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Food Lipids: Chemistry, Nutrition, and Biotechnology

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Figure 2 IR absorption b<strong>and</strong>s for 0.91–45.87% trans when neat mixtures of methyl elaidate<br />

(ME) in methyl oleate (MO) were ‘‘ratioed’’ against neat MO using an ATR liquid cell. (From<br />

Ref. 30.)<br />

[32,33]. Using this procedure, only 50 �L (about 2–3 drops) of neat oil (or esters)<br />

is placed on the horizontal surface of the zinc selenide element of the SB-HATR<br />

infrared cell. The absorbance values obtainable are within the linearity of the instrument.<br />

The test portion of the neat oil can easily be cleaned from the infrared crystal<br />

by wiping with a lint-free tissue before the next neat sample is applied. The method<br />

is accurate for trans concentrations greater than 1%. The SB-HATR FTIR procedure<br />

was used to determine the trans content of 18 food products [32]. Recently, this<br />

procedure has been collaboratively studied <strong>and</strong> good statistical results were obtained.<br />

For triacylglycerols, the reproducibility relative st<strong>and</strong>ard deviations were in the range<br />

18.97–1.62% for 1.95–39.12% trans (as trielaidin) per total fat. For fatty acid methyl<br />

esters, the corresponding values varied from 18.46% to 0.9% for 3.41–39.08% trans<br />

(as methyl elaidate) per total fat. At worst, accuracy was �11% <strong>and</strong> averaged 1%<br />

low bias.<br />

The ATR-FTIR procedure was voted official method AOCS Cd 14d-99 by the<br />

AOCS in 1999 [34] <strong>and</strong> official method 2000.10 by AOAC International in 2000<br />

[35] after testing in a 12-laboratory international collaborative study. Analytical ATR-<br />

FTIR results exhibited high accuracy relative to the gravimetrically determined values.<br />

Comparison of test materials with similar levels of trans fatty acids indicated<br />

that the precision of the current ATR-FTIR method was superior to those of the two<br />

most recently approved transmission infrared official methods: AOAC 965.34 [36]<br />

<strong>and</strong> AOAC 994.14 [37].<br />

The ATR-FTIR method was also evaluated for use with matrices of low trans<br />

fat <strong>and</strong>/or low total fat contents such as milk [38] <strong>and</strong> human adipose tissue [39].<br />

Preliminary results indicated that the presence of low levels (

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