2.2. Preparation and Inoculation of Meatballs

Meatballs were prepared and inoculated as previously described [20]. Briefly, freshly processed and finely ground veal (veal; ca. 97:3% (lean:fat)); finely ground beef (beef; ca. 90:10% (lean:fat)); or finely ground beef, veal, and pork (meat mix containing ca. 1/3 of each species of meat; ca. 90:10% (lean:fat)) were separately inoculated with the rifampicin-resistant STEC-8 cocktail (1 mL of inoculum to 100 g of ground meat) to achieve an initial inoculum of ca. 7.0 log CFU/g. The inoculated ground veal, ground beef, or ground meat mix (ca. 4.5 kg each) were separately combined with pasteurized liquid whole eggs (900 mL; EggBeaters^®; ConAgra Foods Inc., Omaha, NE, USA) and with flavored bread crumbs (850 g; Cento^®; Cento Fine Foods Inc., Thorofare, NJ, USA) using a commercial mixer (Univex SRM12; Univex, Salem, NH, USA). Portions (40 g each) of the inoculated batter were shaped into balls by hand, placed individually into nylon-polyethylene bags (Koch Supplies, Kansas City, MO, USA) and vacuum-sealed to 950 mBar. Each bag was then placed into a second vacuum-sealed nylon-polyethylene bag and stored either at –20 °C (i.e., frozen) or at 4 °C (i.e., refrigerated) for 16 to 18 h, before being subjected to pressurization as described below [21].