Food and nutrition.pdf

Fats and Oils 223oils. Lightly hydrogenated oils have very similar physical characteristicsto regular soy oil, but are more resistant to becoming rancid.Margarine oils need to be mostly solid at 32°C (90 OF) so that themargarine does not melt in warm rooms, yet it needs to be completelyliquid at 37 °C (98 OF), so that it doesn't leave a "lardy" taste in the mouth.Another major use of soy oil is for fry oils. These oils requiresubstantial hydrogenation to keep the polyunsaturates of soy oil frombecoming rancid.Hardening vegetable oil is done by raising a blend of vegetable oiland a catalyst in near-vacuum to very high temperatures, and introducinghydrogen. This causes the carbon atoms of the oil to break double-bondswith other carbons, each carbon forming a new single-bond with ahydrogen atom. Adding these hydrogen atoms to the oil makes it moresolid, raises the smoke point, and makes the oil more stable.Hydrogenated vegetable oils differ in two major ways from other oilswhich are equally saturated. During hydrogenation, it is easier forhydrogen to come into contact with the fatty acids on the end of thetriglyceride, and less easy for them to come into contact with the centrefatty acid. This makes the resulting fat more brittle than a tropical oil; soymargarines are less "spreadable". The other difference is that trans fattyacids (often called trans fat) are formed in the hydrogenation reactor, andmay amount to as much as 40 percent by weight of a partiallyhydrogenated oil. Trans acids are increasingly thought to be unhealthy.SpargingIn the processing of edible oils, the oil is heated under vacuum tonear the smoke point, and water is introduced at the bottom of the oil.The water immediately is converted to steam, which bubbles through theoil, carrying with it any chemicals which are water-soluble. The steamsparging removes impurities that can impart unwanted flavors and odorsto the oil.