Fats And Oils In Human Nutrition Pdf

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Nutritional aspects of fats and oils

Oils and fats form an important part of a healthy diet. Structurally they are esters of glycerol with three fatty acids called either triacylglycerols or triglycerides. It is these fatty acids that give the functionality to fats. Chemically, they can be divided into four main types — saturated, cis- monounsaturated, cis -polyunsaturated and trans fatty acids. In very broad terms, saturated fatty acids and trans fatty acids are solid at room temperature while the cis -unsaturates are liquid at room temperature.

The choice of fat used in any given type of food product often comes down to the required functionality. The main aspects of this functionality choice are a melting point and melting profile how the solid fat content changes with temperature , b crystallization characteristics, c storage stability particularly oxidative stability and d nutritional characteristics.

From a product functionality point of view, different groups of food products will have different requirements. Bakery products e. Chocolate needs to be based on cocoa butter from both a legislative and functionality point of view and any fats used to replace cocoa butter need also to conform to legislation and to melt and crystallise in the same way as cocoa butter.

Often, there is no single natural fat, or even combination of naturally occurring fats, that give the exact functional requirements for a given product application and so oils and fats need to undergo some form of processing. There are three main types of oil modification process used in foods. Hydrogenation is a reaction between hydrogen and the carbon-carbon double bonds in an unsaturated fatty acid. It changes the cis -unsaturated fatty acid either to saturated or to trans -unsaturated.

Both saturated fatty acids and trans -unsaturated fatty acids are higher melting than the naturally occurring cis -unsaturated fatty acids so hydrogenation increases the hardness and solid fat content of the fat. Fractionation starts with oils that can be partially liquid and partially solid at a particular temperature palm oil, shea butter and palm kernel oil are oils that are commonly fractionated. The solid and liquid phases are separated and used in different applications.

Unlike hydrogenation, no chemical changes to the fatty acids themselves take place — it is purely a separation process. Interesterification is a process in which the ester linkages between the fatty acid and glycerol are broken and then re-formed usually in a random but predictable conformation.

However, specific enzymes can be used as catalyst to avoid breaking the ester linkage in the central position of the triglyceride molecule and so allow the production of deliberately structured triglycerides. Each of these modification processes allow the formation of fats with different melting, crystallisation and stability functionalities from the starting oils. On top of all this, the oils and fats used should give rise to no adverse health concerns. During the course of the 20 th century, hydrogenation was probably the most commonly used modification process.

However, it produces high levels of trans fatty acids. These have been shown to be adverse to health particularly in terms of their effects on blood cholesterol levels. They increase the detrimental low density lipoprotein LDL cholesterol and decrease the beneficial high density lipoprotein HDL cholesterol giving rise to a greater risk of cardiovascular disease CVD in some individuals.

As a consequence of this, the early years of the 21 st century saw widespread reformulation of many food products and the development of non-hydrogenated alternatives to previously hydrogenated fats. Saturated fatty acids are somewhere in the middle — they increase both the detrimental and the beneficial cholesterol levels but they also do this to varying extents depending on their fatty acid chain length.

Lauric C12 , myristic C14 and, to a slightly lesser extent, palmitic C16 acids show an overall adverse effect on blood cholesterol, whereas stearic acid C18 is considered to be neutral in its effects.

These recommendations are largely based on research carried out some 15 years or more ago and recent research has shown a greater leniency towards saturated fats.

Nevertheless, saturated fats should still be used with some caution. One recent example is the fashion for coconut oil. Gunstone FD. 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. 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. 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. Higher solid fat levels make the dough difficult to mix; lower solid fat levels risk some of the liquid fat exuding from the final biscuit or pastry making it oily to the touch.

Historically, animal fats such as lard and beef tallow were used in many of these applications and, it has to be said, lard makes excellent pastry, largely because of the form in which it crystallises. As with all hydrogenated fats, these two animal fats have now been almost completely removed from bakery products and have largely been replaced by either palm oil Atkinson, or blends of palm oil and its fractions or with oils such as rapeseed oil.

This crystallises around the bubbles formed during the time the bread dough is proving and rising and forms a crystal monolayer around these bubbles Brooker, Because of the high melting point of the fat used it can retain its structure during the early stages of baking and so holds the aerated structure of the bread. Chocolate and chocolate like coatings need to be solid at ambient temperatures but then melt quickly at mouth temperature.

Cocoa butter does this and is obviously the gold standard as far as this is concerned.

Oils and Fats

Fats and oils collectively called lipids constitute a substantial portion of our diets. The remaining portion of fat in our diets is made up of other lipids such as cholesterol and phospholipid. Fatty acids are the building blocks of the majority of these lipids. The advent of hydrogenation to produce such products as margarines has introduced the unnatural trans fatty acids. Due to the concern over fat consumption, the development of fat substitutes for foods is an active area of research. Medium-chain triglycerides have been used as an alternative source of fat energy for those individuals unable to digest normal fats in the diet. These topics are discussed in detail in this chapter.

Oils and fats form an important part of a healthy diet. Structurally they are esters of glycerol with three fatty acids called either triacylglycerols or triglycerides. It is these fatty acids that give the functionality to fats. Chemically, they can be divided into four main types — saturated, cis- monounsaturated, cis -polyunsaturated and trans fatty acids. In very broad terms, saturated fatty acids and trans fatty acids are solid at room temperature while the cis -unsaturates are liquid at room temperature.

Fats and oils are important functional ingredients in human nutrition and a main source of essential fatty acids. 1 Moreover, the crystalline.

The Functions of Fats

Fats are an important part of the diet; they provide the body with energy and with some important vitamins for example, vitamins A and D. They also provide essential fats, which the body is unable to make for itself. However, eating too much fat, or the wrong balance of fats can be unhealthy.

Fats serve useful functions in both the body and the diet. In the body, fat functions as an important depot for energy storage, offers insulation and protection, and plays important roles in regulating and signaling. Large amounts of dietary fat are not required to meet these functions, because most fat molecules can be synthesized by the body from other organic molecules like carbohydrate and protein with the exception of two essential fatty acids. However, fat also plays unique roles in the diet, including increasing the absorption of fat-soluble vitamins and contributing to the flavor and satisfaction of food.

NCBI Bookshelf. Lipids are compounds that are insoluble in water but are soluble in organic solvents such as ether and chloroform. Lipids that are important to our discussion include fats and oils triglycerides or triacyglycerols , fatty acids, phospholipids, and cholesterol. Fats and oils are esters of glycerol and three fatty acids. They are important in the diet as energy sources and as sources of essential fatty acids and fat-soluble vitamins, which tend to associate with fats.

The animal fats used by humans are butter , suet beef fat , lard pork fat , and fish oils. Important vegetable oils include olive oil , peanut groundnut oil , coconut oil, cottonseed oil, sunflower seed oil, soybean oil, safflower oil, rape oil, sesame gingelly oil, mustard oil, red palm oil, and corn oil. Fats and oils provide more calories per gram than any other food , but they contain no protein and few micronutrients. Only butter and the previously mentioned fish-liver oils contain any vitamin A or D, though red palm oil does contain carotene, which is converted to vitamin A in the body.

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5 Response
  1. Akira R.

    Dietary fat has five important functions: (i) as a source of energy;. (ii) for cell structure and membrane functions;. (iii).

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    hashimototorii.org (accessed 1 October ). FAO. Fats and oils in human nutrition; Report of a joint FAO/WHO Expert. Consultation.

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