In this study, potential of high hydrostatic pressure (HHP) and essential oils (EOs) as natural antimicrobials was evaluated to produce E. coli safe and quality beef product. First, the individual and combined effects of antimicrobial activity (minimum inhibitory concentration) of basil, black cumin, cilantro, cumin, fenugreek, ginger, oregano, black pepper, rosemary, thyme, turmeric oil emulsions on E. coli ATCC 25922 with and without HHP treatment were evaluated. Cumin, oregano and thyme EOs showed highest antimicrobial activity against E. coli ATCC 25922. The synergy of selected EOs against E. coli ATCC 25922 was determined using the checkerboard method to obtain fractional inhibitory concentration index. Although their combinations did not show synergy, they expressed synergy when combined with HHP (400 MPa, 10 min, 20 °C) and the best combination was cumin and oregano EOs with HHP.

Effects of HHP and EO combinations on inactivation of E. coli ATCC 25922 in beef were investigated using response surface methodology (RSM). Statistical analysis showed the model was significant for predicting log reduction with high accuracy. The significant model terms were pressure and time. Compared to control, HHP/EO treated samples showed no-post growth when stored up to 120 days at 4°C. Presented results suggests that the combination of HHP and antimicrobials has not only improved the process parameters (lowered pressure, time, and EO concentration) but also prevented recovery of E. coli ATCC 25922 during storage.

RSM was employed to analyze the synergistic effects of HHP and EOs on beef quality (color, texture and lipid oxidation). Color indices were significantly affected by pressure, time and their interactions. Above 400 MPa the discoloration was similar to cooked beef and EO addition did not help color improvement. However, EOs showed significant antioxidant activity on both treated and untreated samples during storage.

In conclusion, there is a great potential of HHP and EO combinations to enhance pathogen inactivation while keeping the quality of beef. Moreover, presence of EOs can prolong the shelf life of pressure treated beef. Therefore, the combination of HHP and EO is very promising for meat industry.