Abstract:Walnut protein was used as raw material to study the effect of superfine grinding on its structural and functional properties.Eight walnut protein samples with different particle sizes were prepared by superfine grinding under different conditions.Scanning electron microscope（SEM）and Fourier transform infrared spectra（FTIR）were used to study the structure of walnut protein.The effects of superfine grinding on the sulfhydryl group content，solubility，water holding property，oil holding property，foaming properties and emulsifying property of walnut protein were studied，too.The results showed that the particle size of walnut protein was reduced with the decrease of superfine grinding frequency，with minimum particle size of 10.65 μm and specific surface area of 354.2 m2/kg.SEM found that the protein was smaller，more dispersed，and had a larger surface area after superfine grinding.FTIR results showed that the ratio of β-sheet structure decreased，and the ratio of β-turn structure increased after superfine grinding.With the decrease of superfine grinding frequency，the content of free sulfhydryl group first increased and then decreased，the content of free sulfhydryl group of the protein obtained from the upper exit under 35 Hz superfine grinding reached the maximum of 30.01 μmol/g.The solubility of walnut protein increased first and then decreased.The foam stability，water-holding and oil-holding property decreased.The water-holding capacity and the oil-holding capacity of the protein obtained from the upper exit under 15 Hz superfine grinding，compared with those of the raw materials，were reduced by 59.95%and 44.84%，respectively.The foaming property and the emulsifying activity increased significantly，the foaming property and emulsifying activity of the protein obtained from the upper exit under 15 Hz superfine grinding were 1.92 times and 1.4 times of the raw material，respectively.Therefore，the structural and functional properties of walnut protein were significantly affected by superfine grinding.