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.