Quality preservation of deliberately contaminated milk using thyme free and nanoemulsified essential oils

The objective of this study is to evaluate the effect of either a solution of Thymus capitatus essential oil or its nanoemulsion on the quality of milk contaminated by bacteria. After 24 h of S. aureus inoculation, bacterial growth reached 202 × 103 CFU/ml in the presence of the essential oil while it was limited to 132 × 103 CFU/ml when treated with nanoemulsion. The reduction of antioxidant capacity of milk treated with essential oil was higher when treated with nanoemulsion. Moreover, free essential oil was more efficient in protecting proteins from degradation than the nanoemulsion. For instance, after 24 h of E. hirae contamination, 26% of the total proteins were consumed in the presence of nano-encapsulated essential oil, while only 14% of the initial content was consumed when free essential oil was added. Concerning milk acidity increase and the inhibition of peroxide production, no statistical differences have been recorded between the use of free essential oil or its nano-emulsion. In conclusion, bulk or nano-encapsulated T. capitatus essential oil preserve milk quality and can extend its shelf life.