Study On Protein Characteristics And Ultrasonic Modification Of Proteins Isolated From Pleurotus Nebrodensis

Pleurotus nebrodensis is a kind of edible mushroom that has high edible value and is rich in nutrition.The protein content of dried pleurotus nebrodensis is about 20%of its weight and it contains 18 kinds of amino acids,multivitamins and inorganic salts.In this paper,the conditions of preparation process of the protein isolated from pleurotus nebrodensis by alkali extraction were investigated.The nutrition,structure and functional properties of proteins isolated from the fruiting body（FBP）and the mushroom feet（MFP）were compared.The physicochemical properties of the MFP prepared by fractional salt precipitation were studied.The effect of ultrasonic treatment on the physicochemical properties and solubility of the FBP were studied.The results were as follows:（1）The protein content of FBF and MFF was 22.37%and 10.90%,respectively.Both FBF and MFF contained 18 kinds of amino acids,and the EAA/TAA was 33.99%and 32.04%,respectively.Both FBF and MFF were good sources of protein and amino acids.The optimum extraction conditions of protein isolated from pleurotus nebrodensis were p H 10,liquid-to-solid ratio of 1:20,extraction temperature 50℃,extraction time 2.5 h and 2 times extraction.The order of main factors that influenced the protein extraction rate of the pleurotus nebrodensis protein was liquid-to-solid ratio>extraction temperature>extraction time.The exhalation rate of the protein obtained from fruit body and mushroom feet by one step salting out was 71.40%and 54.56%,respectively,while the purity was 44.33%and49.93%,respectively.The exhalation rate of the proteins obtained by one step salting out was higher than that of fractional salting out,while the purity was on the contrary.（2）Both FBP and MFP contained 18 kinds of amino acids and were rich in Ala and Val.Moreover,the protein nutrition value of MFP was higher than that of FBP.The molecular weight of FBP and MFP was about 15.0～49.0 k Da and MFP had more bands with small molecular weight（at about 15.0 k Da）.MFP showed more random coil（12.57%）,α-helix（11.81%）andβ-turn（23.33%）than those of FBP（9.16%,7.00%and 9.36%,respectively）.MFP had higher emission maximum（λmax）values but less surface hydrophobicity（H₀）than those of FBP.The AFM showed that MFP had higher protein aggregation degree than FBP.Both proteins exhibited high emulsifying ability,favorable foaming and good in-vitro digestibility.MFP exhibited higher emulsifying ability and solubility than FBP（P<0.05）.Therefore,both FBP and MFP can be valuable nutrition sources and functional ingredients in food industry.（3）This study investigated the protein properties of MFPs isolated by salting out method.MFPs contained 17 kinds of amino acids and were rich in Ala,Asp and Glu.But the amino acid composition of MFPs was different.MFPs all had one band（at about 31.0 k Da）and the AFM showed that MFPs has lower protein aggregation degree than that of MBP.With the increase of salt saturation of（NH4）₂SO₄,the lower surface hydrophobicity and the fluorescence intensity were,the lesserβ-sheet were observed.MFPs with different physicochemical properties and low degree can be isolated by fractional salting out.（4）With the high intensity ultrasound treatment,the subunits of FBPs did not change significantly under the electrophoretic pattern,but the secondary structure and tertiary structure of FBPs were changed and partial unfold of protein was observed.Moreover,scanning electron microscopy of FBPs showed different micro-structure with larger aggregates compared to non-treated FBP.Free sulfhydryl content,surface hydrophobicity and protein solubility of FBPs were all increased with ultrasonic treatment.In conclusion,ultrasonic treatment resulted in reduction of intermolecular interactions,partial unfolding of FBP,and improved solubility of FBP.