Emulsifier and antimicrobial activity against Propionibacterium acnes and Staphylococcus epidermidis of oxidized fatty acid esters from hydrolyzed castor oil

This study aimed to synthesize esters from oxidized fatty acids produced by castor oil hydrolysis as emulsifiers and antimicrobial compounds. Castor oil was hydrolyzed using KOH and the fatty acids were then oxidized using KMnO₄. The success of oxidation proven by determined the iodine number. Esterification was conducted with varied alcohols, namely methanol, ethanol, isopropanol, and 1-butanol using ZnCl₂ as catalyst and mole ratio was 1:2. The conversion percentage of esterification was determined using titrimetric method and products were characterized using FTIR. From the hydrolysis of castor oil, 84% of fatty acids were produced. Decreasing iodine number from 43.38 mg/g to 13.11 mg/g and increasing intensity of the-OH group absorption in the FTIR spectrum showed the success of fatty acids oxidation. Emulsifier test showed all products have emulsifier ability and emulsions were stable up to 24 hours with a water-in-oil (w/o) emulsion type. The best ability as an emulsifier demonstrated by methyl ester. Antimicrobial assay against Propionibacterium acnes and Staphylococcus epidermidis showed all ester products could inhibit the growth of both bacteria. Largest inhibition zone obtained from isopropyl ester for P. acnes by 16 mm and butyl ester for S. epidermidis by 17 mm.