Thermostability at different pH levels of peroxidase extracted from four vegetables

The stability of crude peroxidase incubated for different period of time and at different pH and temperatures of four vegetables (potato, carrot, eggplant and tomato) was investigated. Peroxidases of high activity were extracted at pH 5.0 from potato and tomato while those of carrot and eggplant were extracted at pH 6.0. Potato tuber contained higher level of peroxidase whereas carrot had lower levels at all pH values. The results showed that the rate of loss of peroxidase activity from the vegetables increased with both increase in temperature and heating time. Biphasic inactivation curves were observed for the enzymes extracted from all samples, where the initial heat inactivation is rapid followed by much slower inactivation periods. The rate of loss of peroxidase activity was shown to be pH dependent. Potato peroxidase was observed to be more stable to heat. A less severe heat treatment is required to inactivate carrot, eggplant and tomato peroxidases. Complete inactivation of carrot peroxidase was accomplished within 4–10 min at 80°C and within 2–10 min at 90°C at pH 8.0, while peroxidase inactivation in eggplant required 8–10 min at 90°C at pH 8.0. Complete inactivation of tomato peroxidase required 6–10 min at 90°C at pH 6.0.