Comparative Phenolic Fingerprint and LC-ESI+QTOF-MS Composition of Oregano and Rosemary Hydrophilic Extracts in Relation to their Antibacterial Effect

Abstract

Rosemary (Rosmarinus officinalis) and oregano (Origanum vulgare) are known aromatic plants used as spice, with good flavoring, preservative, antioxidant and antibacterial activity. Beside their known terpenoid content responsible for the antibacterial activity, the water-soluble compounds (phenolic derivatives) are of high interest not only for their antioxidant activity but as a good alternative or as a hydrophilic new antibacterial solution. Two hydrophilic extracts from each plant were obtained (15% plant in hot water) and the phytochemicals were fingerprinted by UV-Vis and FTIR spectrometry and quantified. The total phenolic content was higher in case of oregano (54.2 mg GAE/g DW) comparing to rosemary (15.35 mg GAE/g dw). By LC-ESI+ QTOF-MS analysis there were identified mainly, in both extracts, flavonoid and diterpene derivatives, mainly carnosol, carnosic acid, rosmarinic acid, kaempferol 3-O-glucuronide. Other flavonoid glucuronides were more specific to one or the other plant, e.g. luteolin 3'-(4''-acetylglucuronide) for rosemary and apigenin 7-O-glucuronide for oregano. Water favorized increased extraction of flavonoid derivatives and soluble diterpenes, but not non-soluble terpenes. The antibacterial activity of both extracts was tested against B. cereus, L. monocytogenes, Salmonella, S. aureus and E. coli. Both oregano and rosemary extracts showed a slight antibacterial activity, which can be related to the low concentration of terpenoids, known to have the most important antibacterial activity in these plants. Nevertheless, the antibacterial activity seems to be strain dependent, Bacillus cereus being the most sensitive bacterial strain comparing with the other four bacteria, the oregano extract having a slightly superior activity comparing to the rosemary extract.