¬¬¬¬ SURVIVAL OF Cronobacter sakazakii IN SKIM MILK DURING SPRAY DRYING, STORAGE AND RECONSTITUTION

Abstract

Cronobacter sakazakii is an emerging pathogen known to survive dry conditions and its presence in powder infant formula (PIF) has been linked to several outbreaks. In Indonesia, isolation of this bacterium from various foods have been reported. The objective of this study was to determine the effect of spray drying and storage humidity on the survival of C. sakazakii YRc3a in skim milk and their viability upon reconstitution. The survival of Cronobacter during spray drying was determined by comparing the number of bacteria before and after drying. The viability of Cronobacter in spray dried skim milk (SDSM) during storage was observed at weeks 1 to 8 and 12. At the same intervals, SDSM containing the pathogens was reconstituted at either 27°C or 50°C and the survivors were enumerated. The data were plotted to yield survival curves. Spray drying caused 4.19 log CFU/g reduction of Cronobacter and the bacteria experiencing drying were less sensitive to reconstitution at 50°C. During storage, the water activity of SDSM reached equilibrium at week 2 and afterwards, they started to decrease when stored at 50% or 90% RH, but maintained its viability at 70% RH. Storage at 50% and 90% RH accelerated the death rate of C. sakazakii YRc3a, resulting in the decline of the viable counts for 3 log cycles. At 50% RH, C. sakazakii Yrc3a decreased significantly, but the survivors exhibited increased heat resistance with the lowest reduction upon reconstitution at 50°C (0.16 log CFU/ml). ABSTRAKCronobacter sakazakii adalah patogen bawaan pangan emerging yang dilaporkan mampu bertahan dalam kondisi kering dan keberadaannya dalam susu formula telah dihubungkan dengn beberapa kejadian luar biasa. Di Indonesia, isolasi bakteri ini dari beberapa jenis pangan telah dilaporkan. Tujuan penelitian ini adalah untuk mengetahui pengaruh pengeringan semprot (spray drying) dan pengaruh kelembaban relatif terhadap sintas C. sakazakii YRc3a dalam susu skim selama penyimpanan serta viabilitasnya setelah direkonstitusi dengan air. Sintas Cronobacter selama pengeringan semprot ditentukan dengan membandingkan jumlah Cronobacter sebelum dan setelah pengeringan. Viabilitas Cronobacter dalam susu skim hasil pengeringan semprot (SSPS) selama penyimpanan diamati setiap minggu dari minggu 1-8 dan minggu ke 12. Pada interval yang sama, SSPS yang mengandung Cronobacter direkonstitusi dengan air bersuhu 27°C atau 50°C dan bakteri yang bertahan hidup dihitung. Data yang diperoleh kemudian diplot untuk menghasilkan kurva sintas. Pengeringan semprot menurunkan Cronobacter sebanyak 4,19 log CFU/g dan bakteri patogen yang telah mengalami pengeringan menjadi kurang sensitif terhadap suhu rekonstitusi 50°C. Selama penyimpanan, aktivitas air (Aw) SSPS mencapai ekuilibrium pada minggu ke 2 dan setelah itu patogen mulai menurun jumlahnya jika disimpan pada RH 50% atau 90%, tetapi dapat mempertahankan viabilitasnya jika disimpan pada RH 70%. Penyimpanan pada RH 50% dan 90% mempercepat laju kematian C. sakazakii YRc3a dan mengakibatkan jumlah bakteri turun sebesar 3 siklu...

Application of pGFPuv mutant to study Cronobacter sakazakii survival in corn flour during storage

“…The amount of decrease C. sakazakii pGFPuv at 50% RH was 4.4-4.7 log CFU/g for 16 weeks, while at 70% RH of 6.59 log CFU/g for 14 weeks and at 90% RH of 6.59 log CFU/g for 12 weeks. A similar thing happened with skim milk, the decrease in the number of C. sakazakii during 12 weeks of storage was greatest at RH 90% compared to RH 50% and 70% [8]. The slow decrease in the number of C. sakazakii pGFPuv at 50% RH was also related to the decrease in its Aw during storage.…”

“…C. sakazakii is still alive in skim milk after spray drying at an inlet temperature of 160 o C and outlet temperature of 82 o C, and survived for 3 months of storage at RH 50%, 70% and 90%. A decrease in the activity of water of skim milk after the drying process and during storage can increase the survival of C. sakazakii Yrc3a during dissolution with water at a temperature of 50 o C [8]. Cronobacter spp.…”