Physicochemical and in vitro antimicrobial activity of the oils and soap of the seed and peel of Citrus sinensis

Citrus sinensis seed and peel oils were extracted by solvent extraction using n-hexane, after air drying and grinding. Soaps were formed by saponification methods. Fatty acid composition of the oil samples were analyzed using Gas Chromatograph-Flame Ionization Detector (GC-FID). Physicochemical properties of the oils and soaps were determined following standard methods. Antimicrobial activities were assessed by the agar disc and hole-in plate methods. The seed and peel oil yield were 38 and 30%, respectively and the colors were golden yellow and brownish-yellow, respectively. Physicochemical properties of the oil samples determined were: refractive index (RI): 1.46 and 1.47, smoke point: 140 and 149, flash point: 150 and 160, pH: 5.2 and 4.2, acid value (AV): 23.6 and 25.1 mgKOH/g, free fatty acid (FFA): 11.86% as oleic acid and 12.61% as oleic acid, iodine value (IV): 78.83I2 g/100 g and 120.10I2 g/100 g, peroxide value (PV): 18.00 mgKOH/g and 5.40 mgKOH/g, saponification value (SV): 222.58 and 41.25 mgKOH/g, ester value (EV): 178.24 and 28.96 mgKOH/g for the seed and the peel oil respectively. Inhibitory antimicrobial activities were assessed for the two oils and the soap produced at concentrations of 40 mg/ml and below, against most of the gram positive and gram negative bacteria as well as the two candida strains, screened as compared with streptomycin (1 mg/L) and acriflavin (6.3 mg/ml) standard controls. Seed oil demonstrated better activities than the peel oil with growth inhibitions obtained against Staphylococcus aureus and Candida albicans at a concentration as low as 2.5 mg/ml. This study has shown that the results obtained for the physicochemical and antimicrobial properties of the oils provide a synergy for the oil samples as suitable raw materials for the cosmetic and pharmaceutical industries.   Key words: Physicochemical properties, antimicrobial activity, soap, seed oil, peel oil.