New acidic proteases from Liza aurata viscera: Characterization and application in gelatin production

The present study reports the extraction and characterisation of acidic protease from the viscera of golden grey mullet (LACAP), and its use in gelatin preparation. The optimum pH for the crude extract activity was 3.0, with high stability over a pH range from 3.0 to 7.0. The enzymatic extract lost about 79% of its activity by pepstatin A. Due to its high activity under acidic conditions, gelatin was extracted from the skin of L. aurata using different levels of LACAP (0, 5 and 10 U/g of skin, named GGSG0, GGSG5 and GGSG10). The extraction yield of GGSG0 was only 3.3% and the addition of acidic proteases increased the yields, which reached 5% and 8.2% at 5 and 10 U/g of skin, respectively. In addition, Fourier transform infrared (FT-IR) and SDS-page profiles of gelatins indicated that the structure was affected by enzymatic pre-treatment. The results of functional properties showed that the emulsion stability and activity indexes (ESI and EAI) of GGSG0 were higher than those of GGSG5 and GGSG10. Furthermore, foam expansion (FE) and foam stability (FS) increased as the concentration of gelatin increased. The results showed that L. aurata by-products can be a potential source of gelatin and protease.