DIGLYCERIDE CONTENT AND COMPOSITION AS INDICATORS OF PALM OIL QUALITY

The diglycerides present in palm oil and palm oil fractions were analy sed using thin-layer and gas chromatography. The diglyceride contents and compositions of commercial palm oils were compared with those of o ils extracted from fresh fruits. The results showed that the diglyceri des present in palm oil and its fractions consist mainly of palmitoylo leoyl-, dioleoyl- and dipalmitoyl-sn-glycerol. The levels of diglyceri des in fresh palm oils (17-38 g kg(-1)) were lower than those in comme rcial palm oils (40-75 g kg(-1)). In the oils from fresh fruits the 1, 2-diglyceride predominates over the 1,3-isomer whereas in commercial o ils the reverse is observed. The ratio of 1,3- to 1,2-diglycerides in fresh oils depends on the degree of maturity of the fruit. Furthermore , the 1,3-diglycerides increase rapidly after the 20th week of anthesi s, while the 1,2-diglycerides decrease rapidly over the same period of time. Storage of ripe fruits and oils over 10 days also resulted in f urther increase of the 1,3: 1,2-diglyceride ratio. Thermal treatment o f oils caused the most significant changes in the ratio. Isomerisation in the fruit and in the oil during thermal treatment is discussed. Ba sed on this study, it is proposed that the diglyceride contents and th eir ratios be used as indicators of oil quality in addition to other w idely used quality parameters such as peroxide and anisidine values.