were better suited for description of the BGN protein isolate gel networks. Concerning the BGN protein-enriched fractions, both rotor and impact milling with air jet sieving and air classification, respectively, were successfully applied to separate these fractions from those high in starch; as evident from compositional analysis, particle size distributions and microscopic imaging. When considering sustainability aspects, dry fractionation could thus be a viable alternative for producing BGN protein-enriched fractions.
Highlights
Pulses are recognised as an important class of legumes due to their nutrient-rich composition and associated health benefits
Protein isolates were extracted from Bambara groundnut black-eye seeds through isoelectric precipitation
Molecular weight analysis revealed that vicilin was the major fraction present in BGN protein isolate (BGN-PI), which was supported by the denaturation temperature of the protein iso lates at pH 7 coinciding with that of BGN vicilin
Summary
Pulses are recognised as an important class of legumes due to their nutrient-rich composition and associated health benefits. Research efforts are increasingly geared towards establishing ingredient functionality of pulse crops, with a large focus on protein functionality. This focus stems from the necessity of producing protein-rich foods from plant proteins as opposed to animal proteins, to contribute positively to a nutritious diet, and to food se curity and sustainability (Boye, Zare, & Pletch, 2010; Day, 2013; Stone, Wang, Tulbek, & Nickerson, 2019). BGN is increasingly recognised as a crop to be valorised; this is seen through the concerted efforts amongst inter national organisations who are focussed on optimising the crop’s per formance under various climatic conditions (Feldman et al, 2019). Noteworthy in terms of protein functionality, is the foaming capacity and emulsifying ability of BGN protein isolates and concentrates which were found to be similar (if not higher) compared to soybean protein
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