Chemical Analysis of Rapeseed Oils

The chemical composition of these four rapeseed oil source was shown in Table ​Table2.2. Acid value, iodine value, refractive index, and specific gravity of four different rapeseed oils were measured by the official methods of the AOCS (American Oil Chemists’ Society 1998; cd 3d-63, cd 1d-92, Cc 7-25, and Cc 10b-25, respectively). Fatty acids were analyzed by gas chromatography at the Institute of Chengdu Grain and Oil Quality Supervision and Inspection Testing Center. Lipids (0.15 to 0.20 g) were extracted by ether from each sample (total of two) and saponified with 5 mL NaOH in methanol for 10 min. Five milliliter BF3-methanol was added and refluxed for 2 min. Then 5 mL of heptane was added to the mixture and boiled for 1 min. The final mixture was transferred into 25 mL volumetric flasks and the volume was adjusted with saturated NaCl to 25 mL of which 1 mL of the heptane phase within the volumetric flasks was used to determine the fatty acids composition. Fatty acids were analyzed with gas chromatography (Agilent 6890 N, Hewlett Packard, Palo Alto, CA) using a capillary column (supel covax 10,60 m × 0.25 mm ID). The chromatographic conditions were: detector temperature 280°C; injector temperature 200°C; initial column temperature 100°C for 8 min and programmed to increase at a rate of 5°C per 5 min up to 200°C and then at 4°C per minute up to the final temperature of 250°C. The helium carrier gas flow was set at 1.2 mL/min, hydrogen at 30 mL/min, and air at 300 mL/min. Injection of the 1 μL samples was performed with a split ratio of 20:1. Identification of individual fatty acids was based on comparisons of retention times of unknown peaks to authentic fatty acid methyl ester standards.

Quality indicators and fatty acid composition of four different oil sources.

¹Abbreviation represented: MH = high erucic acid of Mianyang, DH = high erucic acid of Deyang, ML = low erucic acid of Mianyang, DL = low erucic acid of Deyang.

²“–”means below the detection limit.