Spectroscopic Elucidation of the Biodeterioration Potentials of Aspergillus niger on Lagenaria siceraria Seed Oil

Abstract

Vegetable oil was extracted from Lagenaria siceraria seeds and some physico-chemical analysis determined. The refractive index of 1.47, saponification value of 465.9 mgKOH/g, iodine value of 15.86 I2 /100 g, Acid value mgKOH/g of 2.52 and density of 0.93 were obtained. GC-MS of both the un-inoculated and inoculated oil was measured before and after four weeks of incubation with Aspergillus niger. The disappearance and or appearance of some absorption peaks which correspond to hydroxyl, carbonyl, methyl, and carboxylic acid functional groups were identified. MS provided the mass fragments of the possible components formed during the degradation of the oil to include 12-methyl-methyl ester, tetradecanoic acid, hexadecanoic acid, heptadecanoic acid, oleic acid, 2, 6, 10-Dodecatrien-1-ol, 3, 7, 11-trimethyl (E.E) and pentadecanoic acid as biodegradation by-products. Despite, low acid value obtained which may have suggested stability of the oil to oxidation, its high iodine value indicated a rather high level of unsaturation i.e. presence of double bonds. The position of double bonds was viewed as possible sites for the initial attack by the microorganisms. These absorption bands disappeared after inoculation and incubation with Aspergillus niger after four weeks with prominent peaks noticed to be of fatty acids as a result of the action of Aspergillus niger on the Lagenaria siceraria oil. The fragmentation of the triglycerides suggested that the unsaturation is not on an even number of carbon atom along the chain length resulting in the propyl – like breakage with molecular weight of 42 (C3H7) whereas, fragmentation on even carbon atom resulting in ethyl-like breakage with molecular weight of 28 (C2H2). The GC-MS showed that acidic metabolites were mostly produced. This is similar to the hydrolysis of vegetable oil by other agents where sterol and fatty acids are usually produced in the ratio 1:3. Therefore, it is recommended that the storage of these oils in the presence of common mold such as Aspergillus niger at temperature above 37°C would lead to its deterioration. However, Lagenaria siceraria seed oil can be used as lubricants, for cooking and paint production.