Free radical scavenging activity of Piper nigrum
ฤทธิ์ต้านอนุมูลอิสระของพริกไทย (Piper nigrum)

Niwat Keawpradub, Asst. Prof., D. of Pharmacognosy and Pharmaceutical Botany, F. of Pharmaceutical Sci., PSU.
Nitikan Kantiworapong, D. of Pharmacognosy and Pharmaceutical Botany, F. of Pharmaceutical Sci., PSU.
Corresponding e-mail : kniwat@ratree.psu.ac.th

Grant : Prince of Songkla University
Presented : The 5th NRCT-JSPS Joint Seminar on Natural Medicine, November 15-17, 2000, Chulalongkorn University, Bangkok
Key words : Piper nigrum, free radical scavenging, antioxidant, piperine, piperylin

Acetone, methanol and water extracts prepared from Black pepper and White pepper (Piper nigrum L., Piperaceae) were tested against 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical in order to assess the radical scavenging activity. The water and ethanol extracts of Black pepper were found to be active with EC50 values of 32.6 and 61.2 mg/ml, respectively. On the other hand, the acetone extract of Black pepper and the acetone, methanol and water extracts of White pepper were slightly active against DPPH. At the concentration of 100 mg/ml these four extracts exhibited radical scavenging activity in the range of 19.1-31.7% (EC50>100 m g/ml). The EC50 value of butylated hydroxytoluene (BHT), the positive control, was 18.5 mg/ml. Two alkaloids, piperine [1] and piperylin [2], were iso-lated from the ethanol extract of Black pepper. Their structures were determined by spectroscopic methods. These alkaloids, however, showed very slight radical scavenging activity (EC50 >100 mg/ml). TLC analysis of the water extract of Black pepper revealed that this fraction contains phenolic com-pounds according to the colour formed after spraying with anisaldehyde-sulphuric acid reagent. These polar compounds could be responsible for the observed activity. These results suggest that Black pepper, the spice commonly used in Thai cuisine and for medicinal purposes in Thai traditional me-dicine such as stomachic, carminative and longevity remedies, could be of beneficial for health pro-motion due to its antioxidative effect via free radical scavenging activity.
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