Purpose: This study was designed to determine if the addition of clean-label antimicrobials enhance the thermal inactivation of STEC in seasoned ground beef cooked at 60°C (140°F).
Methods: Thermal inactivation of STEC in a Control seasoned ground beef product was compared to treatments supplemented with 0.5% or 1.0% smoke flavoring fraction (SF; Zesti AM 10) or 0.8% dried vinegar (DF; DuraFresh™ 2016). Products were homogenized with either a 3-strain mixture of E. coli O157:H7 or a 6-strain mixture of non-O157 STEC (including O26, O45, O103, O111, O121, O145) to yield 8-log CFU/g. Samples (1 g portions) were flattened into thin films in moisture-impermeable pouches, vacuum-sealed, and heated to 60°C in a water bath. Triplicate samples were removed at 0, 2.5, 5, 7.5 and 10 minutes and immediately chilled to < 4°C. STEC was enumerated by plating on Sorbitol MacConkey agar overlaid with nonselective Trypticase Soy agar to enhance recovery of injured cells. Study was replicated twice.
Results: D-values at 60°C for the Control were 2.03 and 2.19 min for O157 and non-O157 STEC, respectively; D-values for products supplemented with 0.5% SF were not significantly different (P > 0.05). In contrast, addition of 1% SF reduced D-values to 1.45 and 1.34 min for the O157 and non-O157 treatments, respectively (P < 0.05). Although the additional of 0.8% DF reduced D-values of O157 to 1.02 min (P < 0.05), it did not enhance the thermal inactivation of non-O157 STEC compared to the control (D60=1.75 min; P > 0.05).
Significance: This study demonstrated that addition of certain clean-label antimicrobials can safely reduce the cook time for seasoned ground beef by enhancing the thermal inactivation of STEC, but STEC serotypes differ in sensitivity.