Abstract
Twelve Tunisian Thymus algeriensis populations growing wild in different bioclimatic zones, extending from the subhumid to the upper-arid bioclimates, were compared regarding their phenolic composition and their ability to serve as antioxidant, anti-acetylcholinesterase, and antibacterial agents. A significant variation of phenol profile was observed between the analyzed populations, as assessed by ultra-high-performance liquid chromatography coupled with a diode array detector and an electrospray mass spectrometer (UHPLC-DAD-ESI/MSn) technique. Rosmarinic acid was the main phenolic compound in most populations (383.8–1157.8 µg/mL extract), but still, those from the upper-arid bioclimatic zone were distinguished by the presence of carvacrol (1374.7 and 2221.6 µg/mL extract), which was absent in the remaining ones. T. algeriensis methanolic extracts were found to possess a substantial antioxidant and anti-acetylcholinesterase activities, with significant variation observed between populations, which were correlated to their phenolic contents. The antibacterial activity of the extracts tested against seven bacteria was revealed only by populations collected from upper-arid bioclimate and mainly associated with the presence of carvacrol. Extracts revealed a bacteriostatic effect against all bacteria (MIC = 1.4 mg/mL). Yet, the bactericidal activity (MBC = 1.4mg/mL) was restricted to the gram-negative bacteria Escherchia coli.
Highlights
Nowadays, there is great interest in medicinal plants and their bioactive compounds, namely antioxidant compounds, to be used as health-promoting agents in distinct industrial fields
Algeriensis populations were variable (Table 2), with maximum levels found in plants grown in the upper arid bioclimatic zone (32–34 mg GAE/g leaves DW), intermediate values in population Ta 10 from the lower semi-arid bioclimatic zone (17.1 mg GAE/g leaves DW), and lower levels, not exceeding
Total flavonoids assumed maximum amounts in upper arid samples, while variable amounts ranging from 3 to 9 mg ER/g leaves DW were found in the lower semi-arid, mean semi-arid, upper semi-arid populations, and sub humid
Summary
There is great interest in medicinal plants and their bioactive compounds, namely antioxidant compounds, to be used as health-promoting agents in distinct industrial fields. In most parts of the world, thyme is considered one of the most valuable spices/food preservatives in the food industry [3] It is commonly used in folk medicine because of its medicinal properties, including antispasmodic, antioxidant [4,5,6], antifungal [7,8], antibacterial [9,10,11], antitumor [12] and anti-aflatoxigenic [13] properties. In Tunisia, this species has a wide geographical distribution and grows spontaneously in diverse bioclimatic zones, extending from the subhumid to the lower arid bioclimates. It is largely used, fresh or dried, in food, as a culinary herb and in folk medicine, mainly due to its protection against abortion and respiratory and digestive tube disorders [12,17]
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