Screening of Bacillus sp. protease for hydrolysis of gelatine extracted from fish waste and potential applications for waste valorisation

Abstract

Fish processing generates a large amount of waste products; nearly 75 % of the total fish weight consists of scales, skins, heads, viscera, and bones. These waste by-products are often dumped in landfills or the ocean, contributing to environmental pollution. Solid fish waste has a high collagen content and can be utilized for the extraction of different products such as gelatine, which can be used in different food and pharmaceutical industries. Fish gelatine contains all biogenic amino acids and can be used as a dietary supplement, thus increasing the utilization of fish waste and reducing environmental pollution. Recently, a strong worldwide focus has been directed towards the discovery of new microbial proteases for industrial applications. For that purpose, the Bacillus sp. strains from the laboratory bank were screened for the ability to secrete alkaline proteases. Bacterial strains that produced a larger clear zone on the gelatine agar plate were selected for further study. Selected bacterial strains were cultivated under submerged conditions for the purpose of producing proteases. The supernatant from each isolate was used as a crude enzyme extract for testing gelatine proteolytic activity and hydrolysis products. Bacillus sp. strains 12B, 16A, 17B and 24B showed a high degree of hydrolysis of the gelatine waste and the ability to form proteins of small molecular masses after one hour of hydrolysis. Of these, sp. 12B was the most potent, having twice the proteolytic activity determined by the TNBS method.