Production and applications of a microbial protease for silver biostripping and biorefining slaughterhouse by-products.

Waste radiographic films are hazardous materials, and methods for recycling the silver contained therein raise environmental concerns. Concurrently, slaughterhouse by-products remain underutilized, causing ecological impacts upon inadequate disposal. Therefore, a crude protease from Bacillus pumilus CL33A was evaluated for recovering silver from X-ray films and generating bioactive hydrolysates from slaughterhouse by-products. Protease was obtained via a 4-day submerged fermentation using chicken viscera meal (VM) as non-conventional substrate, and culture supernatants also showed enhanced antioxidant activities. The crude protease (0-80% dilutions) stripped the gelatin-silver emulsion from X-ray films in 4.3-9.4 min (55 °C), while chemical removal took 8.7 min. Enzyme preparations remained effective for three removal cycles (6.4-12.5 min), and biostripped silver formed colloidal suspensions. Furthermore, the crude protease hydrolyzed porcine liver, kidneys, lungs, spleen, VM, and blood meal (4 h; 55 °C), significantly increasing radical-scavenging (1.3- to 4.2-fold), Fe2+-chelating (1.2- to 1.5-fold), and reducing power (1.4- to 4.9-fold) abilities compared to non-hydrolyzed controls. Time-course monitoring demonstrated that a 3-h hydrolysis period sufficed to obtain VM hydrolysates with maximal antioxidant activities. Thus, bacterial processing of a low-cost biomass yields a multi-purpose protease (and antioxidants as co-products), whose applications offer cleaner, sustainable opportunities to advance bio-based frameworks for material and nutrient recycling.