Survival of Listeria monocytogenes on Processed Poultry

The potential for Listeria monocytogenes to survive and proliferate on processed poultry was investigated. Chicken breasts were inoculated with L. monocytogenes, cooked to one of five different internal temperatures, then either vacuum-packaged or wrapped in an oxygen permeable film and stored for up to four wk at 4^oC and 10^oC. Survivors were encountered at each cooking temperature employed. The magnitude of lethality was directly related to the cooking temperature. No significant increase in microbial populations occurred through 2 wk of storage. Bacterial populations in samples that were overwrapped increased significantly by week 4, except for the 160^oF (71.1^oC) treatment. For samples which were vacuum-packaged, only the bacterial population in the 150^oF (65.6^oC) treatment significantly increased. Differences due to packaging were observed at 4^oC storage but not at 10^oC storage.     

Conflict resolution in collaborative planning dialogs

In a collaborative planning environment in which the agents are autonomous and heterogeneous, it is inevitable that discrepancies in the agents' beliefs result in conflicts during the planning process. In such cases, it is important that the agents engage in collaborative negotiation to resolve the detected conflicts in order to determine what should constitute their shared plan of actions and shared beliefs. This paper presents a plan-based model for conflict detection and resolution in collaborative planning dialogs. Our model specifies how a collaborative system should detect conflicts that arise between the system and its user during the planning process. If the detected conflicts warrant resolution, our model initiates collaborative negotiation in an attempt to resolve the conflicts in the agent's beliefs. In addition, when multiple conflicts arise, our model identifies and addresses the most effective aspect in its pursuit of conflict resolution. Furthermore, by capturing the collaborative planning process in a recursive Propose–Evaluate–Modify cycle of actions, our model is capable of handling embedded negotiation during conflict resolution.     

Behaviour of volatile compounds during the shelf life of yoghurt

The production of acetaldehyde, diacetyl and ethanol was evaluated in whole plain yoghurts manufactured with commercial starter cultures, yoghurt acquired in a local market, and milk fermented by a single culture of either Streptococcus thermophilus or Lactobacillus delbrueckii ssp. bulgaricus . The headspace technique was used for sample preparation, following identification and quantification by gas chromatography. During an 8-h incubation period, mixed cultures were the most efficient in lowering the pH (from 6.30 to 4.8), followed by S. thermophilus (from 6.30 to 5.18) and L. bulgaricus (from 6.30 to 5.8). During the storage period, however, a single culture of L. bulgaricus decreased the pH more than S. thermophilus , but still less than the mixed commercial cultures. Plain yoghurts acquired in the market, those made with commercial starter cultures, and fermented milks obtained with single cultures showed, after 21 days of storage, concentrations of acetaldehyde from 11 to 35 mg/L, and of diacetyl from 0 to 0.85 mg/L. An increasing concentration of ethanol was observed during the storage period, and its production was observed even in the incubation stage of all products. It was also observed that the acetaldehyde concentration was inversely correlated to ethanol production in some products. The combination of headspace, identification and quantification techniques by gas chromatography in this work was efficient in the identification and quantification of the major aromatic compounds and ethanol content of yoghurt.     

Effects of Storage Time and Temperature on the Microflora and Amine-Development in Spanish Mackerel (Scomberomorus maculatus)

Microbial content was characterized and levels of three amines (histamine, cadaverine, and putrescine) were determined in Spanish mackerel (Scomberomorus maculatus) decomposed at PC, WC, and 30°C for varying lengths of time. Correlations were shown (1) between the levels of the histamine, cadaverine, and putrescine and the time and temperature of decomposition, (2) between the ratios of cadaverine/histamine and putrescine/histamine levels and the temperature of decomposition, and (3) between increasing total microbial counts and rising amine levels. A total of 14 bacterial species with histidine decarboxylase activity were isolated from decomposing fish, including three species (Acinetobacter lwoffi, Pseudomonas putrefaciens, and Aeromonas hydrophila) not previously reported to have the potential to produce histamine.     

GAMMA GLUTAMYL TRANSPEPTIDASE OF SPROUTED ONION

SUMMARY –An enzyme capable of liberating p-nitroaniline from γ- l -glutamyl p-nitroanilide has been purified 800-fold from sprouted onions. The enzyme acts optimally at pH 9.0, is activated by amino acids and inhibited by borate and competitively by γ-glutamyl derivatives. With the p-nitroanilide as substrate it exhibits a K_m of 14.3 mM whereas the K_i values with glutathione and γ-glutamyl-S-methyl- l -cysteine as inhibitors are 0.20 and 2.14 mM respectively. From chromatography of the reaction products and from kinetic considerations it is concluded that the purified enzyme is a transpeptidase (E.C.2.3.2.1) whereas crude onion extract may, in addition, possess a true γ-glutamyl hydrolase. It is suggested that such enzymes may play a role in the disappearance of peptides in post-dormant onions and may be useful evoking the full flavor potential of onion.     

An assessment of factors characterising the microbiology of Grana Trentino cheese,a Grana‐type cheese

In this study, microbiological aspects of Grana Trentino, a variant of Grana Padano cheese, were defined by plate counts, random amplified polymorphic DNA (RAPD) PCR genotying, 16S rRNA gene sequencing of bacterial isolates and PCR–denaturing gradient gel electrophoresis (PCR–DGGE). Results showed variability in monthly fluctuations of whey culture counts, differences in the diffusion of bacterial genotypes among producers and dairy plant‐specific microbial associations. Moreover, the presence of bacteria not previously reported in this cheese type was highlighted, including coagulase‐negative staphylococci and Lactobacillus sanfranciscensis‐like micro‐organisms.