Estimation of vitamin a in margarine. II. Laboratory control procedures in assaying uncolored margarine

Abstract

SummaryA simple and precise spectrophotometric procedure has been described for the control of vitamin A fortification of margarine made in the plant. This method involves readings taken at 328 mμ of the whole margarine oil dissolved in cyclohexane. The spectrophotometer was set at 100% transmission with the corresponding unfortified oil at the same concentration in cyclohexane. Physico‐chemical and biological assay data have been presented demonstrating that the spectrophotometric method is the most reliable procedure for assaying margarine for vitamin A following fortification with quality vitamin A concentrates. It is far more precise than the biological assay method and equally as specific for vitamin A when the fortifying concentrates used satisfy the requirements set forth in the preceding paper (2).The colorimetric procedure, involving the reaction of vitamin A in the unsaponifiable extract of margarine with antimony trichloride, tends to overestimate on the average by about 600 USP units per pound the true vitamin A content of the margarine. However it is not at all unusual for the overestimates to exceed 1,000 USP units. The colorimetric method is useful as a screening test on open‐market samples for estimating maximal vitamin A potencies and as a check on the reliability of the unfortified oil blanks used in the spectrophotometric assay. Reasons were given for the belief that some conversion of vitamin A to the biologically‐inactive anhydro vitamin A occurs in margarine and that the presence of this derivative is responsible in large part for the discrepancy between colorimetric and spectrophotometric estimates.