Abstract: Alkali-soluble protein was extracted from defatted Pleurotus nebrodensis by ultrasonic-microwave assisted extraction. The optimal extraction conditions that provided maximum protein yield of (10.28 ± 0.62)% were determined as follows: extraction temperature 50 ℃, ultrasonic power 500 W, microwave power 24 W, NaOH concentration 0.09 mol/L, solid-to-solvent ratio 1:30 (g/mL), and extraction time 0.8 h. The functional properties and structure of the protein were studied. The results showed that the protein was most soluble at 70 ℃ and pH 8.5. It had the highest water-holding capacity of (325.27 ± 2.40)% at 60 ℃, and highest oil-holding capacity of (189.60 ± 2.58)% at 50 ℃. The foaming capacity, foam stability, emulsifying capacity and emulsion stability increased with the increase in protein concentration. The total amino acid content of the protein was 810.40 mg/g, as determined by ultra performance liquid chromatography (UPLC) analysis. The essential amino acid content was 322.86 mg/g, with histidine being the first limiting amino acid. Circular dichroism analysis showed that in the protein secondary structure, the contents of α-helix, β-sheet, and β-turn and random coil were 53%, 11% and 14%, and 23%, respectively. The protein consisted of four fractions with molecular masses of 48.9, 26.3, 16.4, and 10.9 kDa, respectively. Fourier transform infrared spectroscopic analysis showed obvious absorption peaks of the functional groups of the protein.

Key words: Pleurotus nebrodensis protein, protein functional characteristics, structure