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: Survival dan pertumbuhan Cronobacter sakazakii dan Lactobacillus selama rekonstitusi susu formula
Abstrak: Cronobactersakazakii (Enterobacter sakazakii) is an emerging foodborne pathogenassociated with powdered infant formula(PIF). The bacterium has been known to cause necrotizing enterocolitis(NEC), meningitis, and sepsis in neonates, especially to those born prematurely and or with low birth weight. C.sakazakiicould be found and survive in PIFas a residual contamination during drying or filling (after pasteurization process) and reconstitution practice in household or hospitals.Recently, somePIF product is being added with Lactobacillus as probiotics, therefore the reconstitution temperature may affect both the Lactobacillus and C. sakazakii. The objectives of this study are to study (1)the influence of various temperature of the water (30, 50, and 70oC) used for reconstitution on (a) the survival and growth of C. sakazakii in PIF, (b) the survival and growth of C. sakazakii and Lactobacillus R23 present together in PIF, and (2) to determine selective enumeration media of C. sakazakii and Lactobacillus R23 when both are present in PIF. A preliminary study was conducted for rapid screening of six isolates to obtain two heat tolerant C. sakazakii isolates by using heat treatment at 54oC for 32 minutes. The main study was evaluation of survival and growth of C. sakazakii YR c3a in PIF followingreconstitution at the above temperatures in the absence or presence of Lactobacillus R23 for up to eight hours. C. sakazakii YR c3a and DES b7b were selected as the more heat tolerant. Reconstitution at 30 and 50 oC did not influence survival and growth of C. sakazakii for up to 8 h hang time.Two log reductionsof C. sakazakii occurred in PIF reconstituted with water at 70oC.At 30 oC, presence of Lactobacillus R23 in PIF also did not affect the survival and growth of C. sakazakii upon reconsitution at irrespective of the initial load ratio. Meanwhile presence of Lactobacillus did not affect C. sakazaki upon reconstitution at 50 oC when the ratio of LactobacillusR23 : C. sakazakiiYR c3a was 1:1, but growth of C. sakazakii YR c3a decreased following reconstitution when ratio of the two bacteria was 103:1.Reconstitution at 70 oC reduced the number of C. sakazakii YR c3a and DES b7b by 2.51 and 2.48 log CFU/ml, respectively. In PIF containing Lactobacillus, regardless of the ratio, Lactobacillus R23 and C. Sakazakii YR c3adecreased for up to <1,00 log CFU/ml and to 1,40 log CFU/ml, respectively. Following reconstitution at this temperature, the growth of C. sakazakiiYR c3a started tobe observed 4 h afterward while Lactobacillus R23 started to increase 2 h afterward.
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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