Encapsulation of Essential Oils in Food Grade Materials

The objective of this study was firstly to assess the ability of liquid skimmed milk in combination with different concentrations of maltodextrin (MD) to emulsify 5% w/w thyme essential oils (EOs). Secondly, to analyse the chemical composition of the used thyme EOs and further examine the physical properties of some EOs components such as solubility, surface activity and partitioning coefficient. Moreover, assessing the antibacterial activity of free and encapsulated EOs in vivo and in vitro mediums. From the results of thyme EOs analysis, 29 compounds were identified that containing different terpenes. The results show that skimmed milk with MD performed as an excellent delivery system for emulsifying thyme EOs with high stability for 60 days and formation of small size droplets < 234 nm. The produced powders obtained by spray drying the initial emulsions were analysed, and the results showed that increasing the concentration of MD from zero to 3 % w/w decreased surface oil, retained higher amounts of EOs with the encapsulation efficiency reaching up to 97.4 %. The antibacterial activity against Escherichia coli and Staphylococcus aureus was assessed by using free and encapsulated thyme EOs in the form of the solution or direct addition to the inoculum or food products. The minimum inhibitory concentration (MIC) was lowest 0.3 mg/mL against both Escherichia coli and Staphylococcus aureus, when encapsulated EOs was directly added to the inoculum and prolonged shelf-life of both skimmed and unpasteurised raw milk were attained with the same formulation. Furthermore, the food matrices had a great role in decreasing the antibacterial activity of EOs by decreasing the availability of the active components and preserving the bacteria cells from them. The encapsulation of EOs increased the bioactivity of thyme EOs. The combination of EOs and low temperatures had a significant role in increasing the shelf-life of whole unpasteurised milk.