Unveiling the potential of pressurized liquid extraction for recovering protein fractions from broken black beans: Insights into thermal and structural properties

Abstract

Pressurized liquid extraction (PLE) is an emerging eco-friendly approach for recovering protein from broken black beans (BBB). This investigation explored the thermal and structural characteristics of BBB protein fractions recovered via PLE compared to the emerging technologies of ultrasound- and microwave-assisted extractions (UAE and MAE) and conventional heating-stirring extraction (HSE) using water and alkaline water (pH 9.0) as solvents. Alkaline water extractions exhibited superior protein yields and purity, resulting in protein aggregates of smaller sizes (<150 nm) in the BBB protein concentrates recovered by PLE and UAE. In comparison, larger aggregates of protein flour were formed when applying HSE (>450 nm), regardless of the solvent used. Nevertheless, heightened pH levels induced substantial modifications in protein conformation, reducing the denaturation temperature (Td) and enthalpy. β-strands and random coil conformations dominated the secondary structure, while α-helix was solely observed in alkaline PLE. The selection of the extraction technique had a pronounced influence on protein partial unfolding, leading to diverse protein profiles and properties. PLE (water) presented a viable and eco-friendly alternative for attaining protein recovery with high purity (86.7%) and thermal stability (Td: 78.7 °C, enthalpy: 207.20 J/g). BBB protein research advancements offer opportunities for sustainable and nutritious plant-based protein sources with global economic and social benefits.