Separation of 1,2(2,3)- and 1,3-positional isomers of diacylglycerols (DAG) from vegetable oils by reversed-phase high-performance liquid chromatography (RP-HPLC) is investigated. The method is based on isocratic elution using 100% acetonitrile and UV detection at 205 nm. The following elution order of DAG molecular species is identified: 1,3-dilinolein < 1,2-dilinolein < 1,3-dimyristin < 1-oleoyl-3-linoleoyl-glycerol < 1,2-dimyristoyl-rac-glycerol < 1(2)-oleoyl-2(3)-linoleoyl-glycerol < 1-linolenoyl-3-stearoyl-glycerol < 1(2)-linolenoyl-2(3)-stearoyl-glycerol < 1,3-diolein < 1-palmitoyl-3-oleoyl-glycerol < 1,2-dioleoyl-sn-glycerol < 1(2)-palmitoyl-2(3)-oleoyl-glycerol < 1-linoleoyl-3-stearoyl-glycerol < 1,3-dipalmitin < 1(2)-linoleoyl-2(3)-stearoyl-glycerol < 1-oleoyl-3-stearoyl-glycerol < 1,2-dipalmitoyl-rac-glycerol < 1-palmitoyl-3-stearoyl-sn-glycerol < 1,3-distearin < 1,2-distearoyl-rac-glycerol. Linearity is observed over three orders of magnitude. Limits of detection and quantitation range 0.2-0.7 microg/mL for 1,3-dilinolein to 0.6-1.9 microg/mL for 1,2-dioleoyl-sn-glycerol, respectively. Precision and accuracy of the method are also demonstrated. The method is developed to separate mixtures of DAG molecular species produced from edible oils.
High-oleic palm oil (HOPO) with an oleic acid content of 59.0% and an iodine value (IV) of 78.2 was crystallized in a 200-kg De Smet crystallizer with a predetermined cooling program and appropriate agitation. The slurry was then fractionated by means of dry fractionation at 4, 8, 10, 12, and 15 degrees C. The oil and the fractionated products were subjected to physical and chemical analyses, including fatty acid composition, triacylglycerol and diacylglycerol composition, solid fat content, cloud point, slip melting point, and cold stability test. Fractionation at 15 degrees C resulted in the highest olein yield but with minimal oleic acid content. Due to the enhanced unsaturation of the oil, fractionation at relatively lower crystallization temperature showed a considerable effect on fatty acid composition as well as triacylglycerol and diacylglycerol composition of liquid fractions compared to higher crystallization temperature. The olein and stearin fractionated at 4 degrees C had the best cold stability at 0 degrees C and sharper melting profile, respectively.
This paper discusses a rapid GC-FID technique for the simultaneous quantitative analysis of FFA, MAG, DAG, TAG, sterols, and squalene in vegetable oils, with special reference to palm oil. The FFA content determined had a lower SE compared with a conventional titrimetric method. Squalene and individual sterols, consisting of beta-sitosterol, stigmasterol, campesterol, and cholesterol, were accurately quantified without any losses. This was achieved through elimination of tedious conventional sample pretreatments, such as saponification and preparative TLC. With this technique, the separation of individual MAG, consisting of 16:0, 18:0, and 18:1 FA, and the DAG species, consisting of the 1,2(2,3)- and 1,3-positions, was sufficient to enable their quantification. This technique enabled the TAG to be determined according to their carbon numbers in the range of C44 to C56. Comparisons were made with conventional methods, and the results were in good agreement with those reported in the literature.
This paper examines the processing steps of extracting palm oil from fresh fruit bunches in a way that may impact on the formation of chloropropandiol fatty esters (3-MCPD esters), particularly during refining. Diacylglycerols (DAGs) do not appear to be a critical factor when crude palm oils are extracted from various qualities of fruit bunches. Highly hydrolysed oils, in spite of the high free fatty acid (FFA) contents, did not show exceptionally high DAGs, and the oils did not display a higher formation of 3-MCPD esters upon heat treatment. However, acidity measured in terms of pH appears to have a strong impact on 3-MCPD ester formation in the crude oil when heated at high temperatures. The differences in the extraction process of crude palm oil from current commercial processes and that from a modified experimental process showed clearly the effect of acidity of the oil on the formation of 3-MCPD esters. This paper concludes that the washing or dilution step in palm oil mills removes the acidity of the vegetative materials and that a well-optimised dilution/washing step in the extraction process will play an important role in reducing formation of 3-MCPD esters in crude palm oil upon further heat processing.
Approximately 900 tonne of crude palm oil (CPO) underwent washing using 5 to 10% hot water (90 to 95°C) at a palm oil mill. The aim of the CPO washing was to eliminate and/or reduce total chlorine content present in the conventional CPO, as it is known as the main precursor for the formation of 3-monochloropropane-1, 2-diol esters (3-MCPDE). By a simple hot water washing, more than 85% of the total chlorine was removed. However, washing did not have significant (p > 0.05) effect on other oil quality parameters such as the deterioration of bleachability index (DOBI), free fatty acid (FFA) content and diacylglycerol (DAG) content of the oil. The latter has been established as the main precursor for glycidyl esters (GE) formation. The treated CPO was then transported using tankers and further refined at a commercial refinery. Refining of washed CPO resulted in significantly (p < 0.05) lower formation of 3-MCPDE, but GE content remained slightly high. Post-treatment of refined oil significantly reduced the GE content (p < 0.05) to an acceptable level whilst almost maintaining the low 3-MCPDE level. The study has proven that water washing of CPO prior to refining and subsequent post-refining is so far the most effective way to produce good quality refined oil with considerably low 3-MCPDE and GE contents. Dry fractionation of refined palm oil showed these contaminants partitioned more into the liquid olein fraction compared to the stearin fraction.