The effect of ethanol/water concentration on phenolic composition, antioxidant, and antimicrobial activities of Rosmarinus tournefortii de Noé hydrodistillation solid residues

Rosemary is one of the well-known aromatic and therapeutic plants recognized for the interesting pharmacological properties of its essential oil. After hydrodistillation, a huge amount of solid residue-remains, which still contains non-volatile
bioactive compounds. Our work aims to study in depth the efect of ethanol/water concentration on the extraction yield,
total phenolic and favonoid content, chemical profle, antioxidant and antimicrobial activities of Rosmarinus tournefortii
de Noé solid residues. Phenolic and favonoid content was estimated spectrophotometrically and for their identifcation,
High-performance liquid chromatography-photodiode array detector (HPLC-DAD) analysis was adopted. The antioxidant
activity was established using common methods such as DPPH, ABTS, and the Beta-carotene/linoleate model system. Furthermore, the antimicrobial capacity was investigated against Escherichia coli ATCC 25,922 and Listeria innocua ATCC
33,090, two well-known organisms representing gram-negative and gram-positive bacteria, respectively, as well as against
the mold Geotrichum.s p and the yeast Rhodotorula glutinis. Based on the statistical analysis, a signifcant efect of ethanol/
water concentration on the phenolic composition, antioxidant, and antifungal activity was revealed, while a slight diference
was observed for the antibacterial activity. On the other hand, HPLC–DAD analysis endorsed the preferential extraction of
gallocatechin and cafeic acid in 20% ethanol, homoplantaginin in 40%, cirsimaritin in 0% ethanol, and rosmarinic acid in
100% ethanol. Additionally, the 80% ethanol/water concentration indicated the highest extraction yield and favonoid content
(yield=51.6%, TFC=21.38±0.23 mg QUE/g DW). On the contrary, 40% ethanol revealed both the highest phenolic content
(TPC=128.18±0.56 mg GAE/g DW) and radical scavenging activities (IC50=0.051±0.008 mg/mL, 0.061±0.002 mg/
mL, and 1.232±0.013 mg/mL for DPPH, ABTS, and beta-carotene/linoleate model system, respectively). Besides, 20%
was the highest concentration for the inhibition of the two bacteria Escherichia coli (7.35±0.05%) and Listeria innocua
(8±0.1%) as well as the mold Geotrichum sp, (16.5±0.3%) and for the yeast Rhodotorula (26±1.2%), 50% ethanol was
found to be the most appropriate concentration. These diferences detected between the studied activities of rosemary solid
residue extracts were strongly infuenced by the target phenolic compounds extracted.