Spectral Studies and Photo-Sensitized Oxidation of Melon Seed Oil

Purified samples of melon seed (Citrullus lanatus) oil extracted from melon seeds obtained from a local market in Yenagoa, Bayelsa State, Nigeria were analyzed by FTIR,1H NMR, 13C and DEPT-135 NMR. The frequency data shows the oil to contain unsaturated acyl chains in its triacylglycerols. The FTIR shows stretch vibrations of the cis-olefin double bond and the ester carbonyl at 1748 cm-1. The 1H NMR confirms the presence of allylic, 1.99-2.04, bis-allylic, 2,726-2.753 vinylic, 5.265-5.328 and glyceryl 4.097-4.238 (Sn-1,3) and 5.421-5.328 (Sn-2) protons. These are further confirmed by data from carbon-13 NMR; signals between 27.17 and 27.18 (allylic carbons); the signal at 25.2 (bis-allylic carbons); signals between 120 and 130 (vinlylic carbons), signals at 68.91 (Sn-1,3) and 62.07 (Sn-2) (glyceryl carbons). Some deductions of the 13C NMR data were further confirmed by data from the DEPT-135. Sensitized oxidation of a sample of the oil in the presence of methylene blue and monitored by thin layer chromatography and chemical analysis shows the formation of peroxide. The results from the sensitized photooxidation indicate that exposure of the oil in the presence of sensitizers such as chromophoric impurities is likely to reduce the shelf-life of the oil.