Abstract:Rice protein is a high-quality plant protein，but its low solubility limits its applications.In the present study，acid deamidation was employed to improve the solubility of rice protein.The treatment conditions were as follows：0.4 mol/L HCl solution was added at a liquid-to-solid ratio of 1∶25（g/mL)，followed by heating and stirring in a water bath at 95 ℃for 4 h.The functional properties such as solubility，foaming，foaming stability，emulsification，emulsification stability，surface hydrophobicity，water and oil holding capacity，and the changes of subunit molecular weight and surface microstructure were analyzed before and after modification.The results showed that the acid deamidation treatment significantly improved the solubility of rice protein.The solubility increased from 0.58% to 56.60% in a neutral environment（pH7）and exceeded 90.00% in an alkaline environment（pH12 and pH13).The foaming and emulsification properties were notably improved at the pH values of 3 and 7.The foaming properties increased from 22.50% to 80.40% and from 78.50% to 151.70%，respectively，and the emulsification properties increased from 4.4 m2/g to 14.3 m2/g and from 6.6 m2/g to 16.5 m2/g，respectively.Excessive hydrolysis led to reduced surface hydrophobicity，which further affected the improvement in interface properties.The acid deamidation modification had a less noticeable effect on water and oil retention of protein.After modification，the molecular weight of protein subunits dramatically reduced，mainly distributed between 6.5 and 20 kDa.The ordered β-sheet structure transformed into an unordered irregular coil structure.The protein microstructure transitioned from aggregation to looseness，the dense spherical structure changed to irregular block structure，and the surface changed from rough to smooth.