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Variation of Phenolics, Antioxidant Activity and Carotenoids Contents in Some Medicinal Plants

H. M. Munjur Murshed
Department of Crop Botany, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh

Md Nesar Uddin
Department of Crop Botany, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh

M. Ashrafuzzaman
Department of Crop Botany, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh

Abstract/ Executive Summary:

Plants being an important source of medicine play a significant role in human health. Total phenolics, free radical scavenging capacity and carotenoids contents in six medicinal plants [Peltata (Cyclea peltata), Pudina (Mentha piperita), Bon tulsi (Ocimum americanum), Kalo tulsi (Ocimum sanctum), Akanadi (Stephania japonica) and Gulancha (Tinospora cordifolia)] from two families (Lamiaceae and Menispermaceae) available at the Bangladesh Agricultural University botanical garden were studied in the present experiment. Total phenolics content in the six medicinal plants ranged from 340.03 (M. piperita) to 890.58 (O. americanum) mg GAE 100 g⁻¹ FW leaf fresh weight. The IC50 value for scavenging 2, 2- diphenyl-l- picrylhydrazyl (DPPH) free radicals ranged from 3.27 (O. americanum) to 57.85 (T. cordifolia) mg mL−1 leaf extract and carotenoid content was maximum in M. piperita leaf (0.380 mg g⁻¹ fresh weight) among the six test species. The high content of phenolics in O. americanum represents the plant species as an important natural source of antioxidants with high potential value for drug preparation.

Keywords: Phenolics, Medicinal plants, Carotenoids, Antioxidant

Location: In Bangladesh

Start Date:

End Date:

Program Area: Development of Host and Medicinal Plants

Commodity: Medicinal Plants

Objectives:

To assess and compare total phenolics and carotenoids contents in above mentioned medicinal plants; and to determine free radical scavenging ability of the plant extracts.

Methodology:

Plant material: The medicinal plants [C. peltata (Menispemaceae), M. piperita (Lamiaceae), O. americanum (Lamiaceae), O. sanctum (Lamiaceae), S. japonica (Menispemaceae) and T. cordifolia (Menispemaceae)] available at the Bangladesh Agricultural University Botanical Garden were choosen for the study. Sample collection: For each sample, three different healthy plants from three different colonies were selected and considered as three replicates. Tender leaves from the selected plants and colonies were collected in the morning and immediately placed in zip lock bags with proper tagging to avoid moisture loss. Leaf samples were immediately brought to the laboratory for chemical analyses. The collected leaves were chopped into small pieces separately to produce working samples for analysis. Total phenolics content assay Total phenolics were assayed with the method modified after Albano and Miguel (2011). Exactly 5 g of the working samples for leaf were taken to a 250 mL beaker and 100 mL ice-cooled methanol were added to it and then each sample was homogenized for 2 minutes using a Homogenizer (model- OV-5 VELP, Italy). The mixture was kept in dark condition for 30 minutes and centrifuged for 5 minutes at 1500 rpm and then its supernatant was treated as working sample extract. An aliquot amount of the extract was used for determining total phenolics content or DPPH scavenging activity. Gallic acid was used here as standard. Exactly 330 μL from different concentrations (what are those concentrations? Mention it) of gallic acid solutions or suitable amount of plant extracts were taken into a 50 mL test tube. Then 0.16 mL of Folin-Ciocalteu reagent and 3 mL of Na2CO3 (10%) solution was added to 1 mL of gallic acid solution (What did the author add to the 50 mL test tube not clear? Clarify it). The mixture was kept in dark condition for half an hour at room temperature (25°C). Then absorbance was measured at 760 nm. The absorbance value is the reflection of the total phenolics content in the sample. After plotting the absorbance in ordinate against the concentration a linear relationship was obtained which was used as a standard curve for the determination of the total phenolics content of the test samples. DPPH radical scavenging assay: Free radical scavenging activity of the plant extracts was determined by using a stable 2,2-diphenyl-1- picrylhydrazyl radical (DPPH) (Brand-Williams et al., 1995). DPPH is a free radical of violet colour. The antioxidants in the sample scavenge the free radicals and turn it into yellow colour. The change of colour from violet to yellow is proportional to the radical scavenging activity. Briefly, the assay contained 2.7 mL of 0.1 mM DPPH in methanol and made up to 3 mL with 300 μL plant extracts (working sample). The contents were mixed well immediately and then incubated for 30 min at room temperature (25°C). The degree of reduction of absorbance was recorded at 517 nm using DR 6000 UV Spectrophotometer. The percentage of scavenging activity was calculated as: (Ac – As)/ Ac × 100 where ‘Ac’ is the absorbance of control (without extract) and ‘As’ is the absorbance of sample with plant extract. The percentage of radical scavenging activity was plotted against the corresponding concentration of the extract to obtain IC50 value. IC50 is defined as the amount of antioxidant material required to scavenge 50% of free radical in the assay system. The IC50 values are inversely proportional to the antioxidant activity (Nisha et al., 2009). Total carotenoids Total carotenoids can be determined in a whole pigment extract of green plant tissue by spectrophotometer (Lichtenthaler, 1987). From the fresh composite leaf sample, 50 mg were taken in a glass bottle and 200 μL distilled water were added to it. Then 16 mL ethanol were added and shaken properly and finally, the content was kept in dark condition for 24h. Absorbance reading was taken in the following day in a spectrophotometer (DR 6000, Hach, USA) at 470, 649, 664 and 750 nm wavelengths. Afterward, amount of total carotenoids (sum of carotene and xanthophyll) were calculated using the following formulae: Carotenoids (Cx+c) = (4.785 A470+3.657 A664−12.76A649) ×16.2/FW where, A649 = Absorbance at 649 nm; A664 = Absorbance at 664 nm; A470 = Absorbance at 470 nm; and FW = Fresh weight of plant tissue (mg). Statistical analyses: Mean values of each parameter studied for the six different medicinal plants were subjected to one-way ANOVA analysis using Minitab 17.3 to determine whether significant differences among the means existed or not. In case of having significant F-ratio, means were subjected to Tukey's post-hoc test to observe the significant differences among the mean values.

Source of Information: J Bangladesh Agril Univ 19(2): 000–000, 2021; ISSN 1810-3030 (Print) 2408-8684 (Online)

Article Link (Online Journal): https://doi.org/10.5455/JBAU.62120

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Results suggest that the species O. americanum (Bon tulsi) contained the highest amount of phenolics in its leaves. The highest radical scavenging ability was detected in O. sanctum (Kalo tulsi) and the lowest in T. cordifolia (Gulancha). M. piperita (Pudina) leaf contained the highest amount of carotenoids. Among the six medicinal plant species Gulancha, Peltata and Akanadi possessed low antioxidative activities while Pudina, Kalo tulsi, Bon tulsi were ranked as the highest i.e. the latter plants have great value in pharmacy and phytotherapy.

Knowledge Management: Journal