Iodine value of fats and oils

Iodine monochloride [7790-99-0] ICl, mol wt 162.38, 78.16% I, is a black crystalline soHd or a reddish brown Hquid. SoHd ICl exists ia two crystalline modifications the a-form, as stable mby-red needles, d = 3.86 g/mL and mp 27.3°C and as metastable brownish red platelets, d = 3.66 g/mL, mp 13.9°C and bp 100°C (dec). Iodine monochloride is used as a halogenation catalyst and as an analytical reagent (Wij s solution) to determine iodine values of fats and oils (see Fats and fatty oils). ICl is prepared by direct reaction of iodine and Hquid chlorine. Aqueous solutions ate obtained by treating a suspension of iodine ia moderately strong hydrochloric acid with chlorine gas or iodic acid (118,119). 

American Oil Chemists Society. 1993b. AOCS Official Method Cd 125. Iodine Value of Fats and Oils—Wijs Method. Champaign, 111. 

Iodine Value of Fats and Oils—Cyclohexane Method (IV) (Cd lb-87) measures the unsaturation of fats and oils in terms of centigrams of iodine absorbed per gram of sample. The method is applicable to all normal fats that do not contain conjugated double bonds. It often is used to estimate the degree of hydrogenation of oils. 

Iodine monochloride. Mol. wt. 162.38, m.p. 14°, 27° b.p. 97°. Suppliers Alfa, E, F, KK, MCB. A solution of iodine monochloride in acetic acid (Wijs solution) is used to determine iodine values of fats and oils. 

Iodine monochloride is used to estimate the iodine values of fats and oils and as a topical anti-infective (Merck 1996). 

American Oil Chemists Society, Iodine value of fats and oils. Official Method Cd 1-25. 2211 West Bradley Ave., Champaign, IL 61826. 

Infrared spectra of fats and oils are similar regardless of their composition. The principal absorption seen is the carbonyl stretching peak which is virtually identical for all triglyceride oils. The most common appHcation of infrared spectroscopy is the determination of trans fatty acids occurring in a partially hydrogenated fat (58,59). Absorption at 965 - 975 cm is unique to the trans functionaHty. Near infrared spectroscopy has been utilized for simultaneous quantitation of fat, protein, and moisture in grain samples (60). The technique has also been reported to be useful for instmmental determination of iodine value (61). 

Tlie drying property of fats and oils is related to their degree of unsauiraliou, and hence, to iodine values. 

The final element of the hydrophobe which can be manipulated is the cis/trans ratio of the unsaturated hydrocarbon fragments. Natural tallow has a cis/trans ratio of about 8-20 [39]. Metal catalyzed hydrogenation of fats and oils results in the reduction of the cis/trans ratio and an increase in the melting point of the oil when compared to a material of similar iodine value and a higher cis/trans ratio [40]. For concentrated fabric softeners, high cis/trans ratios are preferred to reduce the likelihood of gel formation in the final product or during processing [24, 40-42]. 

The density of liquid oils is dependent on their fatty acid composition, minor components, and temperature. An equation taking these into account was developed by Pantzaris (27) using iodine value, saponification value, and temperature. The density of liquid oils is in the range of 0.909-0.921 and for solid fats varies between 0.858 and 0.893. The lower values are for more solid fats such as lard and tallow. In a similar way, the viscosity of various vegetable oils depends on their fatty acids. Generalized methods have been developed that allow calculation of density and viscosity of different oils. Coupland and McClements (28) and Fisher (29) have related viscosity and density, refraction, surface tension, and other physical properties. Viscosity of fats and oils also depends on the temperature. 

Melon, Cucumis melo, is a member of the Cucurbitaceae family and grows best in tropical regions. The pulp of the fruit has pleasant flavor and taste, and the seeds are generally treated as waste however, medicinal effects have been reported for the seeds (24, 25). Hexane-extracted seed oil of Cucumis melo hybrid AF-522 was determined to contain 64 g of linoleic acid per 100 g of total fatty acids (Table 4) (24). Significant amounts of oleic, palmitic, and stearic acids were also detected in the melon seed oil. The specific gravity (28°C), refractive index (28°C), and iodine value of the seed oil were 0.9000, 1.4820, and 112, respectively, under the experimental conditions (24). Earlier in 1986, Lazos (25) extracted the oil from Cucumis melo seeds and examined its physicochemical properties (25). Linoleic acid was the primary fatty acid and accounted for 64.6% of the total fat (w/w), along with 20.1% oleic acid, and 14.7% total saturated fatty acids (Table 4). Iodine value and refractive index (40°) of the seed oil were 124.5 and 1.4662, respectively. 

TABLE 7. Titer and Iodine Values of Fat from Various Livestock Species Including Menhaden Fish Oil. 

Bromine or Iodine Value, Hiibl-Wijs.—Another important chemical constant of fats and oils is one which depends upon the nature of the acid present as an ester. The acids present as esters in fats and oils are of two different classes, viz., those belonging to the saturated series and those belonging to the unsaturated series. We have shown that the distinguishing reaction of these two series of compounds, both in the hydrocarbons and the various classes of their derivatives, is, that unsaturated compounds take up halogen directly with the formation of addition products. It has been found that the glycerol esters of the unsaturated acids form addition products readily, under certain conditions. If, therefore, a fat takes up bromine or iodine directly an ester of an unsaturated acid must be present. The determination of the... 

The average degree of unsaturation of oils and fats is determined by the iodine value the average molecular weight is measured by the saponification number. The FA compositions of oils and fats are determined by gas liquid chromatography analysis of methyl esters of FAs after methanolysis of fats and oils. 

Apart from specifications as to origin, e.g. palm kernel oil, fats are normally supplied on the basis of established parameters. One of these is the iodine value. This reflects the tendency of iodine to react with double bonds. Thus, the higher the iodine value the more saturated the fat is. An iodine value of 86 would approximate to one double bond per chain, while an iodine value of 172 approximates to two double bonds per chain. Another parameter is the peroxide value. This attempts to measure the susceptibility of the fat or oil to free radical oxidation. The test is applied on a freshly produced oil and measures the hydroperoxides present. These hydroperoxides are the first stage of the oxidation process. Obviously, this test would not give reliable results if applied on a stale sample. 

Diacetyl Tartaric Acid Esters of Mono- and Diglycerides occur over a range in appearance from sticky, viscous liquids through a fatlike consistency to a waxy solid, depending on the iodine value of the oils or fats used in their manufacture. They are the reaction product of partial glycerides of edible oils, fats, or fat-forming fatty acids with diacetyl tartaric anhydride. The diacetyl tartaroyl esters are miscible in all proportions with oils and fats. They are soluble in most common fat solvents, in methanol, in acetone, and in ethyl acetate, but are insoluble in other alcohols, in acetic acid, and in water. They are dispersible in water and resistant to hydrolysis for moderate periods of time. The pH of a 3% dispersion in water is between 2 and 3. 

Other parameters that are indirectly related to the composition of edible oils include iodine value and saponification value. The iodine value is a simple chemical constant for a fat or oil. It measures unsaturated or the average number of double bonds in fats and oils. Iodine value is defined as the number of grams of iodine that could be added to 100 g of oil, which is measured with the AOCS Method cd 1-25 (22). Meanwhile, saponification value is a measure of the alkali-reactive groups in fats and oils and is defined as the mg of KOH needed to saponify 1 g of oil. Shorter chain fatty acids give higher saponification values than do longer chain fatty acids. 

The roasted red pepper seed oil contained an extremely high concentration of linoleic acid, approximately 74%, and a high total unsaturated fat level (Table 6) (37). The fatty acid profile was very similar to that of both goldenberry seed (Physalis peruviana L.) and safflower oils (36). The iodine value of roasted red pepper seed oil was determined to be 137-g iodine/lOO-g oil.This shows that there is a high degree of unsaturation in the oil. Oxidative stabilities of the roasted red... 

---