Fat-soluble Vitamins Xxxvi. the Carotene and Vitamin a Content of Butter*

As one would expect from its general dietary importance, butter has frequently been assayed biologically for its total vitamin A activity. The published results of such assays, however, vary widely, not only because of variations in butter itself, but because of variations in the method of assay, in the met,hod of interpreting data, and in t,he method of expressing result’s. Sherman and Smith (1) for example state, “Butter appears to contain about 30 to 50 units of vitamin A per gram, ranking in richness, weight, for weight, with egg yolk and fresh spinach.” Fraps and Traichler (2) find similar variations and report that butter from cows on normal diets ranges from 17 to 50 Sherman units per gm. Crawford, Perry, and Zilva (3) report the minimal daily dose of summer butter necessary to maintain growth equivalent to that produced by an excess of cod liver oil at approximately 0.1 gm. Vitamin A activity in butter fat’ is due to the presence of two different chemical entities, viz. carotene and vitamin A. The presence of carotene was first demonstrated by Palmer and Eckles (4) who used solubility reactions, the phase test, and the position of absorption bands in the spectrum as criteria. For t.he presence of vitamin A itself, evidence from various sources has been available. Stephenson (5) showed that butter fat decolorized with charcoal retained its biological activity. Morton and Heilbron (6) showed the presence of an absorption band at 328 rnp, which