Nanoencapsulation Approach to Improve Antimicrobial and Antioxidant Activity of Thyme Essential Oil in Beef Burgers During Refrigerated Storage

In this study, thyme essential oil (TEO) loaded chitosan nanoparticles (CS-NP-TEO) are prepared by a two-step process including oil/water emulsion and ionic gelation. Five batches of burgers were prepared by following formulation: control (without any TEO), F-0.05-TEO (0.05 % of free TEO), F-0.1-TEO (0.1 % of free TEO), E-0.05-TEO (0.05 % of encapsulated TEO), E-0.1-TEO (0.1 % of encapsulated TEO), and AA-0.05 (0.05 % of ascorbic acid). All samples treated with TEO significantly reduced the population of investigated microbial counts (P < 0.05) compared to the control during 8 days of storage. At the end of storage, E-0.05-TEO and E-0.1-TEO, presented, respectively, 2.2 and 3 log cycles reduction of Enterobacteriaceae, along with 3.1 and 3.7 log cycles reduction of Staphylococcus aureus. Oxymyoglobin content and redness values reduced with the increase of storage time for all samples. However, AA-0.05 and E-0.1-TEO samples were more efficient at inhibiting discoloration in comparison with E-0.05-TEO and burgers treated with free TEO after 6th day of storage. A significant improvement (P < 0.05) in the reduction of thiobarbituric acid reactive substances (TBARS) amount was found for all TEO treated burgers in comparison to control samples after 8 days chilled storage. According to the results of sensory analyses, F-0.1-TEO and AA-0.05 samples at 4 days and F-0.05-TEO sample at 8 days of storage were rejected by assessors and considered as an unacceptable case. On the basis of our results, the encapsulation of TEO in chitosan nanoparticles may be a promising technology for the control of undesirable microbial, chemical, and sensorial changes in meat products.