Characteristics of Fats and Oils

Fats are food. But apart from their nutritive value they are also used as ingredients to modify other foods. Flaky piecrusts, smooth ice cream, and melt-in-your-mouth chocolates owe their properties to the unique characteristics of fats and oils. 

Oils and fats go through a series of increasingly organized crystal phases upon cooling. This multiple form of crystallization (polymorphism) is an important characteristic of fats and oils because it greatly influences the textural and functional properties of fats and fat-based products. 

Crystallization characteristics of fats and oils were described in the section on polymorphism. The size, abundance, and stability of crystals are important in food processing/food service ingredients and consumer products. Clear salad oils are preferred, and are made by selecting low-melting-point oils that are winterized by chilling to crystalline the highermelting triacylglycerols, which are then removed by filtration. 

Lipids are important macromolecules in food. A food product s nutritional value as well as its flavor, texture, general palatability, and storage stability are affected by lipids. Therefore, both physical and chemical criteria are needed by the food processor to assess or monitor the quality of fats and oils. The basic characteristics of certain food items, such as edible oils, will be dependent upon their source. Variation from these norms can be ascertained before the oils are used in other foodstuffs. In effect, knowledge of the quality of the lipid before shipping the product to market, or use in fabricated foods, is of economic importance to the processor. 

Stearic acid is a long chain SFA present, to varying degrees, in virtually all edible fats and oils. Table IV provides the fatty acid composition of fats and oils commonly consumed by humans. The most abundant food sources of stearic acid in the American diet are beef fat and cocoa butter (chocolate). Cocoa butter is valued by chocolate manufacturers because it remains solid at room temperature but dissolves quickly at body temperature, a unique characteristic of chocolate that is due largely to stearic acid. During the last few decades as cocoa butter prices and supplies have fluctuated, food companies began looking for alternative oils that could provide equivalent amounts of stearic acid in order to retain the desirable physical characteristics. Several... 

When a fat or oil is heated, thermal instability may cause decomposition, and depending on the temperature reached, subsequent combustion of volatile gaseous decomposition products (Mehlenbacher, 1960). The thermal stability of fats and oils is thus essentially a chemical characteristic. However, stability is characterized by measuring certain critical temperatures, the smoke, flash and fire points, at which certain heat-induced changes become apparent. It is appropriate, therefore, to include here methods for measuring these critical points. 

The density of fats and oils is an index of the weight of a measured volume of the material. This property is important not only for designing of equipment but also for the estimation of the solid fat index (SFI). The SFI is related, approximately, to the percentage of solids in a fat at a given temperature. When determined at a number of specified temperatures, it can be especially useful to margarine manufacturers or other processors who need to control the characteristics of their manufactured products by blending. 

The physical state of fats and oils and their crystal structures are important for application of such products. In addition, formulation of products for special applications such as bakery, confectionary, frying, salad dressing, margarines, and spreads requires special characteristics that make the products suitable for such purposes. Thus, each source material will be important for its physical and chemical characteristics and hence suitability as a food component. 

The processing technologies employed for production of fats and oils, and associated components, to make them shelf-stable with acceptable sensory characteristics and flavor as well as secondary processing technologies for production of specihc products are important considerations in this area. Food commodities... 

Adulteration of fats and oils is an old problem. Many older tests involved determination of physical properties such as refractive index, melting point, and viscosity. However, color tests were later used for this purpose. Thus, Baudonin reaction for sesame oil and the Halpben test for cottonseed oil have been noted. In both cases, a compound characteristic to an oil determines the presence of the oil. However, today such detections and quantitations are carried out with GC and HPLC procedures. Thus, cholesterol and phytosterols may be determined by gas chromatography for fingerprinting purposes however, fatty acid analysis might also be used for higher levels of contamination (31). Detailed discussion of issues related to oil authentication and adulteration has taken place (11). 

Refractive Index. The refractive index of fats and oils is an important characteristic because of the ease and speed with which it can be determined precisely, the small amount of sample required, and its relationship to structure. It is useful for source oil identification, for observing progress of reactions rapidly, and for establishing purity. The general relationship between refractive index and the composition of an oil product with minor exceptions are as follows (104) ... 

Refractive Index The refractive index is a characteristic property of fats and oils and may be used as a fast measurement of the advance of a hydrogenation operation. The Codex Ahmentarius (Codex-Stan 210-1999) indicates a refractive index (no) of regular sunflower oil in the range of 1.461-1.468 at 40°C Merrien (9) reports the range 1.474—1.476 at 20°C. 

As was stated, oleic acid occurs as an ester in many common fats and oils. In commoh with other unsaturated acids it possesses the characteristic property of forming addition products with the halogens or halogen acids. This property it imparts to the fats and oils in which it is present as an ester giving another important method for the analysis of these substances. This and the other properties and reactions of oleic acid which are important in connection with the analysis of fats and oils will be considered again when we study these substances. 

Some oil-soluble emulsifiers affect the crystallization process and development of polymorphic forms of fats (4-8). Sucrose fatty acid ester or sucrose polyesters (SPE) and lecithins are well-known food emulsifiers (9,10). The main characteristics of lecithins and SPE useful in food applications are their oil-in-water and water-in-oil emulsifying properties, that result in dispersion with condensed milk and coffee whitener, and prevention of blooming in candy products and chocolate (7,9-11). But there are very few reports about two effects of SPE on the crystallization of fats and oils, i.e., enhancement and inhibition (12,13). 

Sucrose esters with a higher degree of substitution, so-called sucrose polyesters (Fig. 8), have characteristic properties of fats and oils. At the same time they are only partly digestible or even nondigestible by the body s lipases and are not absorbed by the human digestive system [7, 22, 42, 43]. Thus, their use as fat replacers appears predetermined and indeed sucrose polyesters with 6-8 acyl moieties were approved by the US Food and Drug Administration (FDA) in 1996 for certain use as fat replacers [43]. Known brand names are Olestra and Olean . They are used in food applications, e.g., in the preparation of dietary fried snacks [2, 42],... 

Hydroperoxides resulting in fat oxidation do not affect the sensory quality of fats and oils, but their decomposition products produce distinctive odours that depend on the concentration of the secondary products and their composition. These reactions are described in detail in other sections. A certain range of oxidation reactions, both enzymatic and non-enzymatic, is often desirable, because it leads to the formation of characteristic flavour active products in many foods (such as fruits, vegetables and fried foods). 

Filter aids may be applied in one of two ways. The first method involves the use of a precoat filter aid, which can be applied as a thin layer over the filter before the suspension is pumped to the apparatus. A precoat prevents fine suspension particles from becoming so entangled in the filter medium that its resistance becomes exces-sive. In addition it facilitates the removal of filter cake at the end of the filtration cycle. The second application method involves incorporation of a certain amount of the material with the suspension before introducing it to the filter. The addition of filter aids increases the porosity of the sludge, decreases its compressibility, and reduces the resistance of the cake. In some cases the filter aid displays an adsorption action, which results in particle separation of sizes down to 0.1 /i. The adsorption ability of certain filter aids, such as bleached earth and activated charcoals, is manifest by a decoloring of the suspension s liquid phase. This practice is widely used for treating fats and oils. The properties of these additives are determined by the characteristics... 

Lakes are prepared by adsorption or precipitation of a soluble dye on an insoluble substrate (e.g., alumina). They are useful in fatty products that have insufficient moisture to dissolve dyes (coated tablets, cake mixes, hard candies, chewing gum). Lakes are insoluble in most solvents including water, have high opacity, are easily incorporated in dry media, and show higher stability to light and heat. They are effective colorants for candies, pills, fats, and oils. The main characteristics and differences between lakes and dyes are well documented. ... 

Proteins are important food components mainly due to their nutritional and functional value. Dietary proteins provide amino acids and nitrogen necessary for organisms. They also play a major role in determining the sensory and textural characteristics of food products. The functional properties are related to their ability to form viscoelastic networks, bind water, entrap flavors, emulsify fat and oil, and form stable foams [105]. 

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