Measurement of Ascorbic acid in Australian native plants

Ascorbic acid is one of the compounds found in a number of commercially important native plants fruits e.g. Kakadu plum, wild lime and bush tomato. High performance liquid chromatography (HPLC) was used to determine ascorbic acid in these native plant fruits. Ascorbic acid degradation of both standards and plant extracts was observed during HPLC sequence runs. These losses were considerable even though factors such as light, temperature and water activity, which accelerate the loss of ascorbic acid, were eliminated. Several concentrations of sodium metabisulphite were added to both standards and plant extracts to evaluate the effect on the rate of ascorbic acid degradation. A concentration of 500 μg/mL was the most effective but did not eliminate the problem. To correct for any loss still occurring, the rate constant k for ascorbic acid degradation was calculated and used to extrapolate back to the original ascorbic acid concentration. The k value was also found to vary for the different plants studied. For example the k value without added sodium metabisulphite for Kakadu plum, wild lime and Kakadu plum intermediate raw material were 0.00532, 0.02710 and 0.04429 respectively. With the addition of 500 μg/mL sodium metabisulphite the k value decreased to 0.00005, 0.00915 and 0.00586 respectively.