*3.1. Materials*

Castor oil was supplied by INTERFAT (Barcelona, Spain), and transesterification was carried out by using methanol (MeOH 99.6%, Panreac, Barcelona, Spain), and the catalyst used was potassium hydroxide (85%, Alfa Aesar, Kandel, Germany). Sulfuric acid (95%–98%, Panreac, Barcelona, Spain) was used to neutralize the catalyst. For oil characterization, all the reagents (Panreac, Barcelona, Spain) were of recognized analytical grade. Methyl ester standards from Merck (Darmstadt, Germany) were used in chromatographic analysis.
