Vitamin c calculation

I have a tablet about 500 mg of vitamin C contains :250mg of ascorbic acid and 285 mg of ascorbate sodium equivalent to 250mg of ascorbic acid.
The molecular weight of ascorbic acid is 176g and ascorbate sodium is 198g , i found the equivalent about 253 mg and not 250mg can someone explain me ?

Please also consider the following aspects while calculating Sodium ascorbate content equivalent to 250 mg of Ascorbic acid, (you may have to consider extra amount),

  • % Purity of Sodium ascorbate
  • Moisture content in Sodium ascorbate
  • Also you may have to add extra amount as “Overages” to compensate for loss on storage up to expiry date of the formulation (stability aspects).

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Thank you very much

The stability of vitamins is affected by a number of factors, such as temperature, moisture, oxygen, light, pH, minerals (especially iron and copper), vitamin-vitamin interactions, and other food components [4]. Vitamin stability is affected most by heat, moisture, pH, and light, but given their chemical heterogeneity, vitamin losses in different foods vary considerably during both processing and storage of the final product. The most unstable vitamins are C, A, D, B1, and B12. Because of their multiple oxidation states, the presence of metal ions (iron and copper) accelerates degradation of vitamins, especially vitamins C, A, and B1. Fortification with several vitamins may give rise to vitamin-vitamin interactions that may accelerate the rate of breakdown of some vitamins; the best-known interactions are those among vitamins C, B1, B2, B12, and folic acid. The extent of these interactions is also dependent on the nature of the product as well as on temperature, moisture level, pH, light, etc. during processing and storage.

Therefore, to maintain the micronutrient levels declared on the product label throughout a product’s shelf life, the amount of vitamins added during processing needs to be higher than the levels reported on the label. The difference between the declared and formulated vitamin levels, termed “overage,” will be different for each food application. Vitamin overages are normally calculated as a percentage of the declared level:

% Overage = [(formulated vitamin level - declared level)] / Declared level on label × 100