Unveiling the potential of beetroot leaf as a sustainable source of proteins: insights into ultrasound-assisted extraction, functional properties and in vitro digestibility

Beetroot leaf, typically discarded as agricultural waste, is a promising source of plant-based proteins. With growing interest in sustainable and eco-friendly food production, extracting high-quality protein from such by-products supports a circular economy. This study optimized ultrasound-assisted alkaline extraction (UAAE) using a Box-Behnken design to maximize protein yield and content from beetroot leaves. The combination of ultrasound and alkaline treatment has been shown to enhance extraction efficiency and protein techno-functionality in comparison with conventional alkaline method (CAE). Optimal UAAE conditions (40 min, pH 11, 27.2 °C) yielded a protein content of 73.4% with a 10% extraction yield. Fourier transform infrared spectroscopy analysis confirmed that the secondary structure of beetroot leaf protein (BLP) obtained by UAAE remained intact, while microscopic analysis revealed a more compact globular morphology. Additionally, BLP obtained by UAAE showed better heat resistance and less aggregations, supported by a higher absolute zeta potential value (−31.06 mV, compared to −24.03 mV for BLP obtained by CAE). Both BLP obtained by UAAE and CAE displayed proportional increases in foaming capacity and stability with higher protein concentrations. UAAE led to improved digestibility of the BLP compared to legume protein isolates such as soy and pea protein. These findings highlight UAAE as an efficient method to produce high-quality protein from beetroot leaves, suitable for vegan foods, supplements, and pharmaceuticals.