食品中反式脂肪的FTIR-ATR定量分析

当液体油被化学改性为固体时，就会形成反式脂肪。这些反式脂肪被用于各种食品中。反式脂肪的过量摄入会增加血液中的低密度脂蛋白（坏）胆固醇，降低高密度脂蛋白的（好）胆固醇。因此，食用反式脂肪产品会增加缺血性心脏病的发病率，因此，食品中的反式脂肪含量备受关注。由于这些原因，量化食品中的反式脂肪含量变得越来越重要。定量分析通常根据监管机构规定的官方方法进行，目前反式脂肪的官方测量方法使用气相色谱法或红外光谱法。广泛使用的GC方法需要一些复杂的程序，如样品的分离、提取和酯化，因此需要相当长的时间和成本。美国分析化学家组织（AOAC）制定了一种方法AOAC 2000.10，使用红外光谱和ATR来评估反式脂肪含量。在这个应用中，我们展示了根据官方AOAC ATR方法进行的校准对几种类型的油中反式脂肪的定量分析。本应用中结果表明采用ATR法，可以简单、快速地测定各种食品油中反式脂肪的含量，而不需要进行复杂的程序。Application Note050-AT-0215 Rapid FTIR Quantitative Analysis of Trans-Fatty Acid atExtremely Low Concentrations using a Liquid Cell2/3Application Note Quantitative Analysis of Trans-Fats in Food Products using an FT/IR-ATR Method Intro d uc t ion Trans-fats are formed when l i q ui d oils a r e chemical l y modi fi ed into solids. T h ese trans-fats are used in a var i ety of food products. The excessive consumpt i on of trans-fats inc r eases LDL (bad) cholesterol in the blood and decreases HDL (good) cholestero l . Consequently，the consumption of trans-fat products can increase the i ncidence of ischem i c cardiac disease and t h us ， the trans-fat content in food is of great concern . Acco r ding to reports by a joint spec i alists conference of the Food a n d Agriculture Organization (FAO) and the FT/IR-4000 and 6000 Series Spectrometers World Health Organizat i on (WHO) of the United Nations， i t is proposed that the intake of t ra n s-fats should be l i mited to less t han 1% of the overa l l calor i c intake. As a result of these f indings， m any foreign countries a r e n ow mandating the disc l osure of t r ans-fat content i n foods； some EU countr i es con tr o l the content in food and some other countr i es suc h as U.S.， Canada and Korea are obligated to include the t r a n s-f at content on all food label i ng. In Japan， t h e Consumer Affairs Agency recen tl y annou n ced that food producers wi l l be obligated to state the trans-f ats con t ent of al l food products. For t hese reasons， it is becoming more i mportant to qua n tify the trans-fat conten t i n food. A quantitative analysis is generally pe r formed accord i ng to official methods prescribed by regulatory bodies， with gas c h romatography (GC) or infrared spectroscopy bei n g currently used for the official methods for the measurement of t r ans-fats. T he GC method widely used requires some complicated procedu r es such as separation， extraction and esterif i cation of the sample，and th u s requires conside r able t ime and cost. The American Organizatio n of Analy t ical Chemists (AOAC) formu l ated a methoc AOAC 2000.10 u sing infra r ed spectroscopy with ATR to eva l uate t h e trans-fat content. In this application， we demonstrated the quantitative analysis of trans-fats in seve r al types of oil with a calibration made according to the offic i al AOAC ATR method. E xp e r i m e ntal The AOAC 2000.10 met h od requ i res a quantitative calibration be developed and the quantitative analysis of u n known samples performed b y measuring the samples usi n g an ATR crystal hea t ed to 65℃ to melt the oils completely. The cis- and trans-f ats contai n ed in natural f ats have IR peaks in the range f rom 1000 cml to 600 cm"'， which i s used for the quan ti tative ana l ysis (F i gure 1). In the off i cial method， cis-tr i olein and trans-t r i elai d in are used as standard samples. The spectrum of c i s-t r iolein i n orange and the spect r um of trans-triela i din i n gree n are overlaid as displayed in Figure 1. Both spectra have similar absorptions i n the m i d-infrared spectral range except for specific peaks assoc i a t ed with the two diffe r en t forms as displayed from 1000 cmto 600 cm . F i gure 1. Mi d -I R s p ectra of cis -fats an d t r a ns -fats (dem o n s tra ti n g t h e signific a n t pea k s i n the h i gh ligh ted a r eas ) Instrument FT/IR-6100 and a thermostatted single reflection ATR accessory Detector DLaTGS Resolution 4cm1 Integration Time 64 scans Apodization Triangle Temperature Method Standard Samples Figure 2. P e aks of t rans -f a ts at 966 c m² JASCO INC. R esu l ts and Discussion The trans-fat has a peak due to the C-H bend i ng mode near 966 cm and the peak area is used for quant i tation in the official method. The over l aid spect r a for each concentration at 966 cm are shown in Figure 2. Figu r e 3 i s a screen shot of the Quantitative Calibratio n Program. The calibration curve calcu l a t ed using the program i s displayed i n Figure 4. Table 1 ou tl ines the results for the q u antitat i ve analysis of seve r al commercial food oils. I n general ， margar i ne ha s a t ra n s-fat content of 1 to 10%， whilst olive oil a n d sesame oil conta in almost no t r ans-fat. Th i s shows that the system as o ut lined is ef f ective for t h e quantitative a n a l ysis of trans-fats. By using the ATR method， t h e quantity of t r ans-fats in various types of food oi l s can be determined simply and qu i c k ly wit h ou t comp li cated procedu r es. Figure 3. Q u anti t ati ve C ali b ra tio n P r o g r a m Figure 4. C a l i b r at ion cur v e f or t r a ns -fat c ontent Table 1. Tr a ns-fat c o n t en t o f f ood o ils JASCO INC. 28600 Mary's Cour t ， E a s to n ， M D 21601US A UASGO T el ： (800) 333-5272， Fa x ： (410) 822-7526 A ppl ic a tio n Lib r ary： ja s c o i n c.com /appli c a t i o ns