Iodine number determination of milk fat and vegetable fats by refractometry

A refractometric method for the estimation of iodine number of milk fat has been suggested. About 0.2 ml of milk fat was iodinated with ca. 10 ml Wijs iodine reagent for 3 min using mercuric acetate as catalyst. The iodinated fat showed a higher refractive index than the original fat. The changes in refractive indices showed a very high correlation with the iodine values of the fats (T=0.9993). The average of the ratios of change in refractive index to iodine number was 50.7×10⁻⁵, from which the iodine number of milk fat can be calculated. The method can also be applied to vegetable fats. The ratios of change in refractive index to iodine number for the oils of peanut, rapeseed, soybean, niger, sesame, and sunflower were similar, and the average was 45.2×10⁻⁵. The ratio for linseed oil was 38.4×10⁻⁵, and for coconut fat it was similar to that of milk fat.