Antibacterial activity and stability of microencapsulated lemon grass essential oil in feeds for broiler chickens

SUMMARY The antibacterial effect of microencapsulated lemon grass (Cymbopogon citratus) essential oil on strains of Escherichia coli (ATCC8739), Staphylococcus aureus (ATCC 6538) and Salmonella enterica subsp. enterica (ATCC 6017), and the stability of this oil in feeds for broiler chickens were evaluated. The Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) were determined by the macrodilution method, using the microencapsulated lemon grass essential oil at concentrations of 160 μL mL−1, 80 μL mL−1, 40 μL mL−1, 20 μL mL−1, and 10 μL mL−1. The oil concentration of 80 μL mL−1 presented the best results against the three bacteria evaluated. Samples of 200 g of feed mixed with 120 μL g−1 of the microencapsulated lemon grass essential oil was stored to evaluate the oil stability. Feed without microencapsulated lemon grass essential oil was prepared as control. The oil remained active for seven days, with significant reduction of S. aureus (3.08 CFU), E. coli (3.01 CFU), and S. enterica (3.10 CFU). The microencapsulated lemon grass essential oil at concentration of 80 μL mL−1 had antibacterial effect against the E. coli, S. enterica and S. aureus, and maintained stability of the feed for seven days, even with presence of organic matter, which is source of nutrients for pathogens.摘要：本研究评估了微胶囊化柠檬草（Cymbopogon citratus）精油对大肠杆菌（ATCC 8739）、金黄色葡萄球菌（ATCC 6538）及肠炎沙门氏菌肠炎亚种（ATCC 6017）菌株的抗菌活性，同时考察了该精油在肉鸡饲料中的稳定性。采用常量稀释法，以浓度分别为160 μL·mL⁻¹、80 μL·mL⁻¹、40 μL·mL⁻¹、20 μL·mL⁻¹及10 μL·mL⁻¹的微胶囊化柠檬草精油测定最低抑菌浓度（Minimum Inhibitory Concentration，MIC）与最低杀菌浓度（Minimum Bactericidal Concentration，MBC）。结果显示，浓度为80 μL·mL⁻¹的该精油对三种受试菌均表现出最优抗菌效果。称取200 g饲料与120 μL·g⁻¹的微胶囊化柠檬草精油混合后储存，以评估精油稳定性；同时制备不含微胶囊化柠檬草精油的饲料作为空白对照。实验结果表明，该精油可维持7天的抗菌活性，受试的金黄色葡萄球菌、大肠杆菌及肠炎沙门氏菌的菌落数分别显著降低3.08 CFU、3.01 CFU及3.10 CFU。浓度为80 μL·mL⁻¹的微胶囊化柠檬草精油对大肠杆菌、肠炎沙门氏菌及金黄色葡萄球菌均具有抗菌活性，且即便存在作为病原菌营养来源的有机物时，仍可使饲料稳定性维持7天。