β-Cyclodextrins and Liposomes as encapsulating vectors of Oregano (Origanum vulgare L.) essential oil: Evaluation of their antimicrobial activity against Listeria monocytogenes and Salmonella spp. in "Kefir Milk" and "Katiki Domokou" cheese

Introduction: Encapsulation of oregano essential oil (OEO) protects it from oxidation and volatilization and is considered an alternative antimicrobial application.

Purpose: To study the antimicrobial activity against L. monocytogenes and Salmonella spp. of encapsulated OEO in two different inclusion complexes (β-CDs and liposomes), compared to free OEO in Kefir milk and Katiki Domokou cream cheese.

Methods: The encapsulation of OEO in β-CDs was performed with the co-precipitation method in two different ratios of OEO:β-CDs (1:99 and 8:92). The thin-film hydration method was used for the incorporation of OEO into liposomes at a concentration of 0.88% v/v. The samples were inoculated with pathogens (6 log CFU/g) and incubated at 7⁰C for 17 days. Yeasts, lactic acid bacteria, pH and a_w were also measured.

Results: At the end of storage time in Kefir, free OEO caused about six-log reduction of L. monocytogenes, OEO encapsulated in 8:92_β-CDs and liposomes caused 5.1 and 3.4 log reduction, respectively. Ratio 1:99 could not be applied to kefir because changed its physicochemical characteristics. Salmonella spp. was much more sensitive as it was below detection limit after 1^st day of incubation at all treatments. In Katiki cheese, when free, 8:92 β-CDs, 1:99 β-CDs and liposomes were applied, the population of L. monocytogenes reduced at 4.6 ± 0.9, 3.9 ± 0.2, 5.6 ± 0.3 and 5.3 ± 0.0 log CFU/g, respectively, after 17 days. When free and 8:92 β-CDs OEO were applied, Salmonella spp dropped below quantification limit by the end of storage time. Conversely, the population of Salmonella was 1.0 ± 0.8 and 1.3 ± 1.3 log CFU/g in the presence of 1:99_β-CDs and liposomes, respectively. Free and encapsulated OEO reduced lactic acid bacteria and yeasts in kefir while had no effect against the microbiota of katiki cheese. The addition of liposomes increased the pH of Kefir.

Significance: Different inclusion complexes had different antimicrobial activity, which may also be affected by food matrix and microorganisms.