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: Pengaruh pengeringan semprot terhadap ketahanan Enterobacter sakazakii (Cronobacter spp.) dalam susu skim bubuk
Abstrak: Enterobacter sakazakii (Cronobacter spp.) which was associated with meningitis and necrotizing enterocolitis (NEC) in preterm neonates, infant, and low weight birth has been isolated in PIF in Indonesia. PIF can be contaminated by Enterobacter sakazakii (Cronobacter spp.) because it is not a sterile product. During PIF production, pasteurization is a step aimed to kill Enterobacter sakazakii (Cronobacter spp.) and other vegetative pathogens. However, processing steps after pasteurization may introduce the pathogens to the products. Therefore the effect of drying on the survival of Enterobacter sakazakii (Cronobacter spp.) need to be evaluated. The objective of this study is to evaluate the effect of spray drying on the survival of several of Enterobacter sakazakii (Cronobacter spp.) strains. This study consist of preliminary and main study. Preliminary studies aimed to determine the best inlet temperature for drying, quality of the resulted powdered skim milk and two most heat resistant strains by rapid screening of six Enterobacter sakazakii (Cronobacter spp.) strains (DESb7a, DES b7b, DESb10, DES c3, DES c13, and DES d3) at 54°C for 32 minutes. The main study was conducted on the two most heat resistant strains (DES b7a and DESb10), YRc3a, and ATCC51329. The bacterial culture was inoculated into ±40% reconstituted skim milk at 107 – 108 cfu/g and dried in a Buchi Mini Spray Drier at 160°C, 170°C, and 180°C inlet temperature and 82°C outlet temperature. The resulting skim milk powder was subsequently analyzed for the Enterobacter sakazakii (Cronobacter spp.) survival. Spray drying at the studied temperatures killed substantial numbers of Enterobacter sakazakii (Cronobacter spp.) but did not yield Enterobacter sakazakii (Cronobacter spp.)–free powder at the levels of contamination used. At an inlet temperature of 160°C, log reduction of Enterobacter sakazakii (Cronobacter spp.) ranged from 2,54 to 3,07 depending upon Enterobacter sakazakii (Cronobacter spp.) strains. Survival of Enterobacter sakazakii (Cronobacter spp.) decreased as spray drying temperature increased. The log reduction of Enterobacter sakazakii (Cronobacter spp.) at inlet temperature of 170°C ranged from 2,77 to 3,25 while at inlet temperature of 180°C, the log reduction ranged from 3,24 to 3,55 of the four strains. YRc3a was the most heat tolerant Enterobacter sakazakii (Cronobacter spp.) strain during spray drying.
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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