Relationship Between the Growth Phase of Pseudomonas fragi and Its Attachment to Stainless Steel.

Attachment of Pseudomonas fragi ATCC 4973 to a sterile stainless steel surface was followed under stationary and dynamic growth conditions at 25°C and 4°C using scanning electron microscopy techniques. The organism was grown in 10% reconstituted nonfat dry milk for 28 hr at 25°C and 9 days at 4°C. Attachment was ob served in both the stationary and dynamic environments at 1/2 hr at 25°C and at 2 hr at 4°C. There appeared to be no difference in the development of attachment fibrils on the organisms in the two environments or at the two temperatures. The extent of attachment increased as the microbial population increased over the growth cycle under both environments at both temperatures.     

Development of a 5-Layer Passive Organic Dermal (POD) Sampler

A 5-layer passive organic dermal sampler was developed to allow the collection, retention, and recovery of a variety of organic compound classes simultaneously. The 5-layers, from outside in, consisted of polypropylene, polyurethane foam, C-18 solid-phase extraction disk, ethylene tetrafluoroethylene, and activated carbon cloth. The layers were enclosed in aluminum foil and placed in a muslin envelope that had a 40.0 mm diameter opening.

Ten samplers were spiked separately with three levels of diesel oil, a 50/50 diesel oil/asphalt mixture, and asphalt binder. For the diesel oil spikes, recoveries were 69.9, 71.3, 88.8, and 95.4% for 10, 10, 50, and 100 mg of diesel oil. For the 50/50 mixture, recoveries were 105.4, 92.8, and 92.0% for 10, 50, and 100 mg of the 50/50 mixture. For the asphalt binder spikes, recoveries were 104.7, 100.2, and 100.1% for 10, 50, and 100 mg of asphalt binder. For repeatability assessment, 7 samplers were spiked with 50 mg of the 50/50 mixture and recoveries averaged 92.6% (standard deviation 8.6). Samplers tested on asphalt paving workers proved functional, comfortable, flexible, and durable.     

DETECTION OF THE VIABLE BUT NONCULTURABLE STATE IN ESCHERICHIA COLI O157:H7

Enterohemorrhagic Escherichia coli O157:H7 (EHEC) is recognized as a frequent cause of gastroenteritis ranging from mild to severe bloody diarrhea. The Shiga-like toxin produced by EHEC can result in hemolytic uremic syndrome, now the major cause of acute kidney failure in children in the United States. Inadequately cooked beef is most commonly implicated in the transmission of EHEC, although only a small fraction of cattle appear to harbor the organism. In several studies EHEC positive herds were detected only in the summer months correlating with the occurrence of human infections. Numerous E. coli strains have been shown to enter a viable but nonculturable (VBNC) state as a result of environmental stresses, including low temperature. Using traditional plating methods and the BacLight Molecular Probe, we monitored EHEC strains incubated in river water (RW) and artificial sea water (ASW) at temperatures of 5C and 25C for their entry into the VBNC state. EHEC strains remained culturable for over 40 days in both ASW and RW incubated at 25C. In ASW, these levels were higher than a non-EHEC control. At 5C, the number of culturable EHEC cells dropped gradually in both RW and ASW. Using the BacLight Molecular Probe, we were able to demonstrate that these cells, though not culturable, were viable indicating entry into the VBNC state. Our study suggests that temperature and not salinity is the primary signal for entry into this state .     

Contribution of Lipids to Volatiles Generation in Extruded Corn-Based Model Systems

Volatile compounds generated by model systems of zein, corn amylopectin and corn oil extruded at barrel temperatures of 120°C and 165°C were analyzed by GC and GU/MS. The largest quantities of lipid oxidation products were detected in systems containing all three components. In each system, the quantity of 2,4-decadienal was low relative to the quantities of hexanal, heptanal, and benzaldehyde. Identification of the Maillard reaction products, 2-methyl-3(or 6)-pen-tylpyrazine, 2-methyl-3(or 6)-hexylpyrazine, and 2,5-dimethyl-3-pen-tylpyrazine, suggested that lipid-derived aldehydes might be involved in the formation of substituted pyrazines.     

HISTAMINE PRODUCTION BY FOOD-BORNE BACTERIAL SPECIES12

A total of 112 bacterial strains representing 38 species were tested for their potential to elicit food poisoning outbreaks via histamine formation in foods. Proteus morganii and Enterobacter aerogenes displayed a quantitative superiority in terms of histamine production on a trypticase-soy broth-histidine (TSBH) medium and a tuna fish infusion broth (TFIB). When bacteria were incubated under standardized conditions in TSBH medium, histamine accumulated to levels exceeding 50 nmoles/ml of media with a total of 23 strains, including 13 of 15 P. morganii strains, 3 of 3 E. aerogenes strains, 3 of 12 Hafnia alvei strains, 1 of 4 Providencia alcalifaciens strains, 1 of 5 Enterobacter cloacae strains, 1 of 1 Proteus rettgeri strains, and 1 of 1 Citrobacter diversus strains. However, only 8 of the 15 P. morganii strains and the 3 E. aerogenes strains were capable of generating histamine in excess of 200 nmoles/ml in the TSBH medium. Of the 23 strains capable of appreciable histamine production in TSBH medium, P. morganii and E. aerogenes were, by far, the most prolific histamine producers in TFIB. Of the organisms tested, only P. morganii and E. aerogenes would appear to have the capability of forming sufficient histamine in scombroid fish products to elicit food poisoning outbreaks.     

EXTRACT RELEASE VOLUME (ERV) RESPONSES WITH ASEPTIC AND INOCULATED PORK

SUMMARY– The extract-release volume (ERV) phenomenon, previously reported as a reliable rapid indicator of bacterial spoilage in meat, was observed for pork muscle obtained aseptically and for that inoculated with pure and mixed cultures of bacteria over a 20-day storage period at 2° and 10°C. ERV values obtained using pork longissimus dorsi muscle were found to be inversely related to bacterial numbers regardless of population type (homogeneous or heterogeneous) of the microorganisms. The correlations between ERV and bacterial numbers did not denote reliable prediction of the bacteriological quality of pork by ERV. Under conditions of mixed culture sample contamination the correlation between ERV and bacterial numbers was much higher than for pure culture sample contamination with psychrophilic, anaerobic, or acid-producing bacteria. Minor initial differences in ERV between control (aseptic) and inoculated samples indicated that ERV responded to growth of the bacteria rather than to their presence per se. Differences in ERV that were attributable to sample source (animal differences) by analysis of variance test indicated there was a wide range of hydration capacities in pork longissimus dorsi muscle samples. This disparity minimized the significance of the influence of bacterial growth on the ERV response for practical applications. Contrary to the usual ERV response observed with meat spoiled under refrigerator conditions, ERV was found to increase with storage time and bacterial growth when pork was contaminated with a putrefactive anaerobe (Clostridium perfringens) and stored at 35°C. Though pH appeared to influence the magnitude of the changes observed in ERV, decreases in ERV with bacterial growth or storage time could not be explained solely as a pH effect.     

Studies of the iced storage characteristics and composition of a variety of Bolivian freshwater fish. 1. Altiplano fish

The iced storage characteristics of three Bolivian freshwater fish species from the Altiplano region were monitored using chemical, microbiological and sensorial methods. Fish studied were: pejerrey (Busilichthys bonariensis) captured in two locations, Lake Poopo and Lake Angostura; trout (Sulmo gairdneri) from Lake Titi-caca and carp (Cyprinus carpio) from Lake Angostura. The proximate composition and physical nature of these fish are presented. The shelf lives of these species, as deter-mined by both sensory and microbiological evaluations, were found to be: pejerrey from Lake Poopo: 20–21 days, pejerrey from Lake Angostura: 15-19 days, carp from Lake Angostura 17–20 days and trout from Lake Titicaca: 15–18 days. The value of the various methods used to monitor quality changes are discussed.     

QUALITY ATTRIBUTES OF CANADIAN HARD WHITE SPRING WHEAT

Quality characteristics of five pilot‐scale milled Canadian hard white spring wheats were compared to a No.1 grade commercial composite Canada Western Red Spring (1CWRS) wheat. One metric ton of samples was milled on the Canadian International Grains Institute pilot Buhler mill (Buhler AG, Uzwil, Switzerland) into straight‐grade (SG), 85% and whole wheat flours. At the SG extraction level, the white wheats with their lighter colored seed coats had improved milling yields (up to 2.6%) and lower ash (0.01–0.09%) than the 1CWRS control wheat. Majority of white wheat flours had higher protein contents than the 1CWRS control flours for all flour extractions. Based on dough rheological properties of the flours, three of the white wheats (Kanata, Snowbird and BW 275 ) were equal to or better than the red 1CWRS control for nearly all farinograph and mixograph parameters at all flour extractions other than farinograph absorption. Two of the white wheat lines (RL 4863 and RL 4858 ) had excessively weak and overly strong dough properties, respectively. Evaluation of pan bread, bagels and tortillas showed that white wheats generally produced end‐products that were comparable or superior to 1CWRS and that their most significantly positive quality compared to 1CWRS was their substantially lighter colored end‐products.     

Kinetics of Pyrazine Formation in Amino Acid-Glucose Systems

The chemistry and kinetics of pyrazine formation were studied in four amino acid-glucose model systems. Different amounts of the same alkylpyrazines were produced in the four systems. The most abundant alkylpyrazine generated in a gylcine-glucose system was 2,3,5-tri-methylpyrazine, while 2-methylpyrazine was most abundant in an arginine-glucose system and 2,5-dimethyIpyrazine predominated in a histidine-glucose system. 2-MethyIpyrazine and 2,5-dimefhylpyrazine were the two most abundant alkypyrazines in a lysine-glucose system. Kinetic data from the arginine-glucose system indicated that each of four selected pyrazines was formed by a pseudo-zero-order reaction. Activation energies in the same system were determined to be 19.5 ± 4.1 Kcal mole^?1 for pyrazine, 24.8 ± 8.7 Kcal Mole″¹ for 2-methylpyrazine, 20.8 ± 4.7 Kcal mole^?1 for 2,6-dimethylpyrazine and 29.0 ± 3.8 Kcal mole^?1 for 2-methyl-6, 7-dihydro-5H-cyclopen-, tapyrazine.