Trans Fat Determination in the Industrially Processed Edible Oils By Transmission FT-IR Spectroscopy By Dr. Syed Tufail Hussain Sherazi E-mail: tufail_sherazi@yahoo.com National Center of Excellence in Analytical Chemistry, University of Sindh, Jamshoro, Pakistan.
TFA and FDA FDA issued a final rule that requires the declaration of the amount of TFA present in foods, including dietary supplements, on the nutrition label by January 1, 2006. Since there was no scientific basis for establishing a daily value (DV) for TFA, the final rule did not require the listing of a % DV as is required for some of the other mandatory nutrients, such as saturated fat.
Determination of Isolated trans Isomers Capillary GC Method Single-bounce attenuated total reflectance (SB- ATR) FT-IR spectroscopy method. Based on the observation that trans double bonds exhibit a characteristic and strong IR absorption band (967 cm -1, H-C=C bending vibration) Widely employed method, particularly in the analysis of hydrogenated oils
Factors Limiting Accuracy of Traditional AOCS Method All triglycerides exhibit a weak absorption band that underlie the trans absorption band Intensity of these underlying absorptions varies with triglyceride composition of the oil; can contribute 3-5 percent to the measured trans values. Sensitivity is limited by inherently short effective pathlength (~4 mm at trans measurement wavelength).
FT-IR Spectral measurements The infrared spectra of the trans standards and samples were collected using Nicolet 5700 FT-IR spectrometer equipped with a 200 µm KCl transmission cell. Trielaidine and partially hydrogenated oil are solids at room temperature. Therefore the viscosity of trielaidine standards and test samples were decreased by the addition of odorless mineral oil spirit (OMS) containing the spectral marker (0.03%) in the ratio of 1:2 to facilitate the loading of transmission cell.
FT-IR Spectral measurements Prior to the loading of 200 µm KCl cell, all standards and samples were heated to 50 0C to avoid any crystallization during the analysis. A total of 32 scans were collected in the range 4000 400 cm-1 at a resolution of 4 cm-1. The transmission FT-IR spectrum of all diluted standards and samples with OMS were recorded under the same parameters and fresh background was subtracted from the each for the accuracy in the results.
Gas Chromatography Fatty acid methyl esters (FAMEs) were prepared using standard (IUPAC method 2.301, 1979) and analyzed on a Perkin Elmer gas chromatograph (8700) a flame ionization detector. Oxygen-free nitrogen gas was used as mobile phase. Oven temperature was programmed as following: The column held initially at 130 C for 2 min; Increased to final temperature 220 C with 4 C/min heating holding for 5 minutes; injector temperature, 260 C; detector (FID) temperature, 270 C; column flow rate, 4 ml/min; split ratio, 40:1; injected volume, 1 μl.
Representative transmission FT-IR spectrum of partially hydrogenated oil (PH-5) with prominent trans peak at 967 cm-1 1 and cooking oil (CO-9). 3 PHO-5 2 Abs 1 0-1 3 CO-9 2 Abs 1 0 4000 3000 2000 Wavenumbers (cm-1) 1000
The absorbance of trans band at 967 cm-1 1 of prepared standards spiking the trielaidine in canola oil ranging from 0.011 to 37.874%. Absorbance 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 23B_Corr(37.874%TRANS) 22B_Corr(23.980%TRANS) 21B_Corr(21.252%TRANS) 20B_Corr16.436%TRANS) 19B_Corr(14.666%TRANS) 18B_Corr(13.300%TRANS) 17B_Corr(10.442%TRANS) 16B_Corr(7.821% TRANS) 15B_Corr(4.751%TRANS) 14B_Corr(3.526%TRANS) 13B_Corr(1.268%TRANS) 12B_Corr(O.938%TRANS) 11B_Corr(0.677%TRANS) 10B_Corr(0.534%TRANS) 9B_Corr(O.352%TRRANS) 8B_Corr(0.17%TRANS) 7B_Corr(0.14%) 6B_Corr(0.11%) 5B_Corr(0.089%) 4B_Corr(0.055%) 3B_Corr(0.041%) 2B_Corr(0.026%) 1B_Corr(0.011) PURE CANOLA B_Corr(0.000%TRANS) 0.4 1000 980 960 Wavenumbers (cm-1)
TQ Analyst calibration of the trans standards (trielaidine added in canola oil)
Plot of trans peak area versus added trans to canola oil 40 Percentage of added Trans 35 30 25 20 15 10 5 0 0 5 10 15 20 Trans Peak Area 990-945cm-1 Linear Regression for Data1_Trans: Y = A + B * X Parameter Value Error A -0.15776 0.05362 B 1.84724 0.00817 R SD N P 0.99979 0.20926 23 <0.0001
Trans fatty acids in partially hydrogenated oils (ghee) and cooking oils by GC and FT-IR Samples GC FT-IR PHO-1 9.12 ±0.23 8.06 ±0.02 PHO-2 26.51 ±0.55 25.74 ±0.05 PHO-3 10.72 ±0.64 9.61 ±0.03 PHO-4 10.69 ±0.22 8.58 ±0.01 PHO-5 16.32 ±0.44 15.17 ±0.04 PHO-6 12.55 ±0.41 12.21 ±0.04 PHO-7 20.21 ±0.61 19.19 ±0.03 CO-8 0.52 ±0.52 0.60 ±0.01 CO-9 0.45 ±0.16 0.61 ±0.01 CO-10 0.52 ±0.12 0.56 ±0.01 CO-11 1.33 ±0.21 1.76 ±0.01 CO-12 1.63 ±0.23 1.83 ±0.01 CO-13 1.17 ±0.16 0.83 ±0.01 CO-14 1.14 ±0.23 1.65 ±0.01
Plot of GC results versus transmission FT-IR 30 Percent Trans by FT-IR 25 20 15 10 5 0 Linear Regression for Data1_B: Y = A + B * X Parameter Value Error A -0.02779 0.28685 B 0.94397 0.02307 R SD N P 0.99703 0.65764 12 <0.0001 0 5 10 15 20 25 30 Percent Trans by GC
Conclusion The results of transmission FT-IR spectroscopy were found in good agreement with the GC results and have shown slightly better sensitivity for low trans values in the analyzed edible oil samples. All hydrogenated edible oils have shown higher amount of trans fat by the both GC and transmission FT-IR spectroscopy, which is very dangerous for the health of consumers.