Production and biochemical properties of proteases secreted by Aspergillus niger under solid state fermentation in response to different agroindustrial substrates

This study reports the proteases production by Aspergillus niger LBA02 under solid state fermentation (SSF) using different agroindustrial by-products as substrates and the correlation between the protease production and some physical-chemical parameters. The biochemical properties of the proteases produced in each substrate were further investigated. The highest protease production was obtained using wheat bran as the substrate at 96 h fermentation. The results for chemical composition showed that the substrates with higher protein content induced the protease production at the first 48 h of fermentation. The crude extracts of proteases from A. niger LBA02 produced in wheat bran (PWB), soybean meal (PSM) and cottonseed meal (PCM) showed different biochemical properties when produced in different agroindustrial by-products. The biochemical characterization showed that the enzymes were most active over the pH range 3.0-4.0 and was stable from pH 2.5-4.5. The optimum temperature for activity was approximately 50.0 °C, and the enzymes were stable at 40.0-50.0 °C. In the study of the substrate specificity, the best substrate was hemoglobin from bovine blood with the highest relative activities of 183.84, 147.06 and 186.81% for PWB, PSM and PCM, respectively. The PWB showed higher ratio milk-clotting/protease activities (15.24) compared to PSM (0.38) and PCM (6.28).