Optical method for detecting oxygen via the chromogenic reaction catalyzed by polyphenol oxidase.

The present work describes a method for detecting the ingress of gas phase oxygen into packed food. It uses the enzyme polyphenol oxidase (PPO)from Mushroom and Mediterranean dwarf palm. The PPO is incorporated into an indubiose film along with a non-toxic polyphenol such as gallic acid or chlorogenic acid. If exposed to oxygen, the test spot undergoes an irreversible and visible color change from pale to deep brown due to the PPO catalyzed oxidation of the respective polyphenol by oxygen. The color change can be detected visually or by spectrophotometry at 470 nm. The effect of the amount of oxygen or substrate, type of enzyme substrate, enzyme source, temperature and duration of storage on the response were studied. Air oxygen can be detected within 30 min under optimized condition. The smallest amount of oxygen that can be detected with acceptable response time (120 min) is 5%. The test is highly selective for oxygen and the detector is stable over time. The detector may be used in any application as long as the presence or absence of oxygen in a sealed space is determined prior to the application using the detector.

Isolation, drug resistance and molecular characterization of Salmonella isolates in northern Morocco.

OBJECTIVES: The objective of this investigation was to assess the methods for the characterization of Salmonella isolates and to identify relationships of Salmonella isolates from human and food sources in northern Morocco. METHODOLOGY: Several Salmonella serotypes were isolated from human and food samples and were characterized using conventional culture methods, biochemical, serological, antimicrobial testing, and phage typing. Molecular analyses such as enterobacterial repetitive intergenic consensus (ERIC)-PCR, macrorestriction profiling by pulsed-field gel electrophoresis (PFGE), and virulence gene analysis were also performed. RESULTS: Sixteen Salmonella strains were isolated in our laboratory, serotyped and identified as S. Kottbus, S. Indiana, S. London, S. Typhi, S. Hadar, S. Corvallis, S. Mbandaka, S. Ouakam, S. Tm var. cop., S. Virchow, and S. Altona. The most common resistance profiles for the isolates was ATCFATSCGKSSS, belonging to phage type PT20, ATASCSS associated with strains DT104L/ad and ATATSS for isolates that were not typeable. The PFGE patterns were different for each Salmonella serotype. All strains were negative for the virulence gene spvR. CONCLUSIONS: To our knowledge, this is the first molecular characterization of Salmonella in food and humans from Morocco. Comparison of molecular techniques for differentiating between human and food isolates of Salmonella in north of Morocco shows that ERIC typing and PFGE were more discriminating than the other techniques used in this study.