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.