Thermophilic fungi and the deterioration of nigerian oil palm kernels

Abstract

The fruits of the oil palm Elaeis guineensis Jacq., are drupes borne in a large compact bunch. The drupe has a thin exocarp, a fleshy mesocarp and a hard endocarp enclosing an oily endosperm. The fruit yields both palm oil and palm kernel which are of economic importance to Nigeria. For some 20 years before the discovery of petroleum in Nigeria palm kernel occupied the third position in value of export commodities, and palm oil was in the fifth position. Cocoa (Theobroma cacao L.) and groundnut (Arachis hypogaea L.) were first and second. Between 1949 and 1969, palm produce (palm oil and palm kernel) formed the number one earner of foreign exchange for Nigeria, contributing about 32 percent of the aggregate export earnings. Nigeria supplies approximately half of the palm produce entering the world market (Coursey et al., 1963; Kilby, 1967; Oyenuga, 1960; Oni, 1969). Palm oil is extracted from the mesocarp of the fruit by pressure after the mesocarp has been separated from the kernel. It is one of the world's most important vegetable oils, used principally in the manufacture of soap, margarine, lubricating oil and candles, and is an important item in the Nigerian diet. It is valuable as a food oil since it contains, among other things, appreciable amounts of carotene, the precursor of vitamin A. In traditional medicine, palm oil is used in the preparation of antidotes to relieve pains and to neutralize the effect of poisons and evil charms. It is an essential ingredient whenever sacrifices are made to appease Ogun, the god of Iron, who is believed to control accidents. The palm kernel of commerce is the endosperm of the palm fruit, obtained by forcibly splitting off the hard covering of endocarp. The oil extracted from the kernel (palm kernel oil) is used principally in the manufacture of soap and margarine and also in the production of biscuits and ice cream. The cake left after the oils are extracted forms a good livestock feed. Extraction of palm oil is done in Nigeria, while the kernels are exported to Britain for the extraction of the palm kernel oil which is normally light yellow in color. However, local people extract the palm kernel oil by heating the kernels in an open pot with gentle stirring. The oil so extracted is black and is separated from the remains of the kernels by running through a basket. This oil is used locally as a hair oil and in the preparation of the African black soap which is of great importance in local medicine. Traditional doctors use the oil in mixing medicinal ingredients both for oral consumption and for external application. Medicinal preparations include those used to relieve stomach pains and headache and those employed in neutralizing the effect of evil charms. The oil is also used in the preparation of purgatives. Palm oil and palm kernels are susceptible to fungal attack during processing and in storage resulting in the breakdown of oil into free fatty acids (f.f.a.) which reduces their market value and leads to considerable loss of revenue. Both mesophilic and thermophilic fungi have been isolated from decomposing oil palm produce in Nigeria (Coursey & Eggins, 1961a, 1961b; Eggins, 1964; Eggins & Coursey, 1964). The present study was designed to find out the effect of thermophilic fungi on the oil content, and hence the quality, of Nigerian palm kernels.