Optimisation of ultrasound-assisted lipid extraction in the pretreatment of purple-spotted bigeye fish skin

The present work investigated the defatting of purple-spotted bigeye fish skin to obtain lipid prior to hydrolysis for gelatine production. Lipid was extracted using ultrasound-assisted extraction (UAE). The drying temperature of the skin on lipid recovery and preliminary kinetic of UAE were studied before a two-stage extraction was optimised by employing response surface methodology. Qualities of lipids and of the remaining solids after extraction were then analysed. The optimal drying temperature was found to be 80°C. The kinetic study that followed indicated that the highest extraction rate was achieved at 30°C, and from UAE using ethanol (UAEE) and sequential UAE using hexane (UAEH), the maximum percentage of total lipid recovery was 91.326 at 30°C, 37 kHz, and 60 min. The qualities determined by peroxide, conjugated diene, thiobarbituric acid reactive substances, and acid values showed that the extracted lipid could be suitable for industry, while the remaining solid could be used as material for gelatine production.