Chemical Properties of Fats and Oils

General Properties of Fats and Oils.—Fats differ from oils simply in their physical properties, the fats being solid at ordinary temperatures while the oils are liquid. They both have exactly the same general character as regards their chemical composition and constitution, as we have above discussed. The acids which are present as glycerol esters are the mono-basic acids of the saturated and the unsaturated series. As we have stated, the fats and oils are complex mixtures of several esters, in some cases as many as eight or ten and their physical and chemical characters will depend, therefore, upon the characters of the different esters present and the proportions in which these occur. 

The fats and oils obtained from various sources differ from one another in the proportion of the several esters present in each. This difference in composition results in a difference in physical properties, such as specific gravity, viscosity, index of refraction, and melting point. All the fats and vegetable oils are soluble in ether, however,—a fact made use of in the analysis of foods to separate fats from the other constituents of food-products. As the physical properties of a fat or an oil obtained from a definite source are more or less constant, the determination of these properties is of value in the analysis of such substances. The chemical analysis of fats and oils is based upon determinations of the proportion of unsaturated compounds present, of the relation between the acids of low and high molecular weight obtained on hydrolysis, and of the proportion of substances which do not undergo hydrolysis. This statement will be made clearer by a brief consideration of a few of the more important methods employed in the analysis of fats and oils. 

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. 

Carbohydrate-based replacements rely on a viscosity increase and smooth gel-like textures to simulate the properties of fats and oils. These substitutes include gums, hydrophilic hydrocolloids that increase product viscosity and improve emulsion stability polydextrose, a polymer of dextrose with small amounts of sorbitol and citric acid made by Pfizer Chemical Division, New York and a variety of com, tapioca and potato starch maltodextrins made by various starch processors. Neither the protein- nor the carbohydrate-based replacements can be used as frying or dry coating oils. 

Although soaps have many physical properties in common with the broader class of surfactants, they also have several distinguishing factors. First, soaps are most often derived direcdy from natural sources of fats and oils (see Fats and fatty oils). Fats and oils are triglycerides, ie, molecules comprised of a glycerol backbone and three ester-linked fatty oils. Other synthetic surfactants may use fats and oils or petrochemicals as initial building blocks, but generally require additional chemical manipulations such as sulfonation, esterification, sulfation, and amidation. 

The interesterification of fats and oils is the only way to create new hybrid products with new physical, and especially new rheological properties. Chemical interesterification is well known, but has no position or chain specificity, and is not very clean. With lipases in micro-aqueous media, the exchange of acyl groups between the different triglycerides may be oriented, and designed according to the specificity of the enzyme. 

Based on its ability to enhance solvating power by increasing fluid density, supercritical fluid extraction offers an attractive alternative for fractionation of fats and oils. It works by the phenomena of selective distillation and simultaneous extraction, as has been shown by many researchers [3-5]. While the use of supercritical fluids in the extraction of numerous biomaterials has been reported, its commercialization has been limited to the decaffeination of coffee and tea and to the extraction of flavors from hops and spices. The chemical complexity of most food ingredients and their tendency to react and degrade at elevated temperatures, emphasize the difficulties of supercritical solvent selection. Carbon dioxide is the preferred supercritical solvent (its properties have previously been cited [6]). 

The use of renewable resources, especially of fats and oils, as feedstocks leads to products that are interesting in an economical as well as a technical way [1]. By the introduction of branching in the fatty acid carbon chain, products with special physical and chemical properties can be synthesized. 

Interesterification. This reaction is of industrial importance (cf. 14.4.3) since it can change the physical properties of fats or oils or their mixtures without altering the chemical structure of the fatty acids. Both intra- and inter-molecular acyl residue exchanges occur in the reaction until an equilibrium is reached which depends on the structure and composition of the TG molecules. The usual catalyst for interesterification is Na-methylate. 

Waste water rules have pH limits, a common range being between 6 and 10. There are also limits for fats and oils, solvents, heavy metals, and a variety of other compounds and ions. The fact that a compound with possible toxic or otherwise undesirable properties is not on the list does not mean it is permissible. Such a matter should be discussed with the proper authorities. The discharged water may also have to pass a test for toxicity to aquatic animals. As one frustrated manager of a chemical plant put it We can no longer put anything but pure tap water into the sewer Of course, it is not really that bad, but some of the requirements often come as a surprise. 

Ultrasonically assisted extraction is also widely used for the isolation of effective medical components and bioactive principles from plant material [195]. The most common application of low-intensity ultrasound is as an analytical technique for providing information about the physico-chemical properties of foods, such as in the analysis of edible fats and oils (oil composition, oil content, droplet size of emulsions, and solid fat content) [171,218]. Ultrasonic techniques are also used for fluids characterisation [219]. 

The physical and chemical properties of individual oils and fats are determined by the nature and proportions of fatty acids that enter into the triglycerides composition. Animal and dairy fat like plant oils are dominated by triacylglycerols, with steroids present as minor components, cholesterol and its esters being the most significant. The triacylglycerols of animal fats differ from plant oils since they contain more of the saturated fatty acids and consequently are solid at room temperature. 

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