Diglyceride content and composition as indicators of palm oil quality

Abstract

AbstractThe diglycerides present in palm oil and palm oil fractions were analysed using thin‐layer and gas chromatography. The diglyceride contents and compositions of commercial palm oils were compared with those of oils extracted from fresh fruits. The results showed that the diglycerides present in palm oil and its fractions consist mainly of palmitoyloleoyl‐, dioleoyl‐ and dipalmitoyl‐sn‐glycerol. The levels of diglycerides in fresh palm oils (17‐38 g kg−1) were lower than those in commercial 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 oils 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 anthesis, 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 further increase of the 1,3 : 1,2‐diglyceride ratio. Thermal treatment of oils caused the most significant changes in the ratio. Isomerisation in the fruit and in the oil during thermal treatment is discussed. Based on this study, it is proposed that the diglyceride contents and their ratios be used as indicators of oil quality in addition to other widely used quality parameters such as peroxide and anisidine values.