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.

Chemistry

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.[1] 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.[2]

An example of interesterification: A triglyceride with two PUFA (linolenic acid) residues and a saturated one undergo interesterification toward two molecules containing one PUFA residue each.

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.[1]

Health effects

Hypotheses

In most vegetable dietary fats, palmitic (C16:0) and stearic acids (C18:0) mainly occupy the 1- and 3-positions of the triacylglycerol molecule, whereas an unsaturated fatty acid such as oleic acid or linoleic acid (18:2 cis,cis-9,12) 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.

In studies addressing the health effects of interesterification as such, a diet high in interesterified fat should be compared with a diet high in a noninteresterified fat with the same fatty acid composition. If the two diets show similar changes in the resulting blood lipid profiles (i.e. not different from each other), this indicates interesterification has no effect on metabolism or biological effects. Conversely, effects of interesterification cannot be properly addressed if the interesterified fat and the noninteresterified fat being compared have different fatty acid compositions.

Individual Studies

Zock et al.[3] compared the effects of an IE test fat with 40% C16:0 on the 2-position with a noninteresterified test fat with only 6.5% C16:0 on the 2-position in a 3-week diet study. Despite the very high intakes and the marked difference in positional distribution, no statistically significant effects on fasting blood lipids were observed in the group as a whole. Nestel et al.[4] examined the effects of an IE fat blend with 25% C16:0 on the 2-position with a native fat blend with only 9% C16:0 on the 2-position. Again, despite a high intake level and the clear difference in positional distribution of the fats fed, no effects were observed on fasting blood lipids. Meijer and Weststrate[5] examined the effects of interesterification, using a ‘real’ hardstock as applied in foods. The control was the same fat blend with a similar fatty acid composition, but not interesterified. The IE fat blend contained more C16:0 on the 2-position (18%) than the control blend (7%). None of the fasting levels of blood lipids measured after 3 weeks showed any change related to treatment of the fat blend. Fasting glucose level was also not affected.

In 1970, Grande et al.[6] used interesterification to prepare a blend of fats and oils mimicking the fatty acid composition of cocoa butter. No difference between the interesterified fat blend and cocoa butter was observed in levels of total cholesterol in fasting blood.

Recently, in a study funded by the Malaysian Palm Oil Board, Sundram et al.[7] compared the effects of three types of fat: native palm olein, a blend with partially hydrogenated soybean oil and an interesterified mixture of oils. They concluded both the IE blend and the partially hydrogenated fat blend increased the fasting LDL/HDL-cholesterol ratio, indicating an adverse effect on CVD risk. Sundram et al. also found that fasting plasma glucose levels were higher after 4 weeks on the interesterified fat than after the other diets. For the postprandial study the glucose incremental area under the curve (IAUC) following the IE meal was 40% greater than after either other meal (p<0.001), and was linked to relatively depressed insulin and C-peptide (p<0.05). As was pointed out in a letter to the Editor by Destaillats et al.,[8] a major limitation of the Sundram study is that the diets differed in overall fatty acid composition. The interesterified fat had 30% more saturated and 57% less monounsaturated fatty acids than the untreated palm olein. The direction of the effects on blood lipids are in line with what can be predicted based on these differences in fatty acid content between the study diets (Mensink 2003).[9]

Another recent study by Berry et al.[10] compared shea butter (3% C18:0 on the 2-position) and interesterified shea butter (23% C18:0 on the 2-position), while keeping overall fatty acid composition of the diets constant. This study found no effects of interesterification on fasting levels of blood lipids, glucose and insulin. This is line with a number of other human intervention studies.[11][12][13][14]

Christophe et al. have studied the effect of interesterification of butter oil. In a small pilot study,[15] they observed an 11% lower blood total cholesterol level after interesterification. However, in a larger, better designed study[16] the same authors could not reproduce the cholesterol-lowering effects.

References

  1. 1 2 Institute of Shortenings and Edible oils (2006). "Food Fats and oils" (PDF). Retrieved 2009-02-19.
  2. ↑ Kellens, Marc (2000). "Interesterification Process Conditions" (PDF). Retrieved 2007-01-29.
  3. ↑ Zock PJ, de Vries JHM, de Fouw NJ, Katan MB (1995), "Positional distribution of fatty acids in dietary triglycerides: effects on fasting blood lipoprotein concentrations in humans." (PDF), Am J Clin Nutr 61: 48–551
  4. ↑ Nestel PJ, Noakes M, Belling GB, et al. (1995), "Effect on plasma lipids of interesterifying a mix of edible oils." (PDF), Am J Clin Nutr 62: 950–55
  5. ↑ Meijer GW, Weststrate JA (1997), "Interesterification of fats in margarine: effect on blood lipids, blood enzymes and hemostasis parameters." (PDF), Eur J Clin Nutr 51: 527–34
  6. ↑ Grande F, Anderson JT, Keys A. (1970), "Comparison of effects of palmitic and stearic acids in the diet on serum cholesterol in man." (PDF), Am J Clin Nutr 23 (9): 1184–93
  7. ↑ Sundram K, Karupaiah T, Hayes K. (2007). "Stearic acid-rich interesterified fat and trans-rich fat raise the LDL/HDL ratio and plasma glucose relative to palm olein in humans" (PDF). Nutr Metab 4: 3. doi:10.1186/1743-7075-4-3. PMC 1783656. PMID 17224066. Retrieved 2007-01-19.
  8. ↑ Destaillats F, Moulin J, Bezelgues J-B (2007), "Letter to the editor: healthy alternatives to trans fats", Nutr and Metab 4: 10
  9. ↑ Mensink RP, Zock, PL, kester AD, Katan MB. (2003), "Effects of dietary fatty acids and carbohydrates on the ratio of serum total to HDL cholesterol and on serum lipids and apolipoproteins: a meta-analysis of 60 controlled trials." (PDF), Am J Clin Nutr 77 (5): 1146–1155
  10. ↑ Berry SEE, Miller GJ, Sanders TAB. (2007), "The solid fat content of stearic acid-rich fats determines their postprandial effects." (PDF), Am J Clin Nutr 85: 1486–94
  11. ↑ Zampelas A, Williams CM, Morgan LM, et al. (1994), "The effect of triacylglycerol fatty acids positional distribution on postprandial plasma metabolite and hormone responses in normal adult men.", Brit J Nutr 71: 401–10
  12. ↑ Yli-Jokipii K, Kallio H, Schwab U, et al. (2001), "Effects of palm oil and transesterified palm oil on chylomicron and VLDL triacylglycerol structures and postprandial lipid response." (PDF), J Lip Res 42: 1618–25
  13. ↑ Berry SEE, Woodward R, Yeoh C, Miller GJ, Sanders TAB. (2007), "Effect of interesterification of palmitic-acid rich tryacylglycerol on postprandial lipid and factor VII response", Lipids 42: 315–323
  14. ↑ Summers LK, Fielding BA, Herd SL, et al. (1999), "Use of structured triacylglycerols containing predominantly stearic and oleic acids to probe early events in metabolic processing of dietary fat" (PDF), J Lip Res 40: 1890–98
  15. ↑ Christophe A, Matthys F, Geers R, Verdonk G. (1978), "Nutritional studies with randomised butter. Cholesterolemic effects of butter oil and randomised butter oil in man.", Arch Intern Biophys Biochim 86: 413–15
  16. ↑ Christophe AB, De Greyt WF, Delanghe JR, Huyghebaert AD. (2000), "Substituting enzymically interesterified butter for native butter has no effect on lipemia or lipoproteinemia in man", Annals of Nutr and Metab 44: 61–67

See also

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