Effect of Ultrasound-Assisted Maceration on Yield Percentage, Chemical Compound and Antimicrobial Activity of Citrus nobilis Peel Essential Oil

Increasing concerns about the activity of antibacterial growth promoters have prompted the need to discover alternatives from natural materials that can be found in various types of plants and herbs. Siamese orange peels (Citrus nobilis) are one of the plentiful organic waste-containing essential oils known for their antibacterial, antioxidant, and other biological properties promising as the potential alternative to antibiotic growth promoters in livestock. This study aimed to evaluate the antimicrobial properties of orange peel essential oil between 2 different extraction methods and the effect of different solvent ratios on the yield of citrus essential oil, chemical compounds, and the antibacterial activity against Escherichia coli and Lactobacillus casei. The evaluated methods were ultrasonic-macerated citrus essential oil (UMCEO) and conventional-macerated citrus essential oil (CMCEO), while the solvent ratios were 1:2, 1:4, and 1:6. The result showed that the solvent ratio was found to significantly give effect (P<0.05) to the yield of citrus peel essential oil with a solvent ratio of 1:2 obtaining the highest yield. Pretreating the citrus peel with ultrasound before hydro-distillation did not give a significant effect (P>0.05) on the chemical compounds of the citrus essential oil as analyzed by GC-MS. Both citrus essential oils were predominantly composed of cycloheptane (CMCEO: 48.5%; UMCEO: 44.09%) and d-limonene (CMCEO: 26.76%; UMCEO: 36.02%). The CMCEO showed a higher inhibition zone against Escherichia coli and Lactobacillus casei. The conclusion is that CMCEO seems to produce citrus peel essential oil with a stronger antibacterial effect against Escherichia coli and Lactobacillus casei, in particular with solvent ratio 1:2.