Structural, thermal and functional properties of protein isolates from oyster mushroom (Pleurotus ostreatus) isolated by alkaline iso-electric, ultra-sonication and enzymatic extraction techniques

Abstract

The protein isolates extracted from oyster mushroom by alkaline isoelectric precipitation, enzymatic and ultrasound assisted extraction methods were evaluated for their physicochemical and functional properties. Enzyme assisted extraction enhanced the zeta potential (-19.8 mV) and reduced particle size (288.5 nm) as compared to the standard alkaline isoelectric precipitation method having the values −5.95 mV and 621.8 nm, respectively. Enzymatic extraction with protease as well as ultrasound-assisted extraction led to a significant enhancement in the colloidal stability of the isolated proteins, attributable to improved dispersion and stronger electrostatic repulsion among protein molecules. Ultrasound assisted extraction showed a time- and amplitude-dependent effect. The highest values for water holding capacity (6.52 g/g), oil holding capacity (8.57 g/g), foaming capacity (52.17 %), and emulsifying activity (2.14 m²/g) were observed in the ultrasound-assisted extraction with 30 % for 10 min treatment, suggesting enhanced interfacial activity and surface functionality. Scanning electron microscopy confirmed structural disintegration and reduced aggregation in proteins isolated by enzymatic and ultrasound-assisted extraction methods. The findings demonstrate that both the enzyme- and ultrasound-assisted extraction methods are effective in enhancing the structural and functional quality of oyster mushroom protein isolates.