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This is a preview of subscription content, log in to check access. Food Fats and Oils. The Institute, Washington, DC. Google Scholar. Bailey, A. Coenen, J. Hydrogenation of edible oils and fats. Food Sci. A , — Erickson, D. Handbook of Soy Oil Processing and Utilization. Louis, MO. Gurr, M. Role of Fats in Food and Nutrition. Nevertheless, saturated fats should still be used with some caution. One recent example is the fashion for coconut oil. Gunstone FD.
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Published by Woodhead Publishing, Cambridge. Oils and fats are important nutrients in a healthy diet. Structurally, they are esters of glycerol with three fatty acids. As such, they are scientifically called triacylglycerols but are commonly referred to in the food industry as triglycerides. Although the terms 'oils' and 'fats' are often used interchangeably, they are usually used to distinguish triglycerides in the liquid state at ambient temperatures oils from those in the solid state fats.
They are commonly of vegetable origin e. The fatty acids found in most commonly consumed oils and fats are composed of long carbon and hydrogen chains, typically containing from 8 to 20 carbon atoms, mainly with even numbers of carbon atoms, although animal fats also contain significant levels of odd-chain fatty acids. It is this carboxylic acid group that reacts with the hydroxyl groups on the glycerol molecule to form the ester linkages of the triacylglycerol molecule. Saturated fatty acids are straight chains of carbon atoms consisting of methylene CH2 groups between the end methyl and carboxylic acid groups.
The most common saturated fatty acids are lauric acid C12 , palmitic acid C16 and stearic acid C Shorter chain saturated fatty acids are found in butterfat e. C4, butyric acid and coconut oil e.
C8, caprylic acid, and C10, capric acid. Monounsaturated fatty acids contain a single carbon-carbon double bond in the carbon chain. The most common monounsaturated fatty acid is oleic acid, containing 18 carbon atoms. In oleic acid, the double bond is between carbon atoms 9 and 10 counting from the COOH group. Polyunsaturated fatty acids have more than one double bond in the carbon chain.
It is, of course, possible to count the position of these double bonds from the other end of the chain, the methyl group end. In these two examples, the first double bond to be encountered in linoleic acid is at the sixth carbon atom and, for this reason, linoleic acid is also called an omega-6 polyunsaturate.
In linolenic acid, the first double bond is at the third carbon atom and so linolenic acid is called an omega-3 polyunsaturate. As such, they can gradually be produced and build up in used frying oils. These fatty acids have not been found to have adverse consequences and may, indeed, be positive. Increasing the chain length of a fatty acid increases its melting point - so stearic acid C18 melts at a higher temperature than lauric acid C Different food applications require different melting points and different melting profiles the change in percentage of solid fat with temperature for both processing and sensory functionalities.
The ability to have a range of fats and oils available with different physical characteristics is of fundamental importance to food product developers. However, fatty acids in these different groups and, in some cases, fatty acids within the same group have different nutritional effects, particularly their effects on blood cholesterol levels which, in turn, can impact on cardiovascular disease risk.
This will be considered in more detail later in this document. We refer to saturated fats but this only says that they are naturally occurring fats in which saturated fatty acids predominate. Different food applications require fats with different functionalities and, therefore, different fatty acid compositions.
These different requirements for specific applications will be considered in more detail in a later section.
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Sometimes, the requirements can be completely fulfilled by a naturally occurring fat or a combination of naturally occurring fats. For example, chocolate can be made purely from cocoa butter or, in the case of milk chocolate, from cocoa butter and butterfat. In some applications, though, the portfolio of fats as they occur in nature do not totally fulfil the functional requirements and so the fats need to undergo some kind of processing to obtain the required functionality.
In the presence of a catalyst usually nickel the double bonds in a liquid oil can react with hydrogen in two ways. Either a hydrogen molecule can react with the carbon atoms in an unsaturated bond to convert it into a saturated single bond.
Oils and Fats
This has a higher melting point and so a liquid oil can be converted into a solid fat. Hydrogenation, therefore, converts liquid oils into potentially more functional solid fats and changes the fatty acid composition of the starting mix of oils significantly. In this case a fat is held at a temperature at which it is partially liquid and partially solid. The solid crystals are separated by filtration to give a solid stearin fraction which is higher melting than the starting oil and a liquid olein fraction which is lower melting than the starting oil.
Generally, only fats that melt over a wide temperature range are suitable for fractionation. The most commonly fractionated fats are palm oil, palm kernel oil, butterfat and shea butter, although coconut oil and cocoa butter are also occasionally fractionated. In most cases, the oil is fractionated once to give the two fractions mentioned — stearin and olein. Oils are normally fractionated in one of two ways Gibon, This solution is then chilled to the point that the stearin fraction crystallises out.
The benefits of dry fractionation are that it is cheaper, has no requirements for flameproof processing and gives a very good quality olein. Wet fractionation, on the other hand, is used where the quality of the stearin or, in the case of palm oil, the mid-fraction is of paramount importance. It does, though, require a flameproof plant and good solvent recovery processing, which makes it a significantly more expensive process. Unlike hydrogenation, there are no chemical changes made to the fatty acids in the oil as a result of fractionation, but there will be a concentration of saturated fatty acids in the stearin and of unsaturated fatty acids in the olein.
In this an oil or a blend of oils is held at an elevated temperature in the presence of either a chemical catalyst or, more commonly these days, an enzyme catalyst. Under these conditions, the ester linkages between the glycerol backbone of a triacylglycerol and the fatty acids that are present break and then re-form. During this, the fatty acid groups can move around in the reaction mix so that they do not necessarily re-form the linkage in the place where it was broken. Hence a randomisation of the positions of the fatty acids on the triacylglycerol molecules occurs.
As melting and crystallisation functionalities of fats are dependent on fatty acid position as well as on fatty acid type, the physical characteristics of the end fat are completely different - but predictably so - from that of the starting blend. Interesterification does not alter the overall fatty acid composition, only the positions of the fatty acids on the glycerol backbone.
In a further modification of the interesterification process, some enzyme catalysts have the ability to break only the linkages between the glycerol backbone of the triacylglycerol and those fatty acids in the outside 1- and 3-positions, leaving any fatty acids esterified in the central 2-position alone.
This enables so-called structured triacylglycerols to be produced for specific properties and functionalities. Different food products have different requirements as far as the functionality of the fat they contain is concerned. These requirements can often be condensed down to four basic headings:. Fats used in bakery products, for example biscuits and pastry, need to have a certain level of solid fat present at the temperature at which the dough is mixed in order to give enough structure to hold a light aerated structure and to stop more liquid triglycerides from separating from the baked end product.
This hypothesis says that:. The validity of this hypothesis, which was initially based on work in the s and s carried out by Ancel Keys Andrade et al, , has often been called into question. Over those years it has monitored health and lifestyle factors and the incidence of a wide range of chronic diseases. There is a large body of evidence for the effects of different fatty acids on blood cholesterol levels. Mensink et al carried out a large meta-analysis of 60 controlled trials.