Enhancing lupin protein isolation: Modulation of extraction parameters to maximize protein and phytochemical recovery, and phytase treatment for improved functionality

The growing demand for plant-based proteins has positioned lupin ( Lupinus spp.) as a promising alternative to soy. However, bioactive phytochemicals in lupin seeds —although offering valorisation potential— pose challenges due to their antinutritional effects and impact on protein functionality. This study investigated how ethanol concentration (EtOH), solvent-to-solute ratio (SSR), and fast heat treatment (HT) using a microwave oven influence the mass yield and composition of lupin protein isolate (LPI), as well as the recovery of phytochemicals in the extraction solvent (ES), using response surface methodology (RSM). Analysis of variance revealed that EtOH and SSR were the most significant factors. The maximum LPI yield was obtained at 11 % EtOH and a 23:1 SSR. Increasing EtOH up to 23 % increased protein content but caused a linear decrease in phytic acid and total phenolic content (TPC) and a linear increase in saponins in LPI, with opposite trends observed in the ES. Increasing SSR reduced LPI protein and phytochemical contents, except for phytic acid, which increased. Conversely, alkaloids, saponins and TPC generally increased with higher SSR in the ES. The addition of phytase during extraction significantly reduced phytic acid levels, improved LPI solubility, and the stability of its emulsifying and foaming properties. However, phytase treatment slightly reduced protein yield and LPI protein content, with changes being statistically significant but of limited practical relevance. These findings demonstrate the importance of tailoring extraction strategies to balance protein yield, content, and phytochemical management, enabling the production of LPI ingredients while facilitating the valorisation of phytochemical-rich side streams.