
Contents
45.1.24
AOAC Official Method 971.30
α-Tocopherol and α-Tocopheryl Acetate in Foods and Feeds: Colorimetric Method
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Published:January 2023
Cite
α-Tocopherol and α-Tocopheryl Acetate in Foods and Feeds: Colorimetric Method', in Dr. George W Latimer, Jr. (ed.), Official Methods of Analysis of AOAC INTERNATIONAL, 22nd Edition (
Extract
First Action 1971
Final Action 1972
Principle
Following methods are designed to determine vitamin E in foods and feeds in the several forms in which it may occur. Unsupplemented food or feed will contain natural α-tocopherol associated with many other reducing substances. This type of product is extracted, lipid residue saponified, and α-tocopherol isolated by TLC and determined colorimetrically. Foods or feeds may be supplemented with α-tocopheryl acetate added either as oil or in various dry forms. Assay for total α-tocopherol (natural plus supplemental) follows same operations described above. To specifically determine α-tocopheryl acetate, test portion is extracted, reducing substances, including natural α-tocopherol, are removed by oxidative chromatography, α-tocopheryl acetate is saponified, and resulting α-tocopherol is determined colorimetrically.
Calculation of assay results for supplemented foods and feeds in terms of International Units (IU) is complicated by fact that natural and synthetic α-tocopheryl acetates have different weight-activity factors. α-Tocopherol occurring naturally is in RRR-form. With products supplemented with RRR-α-tocopheryl acetate (natural), resulting total α-tocopherol is all in RRR-form and IU potency of product can readily be determined by using appropriate factor. With products supplemented with all-rac-α-tocopheryl acetate (synthetic), resulting total α-tocopherol is mixture of RRR- and all-rac-forms. To convert to IU, level of supplementation with all-rac-α-tocopheryl acetate must be determined specifically and natural α-tocopherol is determined by difference. Appropriate factors are then separately applied to determined levels of RRR- and all-rac-forms and results are added to determine IU potency of product. If isomeric nature of supplement is not known, it must be determined separately, 975.43 (see 45.1.25), before IU potency of supplemented products can be determined.
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