Iodine number of fats and oils

Kalbus, G. E. Lieu, V. T. Dietary fat and Health An Experiment on the Determination of Iodine Number of fats and Oils by Goulometric Titration, /. Chem. Educ 1991, 68, 64—65. 

The iodine number of fats and oils provides a quantitative measurement of the degree of unsaturation. A solution containing a 100% excess of IGl is added to the sample, reacting across the double-bonded sites of unsaturation. The excess IGl is converted to I2 by adding KI. The resulting I2 is reacted with a known excess of Na2S203. To complete the analysis the excess 8203 is back titrated with coulometrically generated I2. 

Development of the sensor for determining iodine number of fats and oils... 

No practical apphcations are given in this area to cover food analysis, although the reader is referred to the References section, "additional recent references" portion, for some suggestions. The paper by Kalbus and Lieu represents, for example, a laboratory experiment in the coulometric titration determination of the iodine number of fats and oils. For a practical experiment the following determination of arsenic by coulometric titration is suggested. It is of interest since it presents to alternatives in the final estimation procedure. 

G. E. Kalbus and Van T. Lieu, Dietery Fat and Health An experiment on the determination of iodine number of fats and oils by coulometric titration, J. Chem. Educ. 68 (1), 64-5 (1991). 

USE Has been proposed for use in the determination of iodine numbers of fats and oils. Used as water disinfectant. 

Apart from acid-base titrations various addition-, substitution- and redox-reactions have been found to be of analytical interest. Iodine numbers of fats and essential oils may be determined i and bromine may be used to titrate organic compounds which can form bromoderivatives i. For the titration of phenol with bromine the addition of sodium acetate has been recommended. Redox reagents are in acetic acid chromium(VI) oxide, sodium permanganate, bromine, titanium(III) chloride and chromium(II) saltsi32,i33 xhe titrations are usually carried out in perchloric acid solutions and in an inert atmosphere but traces of water are tolerable. 

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. 

Catalytical studies of synthesized products were tested according to the Hanus Method [18]. Since Triglycerides (fats and oils) are esters of glycerol with three fatty acids. These long chain fatty acids may contain one or more double bonds. With no double bonds, the fatty acid is termed saturated (with hydrogen), and with double bonds, it is termed unsaturated. The iodine number is an indication of the degree of unsaturation of the oil (Scheme 14.4). 

Iodine number as well as melting point is one of the most important factors for quality control of processed fats and oils. However, a time-consuming chemical analysis is generally used for determining iodine number which sometimes stops production. In order to overcome this problem, an on-line NIR sensor has been developed [10]. Transmittance spectra of many kinds of oils were measured in the wavelength region from 1100 nm to 2500 nm to make a calibration equation. 

TABLE 4.12 Iodine (IN) and Saponification Numbers (SN) of Various Edible Fats and Oils... 

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. 

Addition of (SCN)2 to unsaturated acids has a place in the analysis of fats and drying oils. Whereas iodine adds to all C=C bonds, (SCN)2 is only partially added. From the differences between iodine numbers and thiocyanate numbers (see page 114) conclusions can be drawn about, e.g., the composition of fatty acid mixtures containing oleic, linoleic, and linolenic acid. For details of the technique see Kaufmann.785... 

H. Schlenk and Holman (1950) described the separation of urea inclusion compounds, of increasing degrees of unsaturation, by the fractional precipitation of a mixture of fatty acids with methanol solutions of urea. Reiser (1950b), in studies of fat absorption, employed a similar procedure for the preparation of conjugated linoleic acid. Swern and Parker (1953) prepared linoleic acid of 85% to 95% purity from corn oil, in a 72 % to 50 % yield, and 87 % to 89 % pure linolenic acid, in a yield of 71% to 55%, from perilla oil. Achaya et al. (1954b) obtained linoleic acid with an iodine number of 172 to 175 (theory 181.4) in a single operation from safflowerseed fatty acids. 

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