Judul: Kinetika inaktivasi Cronobacter spp. (Enterobacter sakazakii) dalam susu formula dan sistem bufer dengan Berbagai aw dan pH pada proses pemanasan
Abstrak: 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.
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Judul: Sintas Isolat Lokal Enterobacter sakazakii (Cronobacter spp.) dalam Susu Skim Selama Pengeringan, Penyimpanan dan Rekonstitusi
Abstrak: Enterobacter sakazakii (Cronobacter spp.) is an emerging opportunistic pathogen associated with necrotizing enterocolitis, septicemia, bacteremia, and meningitis in neonates, particularly those who are premature or immunocompromised. Contaminated powder infant formula (PIF) has been linked to such outbreaks. Cronobacter spp. is relatively more resistant to osmotic stress and desiccation than other Enterobacteriaceae. This pathogen is known to survive at least for two years in PIF having low water activity (aw). The objective of this study was to determine the effects of spray drying and storage humidity (50%, 70%, and 90%) on the survival of a heat resistant local isolate Cronobacter spp. in skim milk and their viability upon reconstitution at various water temperatures. Survival of Cronobacter spp. during spray drying was determined by comparing the number of bacteria before and after spray drying. Viability of Cronobacter spp. in spray dried milk was observed for 3 month, during which Cronobacter spp. were periodically enumerated on TSA-YE agar. At the same intervals, spray dried milk containing Cronobacter spp. was reconstituted with water at room temperature (27 °C) and 50 °C. The number of Cronobacter spp. after reconstitution was enumerated and compared to the number of surviving Cronobacter spp. in milk prior to drying. In addition water activity (aw) and moisture content of the dried skim milk were also determined. Spray drying process resulted in 4.19 log CFU/g reduction of Cronobacter sp.YRc3a. Decrease in aw of skim milk after drying and during storage resulted in an increased survival of Cronobacter sp.YRc3a upon reconstitution at 50 °C. The logarithmic reduction of Cronobacter sp.YRc3a during reconstitution before drying were significantly higher (0.64 log) than after drying (0.35 log). Increase in survival upon reconstitution was also observed during storage at various humidity, ranging from 0.161 to 0.203 log. During 3 month storage period, Cronobacter sp. YRc3a survived better in dried skim milk at 70% humidity with only 0.21 log reduction in viable counts. Storage of dried skim milk at 50% and 90% humidity accelerated the rate of Cronobacter sp.YRc3a, resulting in decline of viable count for approximately 3 log cycles.
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Judul: Tree berdiameter lima adalah graceful
Abstrak: This manuscript presents some proofs that every tree of diameter five is graceful. A graceful tree is a graph which has a graceful labelling. This labelling assigns absolute difference of connected vertices, such that the resulting edge labels are mutually distinct. There are three theorems to be considered. First theorem proves that every tree of diameter four is graceful. Second theorem proves that every tree of diameter five is graceful or nearly graceful. The third theorem improves the second theorem and shows that every tree of diameter five is nearly graceful, which can be transformed into graceful using some certain patterns.
Keyword: Graf, Pelabelan graceful, Bogor Agricultural University, Institut Pertanian Bogor, IPB