Effect of autoclaving as a pre-treatment in the wet reduction process for extracting fish oil from yellowfin tuna heads

Abstract

Various studies have focused on extracting fish oil using a variety of methods, yet, the wet reduction process is the common industrial method as it is environmentally friendly. However, the use of autoclaving in extracting oils from fish or fish by-products are comparatively less. Therefore, this study was conducted to extract crude oils from the yellowfin tuna (Thunnus albacares) head, the lipids richest body part compared to processing offcuts like skin, viscera etc., by a simple wet reduction process using an autoclave at 121°C as the pre-treatment with different holding times (15, 30, and 45 min). The maximum extraction yield of 5.37±0.22 % was recorded at 30 min holding time of autoclave. No significant changes in peroxide value, moisture content and colour values were observed for the different autoclaving durations (P > 0.05). Conversely, acid value, p-anisidine value and total oxidation value (TOTOX) were increased significantly with a longer autoclaving duration of 45 min (P < 0.05). However, all peroxide values, p-anisidine value, TOTOX value were below the standard values stated by the World Health Organization (WHO) except the acid values which shows the need for refinery before any applications. Based on the spectra of Attenuated total reflectance - Fourier transform infrared (ATR-FTIR), autoclaving for a longer time resulted in lower intensity at wavenumbers around 3,012 - 3,013 and 1,741 - 1,744 cm−1 and shifting of bands to lower wavenumbers showing its effect on the structural changes of molecules in the oil. All extracted oils resulted in a high PUFA content than MUFA and SFA contents based on the fatty acid composition. The DHA (C22:6, n3) was the most prominent fatty acid in all the oil samples. However, PUFA content was reduced slightly by increasing the autoclaving duration at 45 min. Therefore, this study concludes autoclaving at 121°C for 30 minutes as the optimum pre-treatment conditions to extract fish oil from yellowfin tuna heads using the wet reduction process.