Mossoba Magdi M, Moss Julie, Kramer John K G
U.S. Food and Drug Administration, Center for Food Safety and Applied Nutrition, Office of Regulatory Science, College Park, MD 20740, USA.
J AOAC Int. 2009 Sep-Oct;92(5):1284-300.
Trans fatty acids are found in a variety of foods like dairy and meat products, but the major dietary sources are products that contain commercially hydrogenated fats. There has been a renewed need for accurate analytical methods for the quantitation of total trans fat since mandatory requirements to declare the amount of trans fat present in food products and dietary supplements were issued in many countries. Official capillary GC and IR methodologies are the two most common validated methods used to identify and quantify trans fatty acids for regulatory compliance. The present article provides a comprehensive discussion of the GC and IR techniques, including the latest attenuated total reflection (ATR)-FTIR methodology called the negative second derivative ATR-FTIR procedure, which is currently being validated in an international collaborative study. The identification and quantitation of trans fatty acid isomers by GC is reviewed and an alternative GC method is proposed using two temperature programs and combining their results; this proposed method deals more effectively with the resolution of large numbers of geometric and positional monoene, diene, and triene fatty acid isomers present in ruminant fats. In addition, the different methylation procedures that affect quantitative conversion to fatty acid methyl esters are reviewed. There is also a lack of commercial chromatographic standards for many trans fatty acid isomers. This review points to potential sources of interferences in the FTIR determination that may lead to inaccurate results, particularly at low trans levels. The presence of high levels of saturated fats may lead to interferences in the FTIR spectra observed for trans triacylglycerols (TAGs). TAGs require no derivatization, but have to be melted prior to IR measurement. While GC is currently the method of choice, ATR-FTIR spectroscopy is a viable, rapid alternative, and a complementary method to GC for a more rapid determination of total trans fats for food labeling purposes.
反式脂肪酸存在于多种食物中，如乳制品和肉制品，但主要的膳食来源是含有商业氢化脂肪的产品。自从许多国家发布了强制要求标注食品和膳食补充剂中反式脂肪含量的规定以来，对准确分析总反式脂肪含量的方法有了新的需求。官方的毛细管气相色谱法（GC）和红外光谱法（IR）是用于鉴定和定量反式脂肪酸以符合监管要求的两种最常见的经过验证的方法。本文全面讨论了气相色谱法和红外光谱法技术，包括最新的衰减全反射（ATR）-傅里叶变换红外光谱法（FTIR），即负二阶导数ATR-FTIR程序，该方法目前正在一项国际合作研究中进行验证。本文回顾了通过气相色谱法鉴定和定量反式脂肪酸异构体的方法，并提出了一种使用两个温度程序并结合其结果的替代气相色谱法；该方法能更有效地分离反刍动物脂肪中存在的大量几何和位置异构体的单烯、二烯和三烯脂肪酸。此外，还综述了影响脂肪酸甲酯定量转化的不同甲基化程序。许多反式脂肪酸异构体也缺乏商业色谱标准品。本综述指出了傅里叶变换红外光谱法测定中可能导致结果不准确的潜在干扰源，特别是在低反式水平时。高水平饱和脂肪的存在可能会干扰反式三酰甘油（TAG）的傅里叶变换红外光谱。三酰甘油无需衍生化，但在红外测量前必须熔化。虽然气相色谱法目前是首选方法，但衰减全反射傅里叶变换红外光谱法是一种可行、快速的替代方法，并且是气相色谱法的补充方法，可用于更快速地测定食品标签中的总反式脂肪。
