Antioxidant activities of essential oils of Clausena anisata (Rutaceae) and Plectranthus glandulosus (Labiateae), plants used against stored grain insects in North Cameroon

Abstract

This study was carried out to evaluate the overall antioxidant capacity of the essential oils of the leaves of Clausena anisata (Rutaceae) and Plectranthus glandulosus (Labiateae), commonly used in the traditional
method of grain storage in the northern part of Cameroon. Towards this objective, the co-oxidation of β-carotene as well as the reducing power, the radical scavenging capacity and the conjugated dienes profile of the
essential oils during storage for a period of 10 days at 28 ± 2.2 °C and 65±5.7% RH were determined. The least concentration necessary to prevent 50% oxidation (EC50) of β-carotene was found to be 6.53 mg/l, 5.84 mg/l and 524 μg/l respectively for C. anisata, P. glandulosus and butylated hydroxytoluene (BHT) which was the control. On the other hand, the reducing power of the different oils in a decreasing order was found to be P. glandulosus (EC50=2.41) > C. anisata (EC50=1.77 mg/l) while the EC50 of Scavenging abilities were 2.66 and 3.02 mg/l for C. anisata and P. glandulosus respectively. Based on the conjugated dienes profile, the essential oils showed higher antioxidant activity compared to Butylated hydroxytoluene (BHT) activity. The effective time (ET50) of the formulation ranging from 300 to 1000 ppm varied from 2 to 8 days for C. anisata and from 3 to 11 days for P. glandulosus. For the control (BHT), the effect varied from 5 to 15 days at an exposition temperature of 50 °C.

Key words: Antioxidant activity; Clausena anisata; Plectranthus glandulosus; Stored products; Scavenging ability; Reducing power