Physicochemical and functional properties of Pleurotus geesteranus proteins

Edible mushroom protein has been regarded as a promising protein source due to its nutritional value and sustainability. In the present study, Pleurotus geesteranus proteins were extracted with alkaline solution and then precipitated with salting out (PPS) and isoelectric point precipitation (PPI), respectively. The influences of precipitation method on the physicochemical and functional properties of these two kinds of proteins were studied. The results showed that both PPS and PPI had a good balance of essential amino acids. These two proteins were mainly consisted of polypeptides with a molecular weight lower than 70 kDa. Using proteome analysis, a number of 772 and 459 protein compositions were identified in PPS and PPI, respectively. Compared to PPS, PPI showed a higher zeta potential, higher surface hydrophobicity, lower content of β-sheet and β-turn secondary structure, as well as lower denaturation temperature (T_d) and enthalpy change of the denaturation (ΔH). These differences in the physicochemical properties between PPS and PPI resulted in the occurrence of differences in their functional and digestive properties. For example, PPS showed obviously higher protein solubility in water than PPI, especially at natural pH, PPS solution was clear, while PPI showed precipitates. PPI had higher foam capability (FC), lower foaming stability (FS), and lower emulsion stability index (ESI) as compared to PPS. PPI was easier to digest in the pepsin digestion period, while PPS showed a higher nitrogen release after trypsin digestion. These findings on the physicochemical and functional properties of P. geesteranus proteins will help to broaden their applications as protein ingredient in food industry.