Interesterified fat

Interesterified fat is a type of oil where the fatty acids have been moved from one triglyceride molecule to another. This is generally done to modify the melting point, slow rancidification and create an oil more suitable for deep frying or making margarine with good taste and low saturated fat content. It is not the same as partial hydrogenation which produces trans fatty acids, but interesterified fats used in the food industry can come from hydrogenated fat, for simplicity and frugality.

Fats such as soybean oil consist mainly of various triglycerides which are made up of a glycerol backbone esterified to three fatty acid molecules. The triglycerides contain a mixture of saturated, monounsaturated, and polyunsaturated fatty acids. Interesterification is carried out by blending the desired oils and then rearranging the fatty acids over the glycerol backbone with, for instance, the help of catalysts or lipase enzymes.Polyunsaturated fatty acids (PUFAs) decrease the melting point of fats significantly. A triglyceride containing three saturated fatty acids is generally solid at room temperature and not very desirable for many applications. Rearranging these triglycerides with oils containing unsaturated fatty acids lowers the melting point and creates fats with properties better suited for target food products. In addition, blending interesterified oils with liquid oils allows the reduction in saturated fatty acids in many trans fatty acid free food products. The interesterified fats can be separated through controlled crystallization, also called fractionation.

In vegetable polyunsaturated oils, the PUFA is commonly found at the middle position (sn2) on the glycerol. Stearic acid is not usually found at sn2 in vegetable oils used in the human diet.

In most vegetable dietary fats, palmitic (C16:0) and stearic acid (C18:0) mainly occupy the 1- and 3-positions of the triacylglycerol molecule, whereas an unsaturated fatty acid such as oleic acid (18:1ω9) or linoleic acid (18:2ω6) usually occupies the 2-position. In animal fats, this is not the case. Interesterification of vegetable oils will enhance the amount of saturated fatty acids at the 2-position. Fatty acids at the 2-position are biologically different from fatty acids at the 1 and 3 position because they are handled differently during digestion and metabolism, and a relevant scientific question is whether there are health effects following from this. Although this question has received relatively little attention in dietary fats and health research, there are a number of good controlled human intervention studies that have addressed it.

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