Premium
Estimation of vitamin A in margarine. I. Collaborative study of assay methods for estimating the potency of the vitamin A concentrates
Author(s) -
Melnick Daniel,
Luckmann Frederick H.,
Vahlteich Hans W.
Publication year - 1952
Publication title -
journal of the american oil chemists' society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.512
H-Index - 117
eISSN - 1558-9331
pISSN - 0003-021X
DOI - 10.1007/bf02648787
Subject(s) - potency , vitamin , unsaponifiable , chemistry , chromatography , food science , biochemistry , in vitro
Summary A series of 5 vitamin A concentrates of 2 different types were assayed by physico‐chemical methods and by multiple level biological assays. Three independent laboratories collaborated on the physico‐chemical assays and three other laboratories conducted the biological assays. The test oils contained about 200,000 U.S.P. units of vitamin A per gram and were either blends of food fish liver oils of high potency or were distilled vitamin A esters in a vegetable oil solvent. Margarines fortified with each type of concentrate were made on a plant scale and also assayed for vitamin A, using both the physico‐chemical and biological assay techniques. The data show that the type of vitamin A bearing oils for margarine fortification used in the present collaborative study are of high quality and contain considerably less extraneous (non‐vitamin A) materials than the oils used in a comparable U.S.P. collaborative study. A valid and precise estimate of the vitamin A potency of such oils can be obtained by spectrophotometric assay of the whole oil or by colorimetric (SbCl 3 ) assay of the unsaponifiable extract. A conservative estimate of the vitamin A potency is obtained by averaging the colorimetric and the U.S.P. XIV (or Morton‐Stubbs) spectrophotometric values derived from assays of the unsaponifiable extract. It is evident that the Morton‐Stubbs procedure over‐corrects the spectrophotometric estimates of the potency of such vitamin A concentrates. Largely responsible for the over‐correction are the presence of neovitamin A and vitamin A 2 in the natural concentrates and their absence from the U.S.P. Reference Standard. The use of other sources of preformed vitamin A to fortify margarine, such as a) fish liver oils or concentrates of poorer quality than those evaluated in the present study (more irrelevant light‐absorbing materials at 328 mμ and more irrelevant chromogenic materials in the SbCl 3 test), b) whale liver oil and/ or c) synthetic vitamin A preparations, will introduce complications if non‐biological assay methods should be used exclusively by the margarine manufacturer in controlling the vitamin A potency of his product. The same applies to federal and state control laboratories using non‐biological assays as a screening device prior to scheduling biological assays.