The (blue) 2NaI + starch + Na2S4O6 (colorless)

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Last updated: September 20, 2019

The average degree of unsaturation of alipid is measured by Iodine value.

Thisvalue is expressed as the grams of  iodine absorbed per 100g of  lipid and it is directly proportionalto the degree of unsaturation  andinversely proportional to the melting point (M.P.) of lipid.  The higher  iodine value indicates the presence of  greater  number of C=C double bonds and  high susceptibility of lipid to oxidativerancidity due to high degree of unsaturation. Thestandard IUPAC procedure was used to determine the iodine number (IUPAC, Standard Methods, 1987, 7th edition).

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The iodine value of  mustard oil was determined by “Hanusmethod”. All the samples were weighed and dissolved in a suitableorganic solvent and a known excess of  iodine chloridewas added. The following reaction occurred in this procedures: R-CH=CH-R+ IB excess                     R-CHI-CHBr-R  +   IB remaining The amount of  reacted  IBr were determined by measuring the amount of IBr remaining after the reaction hasgone to completion and the  remaining IBrwere determined by adding excess potassium iodide to the solution to liberateiodine, then  titrating with a sodium thiosulfate(Na2S2O3) solution in the presence of starchto determine the concentration of iodine released: IB remaining+ 2KI                   KBr + KI + I2 I2+ starch + 2Na2S2O3 (blue)            2NaI + starch + Na2S4O6(colorless) Aknown mustard oil sample were treated with iodine bromine (IBr) in glacialacetic acid and unreacted iodine bromine is reacted with potassium iodide whichconverts it to iodine. The iodine concentration is then determined by titrationwith standard sodium thiosulphate.

According to standard procedure,Iodine Value = {(B – S) × Normality of Na2S2O3× 12.69} / weight of sample(gm)(Where, Bis the volume of 0.1 N Na2S2O3 required to titrate the blank(ml), S is the volume of 0.1 N Na2S2O3requiredto titrate the sample (ml), 12.69 is the atomic weight of iodine, N is thenormality of Na2S2O3 andweight of the oil in grams.

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