Ascorbic acid, commonly known as Vitamin C (Vc), is ubiquitous in vegetables, fruits, and beverages, as well as in formulated nutraceuticals. However, Vc is unstable and subject to degradation under factors such as high temperature, UV light, moisture content, and metal ions. Metal elements can react with oxygen or hydrogen peroxide, generating hydroxyl radicals, which can further induce Vc degradation and adversely influence the food quality. Many food products, such as apple juice and orange juice, are rich of Vc, and also formulated with some metal ions, such as sodium, potassium, calcium, magnesium, etc. Therefore, stability of Vc in the juice might be affected by the existence of metal ions. In this context, the objective of this study was to investigate the effect of metal ions on the stability of Vc in model systems under room temperature (25°C) in darkness. With aid of HPLC analysis, stability (or degradation) of Vc mixed with different concentrations of metal ions was determined in the course of the treatment. In the chromatographic method, the mobile phase of the HPLC consisted of solvent A: 0.02% phosphoric acid in water and solvent B: acetonitrile. Starting with 90% of solvent A and 10% of solvent B, an isocratic elution was performed for 5 minutes at a flow rate of 0.5 ml min-1, and 254 nm was chosen for detection of wavelength. After storage time of 24 hours, with 100 mg L-1 of metal ions (i.e., Na+, K+, Ca2+, Mg2+) 100 % contents of VC were degraded to around 60% contents of VC. However, compared to the control group, the chloride salts of metal ions (i.e., Na+, K+, Ca2+, Mg2+) did not have significant effects on the degradation of Vc. After storage time of 1.75 hours, Vc with 50 mg L-1 of Cu2+ was fully degraded. After storage time of 24 hours, with 50 mg L-1 of Fe2+, 100% contents of Vc were degraded to 3.3% contents of Vc. Therefore, Copper ion (Cu2+) and iron ion (Fe2+) significantly affected the VC stability compared to other metal ions (i.e., Na+, K+, Ca2+, Mg2+).

Effect of metal ions on stability of vitamin C determined by HPLC

ACS Fall 2021

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