Experimental evaluation of the antioxidant and antitumor activities of thyme and basil essential oils and their phenolic constituents: theoretical antioxidant evaluation

Abstract

Abstract Background Identifying specific biological activities of natural products are of the main concerns worldwide for the use in safe functional food manufacture; essential oils and their components are good candidates in this respect. The present work aims to evaluate the biological activities of basil and thyme oils as well as their phenolic constituents. Using computational methods to predict biological activities are currently effective tools in minimizing and explaining experimental works. Results Chemical composition of thyme and basil oils were determined using GC–MS. The identified phenolic components were thymol (28.21%) and carvacrol (0.47%) in thyme oil and eugenol (11.37%) in basil oil. The antioxidant activity of both oils and their phenolic constituents as expressed by EC50 value were 535.01, 134.37, 176.57, 407.89 and 2.29 µg/mL against DPPH and 131.95, 56.65, 57.15, 82.71and 32.80 µg/mL against hydrogen peroxide, respectively. The order of activity is basil oil > thyme oil while phenolic compound order is eugenol > thymol > carvacrol; reducing power showed the same order. Basil oil showed also higher and good antitumor activity where it reduces the surviving fraction to 38.4% of brain tumor cells (U251) and 61.3% of liver tumor cells (HEPG2) at concentration 10 µg/mL. The antioxidant activity were evaluated theoretically according to the main three mechanisms, Hydrogen-Atom-Transfer (HAT), Single Electron Transfer–Proton Transfer (SET-PT) and the Sequential Proton Loss Electron-Transfer (SPLET); the results proved the experimental order of antioxidant and biological activities, and explained the remarkably higher activities of basil oil and its main phenolic component, eugenol. Conclusion Theoretical calculation can be used successfully to explain and predict the experimental biological activity results. Basil oil and its main phenolic component, eugenol, were found effective as antioxidants. Basil oil was also efficient in reducing the surviving fraction of liver and brain cancer cells where it reduces brain cells even lower than cells treated by doxorubicin, a known anti-cancer agent; thus, basil oil and its main phenolic components, eugenol, can be used safely in food preservation and functional food production. Graphical Abstract