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Wise selection and use of fats and oils is important from the standpoint of nutrition and weight control as well as food qual- ity. There are numerous fats and oils from which to choose. Lard and butter are familiar animal fats, while margarines, shortenings, salad oils, and cooking sprays are produced com- mercially from several plant sources, including corn, soybeans, safflower, cottonseed, sunflower, palm, and olives.

In many areas of food preparation, fats are used to enhance palatability by modifying texture, color, and flavor and by promoting tenderness. Oils and fats are used for frying foods, too. Butter and margarine are used for spreads and some- times in cakes and cookies. Frying is most satisfactory when salad oils are used, but butter or margarine can be used if frying is to be brief. Salad oils are well suited to making salad dress- ings, with olive oil being a favorite choice for some. For most baked products, shortenings are particularly suitable, although some people may prefer lard for making pastry. Specific baked products may be made using oil; chiffon cakes require oil as the lipid, and muffins can be made with oil rather than melted fat, if desired.

Refrigerator storage extends the shelf life of fats and oils, although shortening and salad oils usually can be stored at room temperature for weeks without becoming rancid. Butter, margarine, and lard should be stored in the refrigerator to retard the development of rancidity unless they are to be used promptly.

Fats are composed of glycerol and fatty acids (usually three fatty acids) in each molecule. The melting point of fats is determined by the number of carbon atoms and the amount of unsaturation in the fatty acids. To prepare fats and oils for the commercial market, the fats are rendered or extracted from their animal or plant sources, after which they are refined and sometimes hydrogenated to convert some oils into solid fats.

Blending and tempering are done to achieve the desired mix of fats and oils to achieve a fat that will be quite stable in the beta prime (b´) crystal form. Oils are winterized to remove crystals of fat that form at refrigerator temperatures.

When fats are used to tenderize baked products, their shortening value is of importance, for this determines how much protection from water a particular fat will afford gluten during mixing. Fats with short chain fatty acids and polyun- saturated fatty acids will spread readily to give good coverage. Monoglycerides and fatty acids with at least one double bond will help to block water from gluten by collecting at the inter- face between the fat and water.

Frying—either shallow-fat or deep-fat frying—causes some breakdown of fats. Careful temperature control aids in producing a high-quality fried product with a minimum of fat clinging to it. Extended heating of fat during frying causes fatty acids to split from glycerol; the free glycerol then breaks down to acrolein. The fatty acids polymerize as heating continues, causing increased viscosity of the oil. The smoke point drops as these changes take place.

Rancidity develops as a result of oxidation or of hydro- lysis during extended storage of fats. Oxidative rancidity can be catalyzed by lipoxidases and is evidenced by an increase in the peroxide number due to the loss of hydrogen at double bonds and the uptake of oxygen. Metals and oxygen in the presence of stored fats promote oxidative rancidity, while anti- oxidants retard this change by reacting readily with oxygen that may be present. Hydrolytic rancidity, the splitting off of fatty acids, results in an increasing level of free fatty acids as ran- cidity develops. The presence of water promotes this reaction, but lipases can catalyze hydrolytic rancidity even in dehydrated foods. Heat inactivates lipases.

1. Make an inventory of the various types of fats and oils

available in a supermarket. How do the ingredients com- pare among (a) brands and (b) types of products? Compare the price per pound of each item.

2. Using the same recipe for each product, prepare pastry

using each of the following fats: shortening, butter, stick margarine, lard, and salad oil. Compare the ease of prepa- ration and the palatability characteristics of each pastry. (Continued)

compound in meat) can catalyze oxidative reactions in the fats of meat even during frozen storage. Lipoxidases are enzymes in vegetables capable of catalyzing oxidative ran- cidity. However, freezing or heat will inactivate lipoxidases. Hydrolytic Rancidity

Hydrolytic rancidity occurs when free fatty acids are split from fat molecules as a result of the action of lipases (enzymes catalyzing the breakdown of fats) during

storage. It is determined by measuring the level of free fatty acids in the fat.

Cold temperatures retard development of hydrolytic rancidity, but even frozen storage does not halt this grad- ual deterioration of quality. Flavor changes are particularly objectionable when hydrolytic rancidity results in free fatty acids with 12 or fewer carbon atoms. Fortunately, heat is effective in inactivating lipases.

fats and oils | chapter eight

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3. What factors influence the fluidity of a fat?

4. Why is it important that fat crystals be in the b´ form when

fats are used for making cakes? Does their type of fat crystal have significance if fats are to be used for frying?

5. What changes occur in a fat during prolonged heating?

6. In what ways do fats become rancid? How can use and

storage practices help to delay the onset of rancidity?

7. What fats are the most effective tenderizing agents? Why? 8. What fat or oil would you recommend for deep-fat frying

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