Studies in fish liver oils. Part II. Biological assay of vitamin A in some of the liver oils

Abstract

1. The liver oils of six varieties of fish have been analysed for their Vitamin A content biologically as well as tintometrically. Great variation in the Vitamin A content is observed when the biologically obtained values are compared with those obtained by colorimetric method. Though it is not possible to draw any definite relationship between the yellow colour of the oil and its Vitamin A content, it can be noticed to some extent that a decrease in the percentage of Vitamin A is accompanied by an increase in the red colour of the oil. 2. The ratio I.U./Carr Price Blue Units for the liver oils studied vary from oil to oil indicating that greater discrepancies are likely to be met with if a uniform conversion factor is applied to the Blue values obtained with oils from the livers of different species of fish. It is suggested that as far as possible, whenever a new source of Vitamin A is found it should be subjected to all the three methods of assay before applying any factor to convert the colorimetric or spectrophotometric values into the International Units of Vitamin A. For a rough estimate of Vitamin A in industry a suggestion to take the factor 3 for converting Blue values into the International Units is made. Bomskov factor 4.2 is misleading in the case of liver oils of fish in India.