Inactivation kinetics of Cronobacter sakazakii and Salmonella enterica in reconstituted powdered infant formula and survival during subsequent storage.

Powdered infant formula (PIF) has been implicated as a potential vehicle for foodborne pathogens, such as Cronobacter sakazakii and Salmonella enterica, which can cause life-threatening infections in infants. For high-risk infants, public health agencies recommend using hot water to reconstitute PIF for safety. This study evaluated the influence of reconstitution water temperature on pathogen inactivation and subsequent survival and growth during storage. Milk-based (MB) and soy-based (SB) PIF were inoculated with C. sakazakii or S. enterica via spray atomization and left to stabilize for 1 month. Inoculated PIF was reconstituted using water at 25, 45, 70, 85, or 100 °C. A low-volume (LV) and a high-volume (HV) preparation were assessed. The dynamic log-linear model was applied to describe pathogen inactivation kinetics, and storage studies were subsequently conducted at 5, 10, and 25 °C for up to 48 h. Increasing the initial water temperature significantly enhanced pathogen inactivation in PIF, with substantial population reductions (>4 log CFU/mL) achieved with 85 and 100 °C water. Reconstitution of PIF at 70 °C provided moderate inactivation (2-3 log CFU/mL reduction). Sample volume had inconsistent effects on inactivation rates, with HV samples exhibiting slower cooling but not always greater pathogen reductions. Both pathogens demonstrated heat resistance, with observed outgrowth of S. enterica in SB-PIF at certain volume-temperature combinations. During storage of reconstituted PIF, both pathogens demonstrated regrowth at 25 °C, minimal to no growth at 10 °C, and no growth at 5 °C after 48 h. These findings highlight the need for immediate consumption or refrigeration of reconstituted PIF after preparation. The results of this study provide information on the safe preparation and handling of PIF by quantifying temperature-dependent pathogen inactivation in two different formulations.