PHYSICOCHEMICAL PROPERTIES, ANTIOXIDANT AND ANTIMICROBIAL ACTIVITIES OF MANDARIN (Citrus reticulata Blanco.) PEEL AND PULP OIL

Abstract

The citrus peel which is almost one half of the total fruit mass is a rich source of phenolic compounds such as flavanones, flavonols and many polymethoxylated flavones. The growing interest of shifting from the synthetic antimicrobial agents to natural ones has encouraged research on screening of plant material and other vegetable sources to identify new compounds. On account of such justification the present study was aimed to examine physicochemical properties, antioxidant and antimicrobial activities of oil extracted from mandarin peels and pulp.The oil extraction was done in Soxhelt apparatus using hexane as a solvent. The physicochemical properties of mandarin fruit peel and pulp oil extracts were measured based on oil content, acid value (AV), free fatty acids (FFA), and peroxide value (PV). The antioxidant activity was determined based on free radical scavenging activities of DPPH and hydrogen peroxide, as well as ascorbic acid. The antimicrobial experiment was arranged as 2x1x4 following completely randomized factorial design in two replications using disc diffusion method and broth dilution method. The antimicrobial activity was analyzed in respect to zone of inhibition diameter. The study has shown that, significantly higher oil content (26.00%), specific gravity (0.88%) and acid value (1.54), and FFA (0.78%) were recorded for peel oil extract. However, significantly higher peroxide value (3.10mg/kg) was observed for mandarin fruit pulp oil extract. It was observed that significantly higher DPPH (22.25±0.14) and ascorbic acid content (28.24±3.56) was observed for mandarin fruit pulp oil extract while, significantly higher hydrogen peroxide scavenging activity (48.30±3.11) was obtained for the peel oil extract. The strongest antibacterial activity with maximum zone of inhibition (17.25mm) was recorded for C. reticluata fruit peel oil extracts against E. coli (gram negative) indicating that E. coli was more susceptible to the oil extract than S. aureus. That is Gram negative bacteria are susceptible to the oil extract. The antifungal activity of oil extracts with colony growth inhibitory effect at the highest dose presented considerable mean zone of inhibition ranged from 11.25±0.35 to 14.50±0.71mm. Fluconazole (used as positive control) showed a significant superiority (p<0.05) in the zone of inhibition as compared to the test oil extracts. The strongest antifungal activity with maximum zone of inhibition (14.50mm) was recorded for pulp oil extract against C. albicans while the weakest antifungal activity with minimum zone of inhibition (11.25mm) was recorded for peel oil extract against A. niger indicating that pulp oil exhibited more effective antifungal than peel oil and C. albicans was more susceptible to the antifungal oil extract than A.niger. The peel oil has presented strongest antibacterial activity with MIC (0.03μl/ml, least value) and MBC (0.06μl/ml) against E. coli indicating that the peel oil extract was more effective bacteritoxic than pulp oil and E. coli (gram negative) was more susceptible to the oil extract than S. aureus (gram positive). Further studies are recommended to identify phytoconstituents of the plant and their biological activities by using different techniques and test pathogens