Producing Defatted Hybrid Catfish with High Protease Activity Via Optimization of Sc-CO2 Extraction Process

Abstract

Fish viscera is a great source for recovering polyunsaturated fatty acids (PUFAs), proteins and digestive enzymes. However, the presence of lipids in fish viscera reduces the efficiency of extracting, isolating and purifying the enzymes. Supercritical carbon dioxide (Sc-CO₂), a green solvent, is useful in substituting organic solvent defatting process. Sc-CO₂ helps to remove the lipid in the viscera with minimal denaturing of the proteins and enzymes found in the defatted sample. The viscera of hybrid catfish (C. gariepinus × C. macrocephalus) in this study were defatted by the Sc-CO₂ extraction process. The protease was then, extracted from the defatted viscera. This study aimed to optimize the pressure and temperature of Sc-CO₂ in the defatted viscera. The optimization of Sc-CO₂ parameters was based on the Central Composite Design (CCD) of Response Surface Methodology (RSM). Optimum points were observed within the variables of pressure (P): 17-25 MPa and temperature (T): 39-43 °C with constant CO₂ flow rate (F) and extraction time (t_ext) at 25 g/min and 30 min, respectively. The response variables were executed on the amount of fat residue and protease specific activity in the defatted viscera. The optimum Sc-CO₂ parameters were found to be at P: 18.17 MPa and T: 41.33 °C with the highest protease activity of 77.51 U/mg and fat residue of 71.17 %. The coefficient of determination (R²) for protease specific activity and fat residue was 90.27% and 93.03%, respectively. The differences between the verification and predicted values for both responses were less than 5%.  Hence, the feasible optimum condition to produce a defatted sample with high specific activity at relatively low fat residue as predicted by the RSM in MINITAB statistical software version 16 was acceptable. Nevertheless, the ability of Sc-CO₂ to defat the sample with minimal denaturing proteins and enzymes highlights the usefulness of this technology in substituting other organic solvents for the defatting process.