反式脂肪酸的危害及其测定方法

在不饱和脂肪酸中,会因为双键位置不同而产生几何异构体。反式脂肪酸主要来源于氢化油脂。摄入反式脂肪酸能升高血清总胆固醇和LDL-C水平,降低HDL-C水平,可能导致心血管疾病。另外,摄入反式脂肪酸也能引起必需脂肪酸缺乏,糖尿病,影响新生儿生长发育。因此,需要通过改善人们的饮食结构、减少油脂氢化、精炼过程中反式脂肪酸的产生等措施来降低反式脂肪酸对人体健康的不利影响。本文以反式油酸为例,介绍了反式脂肪酸的性质、危害、测定方法。     

傅立叶变换红外光谱法测定食品中反式脂肪酸

建立了一种食品中反式脂肪酸含量的测定方法,以酸水解法提取食品中脂肪酸,用傅立叶变换红外光谱仪对反式脂肪酸含量进行了快速测定,回收率达到89.26%~106.51%,相对标准偏差2.29%,结果重复性好,准确可靠。     

短链脂肪酸测定方法的研究进展

近年来,短链脂肪酸作为肠道菌群的代谢产物已被证实参与宿主的能量代谢,已成为预测肥胖、糖尿病等代谢性疾病及抑郁症,阿尔兹海默等神经精神疾病的生物标志物。因此,如何精准有效的测定短链脂肪酸的水平,对临床疾病的病症进行有效的的预判或诊断已成为科学家研究的重点。本文通过对近几年SCFAs的测定方法(如气相色谱法、液相色谱法、毛细管电泳法、核磁共振法等)等进行综述,为进一步开发高效灵敏的粪便短链脂肪酸测定方法提供依据。     

气相色谱法测定食品油脂中的十八碳反式脂肪酸

反式脂肪酸是在油脂的加氢反应或高温精炼过程中伴随产生的一类不饱和脂肪酸,过多的食用这些成分可能会对人体健康产生危害。食品油脂中以十八碳反式脂肪酸最为常见。采用气相色谱法对食品中十八碳反式脂肪酸的检测进行了实验摸索,获得了一套准确度高、精确度好的方法,可应用于日常监督检测。     

脂肪酸甘油酯的气相色谱分析

本文以气相色谱法对油脂中的脂肪酸单,双甘油酯进行了定性与定量分析,并对构成油脂的脂肪酸三甘油脂进行色谱分离条件的探讨。     

油中反式脂肪酸含量与地沟油检测方法初探

对市场上6种食用油的反式脂肪酸含量进行了测定。检测结果,6种食用油总反式脂肪酸的平均含量为:橄榄油(0.19%)、茶籽油(1.01%)、花生油(1.09%)、葵花籽油(1.23%)、大豆油(1.32%),玉米油(2.04%)。用本方法测定劣质油中的反式脂肪酸,以期探索检测地沟油的方法。     

油脂中八种脂肪酸的分析测定

油脂经氢氧化钾-甲醇溶液甲酯化后,生成的脂肪酸甲酯用DB-WAX毛细管柱进行分离,GC-FID进行检测。该方法的回收率在91.45%~107.55%,相对标准偏差小于8%,八种脂肪酸的检出限在0.29~1.10μg/mL之间。本方法准确度高,检出限低,能满足实际检测工作的需要。     

气相色谱法测定茶叶中的脂肪酸组成

用乙醚-正庚烷提取茶叶中的脂肪酸,KOH-甲醇甲酯化,JH-FFAP石英毛细管柱作为分析柱,FID为检测器,检测和分析茶叶中的6种脂肪酸,发现各类茶叶中的脂肪酸以不饱和脂肪酸(亚油酸和亚麻酸)为主,该方法简单、便捷,适用于茶叶中脂肪酸的分析.     

Determination of fatty acids and some undesirable fatty acid isomers in selected Turkish margarines

The fatty acid composition and total trans fatty acid content in 10 margarines produced in Turkey were determined by capillary gas chromatography and Fourier transform‐infrared spectroscopy (FT‐IR) spectroscopy. The fatty acid composition ranged as follows: saturated fatty acids, C16:0 (palmitic) 11.3 to 31.8% and C18:0 (stearic) 5.7 to 8.7%, monounsaturated fatty acids, C18:1 (oleic) 21.8 to 35.7% and C18:1 trans isomers 0.4 to 27.4%, polyunsaturated fatty acid, C18:2 linoleic acid 5.2 to 40.2%. Some positional isomers of C18:1 as cis‐11‐octadecenoic acid varied from 0.7 to 4.6% and cis‐13 trace to 2.4%. The total trans fatty acid contents were between 0.9 and 32.0% when measured with capillary gas chromatography and between 0 and 30.2% with FT‐IR spectroscopy. Some of the margarines analyzed contained trace amount of trans fatty acids which could not be detected by FT‐IR spectroscopy.     

The role of trans fatty acids in human nutrition

The role of dietary fats and oils in human nutrition is currently one of the key issues related to diet and health. Nutritional fats and oils contain both saturated and unsaturated fatty acids, mostly of cis‐configuration. Physiological functions of trans fatty acids in foods, especially their possible role in atherosclerosis, the level of blood cholesterol, and coronary heart disease is of concern, but still subject to controversy. Furthermore, the cancer prevention properties of conjugated linoleic acid isomers, present in small quantities in typical diets, remain to be confirmed. An overview on the occurrence and physiological considerations of trans fatty acids is given.     

Determination of trans fatty acids and fatty acid profiles in margarines marketed in spain

Two gas chromatography (GC) procedures were compared for routine analysis of trans fatty acids (TFA) of vegetable margarines, one direct with a 100-m high-polarity column and the other using argentation thin-layer chromatography and GC. There was no difference (P>0.05) in the total trans 18∶1 percentage of margarines with a medium level of TFA (∼18%) made using either of the procedures. Both methods offer good repeatability for determination of total trans 18∶1 percentage. The recoveries of total trans isomers of 18∶1 were not influenced (P>0.1) by the method used. Fatty acid composition of 12 Spanish margarines was determined by the direct GC method. The total contents of trans isomers of oleic, linoleic, and linolenic acids ranged from 0.15 to 20.21, from 0.24 to 0.99, and from 0 to 0.47%, respectively, and the mean values were 8.18, 0.49, and 0.21%. The mean values for the ratios [cis-polyunsaturated/(saturated +TFA)] and [(cis-polyunsaturated + cis-monounsaturated)/(saturated +TFA)] were 1.25±0.39 and 1.92±0.43, respectively. Taking into account the annual per capita consumption of vegetable margarine, the mean fat content of the margarines (63.5%), and the mean total TFA content (8.87%), the daily per capita consumption of TFA from vegetable margarines by Spaniards was estimated at about 0.2 g/person/d.     

Dietary C18:1 trans fatty acids increase conjugated linoleic acid in adipose tissue of pigs

The effect of dietary C18:1 trans fatty acids on back fat composition in pigs was investigated with special emphasis on conjugated linoleic acids (CLA). A total of 12 × 4 siblings of Large White and Swiss Landrace breed were housed in groups and fattened from 22 to 103 kg live weight. Pigs were fed a control diet (barley, wheat, soybean meal) or experimental diets which consisted of the control diet with a 5% replacement of olein or stearin fractions of pork fat, or partially hydrogenated fat. The hydrogenated fat was rich in C18:1 trans fatty acids but contained only negligible amounts of CLA. In contrast olein and stearin fractions contained far less C18:1 trans fatty acids but some CLA. In the control diet no C18:1 trans fatty acids and only traces of CLA were detected. The partially hydrogenated fat led to the highest CLA content in back fat (0.44%). Intermediate amounts of CLA were measured in pigs fed the fractionated pork fat (0.22/0.23%). In pigs fed the control diet, also small amounts of CLA were detected. The results indicate that CLA may be produced by endogenous Δ9‐desaturation out of dietary trans vaccenic acid in pigs.     

Comparison of attenuated total reflection infrared spectroscopy to capillary gas chromatography for trans fatty acid determination

Gas chromatography (GC) has been a standard analytical tool in lipid chemistry. The rapid attenuated total reflection (ATR) infrared (IR) American Oil Chemists’ Society (AOCS) Recommended Practice (Cd 14d-97) was compared to the capillary GC AOCS Recommended Practice (Ce 1f-97) that was optimized to accurately determine total trans fatty acids on highly polar stationary phases. This comparative evaluation was validated in an independent laboratory. These procedures were used to quantitate the total trans fatty acid levels in partially hydrogenated vegetable oils, measured as neat (without solvent) triacylglycerols (TAG) by ATR and as fatty acid methyl ester (FAME) derivatives by capillary GC. Unlike FAME, TAG determination by ATR required no derivatization, but samples had to be melted prior to measurement. Five blind replicates for each of three accuracy standards and three test samples were analyzed by each technique. The GC and ATR determinations were in good agreement. Accuracy was generally high. The ratios of ATR mean trans values (reported as percentage of total TAG) to the true values (based on the amount of trielaidin added gravimetrically) were 0.89, 0.98, and 1.02 for accuracy standards having about 1, 10, and 40% trans levels. The corresponding GC values, determined as percentage of total FAME, were 0.98, 0.99 and 1.04. The ratios of mean trans values determined by these techniques were ATR/GC 0.85, 1.04, and 1.01 for test samples having trans levels of about 0.7, 8, and 38%, respectively. The optimized GC procedure also minimzed the expected low bias in trans values due to GC peak overlap found with the GC Official Method Ce 1c-89. Satisfactory repeatability and reproducibility were obtained by both ATR and GC.     

Substitution of trans fatty acids in foods on the Danish market

Three surveys of the content of trans fatty acids (TFA) in foods on the Danish market were carried out before and after the Danish regulation was introduced in January 2004 restricting the use of industrially produced (IP)‐TFA to a maximum of 2 g per 100 g fat in any food product. For this purpose, food samples were collected in 2002–3, 2004–5, and 2006–7. Of these, 60 paired samples (defined as samples included in two of the three investigations and with higher levels of IP‐TFA in the first determination than in the second) were identified. Comparisons of the fatty acid profiles showed that, in 68% of the products (e.g. sweets, cakes and cookies as well as fast food such as pie and tortilla), IP‐TFA were mainly substituted with saturated fatty acids (SFA). In some cases, the SFA source was coconut fat, whereas in other products, palm oil was added instead of partially hydrogenated oils. However, in important cases like frying fats, healthier fat substitutes with monounsaturated fatty acids were used. The surveys showed that the IP‐TFA content has been reduced or removed from most products with originally high IP‐TFA content, like French fries, microwave oven popcorn and various bakery products, so that IP‐TFA are now insignificant for the intake of TFA in Denmark.     

Influence of triacylglycerol characterics on the determination of free fatty acids in vegetable oils by fourier transform infrared spectroscopy

A rapid and direct Fourier transform infrared (FTIR) spectroscopic method using a 25-μm NaCl transmission cell was developed for the determination of free fatty acids (FFA) in six important vegetable oils (corn, soybean, sunflower, palm, palm kernel, and coconut oils) that differ in fatty acid profile. The calibrations were established by adding either standard FFA (oleic, lauric acids) or a representative mixture of FFA obtained after saponification of the refined oils. For all oils, up to a FFA level of 6.5% for coconut oil, the best correlation coefficient was obtained by linear regression of the free carboxyl absorption at 1711 cm⁻¹. All correlation coefficients were greater than 0.993, and no significant difference between the calibration methods could be detected. Upon validation of the calibration, no significant difference (α=0.05) between the “actual” and the “FTIR predicted” FFA values could be observed. The calibration models developed for the six oils differed significantly and indicate the need to develop a calibration that is specific for each oil. In terms of repeatability and accuracy, the FTIR method developed was excellent. Because of its simplicity, quick analysis time of less than 2 min, and minimal use of solvents and labor, the introduction of FTIR spectroscopy into laboratory routine for FFA determination should be considered.     

Plastic fats with zero trans fatty acids by interesterification of mango,mahua and palm oils

Speciality plastic fats with no trans fatty acids suitable for use in bakery and as vanaspati are prepared by interesterification of blends of palm hard fraction (PSt) with mahua and mango fats at various proportions. It was found that the interesterified samples did not show significant differences in solid fat content (SFC) after 0.5 or 1 h reaction time. The blends containing PSt/mahua (1:1) showed three distinct endotherms, indicating a heterogeneity of triacylglycerols (TG), the proportions of which altered after interesterification. The SFC also showed improved plasticity after interesterification. Similar results were observed with other blends of PSt/mahua (1:2). These changes in melting behavior are due to alterations in TG composition, as the trisaturated‐type TG were reduced and the low‐melting TG increased after interesterification. The blends containing PSt/mango (1:1) showed improvement in plasticity after interesterification, whereas those containing PSt/mango (2:1) were hard and showed high solid contents at higher temperature and hence may not be suitable for bakery or as vanaspati. The blends with palm and mahua oils were softer and may be suitable for margarine‐type products. The results showed that the blends of PSt/mahua (1:1, 1:2) and PSt/mango (1:1) after interesterification for 1 h at 80 °C showed an SFC similar to those of commercial hydrogenated bakery shortenings and vanaspati. Hence, they could be used in these applications in place of hydrogenated fats as they are free from trans acids, which are reported to be risk factors involved in coronary heart disease. For softer consistency like margarine applications, the blends containing palm oil and mahua oil are suitable.     

Rapid quantitative determination of free fatty acids in fats and oils by fourier transform infrared spectroscopy

Rapid direct and indirect Fourier transform infrared (FTIR) spectroscopic methods were developed for the determination of free fatty acids (FFA) in fats and oils based on both transmission and attenuated total reflectance approaches, covering an analytical range of 0.2–8% FFA. Calibration curves were prepared by adding oleic acid to the oil chosen for analysis and measuring the C=O band @ 1711 cm^–1 after ratioing the sample spectrum against that of the same oil free of fatty acids. For fats and oils that may have undergone significant thermal stress or extensive oxidation, an indirect method was developed in which 1% KOH/methanol is used to extract the FFAs and convert them to their potassium salts. The carboxylate anion absorbs @ 1570 cm^–1, well away from interfering absorptions of carbonyl-containing oxidation end products that are commonly present in oxidized oils. Both approaches gave results comparable in precision and accuracy to that of the American Oil Chemists’ Society reference titration method. Through macroprogramming, the FFA analysis procedure was completely automated, making it suitable for routine quality control applications. As such, the method requires no knowledge of FTIR spectroscopy on the part of the operator, and an analysis takes less than 2 min.     

Gas chromatographic separation of the fatty acid methyl esters prepared from dairy products,partially hydrogenated oils,and refined vegetable oils applying a negative temperature gradient

To date no single gas chromatographic method can simultaneously measure all fatty acids (FA), including trans-FA (TFA), that are contained in dairy products, partially hydrogenated oils (PHO), and refined vegetable oils. Using 100% poly(biscyanopropyl siloxane) capillary columns, ruminant and dairy fats are preferentially analyzed by applying temperature programs that separate short chain FA, but not trans-18:3 from 20:1. Refined vegetable oils and PHO are preferentially analyzed by applying isothermal elutions that provide quantification of all 18 carbon TFA including trans-18:3 FA, but not of all short chain FA. In this short communication, we propose a temperature program method capable of simultaneously measuring short chain FA and all 18 carbon TFA including trans-18:3 by applying a negative temperature gradient after the elution of trans-18:1. A simplified version of the method is also described for equipment not able to perform negative temperature gradients.