Preparation and Investigation of Antioxidant, Antibacterial and Antityrosinase Potentials of O/W Nanoemulsions Containing Extract of Tamarindus indica L. Fruit Pulp

Abstract

Tamarindus indica L. or tamarind has been used for medical purposes since ancient time. In addition, interesting biological activities of tamarind make it appropriate for cosmetic or hygienic applications. In the present work, tamarind fruit pulp extract was selected as an active ingredient, aiming for cosmetic uses. The main objectives of the current study were to formulate o/w nanoemulsions as a carrier vehicle for tamarind fruit pulp extract, to investigate the stability of tamarind fruit pulp extract loaded nanoemulsions and to assess the antioxidant, antityrosinase and antibacterial potentials of the tamarind fruit pulp extract loaded nanoemulsions. In the beginning, four samples of tamarind fruit pulp extracts (both sour and sweet types) were investigated for their bioactivities which were antioxidant, antityrosinase, and antibacterial properties against two gram positive bacteria which were Staphylococcus aureus and Staphylococcus epidermidis. Two strains of bacteria commonly cause malodor in axilla areas. Owing to its outstanding bioactivities, the sweet tamarind fruit pulp extract from Guangzhou Phytochem Sciences Inc., China was chosen. Two concentrations of the sweet tamarind fruit pulp extract, 3.3%w/w and 6.6%w/w, which was 50-times and 100-times of ECso of antioxidant activity, were employed. For the formulation process, the blank nanoemulsions were firstly prepared and the optimum formulation would be selected as a vehicle for the sweet tamarind fruit pulp extract. The blank nanoemulsions consisted of 5%w/w surfactant mixture (Tween 80 and Span 80, as an emulsifier), synthetic oil (caprylic/capric triglyceride, as an emollient), water (as a vehicle), glycerine (as a humectant). Apart from the basic ingredients of nanoemulsions (oil phase and water phase), the hydrocolloids with different charge types: xanthan gum (anionic), guar gum (nonionic) and cationic guar gum (as thickeners) were also incorporated into the formulations and the influence of the charge types on the physicochemical properties of the nanoemulsions were also examined. The concentrations of the hydrocolloids used were 0.10 and 0.25%w/w. Seven formulations (F1-F7) of blank nanoemulsions were prepared using a high pressure homogenization process. The prepared blank nanoemulsions were examined for types, physicochemical properties (pH, viscosity, droplet size, zeta potential, polydispersity index (PDI)) and physical stability under stress conditions: 4 freeze- thaw cycles and storage for 1 month at three various temperatures, 4 ± 2°C, room temperature (30 ± 2°C) and 45 ± 2°C. It was found that all blank formulations were indicated as o/w using dye solubility and conductivity tests. The pH values of the formulations were between 6 to 7. The formulations with and without hydrocolloids displayed low viscosity. The droplet sizes of the blank nanoemulsions were in the range of 100-800 nm. The types of hydrocolloids affected the droplet sizes and the zeta potential of blank nanoemulsions. In general, the increased droplet sizes were observed in the formulations containing hydrocolloids. The freshly prepared nanoemulsions containing cationic guar gum displayed net positively charged zeta potential whereas the rest showed negative charge values. However, the surface charge of the formulations containing cationic guar gum changed to negative after 1 month stability test. The formulation without any hydrocolloids (F1) had the highest zeta potential (-63 mV) and low PDI, <0.2 with droplet sizes less than 200 nm. Therefore, the blank nanoemulsion without hydrocolloids (F1) was chosen to produce tamarind fruit pulp extract loaded nanoemulsions (lotions). The tamarind fruit pulp extract loaded nanoemulsions were checked for types, physicochemical properties, physical and chemical stabilities for 2 months as well as bioactivity properties as previously mentioned. The tamarind extract loaded formulations remained o/w type- nanoemulsions. For both concentrations (3.3 and 6.6%w/w), there were significant differences in physicochemical properties, in particular, conductivity values, pH and viscosity, between the blank nanoemulsions and tamarind extract loaded nanoemulsions (p < 0.05). Incorporation of tamarind fruit pulp extract into the blank nanoemulsions (F1) resulted in a decreased pH and a markedly increased viscosity and conductivity of the formulations (p < 0.05). Overall, the tamarind extract loaded nanoemulsions had droplet sizes approximately 130 nm, zeta potential about -38 mV and PDI values less than <0.2. The formulation which contained 3.3% tamarind fruit pulp extract (F1-3.3TE) exhibited better physicochemical properties as well as physical and chemical stabilities when compared with the formulation containing 6.6% tamarind fruit pulp extract (F1-6.6TE). The formulation which contained 6.6%w/w tamarind extract was not stable (phase separation) after storage at three temperatures for 2 months. According to high performance liquid chromatography (HPLC) analysis, tartaric acid, as a marker in tamarind fruit pulp extract, remained greater than 90% under stress conditions in the formulation F1-3.3TE. Using synthetic membrane and diffusion cells (in-house construction), similar to modified Franz diffusion cells, the in vitro release results revealed that the release profiles of tartaric acid (tamarind fruit pulp extract) from o/w nanoemulsions were fitted best to Higuchi model with the highest r2 of 0.97. In the case of bioactivity investigation, both tamarind fruit pulp extract loaded nanoemulsions were found to have antioxidant activity (2, 2-Diphenyl-1-picrylhydrazyl (DPPH) assay), antityrosinase property (Dopachrome technique) and antibacterial activity (agar well diffusion technique) against Staphylococcus aureus and Staphylococcus epidermidis. The most promising biological property of the tamarind fruit pulp extract loaded nanoemulsion was antibacterial activity since the antioxidant and antityrosinase activities of the formulations were declined under the stress temperature conditions. In conclusion, the current results showed the potential of developed tamarind fruit pulp extract loaded nanoemulsions for cosmetic application such as antiaging, skin lightening preparations and deodorant products.