THERMAL RESISTANCE, SURVIVAL AND INACTIVATION OF ENTEROBACTER SAKAZAKII (CRONOBACTER SPP.) IN POWDERED AND RECONSTITUTED INFANT FORMULA

Abstract

ABSTRACTEnterobacter sakazakii has recently been recognized as an opportunistic foodborne pathogen, and dry infant formula serves as the mode of transmission. The objectives of this study were to investigate the heat resistance, survival and inactivation under room and refrigeration temperatures storage of dry and reconstituted infant formula milk (IFM). E. sakazakii strains (eight strains) showed a wide variability in heat resistance at different temperatures (55, 60 and 63C). The D‐values at 55C ranged from 1.51 to 14.83 min, at 60C from 0.17 to 2.71 min and at 63C from 0.05 to 0.88 min. The calculated z values for the studied E. sakazakii strains ranged from 3.76–10.11C. Microwave oven heating of 60‐mL portions of reconstituted IFM for 40–50 s was effective in eradicating inoculated E. sakazakii. Storing powdered IFM for 15 days at 4C resulted in at least a 1‐log reduction in E. sakazakii strains, whereas storing reconstituted IFM at 4C for 2 weeks resulted in more than a 2‐log reduction in E. sakazakii.PRACTICAL APPLICATIONSThis study shows that E. sakazakii strains differ widely in their heat resistance. No differences were observed between biofilm formers and nonformers in terms of heat‐resistance in thermal inactivation kinetics experiments. Conventional high temperature short‐time pasteurization processes are considered sufficient to inactivate all E. sakazakii strains, and a household microwave oven (40–50 s for 60‐mL portions) can be used to inactivate E. sakazakii if present in reconstituted infant formula milk (IFM). Growth of E. sakazakii can be inhibited in powdered and reconstituted IFM by refrigeration. Also, it is recommended that reconstituted IFM be discarded or refrigerated if not immediately consumed. The probiotic L. acidophilus ATCC 4356 was not effective in inhibiting E. sakazakii in powdered or reconstituted IFM.