Effect of hot-air drying temperature on antioxidative activity of sweetpotato leaves

To provide the basic data to dry vegetate the sweetpotato leaves, the total contents of tannin, flavonoid and polyphenol in the methanol extract from the hot- air dried sweetpotato leaves were analyzed and DPPH radical scavenging activity, ABTS radical scavenging ability, nitrite scavenging ability, and others were comparatively analyzed. The total tannin content was decreased from Shinmi of 10.87 mg/g at 40°C to 7.28 mg/g at 70°C and the total flavonoid was decreased from Hayanmi of 55.37 mg/g at 40°C to 39.63 mg/g at 70°C. That is, the low temperature drying contained more of these substances than in the high temperature drying. The DPPH radical scavenging activity was the highest in Shinmi and Hayanmi of 84.33% and 85.25% at 40°C, and the ABTS radical scavenging ability was a high value of over 80% in the treatment plot at 40°C. The nitrite scavenging ability was highest in Shinmi and Hayanmi of 76.15% and 73.74% at 40°C but low at 70°C. That is, the antioxidant effect of the hot-air dried sweetpotato leaves was high in the sample of 40°C and low in the sample of 70°C. Affected by the drying temperature, the high antioxidant effect is resulting from the little decrease of active ingredient when drying at low temperatures.