Ultrasound-assisted extraction of Spirulina platensis protein: physicochemical characteristic and techno-functional properties

Spirulina platensis (SP) contains a high amount of protein. In this study, ultrasound-assisted extraction (UAE) was applied to enhance extraction efficacy to obtain protein with excellent functionalities. The effects of ultrasonic extraction conditions in terms of amplitude (20, 40, 60, 80, 100%), time (10, 20, 30, 40, 50 min), and duty cycle (20, 40, 60, 80, 100%) on protein yield, physicochemical characteristic, and techno-functional properties of protein were studied. The results demonstrated that UAE working at 80% amplitude for 30 min under a duty cycle of 60% could significantly improve the protein yield to 76.83% compared with conventional extraction (C-SP) without ultrasound (32.48%). The in vitro protein digestibility values of SP protein increased from 16.08 to 33.44% after UAE. In addition, thermal analysis indicated that the denaturation enthalpy (ΔHd) of UAE-SP, compared to C-SP, decreased. UAE-SP powder had higher blue color intensity than C-SP. There was no significant difference in particle size and polydispersity index of emulsion stabilized by C-SP, UAE-SP, and soy protein concentrate after ultrasonication. Water holding capacity, emulsifying stability, foaming capacity, and stability of SP protein obtained using UAE method were all improved from 4.39 to 5.97 g/g, 21.10 to 98.17 min, 40.56% to 90.00%, and 35.85 to 79.17%, respectively. The results of this study showed that protein obtained from SP using the UAE method might serve as an alternative and interesting plant-based protein source for further application in the food industry with good techno-functional properties.