The Effect of Heating Treatment on Antioxidant Capacity of Vegetables in Taiwan

Enriching the intake of fruits and vegetables can help reduce the incidence of cancer and other chronic diseases, the main reason is that phytochemicals which have antioxidant properties and other healthcare contents are abundant in fruits and vegetables. People mostly intake raw fruits and cooked vegetables. To understand antioxidant properties of cooked vegetables in Taiwan, this study use ferric reducing antioxidant power assay (FRAP assay) and oxygen radical absorbance capacity assay (ORAC assay) for a series of antioxidant analysis of commercially consumed vegetables in Taiwan .

Fresh tested vegetables after longer homogeneous treatment time, measured antioxidant capacity significantly reduced with longer treatment time. Compare with different vegetables, required homogeneous treatment time on antioxidant capacity occurred significantly reduced phenomenon may differ. In addition, tested vegetables through treatment of different heating methods with different heating time, measured reaction changes of antioxidant capacity may differ with the species and properties of vegetables. Generally speaking, boiled and microwave-boiled heating methods have better effect on enhancing the antioxidant capacity of tested vegetables, and the effect of these two heating methods are similar. To set heating treatment into drained group and not drained group, if heating methods contained more water, which may let tested vegetables lose much antioxidants into the water. Among different heating methods, fried heating method may have better maintained/retained effect on antioxidant capacity of tested vegetables.

According to different species and characteristics of vegetables, heating treatment may have (or not have) enhancing effect on their antioxidant capacity, but if their response want to occur significant changes, heating intensity may up to a certain level. To take microwave heating as example, heating firepower up to medium intensity and upward would be better.

This study also used medium-high intensity heating treatment of microwave firepower on a total of 43 kinds vegetables, with heating time was fixed in 3 minutes, among same treatment includes drained and not drained groups, measured their antioxidant capacity (FRAP and ORAC value) after foresaid heating treatment. The results show, under determination of two antioxidant assays, significantly increased antioxidant capacity of tested vegetables among drained group on the basis of ranking were following 10 vegetables: green leafy sweet potato vines, fennel, gynura, garland chrysanthemum, water spinach, crisphead lettuce, broccoli, eggplant ‘Ma-Zu’, snap peas and asparagus.

To conclude, if select proper processing method according to response changes of vegetables through heating treatment, would enhance intake antioxidants content, and also with potential health-care benefits.