How are vitamin amounts in foods measured?

To determine the vitamin content of foods, researchers utilize three primary methods of quantitative analysis:

• Physicochemical methods: These techniques measure physical or chemical characteristics, such as light absorption, fluorescence, or chemically reactive groups. While highly accurate and capable of detecting small amounts, they may not distinguish between biologically available and unavailable forms of a vitamin and can be interfered with by inactive derivatives.12
• Microbiological assay: Used specifically for B vitamins, this method measures the growth rate of microorganisms in media containing the foodstuff. The growth response is compared against a known quantity of pure vitamin to estimate the amount present.13
• Animal assay: Applicable to most vitamins (except B12), this technique measures biological responses in animals, such as weight gain or the reversal of deficiency symptoms. Because animals respond only to biologically active forms, this method is highly relevant, though it requires rigorous standardization to control for complicating factors. Specific approaches include growth assays, reaction time assays, and graded response assays, such as measuring bone calcification for vitamin D or fertility rates for vitamin E.14