Air-water interfacial and foaming properties of native protein in aqueous quinoa (Chenopodium quinoa Willd.) extracts: Impact of pH- and heat-induced aggregation

Abstract

The shift from animal-based towards more sustainable plant-based food systems has increased the interest in leguminous protein such as that from the pseudo-cereal quinoa. In spite of the importance of foaming agents in a wide variety of food systems, the foaming properties of quinoa protein are still poorly understood. In this research paper, the air-water (A-W) interfacial and foaming properties of aqueous extracts from defatted quinoa wholemeal were investigated. Foams contained both albumins and 11S globulins, but no 7S globulins, despite the presence of the latter proteins in the extracts. At pH 7.0, both albumins and 11S globulins were soluble and jointly adsorbed at the A-W interface. Closer to the 11S globulin isoelectric point (pH 5.0), only albumins adsorbed at the A-W interface. Cultivar-dependent differences in protein composition and functionality allowed to hypothesize that 11S globulins foam better when present as dissociated acidic and basic subunits rather than as monomers. Heat-induced aggregation of 11S globulins led to enrichment of albumins at the A-W interface. This was associated with an increased surface tension and a decreased surface dilatational modulus. Presumably, quinoa albumins have low tendency to interact at the A-W interface resulting in a weakly elastic interfacial network. At the same time, globulin aggregates formed during heating at pH 5.0 and 7.0 lead to unstable and stable foams, respectively. As protein functional properties are important for the quality of many food products, these insights are valuable when developing novel quinoa-based food products requiring interfacial stability.