Survey for psychrotrophic bacterial pathogens in minimally processed lettuce

A total of 120 minimally processed, cut and packaged lettuce samples were purchased from retail supermarkets or provided by a salad production facility over an 8-month period. The samples were tested for total aerobic plate counts and for the presence of potentially pathogenic species belonging to the genera of Listeria, Aeromonas and Yersinia. The aerobic plate counts ranged from 103 to 109 colony forming units (cfu) g-1. Most samples (76%) contained between 105 and 107 cfu g-1 total aerobic bacteria. Listeria monocytogenes was isolated from three samples, Aeromonas hydrophila or Aeromonas caviae from 66 samples, and Yersinia enterocolitica from 71 samples. The pathogenic potential of Y. enterocolitica isolates was determined by screening for an array of biochemical, serological and genetic traits (heat-stable enterotoxin gene, the attachment and invasion gene locus, the invasin gene locus and the virulence plasmid). The Y. enterocolitica isolates lacked many of the phenotypic and genetic markers associated with virulence in primary pathogenic strains. As the roles of the reputed virulence factors of Aeromonas spp. in human infection are uncertain, the pathogenic potential of the Aeromonas isolates in lettuce remains unclear.     

Purification of bacteriorhodopsin and characterization of mature and partially processed forms

Bacteriorhodopsin (BR) essentially free of native lipids has been prepared in a highly stable state. Purple membrane was solubilized in Triton X-100 and BR was purified by size exclusion chromatography using 3-[cholamidopropyl)dimethylammonio]-2-hydroxyl-1-propanesulfonic acid (CHAPSO) detergent at pH 5. Molar ratios of phospholipid/BR ranged from 0.4 to 0.05 corresponding to 94-98% phospholipid removal. Purified BR has an absorbance ratio (A280nm/A548nm) of 1.5-1.6 in the dark-adapted state which is the highest purified BR/protein ratio reported to date. The purified BR in CHAPSO shows maximum stability in the pH range 5.0-5.5. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles of native purple membrane and solubilized BR from most Halobacterium halobium JW-3 cultures show 3 higher molecular weight bands in addition to BR. Immunological staining and amino acid sequencing indicates that these additional proteins are partially processed forms of the BR precursor protein. The BR preprotein contains 13 additional amino acids on the NH2 terminus which are removed by post-translational processing in at least four steps. Isoelectric focusing separated most delipidated and non-delipidated BR samples into 8 bands. Incomplete BR post-translational processing BR is thought to be largely responsible for the multiplicity of isoelectric BR species. The principal components have pI values of 5.20 and 5.24 and both have absorption maxima at 550 nm, characteristic of detergent-solubilized BR. BR in Triton X-100 or nonylglucoside, delipidated BR in CHAPSO, and BR in intact purple membrane all have a dark-adapted ratio of 13-cis to all-trans-retinal of 1.9:1.     

Effect of heat shock on browning-related enzymes in minimally processed iceberg lettuce and crude extracts

The effects of heat shock on PPO and POD activity in minimally processed Iceberg lettuce was examined during storage (10 days). The results were compared with the effect of temperature on crude extracts of these enzymes (in vitro analysis). Fresh-cut lettuce washed at 50 degrees C showed significantly lower PPO and POD activity throughout storage than lettuce washed at 4 degrees C and 25 degrees C. These results were consistent with a sensory analysis in which the panellists found the lowest browning scores in those samples treated at 50 degrees C.When PPO and POD were analysed in vitro, the samples treated at 50 degrees C showed a rapid loss of POD activity and a similar but slower loss of PPO activity in all tissues, while incubation at 4 degrees C and 25 degrees C showed no significant loss of activity. While heat shock did not lead to significant loss of activity it did repress the synthesis of PPO and POD during storage.     

Osmotic lysis of corpora cardiaca using distilled water reveals the presence of partially processed peptides and peptide fragments

Abstract. A simple, single-step aqueous extraction method has been developed to study the neuropeptide content of small neuroendocrine organs. Perifusion of these tissues with deionized water causes osmotic bursting of the cells and release of their content into the surrounding fluid. The neuropeptides are immediately retained from the perifusion fluid using disposable C18 cartridges. After one separation step and mass spectrometry, it was possible to identify a large number of known neuropeptides from the corpora cardiaca of Locusta migratoria (L). Also present in the extract were a number of neuropeptide fragments and two incompletely processed peptides. Using this method, a 959Da peptide present in the corpora cardiaca was sequenced de novo . The full sequence, deduced using Collision Induced Dissociation Tandem Mass Spectrometry (CID MS/MS), is Ser-Pro-Leu-Asp-Ala-His-His-Leu-Ala. This nonapeptide is predicted from the gene encoding the ion transport peptide precursor and from the gene encoding the ion transport-like peptide precursor. In both cases, this nonapeptide, which was named ion transport peptide-copeptide, is flanked by the signal sequence at the N -terminus and a dibasic cleavage site (Lys-Arg) at the C -terminus. This structural feature is common to many physiologically important locust preproneuropeptides and indicates that this copeptide might have a physiological function, but this is not yet known.     

Microflora of Barley Kernels

Numbers and kinds of microflora were determined in 160 samples of barley grown in different regions of the United States; microflora were more abundant in the grains grown in the central states than in those grown in the western states. During steeping and germination in micromalting equipment, the number of colonies of filamentous fungi increased from two to five times, colonies of yeasts from five to ten times, and bacteria from 50 to more than 100 times the numbers present in the grain before malting. Kiln drying according to a commercial schedule reduced the number of all types of microflora below the number present before kilning, but all were present in larger numbers in the kilned malt than in the original grain. In barley stored at room temperature and at a moisture content of 15 to 18%, members of the Aspergillus glaucus group increased with increasing time and increasing moisture content, and germination percentage of the seeds decreased. Stored free of storage fungi at room temperature, barley with a moisture content just over 15% retained a high germination percentage for 5 months, but at a moisture content of 16% the germination decreased to zero.     

Antimicrobial (BN/PE) film combined with modified atmosphere packaging extends the shelf life of minimally processed fresh-cut iceberg lettuce

This study was conducted to investigate the effect of modified atmosphere packaging (MAP) in combination with BN/PE film on the shelf life and quality of fresh-cut iceberg lettuce during cold storage. The total mesophilic population in the sample packed in BN/PE film under MAP conditions was dramatically reduced in comparison with that of PE film, PE film under MAP conditions, and BN/PE film. The O2 concentration in the BN/PE film under MAP conditions decreased slightly as the storage period progressed. The coloration of the iceberg lettuce progressed the slowest when it was packaged in BN/PE film under MAP conditions, followed by BN/PE film, PE film, and PE film under MAP conditions. The shelf life of fresh-cut iceberg lettuce packaged in the BN/PE film under MAP conditions was extended by more than 2 days at 10 degrees as compared with that of the BN/PE film in which the extension effect was more than 2 days longer than that of PE, PET, and OPP films.     

Microflora of Barley Kernels

Numbers and kinds of microflora were determined in 160 samples of barley grown in different regions of the United States; microflora were more abundant in the grains grown in the central states than in those grown in the western states. During steeping and germination in micromalting equipment, the number of colonies of filamentous fungi increased from two to five times, colonies of yeasts from five to ten times, and bacteria from 50 to more than 100 times the numbers present in the grain before malting. Kiln drying according to a commercial schedule reduced the number of all types of microflora below the number present before kilning, but all were present in larger numbers in the kilned malt than in the original grain. In barley stored at room temperature and at a moisture content of 15 to 18%, members of the Aspergillus glaucus group increased with increasing time and increasing moisture content, and germination percentage of the seeds decreased. Stored free of storage fungi at room temperature, barley with a moisture content just over 15% retained a high germination percentage for 5 months, but at a moisture content of 16% the germination decreased to zero.     

Microflora of raw cacao beans

Whole non-moldy cacao beans from 14 sources cultured on Czapek's agar with six percent NaCl yielded species ofAspergillus glaucus group,Mucor pusillus and unidentified yeast and bacteria. The average number of bacterial colonies from the 14 sources of non-moldy cacao beans was 32.7 million per gram. The average number of colonies of filamentous fungi in dilution cultures was 57,000 colonies per gram. Yeast colonies were present in the amount of 15.8 million colonies per gram. The moldy beans analyzed contained fungi and bacterial counts in the billions; also, yeast was not isolated from the moldy samples.Paper Number 3170 of the Journal Series of the North Carolina State University Agricultural Experiment Station, Raleigh, North Carolina 27607.     

Microflora blastomicetica dei tabacchi

Riassunto L'esame di tabacchi tipo Kentucky e Maryland in fermentazione ripetuto più volte nel corso di oltre un decennio ha mostrato che la microflora blastomicetia di essi è da ritenersi rappresentata da specie riferibili al Gen.Debaryomyces. Quelli isolati dal tabacco Kentucky in fermentazione, per la produzione dei sigari toscani, sono stati descritti comeDeb. nicotianae n. sp., altri stipiti come una varietà di questa, denominataDeb. nicotianae var.minor. Anche dal tabacco Maryland in fermentazione furono isolate forme riportabili alGen. Debaryomyces. Due di queste sono descritte comeDeb. MaryIandii n. sp. eDeb. Cavensis n. sp., una terza fu identificata colDeb. Matruchoti GRIGORAKI et PEJU. Lo sviluppo di questi lieviti è molto numeroso, raggiunge durante la fermentazione dei tabacchi le cifre da centinaia di migliaia ad alcune decine di milioni per gr. di tabacco sostanza secca. Nel tabacco Kentucky, in fase di fermentazione per sigari toscani, lo sviluppo si verifica nei primi stadi fermentativi ed è capace di avverarsi anche nell'interno dei itessuti fogliari; col procedere della fermentazione diminuisce rapidamente e quindi cessa. Altri rappresentanti della flora blastomicetica ma in scarsissimo numero, tale da non attribuirgli importanza pratica, sono dei lieviti asporigeni a pigmento rosa-rosso riferibili al Gen.Rhodothorula HARRISON. Di quattro stipiti isolati due di essi sono considerati una nuova varietà della Rhod.mucillaginosa (JORG). HARRISON e denominata quale var.Kentuckyi, un altro stipiti un'altra varietià della stessa specie designata come car.Scafatii, e il quarto stipite una nuova specie denominataRhod. polimorpha. Infine vengono svolte delle considerazioni sugli effetti che possono determinare le aggiunte di colture di lieviti ai tabacchi.

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SummaryBlastomycetic microflora of tobaccos The study of fermenting tobaccos of the Kentucky and Maryland types, often repeated in the course of ten years, could demonstrate that their blastomycetic microflora is to be considered as typified by species belonging to theDebaryomyces genus. The ones isolated by the Kentucky tobacco during its fermentation for the production of,toscani cigars have been referred to asD. nicotianae, n. sp.; other strains as a variety of the former:D. nicotianae var.minor. Also by the fermenting Maryland tobacco have been ae isolated forms likely to be annexed toDebaryomyces gen. Two of the laater have been referred to asD. Marylandi n. sp. andD. Cavensis n. sp.; a third one has been identified asD. Matruchoti Grigoraki et Peju.The growth of these yeasts is quite fair and reaches, during the fermentation, numbers of hundreds of thousands and even tens of millions of blastospores per gram of dry substance.Other blastomycetes, considered however of a very little importance because of their neglectable number, belong to the genusRhodotorula Harrison. Two of them are a variety ofR. mucillaginosa (Jörg.) Harrison:R. mucillaginosa var.Kentucky; another is theR. mucillaginosa var.Scafatii; a fourth strain is typified byRhodotorula polimorpha.

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Crediamo opportune inserire nella presente rivista questo lavoro riassuntivo del Prof. GIOVANNOZZI sulla flora dei lieviti del tabacco-cui si è specialmente dedicatoper i possibili nessi epidemiologici tra le blastomicosi umane e tale flora. Dimostrata, ormal, la scarsa o nulla specificità dei lieviti usuali per l'uomo, e i sempre più frequenti nessi tra flora blastomicetica dell'ambiente e forme patogene per l'uomo e gli animali, appare evidente il notevole interesse che sempre offrono gli studi intesi a mettere in evidenza i lieviti esistenti nelle sostanze usualmente a contatto con l'uomo (N. d. R.)     

Microflora of Black and Red Pepper

Dilution cultures of 30 samples of ground black pepper yielded an average of 39,000 colonies of fungi per g, with a range of 1,700 to 310,000 per g. Total numbers of colonies of bacteria from 11 samples averaged 194,000,000 per g, with a range from 8,300,000 to 704,000,000 per g. A variety of fungi grew from nearly all surface-disinfected whole peppercorns that were cultured. Thirteen samples of ground red pepper from the United States yielded an average of 1,600 colonies of storage fungi per g and an equal number of other fungi; five samples from India yielded an average of 78,900 colonies of storage fungi per g and 169,400 colonies of other fungi per g. Among the fungi from both black and red pepper were Aspergillus flavus and A. ochraceus, some isolates of which, when grown for 8 to 10 days on moist autoclaved corn and fed to white rats or to 2-day-old Pekin ducklings, were rapidly lethal to them. Aflatoxin B₁ was isolated from one of the samples of corn on which A. flavus from black pepper was grown. Among the bacteria isolated from ground black pepper were Escherichia coli, E. freudii, Serratia sp., Klebsiella sp., Bacillus sp., Staphylococcus sp., and Streptococcus sp. No cultures of Shigella or Salmonella were found.     

Microflora of Maize Prepared as Tortillas

Very little is known of the microflora in tortillas, the major component in the diet of many Guatemalans and other Central Americans. Based in a Guatemalan highland Indian village, this study examined the types and amounts of bacteria, yeasts, and molds in tortillas and in their maize precursors. Coliforms. Bacillus cereus, two species of Staphylococcus, and many types of yeast were the main contaminants, but low concentrations of alpha-hemolytic Streptococcus, facultative Clostridium, and other bacterial types were also found. When tortillas were first cooked, the bacterial counts dropped to 1,000 or fewer organisms per g, a safe level for consumption. Under village conditions, bacterial counts regained precooking levels (about 10⁸ organisms/g) within 24 h and rose even higher after 48 h. Reheating caused very little change; hence, bacterial levels remained very high in old tortillas kept for later consumption. A search for the sources of contamination showed that most came from water used in preparation and from the soiled hands of women preparing the tortillas. As an attempt to correct certain nutritional needs of the population, the Institute of Nutrition for Central America and Panama initiated a tortilla fortification project in the Guatemalan village. The bacterial counts in fortified tortillas did not differ significantly from those in ordinary tortillas. Furthermore, the level of contamination was constant among tortillas of different sizes and among tortillas made from different types of maize.     

Microflora of four fermented fish sauces

Thirty-nine microorganisms representing 11 species of bacteria, one yeast, and three filamentous fungi were isolated and identified from four fermented fish sauces: nampla, patis, koami, and ounago.