Characteristics and Application of Lipase from Asian Seabass Liver Fractionated Using Aqueous Two-phase Partition Technique for Defatting Fish Skin before Collagen Extraction

Lipase, from crude extract of fish viscera including liver, is highly contaminated with other hydrolytic enzymes such as proteases that would cause severe degradation of native collagen during defatting. Asian seabass liver lipase was therefore subjected to fractionation with the aqueous two-phase system (ATPS) to remove proteases from lipase. ATPS was carried out using various salts and polyethylene glycol (PEG) having various molecular weights at different concentrations. The concentration of 20% ammonium sulfate (w/v) and 50% PEG-6000 (w/w) could reduce protease by 85%. Lipase-rich fraction showed a specific activity of 68 U/mg protein, purification fold of 9, selectivity of 167, and yield of 48%. When pulse electric field (PEF) was treated Asian seabass fish skin was defatted, and the acid-soluble collagen was extracted and characterized. The ATPS fractionated lipase could remove more than 92% of lipid contents. Polyunsaturated and monounsaturated fatty acids were mainly eliminated. The extracted collagen from defatted skin showed typical type Ⅰ collagen with negligible degradation. FTIR spectra substantiated the presence of amide groups in resulting skin collagen. Thus, the fractionation of Asian seabass liver crude extract with ATPS could significantly remove the contaminated proteases. The obtained fraction could be used to defat Asian seabass skin without drastic damage to the extracted native collagen.