Interactions and complex formation between pea proteins (Pisum sativum L.) and betanin from red beet (Beta vulgaris L.) extract – effect of foam fractionation

Pea proteins show promise as vegan-friendly food ingredients, where their functional properties can be affected by extraction and purification processes. Red beets are a source of betanin, a natural colorant that is susceptible to degradation, limiting its application. This study examined the interactions between pea protein flour (PPF) proteins and betanin in red beet extract (RBE) and assessed whether foam fractionation could improve the functional properties and thermal stability of PPF-RBE complexes. Spectrophotometric, thermal, and morphological analyses indicated that both non-foamed and foamed proteins formed complexes with RBE. The secondary and tertiary structures of PPF proteins were likely altered and their flexibility was increased due to unfolding during foam fractionation and subsequent pH adjustment. Circular dichroism and Fourier transform infrared spectra indicated that non-foamed PPF proteins had an α-helical structure, which was more pronounced in the foamed PPF proteins. After interacting with RBE, the foamed PPF-RBE complex exhibited β-sheet structuring that was more pronounced than the non-foamed complex, resulting in improved functional properties such as soluble protein content, foaming, and emulsifying abilities. This increase in β-sheet structure might have also improved the thermal stability of foamed PPF-RBE complex. Scanning electron microscopy showed larger particles in the non-foamed and foamed PPF-RBE complexes than in the respective protein controls. Foamed proteins, which may have had more phenolic hydroxyl groups, also had the highest antioxidant activity. Consequently, foam-fractionated PPF-RBE complexes appear to be promising ingredients for commercial products with improved functional properties. • Pea proteins (foamed/non-foamed) formed complexes with betanin in red beet extract • Foamed pea protein demonstrated improved functional properties when compared to the non-foamed pea protein under identical pH conditions, suggesting that the observed differences are attributable to foam fractionation rather than pH adjustment • Interaction between foamed pea protein and betanin in pea protein/betanin complexes further enhanced the functionality • Foamed pea protein/betanin complexes had better thermal stability than protein alone • Foamed pea protein/betanin complexes had better antioxidant properties