Rapid detection of meat spoilage by measuring volatile organic compounds by using proton transfer reaction mass spectrometry.

The evolution of the microbial spoilage population for air- and vacuum-packaged meat (beef and pork) stored at 4 degrees C was investigated over 11 days. We monitored the viable counts (mesophilic total aerobic bacteria, Pseudomonas spp., Enterobacteriaceae, lactic acid bacteria, and Enterococcus spp.) by the microbiological standard technique and by measuring the emission of volatile organic compounds (VOCs) with the recently developed proton transfer reaction mass spectrometry system. Storage time, packaging type, and meat type had statistically significant (P < 0.05) effects on the development of the bacterial numbers. The concentrations of many of the measured VOCs, e.g., sulfur compounds, largely increased over the storage time. We also observed a large difference in the emissions between vacuum- and air-packaged meat. We found statistically significant strong correlations (up to 99%) between some of the VOCs and the bacterial contamination. The concentrations of these VOCs increased linearly with the bacterial numbers. This study is a first step toward replacing the time-consuming plate counting by fast headspace air measurements, where the bacterial spoilage can be determined within minutes instead of days.

Salmonella enterica serotype Oranienburg infections associated with consumption of locally produced Tyrolean cheese.

Sixteen culture confirmed cases of enteric infection with Salmonella enterica serotype Oranienburg were detected between August 10 and September 29 1999 in Tyrol (Austria). Ten of them suffered bloody diarrhoea and six were asymptomatic carriers. Intervie

Detection of a new enzyme for stereoselective hydrolysis of linalyl acetate using simple plate assays for the characterization of cloned esterases from Burkholderia gladioli.

Plate assays were developed for the identification of specific hydrolytic activities of esterases from Burkholderia gladioli, cloned and expressed in Escherichia coli. Clones showing different substrate specificities were identified by fluorescence or azo-dye formation caused by the released alcohol moiety of the hydrolyzed substrates, or by colour change of pH indicators mediated by decreased pH. The use of 1-hydroxypyrene-3,6,8-trisulfonic acid (HPTS-) esters and linalyl acetate for these assays clearly allowed to discriminate substrate specificities for two different cloned esterases, EP6 and EP10. Long chain fatty acid HPTS-esters were only hydrolyzed by the EP10 clone. On the other hand, the EP6 clone showed significant activity in hydrolysis of the sterically hindered ester linalyl-acetate. Enantioselective hydrolysis of linalyl acetate could be verified with a crude EP6 preparation on a preparative scale.

Efficient secretion of Bacillus subtilis levanase by Saccharomyces cerevisiae.

The secretion of Bacillus subtilis (Bs) levanase (Lev) was studied in the yeast Saccharomyces cerevisiae. A set of different yeast expression plasmids, based on the constitutive PGK promoter and harbouring the Bs Lev-encoding gene (sacC), was constructed. In these plasmids, the original Bs signal sequence was either intact, partially deleted or entirely missing. With all constructs, Lev was produced from yeast transformants. However, only when the intact bacterial signal peptide was present was the synthesized enzyme secreted; around 20% was found in the periplasm and 30% in the culture medium. The secreted protein found in the periplasmic space was mainly core-glycosylated and unglycosylated, and had a size of 80-90 and 74 kDa, respectively. In contrast, Lev found in the culture medium was mainly hyper-glycosylated and had a size of 180-200 kDa. Yeast transformants harbouring sacC, but lacking parts of the bacterial signal sequence, only produced cytoplasmic protein which was not glycosylated and had a size of about 74 kDa. The deletion of the entire signal peptide and a further 22 amino acids at the N terminus of mature Lev resulted in a 71-kDa cytoplasmic protein which was not active.