Abstract:The antibacterial activity and antioxidant effect of the compounds α-terpineol, linalool, eucalyptol and α-pinene obtained from essential oils (EOs), against pathogenic and spoilage forming bacteria were determined. The antibacterial activities of these compounds were observed in vitro on four Gram-negative and three Gram-positive strains. S. putrefaciens was the most resistant bacteria to all tested components, with MIC values of 2% or higher, whereas E. coli O157:H7 was the most sensitive strain among the tested bacteria. Eucalyptol extended the lag phase of S. Typhimurium, E. coli O157:H7 and S. aureus at the concentrations of 0.7%, 0.6% and 1%, respectively. In vitro cell growth experiments showed the tested compounds had toxic effects on all bacterial species with different level of potency. Synergistic and additive effects were observed at least one dose pair of combination against S. Typhimurium, E. coli O157:H7 and S. aureus, however antagonistic effects were not found in these combinations. The results of this first study are encouraging for further investigations on mechanisms of antimicrobial activity of these EO components.

The efficacy of short wave ultraviolet light (UV-C) as a non-thermal process for liquid egg products (LEP) was investigated. Nonpathogenic Escherichia coli strain (ATCC 8739), which shows lower sensitivity to UV-C light than E. coli O157:H7 and Salmonella typhimurium, was chosen as a target microorganism. The inactivation of UV resistant strain of E. coli in LEP was examined by evaluating the effects of depth of liquid food medium (0.5, 0.3 and 0.153 cm), UV light intensity (1.314, 0.709 and 0.383 mW/cm 2 ) and exposure time (0, 5, 10, and 20 min) by using a collimated beam apparatus. The best reduction (>2-log) was achieved in liquid egg white (LEW) when the fluid depth and UV intensity were 0.153 cm and 1.314 mW/cm 2 , respectively. Maximum inactivation was 0.675-log CFU/ml in liquid egg yolk (LEY) and 0.316-log CFU/ml in liquid whole egg (LWE) at the same conditions. The kinetics of UV inactivation of E. coli in LEP was nonlinear. Our results emphasize that UV-C radiation can be used as a pre-treatment process or combined with mild heat treatment to reduce the adverse effects of thermal pasteurization of LEP.

The efficiency of UV-C irradiation as a non-thermal pasteurization process for liquid egg white (LEW) was investigated. LEW inoculated with Escherichia coli K-12 (ATCC 25253), pathogenic strain of Escherichia coli O157:H7 (NCTC12900) and Listeria innocua (NRRL B33314) were treated with UV light using a bench top collimated beam apparatus. Inoculated LEW samples were exposed to UV-C irradiation of known UV intensity of 1.314 mW/cm 2 and sample depth of 0.153 cm for 0, 3 5, 7, 10, 13, 17 and 20 min. The populations of E. coli K-12, E. coli O157:H7 and L. innocua were reduced after 20 min of exposure by 0.896, 1.403 and 0.960 log CFU respectively. Additionally, the inactivation data obtained for each strain suspended in LEW was correlated by using Weibull (2 parameter), Log-Linear (1 parameter), Hom (2 parameter) and modified Chick Watson (2 parameter) models. The inactivation kinetics of E. coli K-12, E. coli O157:H7 and L. innocua were best described by modified Chick Watson model with the smallest root mean squared error (RMSE) (R 2 ≥ 0.92).

In this study, thyme and clove essential oils (EOs) were studied for their chemical composition, antioxidant, antiradical and antibacterial activity and application in ground beef. Carvacrol (75.27%) and eugenol (75.2%) were detected by gas chromatography-mass spectrometry analysis as the main components of thyme and clove EOs, respectively. Broth microdilution method showed all bacteria inhibited by the EOs, while Shewanella putrefaciens and Listeria innocua were the most resistant bacteria to thyme and clove EOs, respectively. EO treatment restricted the growth of artificially inoculated Salmonella typhimurium and native Coliforms in the ground beef. Antioxidant activity determined by ferric-reducing antioxidant power and 1,1 diphenyl-2-picrylhydrazyl methods demonstrated that clove EO had higher in vitro antioxidant activity than thyme EO. Similar results were obtained in ground beef application using 2-thiobarbituric acid value. EOs of clove (2MIC) exerted remarkable higher antioxidant activity in ground beef than EOs of thyme (4MIC), which represent valid alternative antioxidant in meat products. PRACTICAL APPLICATIONSPlant essential oils (EOs) serve as a "safe" alternative to chemical or synthetic antimicrobials and antioxidants to struggle with the foodborne pathogens or spoilage organisms, inhibiting lipid oxidation and thus extending shelf life. Antioxidant activity determined by ferric-reducing antioxidant power and 1,1 diphenyl-2-picrylhydrazyl methods showed that clove EO had higher in vitro antioxidant activity than thyme EO. Results obtained using 2-thiobarbituric acid value in ground beef application were found similar. EOs of clove (2MIC) exerted higher antioxidant activity in ground beef than EOs of thyme (4MIC). Therefore, EOs could be a valid alternative antioxidant in meat products.

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