Physiochemical properties, antibacterial, antifungal, and antioxidant activities of essential oils from orange (Citrus nobilis) peel

The continuous fresh consumption or juice production of orange fruits (citrus nobilis) has discarded a vast number of orange peels, which has caused significant impacts on environmental issues. This study attempted to utilize discarded orange peels to extract essential oils (EOs) and evaluated their physiochemical properties, antibacterial, antifungal, and antioxidant activities. EOs were extracted via a distillation system using a Clevenger apparatus and gas chromatography - mass spectrometry analysis was employed to characterize their chemical components. The antibacterial and antifungal test were evaluated using a well diffusion method, and antioxidant activity was determined based on DPPH radicals scavenging effect and ferric reducing antioxidant power (FRAP). The obtained EOs with the yield of 3.29 ± 0.24% in which limonene was found to be the most abundant compound in the EOs (90.42%) followed by β-myrcene (4.7%) and α-pinene (1.22%). The result showed that Gram-positive bacterium (Bacillus cereus) was susceptible to the 50% EOs than Gram-negative bacterium (Escherichia coli) with respect to inhibitory zone diameter of 15.00 ± 0.58 mm and 11.33 ± 0.58 mm. The 50% EOs also inhibited nearly 70% of the mycelial growth of Aspergillus flavus as well as exhibiting antioxidant activity with IC50 values of  0.15 ± 0.01 mg/mL and 18.29 ± 0.13 mg/mL for DPPH and FRAP assay, respectively. The orange peel EOs could be a promising alternative to synthetic preservatives in food industry due to their antimicrobial and antifungal activity as well as their antioxidant activity.