FLAX STUDIES: III. A REFRACTOMETRIC METHOD FOR THE ESTIMATION OF IODINE VALUE OF RAW LINSEED OIL

Abstract

A rapid refractometric method for the estimation of the iodine value of freshly prepared linseed oil is described. This involves expression of the oil at laboratory temperature from finely ground flaxseed, determining the refractive index at 25 °C. and converting to Wijs iodine value by means of the regression equation expressing the relation between these variables. In a study of cold pressed linseed oils prepared from 339 samples of sound Canadian flaxseed varying in Wijs iodine value from 153 to 202 units, a correlation of 0.980 between refractive index and Wijs iodine value was found which permits the estimation of iodine value with a standard error of prediction of 2.1 units.Ethyl ether extracts obtained by the usual extraction procedure for determining oil content are not recommended, owing to differences in the characteristics of the oil and a lower degree of association between refractive index and iodine value.Since the refractive index of linseed oil and its relation to iodine value are influenced by free fatty acids, oxidation and polymerization, the method is not applicable to commercially prepared oils nor to flaxseed which has heated or become musty.The method is considered sufficiently accurate for surveys of the quality of flaxseed produced in different districts and of new varieties and hybrids submitted by plant breeders. It should also prove of considerable utility to linseed crushers for securing a measure of the intrinsic drying value of their raw material.