Abstract:In order to study the properties of acid protease (Ap) from Trichoderma harzianum, the acid protease gene was cloned using RT-PCR and then transferred to the Pichia pastoris GS115 strain to obtain high expression. Subsequently, the enzymatic properties of this recombinant acid protease (rAp) and its performance in hydrolyzing soybean protein isolate were determined. It was observed that the activity of rAp in the fermentation broth reached 21.5 U/mL when the recombinant P. pastoris was induced in a 500 mL triangular flask. This rAp is an aspartic protease with an optimal temperature of 55 ℃ and an optimum pH value of 2.5, which exhibited strong thermal stability after treatment at 40 ℃ for 120 min. After 24 h treatments in buffers of different pH, rAp still demonstrated excellent stability in the pH range of 2.00~5.00. The relative activity of rAp significantly increased to 116.21%, 113.79%, and 117.44% by Cu2+, Ni2+, and Mn2+, respectively. In the meantime, rAp activity was significantly inhibited by Fe2+, Fe3+, 0.50% SDS, and 5.00% Triton X-100, and the resulting relative enzyme activity was 78.02%, 79.26%, 2.6%, and 13.19%, respectively. After hydrolysis of soybean protein isolates by rAp and pepsin, the relative protein contents of the hydrolyzed products were 14.67% and 3.64%, respectively. Moreover, the β-conglycinin antigenicity is reduced by 30.01% and 26.11%, respectively, and the antigenicity of globulin is decreased by 22.37% and 15.63%, respectively. Based on these results, it is clear that rAp has a strong ability to hydrolyze and reduce the antigenicity of soybean isolates, demonstrating its potential development and application value.