Investigations of the structure and antioxidant activity of broccoli pigment protein isolates with ultrasonic treatment

The effects of ultrasonic treatment on the physicochemical properties, structure and antioxidant activity of broccoli pigment protein isolates (BPPIs) were investigated. BPPIs were exposed to ultrasound treatments at 20 kHz with the power levels of 120, 180 and 240W for a duration of 15 min. The cavitation effect induced by ultrasonic treatment led to the unfolding of BPPIs, thereby exposing more hydrophobic groups. Ultraviolet–visible spectroscopy and fluorescence spectroscopy analyses indicated that ultrasonic treatment caused fluorescence quenching, increased chromophore exposure, and induced changes in the tertiary structure of MPPIs. After ultrasonic treatment, the α-helix content of BPPIs increased from 22.1 to 33.4%. Ultrasonic treatment significantly reduced the particle size of BBPIs, especially after 240W ultrasonic treatment, the average particle size was significantly reduced from 160.97 nm to 130.73 nm (p < 0.05). The SEM results revealed that as ultrasonic power increased, the surface morphology of BPPIs was significantly altered, with more fragmented and disordered particles observed in the powdered form. Importantly, ultrasonic treatment also enhanced the antioxidant activities of BPPIs. The highest DPPH and OH free radical clearance rates were observed in BPPIs treated with 240W ultrasound, reaching 41.92% and 50.38%, respectively. This study demonstrates that BPPIs, as a promising functional plant protein, have the potential to broaden their applications in the food industry.