Thermal inactivation kinetics of Cronobacter spp. (Enterobacter sakazakii) in infant formula and buffer system with Various aw and pH.

Abstract

Cronobacter spp. (Enterobacter sakazakii) is an emerging opportunistic pathogen thas has been reported to cause meningitis, septicemia, dan necrotizing enterocolitis (NEC) outbreaks linked to Powdered Infant Formula (PIF) consumption. Most of the outbreaks occurred in the hospital involving infants younger than 28 days old, premature infants, or infants with low birth weight (< 2500 g) possibly due to their undeveloped immune system. Cronobacter spp. may contaminate PIF during processing and or during its preparation prior to consumption. Several Cronobacter spp. isolates have been reported to have a higher heat resistance than other Enterobacter. Isolation of Cronobacter spp. from PIF, weaning foods, and other dry food has been reported in Indonesia. However, assessment on the heat resistance of the isolates is still limited. This research aimed to obtain the inactivation kinetics parameters (D, Z values) of local isolates of Cronobacter spp. in PIF and menstruum modified to achieve various aw and pH. The study was conducted by inoculating late log phase culture of Cronobacter spp. into thermal death time (TDT) tubes containing PIF or PIF with various aw (modified with sucrosa or NaCl) or adjusted with buffer Mcllvaine to achieve several pHs. TDT tubes were heated at constant temperatures of 50, 52, 54, 56, or 58 oC for 0-182 minutes. The number of Cronobacter spp. surviving the heating proces was enumerated on TSAYE. The correlation between heating time at different temperatures with the number of surviving Cronobacter spp. were plotted into TDT curves and the D and Z values were calculated. D-values of isolates of Cronobacter spp. obtained in this study were in the range of 3.61-11.36 minutes at 56 oC and 68.97-256.41 minutes at 50 oC. These values were similar with the values reported by other researcher. Z-values calculated for isolates of Cronobacter spp. studied were 3.54-5.69 oC. The Z-values obtained were also within the range of those reported in the literatures. This study showed no significant effect of water activity (aw) and pH on inactivation kinetics of YR t2a isolate.