Cis-Trans Isomerization of Unsaturated Fatty Acid Methyl Ester by Natural Sulfur Compounds in Model Systems.

Growing evidence indicates that the intake of trans fatty acids (TFAs) increases the risk of numerous diseases, such as cardiovascular diseases. Recently, our group found that certain natural sulfur compounds (allyl isothiocyanate [AITC] and diallyl disulfide [DADS]) promote cis to trans isomerization of fatty acid esters during heat treatment. However, little information is available on the fatty acid isomerization with them. In this study, we investigated the effects of oxygen and α-tocopherol (antioxidant) on isomerization of oleic acid (18:1) methyl ester (OA-ME) in the presence of AITC and DADS. Furthermore, the effect of the simultaneous use of AITC and DADS was evaluated. Our results indicate that oxygen enhances the AITC-induced trans isomerization, and DADS was found to promote trans isomerization but inhibit AITC-induced trans isomerization during heating. Both AITC- and DADS-induced trans isomerization were inhibited by α-tocopherol. These results indicate that the trans isomerization of fatty acids induced by sulfur compounds can be controlled by devising a cooking process and the food ingredients used together.

Natural Sulfur Compounds, Allyl Isothiocyanate and Diallyl Disulfide, Promote Cis to Trans Isomerization of Fatty Acid Esters during Heat Treatment.

The effects of allyl isothiocyanate (AITC) and diallyl disulfide (DADS), widely found in edible vegetables, on thermal isomerization of unsaturated fatty acid esters (oleic acid methyl ester [OA-ME], linoleic acid methyl ester [LA-ME], and eicosapentaenoic acid ethyl ester [EPA-EE]) were investigated. Although heating with AITC and DADS significantly promoted cis to trans isomerization of all fatty acid esters, the isomerization trends varied greatly depending on the type of fatty acid. Specifically, AITC promoted thermal isomerization of OA-ME and LA-ME more efficiently than DADS; however, an opposite result was obtained for EPA-EE. For example, when OA-ME was heated at 180°C for 1 h with 1.0 equivalent of AITC and DADS, its trans isomer ratios reached 29.0 ± 7.1 and 7.6 ± 0.6%, respectively, and when EPA-EE was heated under the same conditions, its trans isomer ratios reached 4.2 ± 0.4 and 8.6 ± 0.2%, respectively. These results indicate that isothiocyanates and polysulfides would promote the formation of trans fatty acids in food processing under heating conditions.

Analysis of hydroxy triacylglycerol as a lactone precursor in milk fat using liquid chromatography electrospray ionization tandem mass spectrometry.

Heating milk fat leads to lactone formation. Hydroxy fatty acids, esterified in triacylglycerol (TAG), are likely precursors of lactones in milk fat, but respective hydroxy TAG isomers have not been directly detected for several decades. In this study, we separated hydroxy TAG isomers-1,2-dipalmitoyl-3-(5-hydroxy decanoyl)-rac-glycerol (PP(C10-5OH)-TAG), 1,2-dipalmitoyl-3-(5-hydroxy dodecanoyl)-rac-glycerol (PP(C12-5OH)-TAG), 1,2-dipalmitoyl-3-(5-hydroxy tetradecanoyl)-rac-glycerol (PP(C14-5OH)-TAG), and 1,2-dipalmitoyl-3-(4-hydroxy dodecanoyl)-rac-glycerol-by using liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) with an octacocyl silylation column. This method revealed the presence of PP(C10-5OH)-TAG, PP(C12-5OH)-TAG, and PP(C14-5OH)-TAG in butter oil, whereas no hydroxy TAG isomers were detected in heat-treated butter oil. Furthermore, a heating test of hydroxy TAG standards showed a decrease in hydroxy TAG levels and an increase in the corresponding lactone levels. These changes were stimulated by adding a small amount of water. This is the first reported analysis of respective hydroxy TAG isomers in milk fat using LC-ESI-MS/MS.

Simple Quantification of Lactones in Milk Fat by Solvent Extraction Using Gas Chromatography-Mass Spectrometry.

The analysis of lactones as an indicator of milk quality is important in food manufacturing. However, the extraction of lactones requires sensitive conditions due to their volatility. In this study, the parameters for resolution of lactone standards were evaluated by gas chromatography-electron ionization/mass spectrometry (GC-EI/MS) to develop a rapid and simple method for the quantification and compositional analysis of lactones in edible fats, especially milk fat. Fourteen lactone standards consisting of 6-16 carbon atoms were analyzed and their correction factors (CFs) were obtained by using δ-undecalactone as an internal standard. The CFs of the lactone standards followed the same trend for δ-lactones and γ-lactones. Three volume equivalents of organic solvent per unit sample yielded the best recovery in the lactone analysis. Notably, 91-114% lactone recovery for the standards was achieved with methanol as the extractant. This method was also applicable to other fat samples, such as virgin coconut oil that is thought to contain large amounts of lactones. The recovery of lactones from virgin coconut oil was in the range of 87-104%, indicating that the developed method is also applicable to solid or semi-solid fat samples. The lactone content of butter oil, coconut oil, and butter samples was calculated by using the obtained CFs and the results were in good agreement with those of previous reports. Consequently, the GC-EI/MS method developed in this study is deemed applicable for the quantification of lactones in fat samples.

Quantification of Triacylglycerol Molecular Species in Edible Fats and Oils by Gas Chromatography-Flame Ionization Detector Using Correction Factors.

In the present study, the resolution parameters and correction factors (CFs) of triacylglycerol (TAG) standards were estimated by gas chromatography-flame ionization detector (GC-FID) to achieve the precise quantification of the TAG composition in edible fats and oils. Forty seven TAG standards comprising capric acid, lauric acid, myristic acid, pentadecanoic acid, palmitic acid, palmitoleic acid, stearic acid, oleic acid, linoleic acid, and/or linolenic acid were analyzed, and the CFs of these TAGs were obtained against tripentadecanoyl glycerol as the internal standard. The capillary column was Ultra ALLOY+-65 (30 m × 0.25 mm i.d., 0.10 µm thickness) and the column temperature was programmed to rise from 250°C to 360°C at 4°C/min and then hold for 25 min. The limit of detection (LOD) and limit of quantification (LOQ) values of the TAG standards were > 0.10 mg and > 0.32 mg per 100 mg fat and oil, respectively, except for LnLnLn, and the LOD and LOQ values of LnLnLn were 0.55 mg and 1.84 mg per 100 mg fat and oil, respectively. The CFs of TAG standards decreased with increasing total acyl carbon number and degree of desaturation of TAG molecules. Also, there were no remarkable differences in the CFs between TAG positional isomers such as 1-palmitoyl-2-oleoyl-3-stearoyl-rac-glycerol, 1-stearoyl-2-palmitoyl-3-oleoyl-rac-glycerol, and 1-palmitoyl-2-stearoyl-3-oleoyl-rac-glycerol, which cannot be separated by GC-FID. Furthermore, this method was able to predict the CFs of heterogeneous (AAB- and ABC-type) TAGs from the CFs of homogenous (AAA-, BBB-, and CCC-type) TAGs. In addition, the TAG composition in cocoa butter, palm oil, and canola oil was determined using CFs, and the results were found to be in good agreement with those reported in the literature. Therefore, the GC-FID method using CFs can be successfully used for the quantification of TAG molecular species in natural fats and oils.