Abstract: In this study, the structure and functional properties of proteins prepared from zinc-enriched and selenium-enriched Pleurotus geesteranus by ultrasound-assisted alkali extraction followed by acid precipitation were evaluated. The results showed that the total protein content of zinc-enriched P. geesteranus Zn200 was the highest up to 25.41%, 18.35% higher than that of the control group without zinc or selenium enrichment; the crude protein content of selenium-enriched mushroom Se60 was the highest up to 62.92%, 7.63% higher than that of the control group; the extraction rate of proteins from Se20 was the highest up to 29.05%. Sequential extraction revealed that albumin was the most abundant protein (up to 31.02%), followed sequentially by globulin, glutenin, gliadin, gliadin-like protein and glutenin-like protein. The structural characterization was performed by spectrophotometry, which demonstrated that the surface hydrophobicity of proteins from zinc-enriched and selenium-enriched P. geesteranus increased compared with the control group, while the sulfhydryl and disulfide bond contents decreased. Four secondary structures were identified in proteins from zinc-enrich and selenium-enriched P. geesteranus by Fourier transform infrared (FTIR) spectroscopy; the highest content of α-helix and β-sheet were found in Zn500 (18.89%) and the control group (39.24%), respectively. According to sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), the relative molecular mass masses of proteins from zinc-enriched and selenium-enriched P. geesteranus were mainly distributed between 32.4 and 40.3 kDa. The protein digestibility, water-holding capacity (WHC) and oil-holding capacity (OHC) of proteins from zinc-enriched and selenium-enriched P. geesteranus were lower than those of the blank group. The proteins from zinc-enriched P. geesteranus had the best foaming capacity, but had the weakest foam stability, while the emulsifying properties of the proteins from zinc-enriched and selenium-enriched P. geesteranus were improved relative to the control group.

Key words: Pleurotus geesteranus; zinc-enriched; selenium-enriched; protein; functional properties