Fatty acid and quality indices analysis
Fatty acids composition of each sample was analyzed through GC/FID. Following the AOCS official method Ce 2–6616, triacylglycerol was first converted to methyl ester, and then by using a DB–23 column (30 m×0.25 mm×0.25 μm) with helium at flow rate of 1.0 ml/min, methyl esters were being separated. The condition of oven temperature is as follow: I) held at 200°C for 8 min in the beginning, II) increased to 220°C (speed of 10°C/min), then held for 40 min. The FID and the injector (split mode 1:40, 4 mm liner) was maintained at 270°C and 250°C, respectively. The quantification using the normalization method for each oil sample, the determination of quality indices, including the acidity value (AV), peroxide value (POV), anisidine value (p–AV), and color, was performed using various instruments. The AV (mg KOH/g) was measured by titration using 0.1N KOH/alcoholic solution. The POV (meq/Kg) was measured using a titration with 0.01N sodium thiosulfate solution. The p–AV was measured using 0.25% anisidine/glacical acetic acid by UV absorbance at 350 nm. The Totox value was then calculated using the formula AV + 2POV to defined the given oil sample’s overall oxidation state. The color analysis was using UV–light absorption and the browning index (BI) according to previous research (Yang et al., 2018).