399. The estimation of vitamin A in butter: A critical study of methods

Abstract

1. The Lovibond Tintometer has been found more reliable than either the Pulfrich Photometer or the Spekker Absorptiometer for the assessment of the blue colour from the Carr-Price test on butterfat unsaponifiable residues.2. Using a Beckman Spectrophotometer, vitamin A in butterfat unsaponifiable residues has been estimated also by the intensity of absorption at 325 mµ. From spectrophotometric readings at this wavelength and at 450 mµ, the irrelevant absorption, due both to carotenoid and non-carotenoid compounds, may be calculated as follows:Corrected density reading at 325 mµ = 9/10 (A – 12/100B),where A = density reading of the unsaponifiable residue in petrol ether at 325 mµ, B = density reading of the same solution at 450 mµ.3. The Morton & Stubbs equation for irrelevant absorption in fish-liver oils is not generally applicable to butterfat unsaponifiable residues.4. A comparison of the vitamin A content of butterfat samples by the Carr-Price test and by the direct spectrophotometric method has shown a reasonably good agreement between the two values.

502. The vitamin A potency of New Zealand butter

“…Preparation of sample for analysis. Butterfat was used in preference to butter (17). It was prepared by melting the butter sample, decanting the fat, and filtering at 60° C.…”

“…Vitamin A was estimated in one portion (50 ml.) of the extract, by means of the Carr-Price test, according to the procedure already described (17). Carotene was estimated in the remaining 50 ml.…”

Section D. Nutritive value of milk and milk products

“…The Carr-Price reaction was largely used for vitamin A, which was mostly assessed by measuring absorption visually or photometrically, or by direct colour-matching methods (59,60,6i,62,63,64,65,66,67,68). Barnicoat(62), however, used a Lovibond tintometer, and preference for this instrument is indicated in paper (63). In this paper, and also in (62), factors are quoted for the conversion of Moore blue units to international units.…”

“…According to (64), the same values were found for vitamin A, whether measurement was done with milk or with the fat extracted from it. Vitamin A in milk was also measured by ultra-violet absorption (63). A new sensitive colour reaction with activated 1:3-dichloro-2-propanol is described in (73); it measures both vitamin A and carotene, and is said to be simpler than, and as satisfactory as, the usual methods.…”

617. Variations in the carotene and vitamin A contents of herd butterfats throughout lactation

“…The cream samples from the Institute farm were held overnight before churning to butter in the laboratory (11). Butterfats from these butters and from the factory samples were prepared by melting and decanting (12). Carotene and vitamin A were estimated by the methods previously described (10,12).…”