CONICET | Buscador de Institutos y Recursos Humanos

Bergamot essential oil (BEO) is an aromatic oil with many health benefits: digestive, antifungal, bacteriostatic, antibacterial and antioxidant. This work aimed to study the antibacterial activity of bergamot essential oil encapsulated in β-cyclodextrin (BCD) by ultrasound-assisted co-precipitation method. Two bacterial strains were used to study the samples bioactivity, Staphylococcus aureus and Escherichia coli. These strains were selected due to their importance in the food industry. The antimicrobial activity was studied by two methodologies. First, an Agar diffusion test was performed according to the protocols described by the Clinical & Laboratory Standards Institute. Briefly, sterile blank filter discs of 13 mm diameter were dispensed over the surface of the Petri dishes with Muller-Hinton Agar and were impregnated with 100 μL of BEO or the equivalent oil in BEO-BCD complexes diluted in ethanol. Then, plates were inverted and placed at 36°C for 24h. Ethanol and BCD aqueous solution were used as negative controls, and ceftriaxone as positive control. On the other hand, inhibition in broth test was performed with S. aureus. BEO or the complexes were added to Peptone water (PWS, 0.1%) containing the microbial inoculum (103 UFC/mL) to obtain a 0.88 mg mL‒1 BEO concentration. The PWS with the microbial inoculum only or and with BCD were used as controls. The systems were shaken at 100 rpm, 35 °C for 2 h. Then, decimal dilutions were performed to seed plate seeding into Plate Count Agar. The plates were inverted and placed in an incubator at 35 °C for 24 h. In the Agar diffusion test, BEO demonstrated antimicrobial activity against E. coli and S. aureus. However, this test could not be performed for the BEO-BCD complexes at the proposed concentration because the amount of powder needed cannot be diluted to the desire concentration and held in the discs. The results indicated that BEO at the concentration tested had a strong antimicrobial activity against on S. aureus (32±1 mm inhibition), while on E. Coli, it had a moderate activity (18.1±0.5 mm inhibition). The study carried out by the broth dilution method allowed compares the microbial activity of the oil alone and of the complex. It showed that the inhibition of S. aureus growth was similar for the free BEO and for the complexes, being the inhibition 96.6 and 88.5 %, respectively. Encapsulation in BCD allows to have an antimicrobial oil in powder, easy to handle and storage, and probably more stable than in the liquid form. Results suggest that these BEO-BCD complexes could be interesting and practical for its use as a natural preservative in food.

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