Tom Verleyen

Gas chromatographic characterization of vegetable oil deodorization distillate

Because of its complex nature, the analysis of deodorizer distillate is a challenging problem. Deodorizer distillate obtained from the deodorization process of vegetable oils consists of many components including free fatty acids, tocopherols, sterols, squalene and neutral oil. A gas chromatographic method for the analysis of deodorizer distillate without saponification of the sample is described. After a concise sample preparation including derivatization and silylation, distillate samples were injected on column at 60 degrees C followed by a gradual increase of the oven temperature towards 340 degrees C. The temperature profile of the oven was optimized in order to obtain a baseline separation of the different distillate components including free fatty acids, tocopherols, sterols, squalene and neutral oil. Good recoveries for delta-tocopherol, alpha-tocopherol, stigmasterol and cholesteryl palmitate of 97, 94.4, 95.6 and 92%, respectively were obtained. Repeatability of the described gas chromatographic method was evaluated by analyzing five replicates of a soybean distillate. Tocopherols and sterols had low relative standard deviations ranging between 1.67 and 2.25%. Squalene, mono- and diacylglycerides had higher relative standard deviations ranging between 3.33 and 4.12%. Several industrial deodorizer distillates obtained from chemical and physical refining of corn, canola, sunflower and soybean have been analyzed for their composition.

Modeling of alpha-tocopherol loss and oxidation products formed during thermoxidation in triolein and tripalmitin mixtures.

The degradation of α-tocopherol and the formation of α-tocopherol and triacylglycerol oxidation products at high temperatures (150–250°C) over a heating period (0–4h) for a model system ranging between triolein and tripalmitin were modeled by use of an experimental design. The oxidation products of α-tocopherol formed under these conditions were α-tocopherolquinone (1.4–7.7%) and epoxy-α-tocopherolquinones (4.3–34.8%). The results indicate a very high susceptibility of α-tocopherol to capture peroxyl radicals upon oxidation, leading to the formation of polar tocopherol oxidation products. Both α-tocopherolquinone and epoxy-α-tocopherolquinones were not stable upon prolonged heating and were further degraded to other unknown oxidation products. The kinetics of α-tocopherol oxidation were significantly influenced by the triolein/tripalmitin ratio. By increasing the level of triacylglycerol unsaturation the rate of α-tocopherol recovery after heating increased significantly from 2.2 to 44.2% whereas in the meantime triacylglycerol polymerization increased from 0 to 3.7%.

Evaluation of GC and GC–MS methods for the analysis of cholesterol oxidation products

Abstract Various methods are used to analyse cholesterol oxidation products (COP) due to the unavailability of a standard method. In order to select a suitable method for the enrichment of COP, three methods of saponification (A–C), and transesterification (D) of tallow with three levels (5, 10 and 20 μg) of spiked COP, were evaluated. Further enrichment of COP was done by solid phase extraction, quantified by GC, and confirmed by GC–MS. The in-house method A, and method D showed,the best results among the four methods evaluated. The recoveries at all levels of spiked COP were generally higher than 60% in method A. The recoveries of all spiked COP at 5 μg level were consistently lower in method D compared with method A. From the results of this study it can be concluded that method A may be more suitable for the analysis of very low levels of COP in foods.

Comparison of steradiene analysis between GC and HPLC

Steradienes are sterol dehydration products formed in the vegetable oil refining process during the bleaching and deodorization process. The 3,5-stigmastadiene content of vegetable oils was quantified by GC as well as by HPLC. A good repeatability, as indicated by the low relative standard deviation of 1.11 and 2.46%, and accuracy levels of 113.9 and 107.7% were obtained for the GC and HPLC analytical method respectively. Although a good comparison between both analytical methods was observed, GC data consistently gave on average a higher 3,5-stigmastadiene content of 19.6% compared to HPLC data. Probably there is an overestimation of the steradiene content analyzed by GC due to peak overlap with other hydrocarbons as the FID detector is not as selective compared to the UV detector applied in the HPLC analysis.

Cholesterol oxidation in tallow during processing

Abstract The oxidation of cholesterol during the bleaching and deodorization process of tallow was studied. Eight polar cholesterol oxidation products were targeted, but only cholest-5-en-3β,7β-diol (7β-HC) and 5β, 6β-epoxy-5β-cholestan-3β-ol (β-CE) could be quantified in the samples analysed. The content of 7β-HC was slightly higher in the processed tallow (0.6–0.7 μg/g) compared with natural tallow (0.2 μg/g). However, the content of β-CE was considerably increased during processing, ranging from 0.8 to 3.4 μg/g, compared with 0.6 μg/g in the natural tallow. The general observation was that the content of β-CE was influenced by temperature, duration and type of bleaching earth.