Influence of Extraction Duration on the Chemical Composition and Biological Activities of Essential Oil of Thymus pallescens de Noe

Thymus pallescens de No, essential oils were isolated from the plant's dried leaves, by hydrodistillation, with different distillation times (30 min, 1, 2 and 3 h). The essential oils compositions and their antioxidant, antimicrobial and insecticidal activities were examined. The chemical compositions of the oils were determined by GC and GC-MS. The antioxidant capacity was tested by four complementary methods: thiobarbituric acid reactive substances, ferric reducing power and scavenging of radicals DPPHaEuro cent (2,2-diphenyl-1-picrylhydrazyl) and ABTS(aEuro cent+) [2,2'-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid)]. The antimicrobial activity was tested against three bacteria, two gram-positive (Staphylococcus aureus and Bacillus subtilis) and one gram-negative (Escherichia coli) and one yeast (Candida albicans). The insecticidal activity against confused flour beetle Tribolium confusum Jacquelin du Val (Coleoptera: Tenebrionidae) was evaluated using direct contact application and fumigant method. The predominant components in the oils were carvacrol (63.3-68.2 %), gamma-terpinene (6.9-9.1 %), p-cymene (6.2-10.3 %) and thymol (6.5-7.5 %). The antioxidant activities were dependent on the time of hydrodistillation and the method used. The essential oils extracted for 30 min and 1 h were the most efficient against all the bacteria used. Toxicity tests against T. confusum showed that the oils isolated for 3 h and 30 min caused highest mortality with contact method and fumigant test, respectively. The results suggest that distillation time can determine the value of the oil designed to be applied to any biological material.