The Vitamin A Activity of Butter Produced by Guernsey and Ayrshire Cows

The natural color of butter is known to vary with breeds of cows. This color is due almost entirely to carotin. Since carotin is now recognized as a precursor of vitamin A and as such acts biologically as vitamin A, it might seem logical to assume that butter rich in this pigment, might also possess greater vitamin A activity than the paler colored butters. If this were true, butter produced by such breeds as Jersey and Guernsey cows should possess greater vitamin A potency than that produced by Holstein and Ayrshire cows. However, butter does not owe its entire vitamin A activity to carotin. Since Stephenson (1) reported decolorizing butter with charcoal without apparently impairing its vitamin A activity, it must be assumed that vitamin A (per se) is present in butter. This fact was later confirmed by Morton and Heilbron (2) who demonstrated by spectroscopic analyses that both carotin and vitamin A are present in butter. Similar results were reported by Moore (3) who also demonstrated that cows were able to convert carotin into vitamin A. With carotin and vitamin A contributing to the vitamin A activity of butter, the variation in color of butters produced from different breeds may be less significant than generally supposed.