Phytochemical Analysis and Antioxidant and Antifungal Activities of Powders, Methanol Extracts, and Essential Oils from Rosmarinus officinalis L. and Thymus ciliatus Desf. Benth

Abstract

Chemical residues in food pose health risks such as cancer and liver issues. This has driven the search for safer natural alternatives to synthetic fungicides and preservatives. The aim of this study was to characterize the chemical composition of the essential oils (EO), determine the polyphenolic contents, and evaluate the in vitro antioxidant and antifungal activities of methanol extracts (ME), essential oils (EO), and powders from Rosmarinus officinalis L. (rosemary) and Thymus ciliatus (Desf) Benth. (thyme) from the M'sila region, Algeria. The chemical composition of the EOs was determined by GC-MS. R. officinalis EO was composed of 31 components, mainly camphor (41.22%), camphene (18.14%), and α-pinene (17.49%); T. ciliatus EO was composed of 58 components, mainly, in percentage, α-pinene (22.18), myrcene (13.13), β-pinene (7.73), β-caryophyllene (10.21), and germacrene D (9.90). The total phenols and flavonoids were determined spectrophotometrically, and the rosemary ME was found to possess the highest polyphenolic content (127.1 ± 2.40 µg GAE/mg), while the thyme ME had the highest flavonoid content (48.01 ± 0.99 µg QE/mg). The antioxidant activity was assessed using three methods: rosemary ME was the most potent, followed by DPPH (IC₅₀ = 13.43 ± 0.14 µg/mL), β-carotene/linoleic acid (IC₅₀ = 39.01 ± 2.16 μg/mL), and reducing power (EC₅₀ = 15.03 ± 1.43 µg/mL). Antifungal activity was assessed for 32 pathogenic and foodborne fungi. Four methods were applied to the solid medium. Incorporating the powdered plant into the culture medium (at 10%) reduced the fungal growth to greater than 50% in 21.88% and 6.25% of all fungal isolates, for R. officinalis and T. ciliatus, respectively. The ME, applied by the well diffusion method (0.1 g/mL), was less effective. Different concentrations of EO were tested. Incorporating the EO into the culture medium (1500 μL/L) inhibited 50% of the molds to levels of 50 and 75% for R. officinalis and T. ciliatus, respectively, with the complete inhibition of four fungi. Fumigated EO (15 μL) inhibited 65% of the molds to levels of 65 and 81.25% for R. officinalis and T. ciliatus, respectively, with the complete inhibition of five fungi. There was little to no sporulation in conjunction with the inhibition. Our results revealed some of the potential of the studied plants to fight foodborne molds and presented their promising characteristics as a source of alternatives to chemical pesticides and synthetic preservatives. Further studies are needed to find adequate application techniques in the food safety area.

Keywords: Rosmarinus officinalis; Thymus ciliatus; antifungal activity; antioxidant activity; chemical composition; essential oils; polyphenolic contents.

Figure 1

Effect of powders and methanol extracts of R. officinalis and T. ciliatus on the radial growth of tested molds grown on Potato Dextrose Agar (PDA). (A) Powder (10%, w/v); (B) methanol extract (0.1 g/mL). The data are represented as the average ± SD (n = 3). Different letters indicate significant differences (p < 0.05) between the two tested plants on each mold, according to Sidak’s multiple comparisons test.

Figure 2

Effect of the powdered plant on the radial growth of some tested fungi; 1—A. ochraceus, 2—A. parasiticus, 3—B. aclada, 4—F. oxysporum, 5—P. expansum; (a) control, (b) PDA medium supplemented with R. officinalis, and (c) PDA medium supplemented with T. ciliatus.

Figure 3

Effect of the plant ME on the radial growth of some tested fungi; 1—P. digitatum, 2—F. graminearum, 3—A. alternata, 4—F. oxysporum, 5—F. proliferatum; (a) control, (b) PDA medium supplemented with R. officinalis, (c) PDA medium supplemented with T. ciliatus.

Figure 4

Effect of EOs of R. officinalis and T. ciliatus on the radial growth of the tested molds grown on PDA by direct contact method of (A) 500, (B) 1000, and (C) 1500 μL/L. The data are represented as the average ± SD (n = 3). Different letters indicate significant differences (p < 0.05) between the two tested plants on each mold, according to Sidak’s multiple comparisons test.

Figure 5

Effect of EOs of R. officinalis and T. ciliatus on the radial growth of the tested molds grown on PDA by direct contact method of (A) 5, (B) 10, and (C) 15 μL. The data are represented as the average ± SD (n = 3). Different letters indicate significant differences (p < 0.05) between the two tested plants on each mold, according to Sidak’s multiple comparisons test.

Figure 6

Effect of direct contact with EO on the radial growth of (1) M. suaveolens, (2) F. culmorum, (3) P. griseofulvum, and (4) P. expansum; a: Control; b,c: mold exposed to concentrations of 1000 and 1500 µL/mL of R. officinalis EO, respectively; d–f: mold exposed to concentrations of 500, 1000, and 1500 µL/mL of T. ciliatus EO, respectively.

Figure 7

Effect of EO fumigation on the radial growth of (1) B. cinerea, (2) A. alternata, (3) F. graminearum, and (4) A. flavus; a: Control; b,c: mold exposed to fumigation of 10 and 15 µL of R. officinalis EO, respectively; d–f: mold exposed to fumigation of 5, 10, and 15 µL of T. ciliatus EO, respectively.