Antioxidative and antibacterial properties of organically grown thyme (Thymus sp.) and basil (Ocimum basilicum L.)

Abstract

The biomass per plant and total phenolics (TPH) of ethanol extracts of 3 species of thyme, Thymus vulgaris, T. serpyllum,and T. citriodorus, and 3 varieties of basil (Ocimum basilicum), Genovese, Thai, and Cinnamon, were investigated. All were grownorganically. The 2 herbs that showed the greatest biomass were T. citriodorus (26.5 g/plant) and O. basilicum var. Cinnamon (105 g/plant). For these, total flavonoids (TFL), total flavones and flavonols (TFF), and total flavanones and dihydroflavonols (TFDH) were alsodetermined for their ethanol extracts. Furthermore, the antioxidant potential (AOP) and antibacterial activity were determined againstfoodborne bacteria: Staphylococcus aureus, Listeria monocytogenes, Campylobacter jejuni, and verotoxin-producing Escherichia coli(VTEC). The highest TPH (36 mg chlorogenic acid equivalents per gram of fresh weight) was seen for T. citriodorus collected in 2010.The thyme ethanol extracts contained more TPH and TFL, and their subgroups of TFF and TFDH, than the ethanol extracts from basil,and had AOP comparable to the ethanol extracts from basil, although all of them were lower than the synthetic antioxidant, t-butylatedhydroxytoluene. Drying of these herbs decreased TFF and TFDH, while TPH and TFL remained unchanged (for T. citriodorus) or evenincreased (for Cinnamon basil), and AOP was higher than that of the ethanol extracts from the frozen herbs. The antimicrobial activitiesof these ethanol extracts depended mainly on the bacterial target. They were weak against gram-negative VTEC, while their effectsagainst C. jejuni, S. aureus, and L. monocytogenes correlated with their TPH and chemical compositions.