The Structure of Fats and Oils

The fatty acids are important building blocks for more complex lipids. 1 turn to these in this chapter, including the role of fats and oils as energy storehouses and that for other complex lipids in the structure and properties of biological membranes. 

A fat is a solid (at room temperature) triester of glycerin (glycerol) with fatty acids (long-chain carboxylic acids). An oil is similar to a fat however, an oil is a liquid at room temperature. The general structure of fats and oils appears in Figure 16-27. 

Antioxidants have to form stable low-energy free radicals that will not further propagate the oxidation of fats and oils. From this point of view, the most convenient compounds are the phenolic compounds, which structure allows them to form low-energy radicals through stable resonance hybrids, as follows ... 

Solid Fat Index. This analysis has become the most important criterion for the melting behavior and crystalline structure of fats and oils products. It determines the proportion of solid and liquid materials at a given temperature. The solid fat index (SFI) analysis is an empirical measure of the solid fat content. It is calculated from the specific volume at various temperatures using a dilatometric scale graduated in units of milliliters times 1000. Values for the solid contents are usually determined at 50°F, 70°F, 80°F, 92°F, and 104°F or 10°C, 21.1°C, 26.7°C, 33.3°C, and 40°C. Unlike the tropical oils, cottonseed and the other oleic- and lino-leic-classification oils do not contain any significant quantity of triglycerides made up of two or three saturated fatty acids therefore, the solid fat index at the lowest temperature usually measured would have minimal values. Natural cottonseed oil can have a solid fat index content at 50°F or 10°C but not at the higher temperature measurements. 

After immobilization, one can also notice a shift toward higher optimum temperatures. As immobilization provides a rigid external backbone for the lipase molecules, the effect of higher temperatures in breaking the interactions that are responsible for the catalytically active structure becomes less prominent, and so temperature optimum is expected to increase. Immobilization also affixes the enzyme in one conformation, which reduces the susceptibility of the enzyme to denamration by heat. Immobilized lipases, such as those from Mucor miehei and Candida antarctica (34), show good thermal stability at temperatures required to process most fats and oils and are therefore most appropriate for the biomodification of fats and oils. 

Another application is in the manufacture of fats and oils containing nutritionally important PUFAs, such as EPA and DHA. For example, various vegetable and marine oils have been enriched with EPA and DHA using enzyme-catalyzed reactions (35, 51, 52). Use of this technique to produce structured lipids with MCEAs and PUEAs located specifically in either the sn-2 or sn-l,3 positions of the TAGs has been described. Enzymatic processes are particularly suitable for the production and modihcation of lipids containing PUFAs, because these unstable fatty acids are susceptible to damage under the more severe conditions used for chemical processing. 

Saccharide-based fat mimetics differ strongly from fats and oils. Generally they absorb a substantial amount of water and are therefore not suitable for frying. As they can carry only water-soluble flavors, they lack the flavor of fats and oils. Inulin and starch hydrolysates (dextrose equivalent 2) are striking examples of a fat mimetic. The fat substitution is based on its ability to stabilize water into a creamy structure that has a fat-like mouth feel (Blomsma, 1997). 

Moisture and hydroxyl number are important parameters, which are determined by measuring either the first overtone at 6890 cm or the combination band at 5180 cm . A few details about chemical structure are accessible by interpretation of these bands. Changes in hydrogen bonding lead to changes in the band shape and band location. Difference spectra or second derivatives must be calculated in order to detect minor chemical interactions of OH with other molecular species in the sample. The number of double bonds is another important parameter to describe the properties of fats and oils, e. g. their degree of unsaturation. 

Christie (1987) discussed various functions of lipids as follow their involvement in disturbances of lipid metabolism associated with specific lipid disorders accumulation of various neutral, complex, and conjugated lipids in coronary artery and heart disease the role of lipids in nutrition, disease, and human welfare the importance of fats and oils as agricultural products and as major items in international trade the role of fats as a major dietary component and supplier of calories for humans in developed countries and the contribution that fats make to the taste and structure of foods. Ando and Saito (1987) contributed a review on TLC and HPTLC lipid analysis of normal and pathological tissues associated with specific lipidoses and gangliosidoses. 

Up to this point, we have simply noted that fatty acids are key components of fats and oils. It is time to move on and consider just what fats and oils actually look like structurally. 1 begin that task in the next chapter. 

While the analysis of the composition products from the thermal and oxidative treatment of fats and oils has been widely studied, systematic studies concerning separation, determination, and elucidation of the chemical structure of the higher-molecular-weight materials such as dimers and... 

Selected analytical methods, adopted by the American Oil Chemists Society (AOCS)22 for characterizing the composition, structure, physical properties, and stability of fats and oils, are summarized below. Prescribed equipment must be used and... 

Draw the structures of fats, oils, steroids and other lipids. 

Here you find the pastes. Hazelnut paste is a dispersion of particles in a thick emulsion of two liquids, as is peanut butter. Jam is thickened by natural polymers. Soft cheese, butter and margarine are in the refrigerator these are complicated structures of fat crystals, oil, water and many other components. All these pastes have a yield stress that is low enough to let them be spread by a knife, but not so low that they run off bread. Users do find the cold butter a bit stiff and the jam a bit thin. As a developer you might want to improve these things. Bread - a solid foam - is a surprising structure when looked at it closely. Fresh bread is often too soft to cut easily. 

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. 

Analytical methods for measuring hydroperoxides in fats and oils can be classified as those determining the total amount of hydroperoxides and those based on chromatographic techniques giving detailed information on the structure and the amount of specific hydroperoxides present in a certain oil sample (8). The PV represents the total hydroperoxide content and is one of the most common quality indicators of fats and oils during production and storage (9, 18). A number of methods have been developed for determination of PV, among which the iodometric titration, ferric ion complex measurement spectrophotometry, and infrared spectroscopy are most frequently used (19). 

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) ... 

The term morphology is used to denote the general relation of the physical behavior and performance of fats and oils to their crystal structure and the molecular configuration of their triglyceride components (7). 

A fused multiple-ring system is the structural framework for steroids. Cholesterol is the nonpolar, nonsaponifiable progenitor of the metabolic and gonadal hormones such as cortisol, testosterone and estrogen as well as the bile acids used for the intestinal absorption of fats and oils. Many toxins fit into this lipid subclass. 

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