Phytochemicals and biological activities of Sudanese Frankincense (Boswellia Papyrifera) extracts

Abstract

There are certain negative residual side effects of synthetic drugs. So, natural products from plants have been identified as alternative sources of bioactive compounds to combat diseases related to oxidation, cancer, diabetes, and microbial infections. Researchers have harnessed the plant metabolites as sources of bioactive compounds that can help withstand biotic and abiotic stress in the environment. Recent advancement in technology has greatly assisted in exploring the natural products in plant. Resin exudates from the Sudanese Frankincense (Boswellia papyrifera) have been traditionally used as incense and raw material in the food, perfume, and pharmaceutical industries. It is believed that it contains bioactive compounds. Thus, potential application in natural therapeutic drug and as food supplement. However, scientific data that can support the wider acceptance of the Sudanese Frankincense is still lacking. This study aims to systematically elucidate the potential bioactive content of Sudanese Frankincens. It attempted to select the suitable extraction methods to recover these bioactive compounds, optimize the process conditions for the recovery followed by the investigation of its bioactivities. Three samples of Sudanese Frankincens have been collected from three different geographical locations of Sudan. The resin exudates were subjected to proximate analysis, minerals tests, solubility, and phytochemical screening before extraction with different solvents and methods, namely maceration (chloroform, methanol, petroleum ether, hexane, acetone, and ethyl acetate), steam and hydro distillation, Soxhlet extraction (hexane and ethyl acetate) and supercritical fluid extraction. Also, optimization of extraction by maceration method was conducted using Face-Centered Central Composite design (FCCCD, Design- Expert software version 7.0) under Response Surface Methodology (RSM) and Soxhlet extraction using One-Factor at a Time (OFAT). For maceration extraction, the factors considered were time, agitation, and sample to solvent ratio. For characterization, two techniques were implored which are: Gas Chromatography-Mass Spectrometry (GC- MS) and Fourier Transform Infra-Red spectroscopy (FTIR). The extract recovered by optimal process conditions underwent bioactivity tests (antioxidants with three different assays, antibacterial for four strains, antidiabetic, and anticancer assays). Proximate analysis results showed that the extract, among others, contains significant amounts of minerals like calcium and iron and insignificant amounts of heavy metals such as cadmium and lead. Overall, Soxhlet extraction gave higher yield and showed the most bioactivity among other methods of extraction attempted. The optimization study on the extraction condition was carried out using DPPH activities and yield as the response. It was revealed that extraction time impacts yield and solvent ratio impacts the DPPH activities. The yield of the crude extracts varied greatly over different extraction technique and localized species. Soxhlet extraction using ethyl acetate gave the highest yield while supercritical fluid extraction gave the lowest yield. The yields from the various extraction techniques in increasing order was found to be: SFE < HD < MC < SE (ethyl acetate). As for the optimization of the maceration technique, the FCCCD result showed that the yield ranges from 50.00 to 93.00% and the DPPH antioxidant activities ranges from 11.00 to 48.00 in all the 20 runs. The ANOVA results show that Lack of Fit is not significant with p-values of 0.9779 and 0.8442 respectively for yield and DPPH. Anticancer studies showed that the extracts were positive against two melanoma cells, namely A375 and 3T3 cell lines. The results showed that the extract was dose-dependently inhibiting the proliferation of these two cancer cell lines whereby the IC50 values were 44 µg/ml and 39.36 µg/ml for A375 and 3T3 cell lines, respectively. The Sudanese Frankincense extract was also shown to demonstrate some potential antidiabetic activities when it showed positive responses towards α-amylase assay and α-glucosidase inhibitory assays. Antibacterial studies showed that the freeze- dried Soxhlet ethyl acetate and hydro distillation extract inhibition zones against B. subtilis are 1 mm and 2-3 mm, respectively. It was observed that all extracts have an antibacterial effect against the bacteria P. aeruginosa. All FTIR spectra of different extracts showed bands at 3445.91cm-1 that correspond to OH stretching but at different intensities. Some other spectra were observed, inferring the presence of different molecules in the extracts, such as 1260.75 cm-1 ascribed to S=O stretching vibration, 1624.25 cm-1 to COOH of carboxyl groups, 2958.3 cm-1 to C-H stretching, 1418.77 cm- 1 to scissoring vibration of CH2 and 817.94 cm-1 for C-O-S. Analyses of the essential oils of the Sudanese Frankincense by GC-MS revealed that it contains α amyrin, (1S,2E,4S,5R,7E,11E)-Cembra-2,7,11-trien-4,5-diol, β amyrin, acetic acid, octyl ester, 1,3,6-Octatriene, 3,7-dimethyl, 1-octanol-1,6-octadien-3-ol, 3,7-dimethyl-nerolidyl propionate, 1,3-dimethyl-1-cyclohexene, trans-β-ocimene, eucalyptol, cineole, β- myrcene, geranyl acetate, nerolidol isobutyrate, (4E) cyclohexane, D. limonene, pinenes, and others. Based on the proximate results it is suggested that the extract can be used in beverages and functional foods since it contains significant amounts of minerals like calcium and iron which can be taken as a food supplement.