Biological screening of herbal extracts and essential oil from Plectranthus species: α-amylase and 5-lipoxygenase inhibition and antioxidant and anti-Candida potentials

Abstract The phenolic compound content, the antioxidant and α-amylase inhibition potentials of different extracts of the Plectranthus amboinicus, P. barbatus and P. ornatus were evaluated. We also evaluated the influence of plant growth and harvest time on the chemical composition of the essential oil (EO) of P. amboinicus, its antioxidant and anti-Candida activities and the α-amylase and lipoxygenase inhibitions. The turbo-extract of P. barbatus showed the greatest phenolic compound content and antioxidant activity. No α-amylase inhibition activity was observed in the analyzed extracts, but the turbo-extraction and refluxing extracts possessed high antioxidant activities. Protected cultivation and morning harvest conditions gave the best antioxidant activities, which was associated to the highest carvacrol content. P. amboinicus EO antioxidant activity could contribute to the reduction of oxidative stress in diabetes. Causal Candida strains of diabetic foot ulcers showed sensitivity to P. amboinicus EO. C. albicans and C. dubliniensis were the most sensitive of the selected Candida strains. Turbo-extracts or refluxing of the three species extracts and the EO of P. amboinicus should be considered as a potential candidate for the management the complications of type 2 diabetes.

Phenol content and antioxidant activity of different young and adult plant parts of tobacco from Tunisia, dried at 40 and 70 ºC.

Different parts of tobacco plants were dried at 40 and 70 ºC. Some of them were also dried at room temperature. Dried plant material was extracted by sonication for obtaining hydro-alcoholic extracts (70%). Total phenol and total flavonoids were determined as well as antioxidant activities which were evaluated through different methods (capacity for scavenging DPPH, ABTS, superoxide and hydroxyl radicals; capacity for preventing lipid peroxidation using egg yolk as substrate; and reducing power). In young and adult plants, leaves generally had higher amounts of phenols (14.46-23.05 mg GAE g-1) than the remaining parts of the plant, independent on the temperature used. Generally, roots had lower amounts of phenols (1.56-4.63 mg GAE g-1). Leaves and flower had significantly higher concentrations of flavonoids (3.08-4.17 mg QE g-1 and 1.17-2.12 mg QE g-1, respectively) than the remaining parts. The antioxidant activity was generally higher in leaf extracts, although stalk ones had also a good capacity for scavenging hydroxyl radicals. Generally, young plants had the best capacity for scavenging DPPH and hydroxyl free radicals which may be related with the phenol content. Concerning drying temperatures, the results were not conclusive.