Trans fat

A few fatty acids with trans double bonds (trans fatty acids) occur naturally but the major source of trans fats comes from partial hydrogenation of vegetable oils m for example the preparation of margarine However the same catalysts that catalyze the... 

The intermediate m hydrogenation formed by reaction of the unsaturated ester with the hydrogenated surface of the metal catalyst not only can proceed to the saturated fatty acid ester but also can dissociate to the original ester having a cis double bond or to its trans stereoisomer Unlike polyunsaturated vegetable oils which tend to reduce serum cholesterol levels the trans fats produced by partial hydrogenation have cholesterol raising effects similar to those of saturated fats... 

Figure 7.8 Catalytic hydrogenation of polyunsaturated fats leads to saturated products, along with a small amount of isomerized trans fats.

Above, 1 provided a short explanation for the recommendation to limit the dietary intake of saturated fats. That is not the only recommendation that we get from health authorities about dietary fats. Two more recommendations come to mind immediately (a) limit your intake of trans fats and (b) consume substantial amounts of omega-3 fatty acids. Let s have a look at the basis for both recommendations. 

There are good reasons for avoiding trans fats... 

Note that the term trans fats refers to fats containing trans fatty acids. At a couple of points earlier, 1 emphasized that aU the common unsaturated fatty acids possess cis carbon-carbon double bonds. It is true that some common foods—beef and dairy products—contain very small amounts of trans fatty acids but it is also true that the vast preponderance of dietary trans fats come from processed foods. Here is one example of a normal cis fatty acid—oleic acid—and its trans isomer ... 

Effective January 1, 2006, the FDA in the United States required food companies to list trans fat content on the Nutrition Facts panel of all packaged foods. This should... 

This finding has been replicated several times in clinical studies. Let me cite one example. In a careful metabolic study carried out in 1990, Mensink and Katan determined the plasma LDL/HDL ratio when 10% of the energy from oleic acid was replaced in the diet by either the corresponding trans fat or the corresponding saturated fatty acid, stearic acid. The resulting LDL/HDL ratios were 2.02 on the oleic acid diet, 2.34 on the stearic acid diet, and 2.58 on the trans fatty acid diet. This is one more example of the impact of small structural changes in molecules on their biological properties. 

Trans fats fats containing unsaturated fatty acids that have the trans geometry at their carbon-carbon double bonds. 

A further example of process quality monitoring and reactor batch profiling using NIRS comes with oleo-chemical and biodiesel production. An established use of FT-NIR analysis (AOCS Method Cd le 01) is the determination of the key vegetable oil processing parameters - iodine value (IV) and percentage trans fat content (%Trans) (Figure 5.38). 

You can hydrogenate some of the double bonds in any polyunsaturated fat. Hydrogenation, whether complete or partial, results in an increase in the melting point, a fact that makes it possible to convert a liquid oil to a solid fat. (Note that partial hydrogenation may convert some of the cis double bonds into tram double bonds, thereby producing a trans fat.)... 

Many studies have now linked consumption of trans fats to elevated LDL or bad" cholesterol levels, decreased HDL or "good" cholesterol levels, and a presumed higher risk of atherosclerosis, just as with saturated fats. 

The answer is B. Saturated fatty acids and trans fatty acids are structurally similar their hydrocarbon tails are relatively linear. This allows them to pack tightly together in semi-crystalline arrays such as the membrane bilayer. Such arrays have similar biochemical properties in terms of melting temperature (fluidity). Although some of the other properties listed are also shared by saturated and trans fats, they are not thought to account for the tendency of these fats to contribute to atherosclerosis. 

Dietary measures are initiated first—unless the patient has evident coronary or peripheral vascular disease—and may obviate the need for drugs. Patients with familial hypercholesterolemia or familial combined hyperlipidemia always require drug therapy. Cholesterol and saturated and trans-fats are the principal factors that increase LDL, whereas total fat, alcohol, and excess calories increase triglycerides. 

Humans produce about 1 gram of cholesterol daily in the liver. Dietary cholesterol is consumed through food. High cholesterol foods are associated with saturated fats and trans-fatty acids (commonly called trans fats). Dietary cholesterol comes from animal products (plants contain minute amounts of cholesterol) such as meats and dairy products. Table 26.1 shows the amount of cholesterol in common foods. 

This web page of the Food and Drug Administration describes trans fats and also shows a listing oftrans fats found in common food. Also noted is that the average daily trans fat intake for the American adult is 5-8 grams, which is 2.6percent of daily consumed Calories. 

List the following products in order of increasing proportion of trans fats stick margarine, soft tub margarine,butter. 

Interestingly, trans fats occur naturally, but only to a very small extent. The trans fat content of butter is therefore negligible. The soft tub margarine is soft because it wasn t hydrogenated for very long, which means that it has fewer trans fats than does the... 

Today, in the United States margarine outsells butter by a 2 1 ratio. Do you generally use margarine or butter or neither Why Also, butter has practically no trans fats. Does this mean that butter is better for you than margarine ... 

Trans fats have been added to the nutrition labels of foods. What next Will nutrition labels eventually become so detailed that they rarely get read by consumers At what point does a label provide "too much information" ... 

This is the web page for an article published by the U.S. Food and Drug Administration explaining the nature of trans fats and why their intake should be minimized. 

Mcnsink. R.P. and M.B. Katan "Etfect of Dietary Trans Fatly Acids on High-Density and Low. Density Lipoprotein Cholcslerol Levels in Healthy Subjects.". V Toy. J. Med.. 439 (August 16. I990i... 

The fatty acid composition of the trans-free reference fat plays a critical role. If the selected trans-free fat is significantly different from the matrix of the fat investigated, it may have an adverse impact on accuracy, particularly near the official method s lowest trans level of quantitation, 5% (AOAC International, 2000) or 1% (AOCS, 1999a). This trans-free reference fat must be carefully selected and should represent as much as possible t e composition of the unknown trans fat or oil being determined. 

Melt the trans fat test samples in a water bath if necessary. Using a disposable pipet, place each on the ATR horizontal surface making sure that the surface of the ZnSe or diamond crytal is completely covered, collect a 128-scan single-beam FTIR spectrum (Fig. D1.7.1B) at 4 cm-1 resolution, and save it. Repeat step 5 after each measurement. 

Figure D1.7.1 (A) Absorption spectra for neat (without solvent) trans fat (test samples). (B)...

Electronically generate the absorbance spectra (Fig. D1.7.1 A) for all the calibration standards and the trans fat test samples by ratioing each of the saved single-beam spectra against that of the trans-free reference fat. 

For each of the calibration standards and the trans fat test samples, display the absorbance spectrum in the expanded wavenumber range of 1050 to 900 cm 1, and electronically integrate the area under the 966 cm"1 band between the 990 and 945 cm"1 limits. 

---