Encapsulation process optimization, physicochemical and in-vitro biological activity investigation of Boswellia Carterii essential oil

Abstract

Boswellia carterii essential oil (BCEO) is considered a biologically important aromatic volatile oil for its antimicrobial and antioxidant activities. It is extracted from the harvested oleo gum resin, mostly by the hydro-distillation process. However, the delicacy and vulnerability of the BCEO to the environmental conditions (temperature, humidity, and extreme pH) reduced its biological activity tremendously. Hence, to overcome these challenges this research implemented the microencapsulation method of BCEO by the spray drying process. Chitosan, Polyethylene glycol (PEG), and Gum Arabic (GA) were compared for their encapsulating abilities of BCEO. Hence, the first two polymers showed less solubility in water and incompatibility to the spray drying process, respectively. Whereas the GA shows excellent water solubility and high compatibility with the spray drying process, hence, optimization of the process parameters was performed to obtain the best microencapsulation efficiency (EE). Effects of three factors i.e. inlet air temperature (IAT) feed flow rate (FFR) and aspirator (AS) on the quality of the micro-particles obtained were investigated. Hence, the BCEO Microparticles (mp) obtained by IAT, FFR, and AS at 160oC, 5-7ml/min, and 80-90%, respectively, show the highest EE (75%), the lowest moisture content (4%), and the best antimicrobial and antioxidant activities. Microparticles characterization analysis showed that it has good stability with (ζ-potential of -28mV), non-homogenous particle size, hence higher Polydispersity index (PDI >0.5), lower moisture content (4 to 12%), which is good for the prolonged shelf life of the particles. Furthermore, scanning electron microscopy (SEM), Thermogravimetric, and differential scanning calorimetry analysis (TGA & DSC) of the samples uncovered a spherical shape of the particles and their maximum degradation point of 300oC respectively. No functional group interaction was noticed between encapsulated BCEO and its coating GA polymer when Fourier transform infrared spectroscopy (FTIR) was implemented. Finally, the selected sample of BCEOmp has been tested for its biological (antimicrobial and antioxidant) activity, the DPPH method was implemented for antioxidant activity elucidation, hence, the gradient increase trend of the antioxidant activity is showing a dose-dependent phenomenon. The IC50 value of the Ascorbic acid (AA) was approximated at 7.5μg/mL, whereas the IC50 value of the microencapsulated BCEO was estimated at 9.79μg/ml. Moreover, the encapsulated BCEO exhibited a highly significant zone of inhibition (30±3mm), which are comparable to and even sometimes better than that of the Tetracycline drug (used as a positive control). Adding to that its minimum inhibitory and minimum bactericidal concentrations (MIC & MBC) (16 - 32 μg/mL and 32 - 60 μg/mL respectively) are highly significant, considering this is a crude EO and not a purified compound contrary to that of the standard drug. In conclusion, the BCEO's vulnerability to the environmental conditions could be overcome by implementing the microencapsulation method which protected the EO from surrounding environmental conditions. Moreover, the GA polymer exhibited excellent encapsulating properties.