Stevia rebaudiana Bertoni is a perennial herbal species with a number of therapeutic properties. The leaves of S. rebaudiana are the most important part of the plant as they contain high
level of sweetener compounds known as steviol glycosides; which are known to possess
antioxidant, antimicrobial, and antifungal activities. Among the steviol glycosides, stevioside
and rebaudioside A are the most abundant sweetening compounds of interest, documented to
be 30 - 250 folds sweeter than sucrose or refined sugar. The therapeutic properties of the
species make it more interesting as they play important roles as anti-hyperglycaemic agent to
lower glucose levels in the blood, thus commonly used in the treatment of diabetes mellitus
and obesity. Known to have sweet tasting leaves, its extract which contains antioxidant
compounds have been used to treat cancer, reduce inflammatory, and hypertension. S. rebaudiana has drawn the attention of health-conscious fitness lovers all over the world as non-caloric sweetener, and has been widely cultivated for being the most suitable sweetening substitution.
This review article presents a comprehensive review pertaining to antioxidants and various assays that determined enzymatic and nonenzymatic antioxidants. Antioxidants have gained attention at the global scale on its prominent beneficial roles that can fight against many chronic infirmities, including cancer and cardiovascular diseases. Many studies have investigated different types of samples, such as medicinal plants, fruits, and vegetables, by using various antioxidant assays. Antioxidants can be grouped into enzymatic and nonenzymatic antioxidants. To date, most studies had looked into nonenzymatic antioxidants due to lack of references on enzymatic antioxidant assays. Therefore, this review article depicts on seven assays of enzymatic antioxidants (superoxide dismutase, catalase, peroxidase, ascorbate peroxidase, ascorbate oxidase, guaiacol peroxidase, and glutathione reductase) and fifteen activities of nonenzymatic antioxidants (total polyphenol, total phenolic acids, total flavonoids, total ascorbic acid, anthocyanin content, DPPH scavenging activity, FRAP assay, hydrogen peroxide scavenging activity, nitric oxide scavenging activity, superoxide radical scavenging activity, hydroxyl radical scavenging activity, phosphomolybdate assay, reducing power, metal ion chelating activity, and β-carotene), which are described in detail to ease further investigations on antioxidants in future.
Clinacanthus nutans, commonly known as Sabah snake grass, is one of the more important medicinal plants in Malaysia's herbal industry. C. nutans has gained the attention of medical practitioners due to its wide range of bioactive compounds responsible for various biological activities, such as anti-cancer, anti-venom and anti-viral activities. Due to its high pharmacological properties, the species has been overexploited to meet the demands of the pharmaceutical industry. The present study was conducted to establish a suitable in vitro culture procedure for the mass propagation of C. nutans. Murashige and Skoog (MS) basal medium, supplemented with different types of cytokinins, auxins, basal medium strength and sucrose concentrations, were tested. Based on the results, a full-strength MS basal medium supplemented with 12 µM 6-benzylaminopurine (BAP) and 30 g/L sucrose was recorded as the best outcome for all the parameters measured including the regeneration percentage, number of shoots, length of shoots, number of leaves and fresh weight of leaves. In the analysis of the phenolics content and antioxidant activities, tissue-cultured leaf extracts assayed at 100 °C exhibited the highest phenolic content and antioxidant activities. The propagation of C. nutans via a plant tissue culture technique was recorded to be able to produce high phenolic contents as well as exhibit high antioxidant activities.
A study was conducted to establish in vitro culture conditions for maximum production of biomass and flavonoid content for Ficus deltoidea var. kunstleri, locally named as Mas Cotek, known to have a wide variety of potential beneficial attributes for human health. Size of initial inoculum, cell aggregate and initial pH value have been suggested to influent content of biomass and flavonoid for cell suspension culture in several plant species. In the present study, leaf explants were cultured by cell suspension culture procedures in MSB5 basal medium supplemented with predetermined supplements of 30 g/L sucrose, 2.75 g/L gelrite, 2 mg/L picloram and 1 mg/L kinetin with continuous agitation of 120 rpm in a standard laboratory environment. Establishment of cell suspension culture was accomplished by culturing resulting callus in different initial fresh weight of cells (0.10, 0.25, 0.50, 1.0, and 2.0 g/25 mL of media) using similar basal medium. The results showed that the highest production of biomass (0.65 g/25 mL of media) was recorded from an initial inoculum size of 2.0 g/25 mL media, whereas the highest flavonoid (3.3 mg RE/g DW) was found in 0.5 g/25 mL of media. Cell suspension fractions classified according to their sizes (500-750 µm, 250-500 µm, and <250 µm). Large cell aggregate size (500-750 µm) cultured at pH 5.75 produced the highest cell biomass (0.28 g/25 mL media) and flavonoid content (3.3 mg RE/g DW). The study had established the optimum conditions for the production of total antioxidant and flavonoid content using DPPH and FRAP assays in cell suspension culture of F. deltoidea var. kunstleri.
This study aimed to evaluate the significant extraction factors in achieving higher recovery yield of total polyphenols, phenolic acids and flavonoids content from Citrus limon peel using two-level factorial design. The effect of five independent factors including drying temperature (40-60 °C), methanol concentration (20-60%), extraction temperature (28-60 °C), extraction time (30-60 min) and storage duration (0-14 days) were evaluated. Among all the examined factors, results showed that drying temperature, storage duration and extraction temperature were the most significant and contributing factors affecting the total polyphenols, phenolic acids and flavonoids content of lemon peel at P