Hydrogenation and Trans-Fats
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Student Name: ___________________________________________ Pd: ____ Date: _______________ What’s the Skinny on Trans-fats? Hydrogenation and Trans-fats INFORMATION Hydrogenation of Vegetable Oils Unsaturated fatty acids are cheap, plentiful natural products, but their usefulness in food products is limited since, at room temperature, these fats are oils – liquid fats (for example, the healthy triacylglyceride trilinolein, has a melting point of -43 degrees Celsius). Prior to the invention of an artificial alternative, food products were manufactured using “firmer” but more expensive and less plentiful ingredients like butter or animal fat (lard). What the food industry needed was an inexpensive and easy-to-get alternative to animal productes. Hydrogenation solved that problem. Hydrogenation of vegetable oils is an industrial process that was invented by the German industrial chemist Wilhelm Normann in 1901. Normann realized that at high temperatures and pressures in the presence of a catalyst, the double bonds in unsaturated vegetable oils become saturated – that is, hydrogen is added to the carbon atoms. In most cases, the most desirable product was one that had been subjected to partial hydrogenation – that is, on some of the double bonds in polyunsaturated fats are converted to saturated carbons. This increased the “firmness” to make them more like natural fats like lard and butter. Vegetable shortening, made from partially hydrogenated vegetable oil, was born. By the mid 1940, these products were found in all manner of manufactured food product. Cis- Versus Trans- The double bonds in fatty acids can take two forms, or confromations – cis- and trans-. Consider Model 1, below. MODEL 1 – cis- and trans-Fatty Acids Cis-fatty acids are the most common in nature – there are very few natural trans-fats (and those found mostly in the form of healthy vaccenic acid in animal tissues and milkfat products). Elaidic acid is the trans- conformer of the much more plentiful cis- conformer oleic acid (which is found in great quantities in olive oil). Scientists discovered in the 1970s that a side effect of the process of partial hydrogenation resulted in some of the bonds in fatty acids taking the artificial conformation of trans-. Key Questions 1. In Model 1, label the trans- and cis- bonds. Do you see any other differences in the two molecules? 2. Using complete, grammatically correct sentences, explain why partially hydrogenated fatty acids would be likely to be firmer (that is, have a higher melting point) than their unhydrogenated counterparts. 3. If 500 g of linoleic acid (18:2, omega 9) is partially hydrogenated so that only one double bond on each molecule becomes saturated, what volume of hydrogen gas at 800 K and 20 atm would be required for this process? 4. Draw the following: a. A 16:0 fatty acid b. A 14:1, trans- omega-6 fatty acid c. An 20:3, omega-3 fatty acid, trans- at the omega-3 and omega-6 positions a. A triacylglyceride consisting of the three fatty acids in (a), (b), and (c). .