Effect of Sample Preparation Methods and Extraction Time on Yield and Antioxidant Activity from Kradonbok (Careya sphaerica Roxb.) Leaves

Abstract

Kradonbok (Careya sphaerica Roxb.), one of Thai indigenous vegetables, was selected for studying the effect of sample preparation method and extraction time on antioxidant activity. The results showed that sample preparation methods gave significant effect on total phenolic content and antioxidant activity but had no marked effects on yield of the extract. Freezing, especially fast freezing, for keeping the leaves until the analysis time gave a higher yield of the extract, a higher total phenolic content and a greater antioxidant activity compared with those obtained from other drying methods. Kradonbok leaves kept by fast freezing were extracted with ethanol for 0.25, 0.5, 1, 3, 4.5, 6, 24, 48, 96 and 168 h. The results showed that yield of the extract and total phenolic content were almost constant after 3 h of extraction time at room temperature. However, extraction time from 4.5 to 6 h gave the lowest EC50 value, comparing with those from other extraction times. These results suggested that fast freezing was the appropriate preparation method to keep the plant leaf for further investigating the antioxidant activity and extraction time to obtain the highest yield of the extract and antioxidant activity should be carried out for 4.5 to 6 h.