High-power ultrasound pretreatment for enhanced protein extraction from lupin flour: Impact on yield, anti-technological and anti-nutritional factors, and techno-functional properties

Quality of lupin protein is considerably compromised by the presence of anti-nutritional (ANF), such as polyphenols, alkaloids and saponins and anti-technological factors (ATF), like polyphenols and fat. This work explores how high-power ultrasound-assisted (HPU) pretreatment of lupin flour (LF) before protein extraction could affect ANF and ATF content, as well as protein yield and techno-functional properties. LF pretreatments for 3 and 9 min, using water and ethanol–water (1:4 v/v), were carried using conventional mechanical stirring (952 rpm) and HPU (sonotrode, 24 kHz) at 30 and 60 °C. Ultrasonic field was characterized by computing acoustic pressure from frequency spectra analysis.In general terms, pretreatment reduced noticeably ANF and ATF in both LF and protein isolate (LPI), while also producing a protein concentrate (LPC, avg. 65 g protein/100 g) with low ANF and ATF content. Total protein yield, adding LPC and LPI, was increased by 15 % due to the pretreatment, which also enhanced the techno-functional properties of LPI, such as water absorption index (avg. 26 %) and foaming (avg. 8 %) and emulsifying properties (avg. 14 %). But, the efficiency of the pretreatment was largely affected by process variables. In particular, HPU reduced fat (avg. 27 %), saponin (avg. 21 %) and phenolic content (avg. 17 %), as well as antioxidant activity (avg. 11 %). In addition, the highest protein yield was achieved by sonication using water at 30 °C. This may be explained by ultrasonic field measurements, which revealed higher acoustic pressure levels under these conditions.