Determination of cis and trans -Octadecenoic acids in margarines by gas liquid chromatography-infrared spectrophotometry

Analysis of Trans Fat in Edible Oils with Cooking Process

Trans fat is a unsaturated fatty acid with trans configuration and separated double bonds. Analytical methods have been introduced to analyze trans fat content in foods including infrared (IR) spectroscopy, gas chromatography (GC), Fourier transform-infrared (FT-IR) spectroscopy, reverses-phase silver ion high performance liquid chromatography, and silver nitrate thin layer chromatography. Currently, FT-IR spectroscopy and GC are mostly used methods. Trans fat content in 6 vegetable oils were analyzed and processing effects including baking, stir-frying, pan-frying, and frying on the formation of trans fat in corn oil was evaluated by GC. Among tested vegetable oils, corn oil has 0.25 g trans fat/100 g, whereas other oils including rapeseed, soybean, olive, perilla, and sesame oils did not have detectable amount of trans fat content. Among cooking methods, stir-frying increased trans fat in corn oil whereas baking, pan-frying, and frying procedures did not make changes in trans fat content compared to untreated corn oils. However, the trans fat content was so low and food label can be declared as ‘0’ trans based on the regulation of Ministry of Food ad Drug Safety (MFDS) (< 2 g/100 g edible oil).

Ácidos graxos trans: implicações nutricionais e fontes na dieta

Este artigo revisa as principais fontes de ácidos graxos trans na dieta e as implicações nutricionais da ingestão elevada destes isômeros. São apresentados resumidamente os métodos analíticos utilizados na identificação e quantificação dos ácidos graxos trans, sendo abordados as suas vantagens e desvantagens. Os alimentos que empregam gordura parcialmente hidrogenada na sua produção, são fontes importantes de isômeros trans na dieta da maior parte da população em países industrializados. Este estudo compara os níveis de ácidos graxos trans em gorduras hidrogenadas, margarinas e batatas frita, analisados em diversos países, incluindo o Brasil. Esta avaliação indica a presença de níveis elevados de isômeros trans em alimentos produzidos no Brasil.

Trans fatty acids in margarines and shortenings marketed in Austria

Margarines and shortenings available in Austria were repeatedly sampled in 1991/1992 and the content of trans fatty acids (TFA) determined by using capillary GLC. Wide variations of the TFA contents with respect to intra- and inter-brand differences were observed. Diet margarines contained up to 1% TFA, while TFA concentrations in tub or stick margarines were much higher (15.7 +/- 5.8% and 21.3 +/- 5.3%, respectively). A sub-set of samples was also purchased in 1995 and a general reduction of the TFA content was noticed. Taking into account different market shares of certain margarine types, a weighted average of 15.7% TFA and 6.5% TFA was calculated for the 1991/1992 and the 1995 samples. Based on availability data the amount of TFA supplied with margarines was estimated to be 3.7 g per person per day, while a more accurate method of measuring dietary intakes, i.e. diet history and food frequency data, approximates the amount of TFA supplied with margarines to be 1.5 g per person per day for the 1991/1992 samples and 0.6 g for the 1995 samples.

Unusual fatty acids in the depot fat of the Canadian beaver (Castor canadensis)

Unusual fatty acids in the adipose tissue of the Canadian beaver were analysed by argentation thin-layer chromatography, gas-liquid chromatography and gas chromatography-mass spectrometry of several adducts and spectroscopic measurements. The total proportion of trans-octadecenoic fatty acids and the distribution of double bonds in these acids resembled those of ruminant fats. Because trans-11-18:1 was the main trans-18:1 isomer of beaver fat and a conjugated diene cis-9, trans-11-18:2 was also detected, it can be deduced that linoleic acid (cis-9, cis-12-18:2) is biohydrogenated in the beaver. The ideas that microbial processes intervene before normal absorption and fatty acid metabolism of the beaver is also supported by the larger amounts of anteiso odd-chain fatty acids with respect to the corresponding iso acids in the beaver depots. In addition, the distribution of double bonds in the cis-octadecenoic acids was wide, as it is in the depot fats of ruminants.

General strategies in chromatographic analysis of lipids

Lipid extracts of natural sources contain a large number of lipid classes and molecular species. Completely reproducible samples are obtained only with great care and skill. Analytical methods other than chromatography and/or mass spectrometry are of little use for resolution and identification of lipid molecules even in simple mixtures. The analytical information desired governs the selection of the chromatographic and mass spectrometric method, which determine the sample preparation and derivative needed. Usually a combination of chromatographic methods is necessary to identify specific species of lipids. The recent development of soft ionization techniques, that are readily interfaced with mass spectrometers, have greatly simplified the sample preparation and have largely eliminated the need for derivatization. Because these techniques require expensive equipment and dedicated operators, the methods selected must be consistent with the true analytical needs and the available resources. Although personal preference cannot be eliminated entirely, the general strategies outlined below should help to reduce the number of possibilities facing a lipid analyst to a few practical choices.

Fatty acid profiles of lipid samples

Most lipids are best characterized by their fatty acids which differ in chain length, the degree of unsaturation, configuration and position of the double bonds, and the presence of other functionalities. The fatty acid profiles are currently most frequently determined by capillary gas chromatography of the methyl esters which are prepared by a variety of methods. These are discussed with an emphasis on more recent developments, along with the stationary phases used for the separations and the methods employed for identification of the fatty acids. HPLC is applied less frequently for ascertaining fatty acid profiles than GC, but a very large number of derivatives for ultraviolet and fluorescence detection have been proposed. This method continues to evoke increasing interest, particularly in conjunction with fluorescence detection. This technique enables attainment of greater sensitivities than with standard GC methods employing flame ionization detection. Extensive applications of it to the analysis of free fatty acids in blood and other biomedical samples are clearly discernible. Other methods, including supercritical fluid chromatography, have found only limited application for fatty acid profiling.

Confirmation by gas chromatography/mass spectrometry of two unusual trans-3-monoethylenic fatty acids from the Nova Scotian seaweeds Palmaria palmata and Chondrus crispus

The structures of two unusual fatty acids, the known trans-3-hexadecenoic acid and a novel trans-3-tetradecenoic acid, both isolated from the Nova Scotian seaweeds Palmaria palmata and Chondrus crispus, were positively identified. After the extraction of the total fatty acids by saponification, followed by methylation, the monoenoic trans fractions were isolated by thin-layer chromatography on silica gel impregnated with silver nitrate. The monoenoic trans fractions were derivatized with 2-amino-2-methyl-propanol prior to analysis by gas chromatography/mass spectrometry. The mass spectra showed prominent [M + 1]+ ions but lacked the 12 amu interval useful for identifying the double bond position. Hence, alternative diagnostic peaks were used to confirm the position of the double bond in these two fatty acids. As the trans-3-hexadecenoic acid is found in the photosynthetic tissue of all plants, it may also be present in ruminant fats and, presumably, in human adipose tissue.

Fatty acids in some common food items in Canada

Fat content and fatty acid (FA) composition of 100 common items in 17 food categories from the Canadian retail market were determined. Of these, 52 samples were made from partially hydrogenated fat. Their fat (in parentheses) and trans FA levels were as follows: breads (3.7% fat) 15.7%, hamburger buns (5.5% fat) 26.3%, cakes (8.7-36.7% fat) 10.1-25.7%, candies/chocolates (27.1% fat) 11.1%, cereals (1.3-12.9% fat) 9.2-33.7%, cookies (5.0-40.5% fat) 7.6-38.7%, crackers (9.2-33.0% fat) 13.8-35.4%, donuts (16.6-29.6% fat) 27.7-32.7%, french fries (pre-cooked) (4.3-4.5% fat) 32.8-42.8%, muffins (12.5-23.7% fat) 16.5-24.2%, pizza crusts (6.0-7.2% fat) 22.1-28.8%, shortenings (100% fat) 17.4-20.2%, potato chips (33.2-40.0% fat) 29.7-39.7%, and corn chips (25.0-34.2%) 29.9-33.9%. Generally the sum of saturated and trans FA in the food items made with partially hydrogenated fat was higher than that of the corresponding food items made with unhydrogenated oils. The higher levels of saturates plus trans were at the expense of the essential fatty acids (EFA). The high-fat foods, such as cakes, cookies, crackers, donuts and potato chips, made with partially hydrogenated fat, were substantially lower in EFA and contained relatively higher levels of trans polyunsaturated fatty acids (PUFA). In some samples of potato chips and french fries, the level of trans PUFA was almost the same or more than the sum of linoleic and linolenic acids.

Preferential incorporation of dietary cis-9,cis-12,trans-15 18:3 acid into rat cardiolipins

Cardiolipins from mitochondria of different rat organs (heart; liver and kidney) appear to be privileged targets for the incorporation of cis-9,cis-12,trans-15 18:3 acid, a compound commonly found in deodorized edible linolenic acid-containing oils. When this acid (together with other linolenic acid geometrical isomers (LAGI)) is fed at high load to rats that had been reared on a fat-free diet since weaned for a few days, it replaces the endogenously synthesized monoenoic acids that had accumulated in cardiolipin during fat deficiency. Although there is no discrimination in deposition of any LAGI in adipose tissue triacylglycerols, a high selectivity of incorporation of the cis-9,cis-12,trans-15 18:3 acid over other isomers (including the all-cis 18:3(n-3) acid) is observed either in diradylphospholipids or in cardiolipins. However, cis-9,cis-12,trans-15 18:3 acid accumulates in cardiolipins at a considerably higher level than in other phospholipids (11 times in liver, 5-7 times in heart and kidney). It reaches 22-24% of total fatty acids in cardiolipins from heart and liver, and 13-14% in kidney. The cis-9,cis-12,trans-15 18:3 acid is esterified to both the 1(1")- and 2(2")-positions of liver mitochondria cardiolipin, with a well-marked selectivity for positions 1(1"). Its 1(1")/2(2") selectivity ratio is about the same as that of 18:2(n-6) acid: 2.1 vs 2.2. It is concluded that the trans-15 ethylenic bond is probably perceived as a single bond by enzymic systems that ensure acylation of cardiolipins. The cis-9,cis-12,trans-15 isomer is able to reverse the fatty acid modifications induced in cardiolipins by a diet devoid of essential fatty acids, in a way similar to that of 18:2(n-6) acid supplementation.

Gas chromatography of fatty acids

Lipids in foods contain a wide variety of fatty acids differing in chain length, degree of unsaturation, position and configuration of double bonds and the presence of special functional groups. Modern capillary gas chromatography offers excellent separation of fatty acids. Fused-silica capillary columns with stationary phases of medium polarity and non-polar methylsilicone stationary phases successfully separate most of the natural fatty acids. Special applications, such as the separation of complex cis-trans fatty acid mixtures and cyclic fatty acids, required particular chromatographic conditions, including the use of very long capillary columns or more polar stationary phases. The derivatization methods for the preparation of fatty acid esters also need to be optimized to obtain accurate quantitative results. This paper reviews the derivatization techniques, capillary columns and stationary phases commonly used in the gas chromatography of fatty acids in food.