1984 Volume 31 Issue 4 Pages 248-253
A preparation of ascorbate oxidase (AAO, EC 1.10.3.3) was obtained from the peel of young fruit of Satsuma mandarin (Citrus unshiu Marc., 1-3cm in diameter). The effects of temperature and pH on the AAO activity were studied using the difference spectral method described previously. The enzyme showed strong activity at the temperature from 30 to 35°C and at pH about 5.5. It was stable at a temperature below 50°C and in the pH ranges of 5 to 9. On the basis of these results, we carried out the enzymatic oxidation of L-ascorbic acid (AsA) at 30°C at pH 6. A linear relationship was observed between the AsA oxidation, which was expressed as a peak height of difference spectra (ΔE243), and the reaction time, within 10min. The rate of the AsA oxidation was proportional to the amount of the enzyme present. This shows that the oxidation rate can be adopted for determining AAO activity. The AAO activity in the peel of Satsuma mandarin during fruit ripening was measured by this difference spectral method. The strong a ctivity was found in a young fruit and it sharply droped as the fruit developed.
