Produção e aplicação da protease bruta de Bacillus sp. CL14: abordagens para a valorização de subprodutos agroindustriais e recuperação de prata

Abstract

Economical production of microbial enzymes is a significant matter, considering the technological importance of biocatalysis. Among enzyme-based processes, the use of proteases to recover silver from used X-ray films and to generate bioactive protein hydrolysates has been explored. Thus, diverse organic substrates were initially evaluated to maximize protease production by Bacillus sp. CL14. The crude enzyme was then assessed for silver recovery and for the production of bioactive hydrolysates from protein-rich animal substrates. Among 19 substrates (10 g/L), highest protease yields were obtained after 5 days of cultivation with canola meal (1,976.8 U/mL), which was 132% higher than peptone (849.2 U/mL, day 4). By increasing canola meal concentration to 30 g/L, enzyme production was further increased by 49% higher (2,950.4 U/mL, day 4). Addition of selected organic co-substrates (5 g/L) had no beneficial effect on protease yields. The crude protease and its dilutions (4:1, 1:1, 1:4) effectively removed the gelatin-silver layer of waste X-ray films (4-8 min; 55 °C), and biocatalyst might be used for at least five successive removal cycles. In addition, the crude enzyme hydrolyzed milled feathers, hydrolyzed feather meal, blood meal, meat and bone meal, and viscera meal (VM), and the hydrolysates displayed increased radical-scavenging, Fe2+-chelating and reducing power abilities. Experiments of VM hydrolysis, performed at different times (0-360 min) and enzyme-to-substrate ratios (E/S; 7,250 and 3,480 U/g substrate), indicated that the release of soluble proteins and the antioxidant activities were increased over time, initially at faster rates and then tending to stabilize at longer periods. Maximal antioxidant activities were reached earlier (240 min) during hydrolysis with the higher E/S. In summary, low-cost biomasses, abundantly available from the Brazilian agroindustry, were promising substrates to obtain a bacterial protease, which might be employed for the safe and cost-effective recovery of silver from X-ray films, and for the valorization of rendered animal protein meals. Particularly, the production of antioxidant hydrolysates might expand the applicability of such meals, with potential uses in feed and food technology.