Lupinus angustifolius L. lactofermentation and protein isolation: effects on phenolic compounds and genistein, antioxidant properties, trypsin inhibitor activity, and protein digestibility

In some European countries, lupin seeds are not used efficiently enough, due to a lack of processing technologies for the preparation of attractive higher-value products; fermentation could be a promising process to increase the value of lupin seeds and their protein isolates. In this study, the influence of a range of factors—seeds of Lupinus angustifolius L. hybrid line (HL) Nos. 1700, 1701, 1800, and 1072, solid state and submerged fermentation methods (FMs) with different Pediococcus pentosaceus strains (05–8, 05–9, and 05–10), and the use of a protein isolation (PI) process—on the total content of phenolic compounds (TPC) and isoflavones, antioxidant properties, trypsin inhibitor activity (TIA), and protein digestibility (PD) of lupin wholemeal and protein isolates was evaluated. In addition, changes in the SDS-PAGE profiles of fermented lupin protein isolates were analysed. The selected Pediococcus strains were found to be suitable starters for the fermentation of lupin seeds. The protein content in isolates ranged from 80.43 to 89.08% on a dry weight basis and was significantly influenced by FM (p = 0.0001). The most common protein fractions in isolates ranged in molecular weight from 15 to 167 kDa. The PD of lupin wholemeal samples was on average 3.13% higher than that of protein isolates. The genistein content of lupin samples showed a significant correlation with PI and HL (p = 0.002 and p = 0.0001, respectively), and a lower genistein content was observed in lupin protein isolates. Fermentation can provide a basis for the development of higher-value products, but the technological parameters should be selected by taking into account that some technological steps (PI) can reduce the amount of genistein.