Producing amino acid fertilizer by hydrolysis of the fermented mash of food waste with the synergy of three proteases expressed by engineered Candida utilis

Abstract

Engineered C. utilis strains were constructed to express three exogenous proteases, carboxypeptidase pepF, aminopeptidase YPDF and endopeptidase pepA. These three proteases could be constitutively expressed and secreted by the recombinant strains. The enzyme activities and the synergistic effect of three proteases were investigated in hydrolysis of food waste fermentation mash. Synergism was apparently observed between endopeptidases and exopeptidases. The synergistic effect between two exopeptidases was less strong. The highest amino acid yield was obtained by using P2A11, the combination of 15.5% pepF and 84.5% pepA. At 60 h, the yield of amino acid by using P2A11 reached 23.9 mg/mL, and the protein hydrolysis rate was 51.2%. It was 73.8% of that by using 0.2% g/g commercial Novozymes Flavorzyme. This study is first focused on the fermented mash of food waste, which was hydrolyzed into amino acid fertilizer by biological means, so as to achieve the secondary utilization of waste.