Agnes Weiss

Evaluation of lactic acid bacteria for sourdough fermentation of amaranth

Spontaneous fermented sourdoughs prepared from five amaranth flours were investigated for the presence of lactic acid bacteria predominating the autochthonous microbiota and thus may be suitable as starter cultures. The doughs were fermented with daily back-slopping on a laboratory scale at 30 degrees C for 10 days. Each day, pH-values and total titratable acidity degrees were determined and samples were analyzed for lactic acid bacteria and yeasts by cultural methods. The identity of the strains was tracked with randomly amplified polymorphic DNA-PCR during fermentation. Taxonomic identity of the strains was revealed by sequence analysis of 16S rDNA. Sugar and organic acid profiles of fermented doughs were determined with HPLC. The strains Lactobacillus plantarum RTa12, L. sakei RTa14, and Pediococcus pentosaceus RTa11 were selected and applied as starters in laboratory scale fermentations. All strains were predominant in repeated experiments, both as single strains and in combination, regardless of the amaranth flour used. The competitiveness of the strains L. plantarum RTa12 and P. pentosaceus RTa11 was characterized in further growth experiments. Both strains facilitated fast declines of pH-values, overgrew the autochthonous microbiota, and allowed stable fermentation characteristics at different temperatures. Thus, the characterized strains may be considered as candidates for amaranth sourdough starter cultures.

Surface adhesins and exopolymers of selected foodborne pathogens

The ability of bacteria to bind different compounds and to adhere to biotic and abiotic surfaces provides them with a range of advantages, such as colonization of various tissues, internalization, avoidance of an immune response, and survival and persistence in the environment. A variety of bacterial surface structures are involved in this process and these promote bacterial adhesion in a more or less specific manner. In this review, we will focus on those surface adhesins and exopolymers in selected foodborne pathogens that are involved mainly in primary adhesion. Their role in biofilm development will also be considered when appropriate. Both the clinical impact and the implications for food safety of such adhesion will be discussed.

Effect of Water Jet Cutting and Moderate Heat Treatment on Quality of Fresh-Cut Red Oak Leaf Lettuce (Lactuca sativa L. var. crispa)

Fresh-cut red oak leaf lettuce was produced by six different processing lines in order to assess the effect of water jet cutting (nozzle diameter 0.1 mm, pressure 2,500 bar) versus blade cutting as well as washing with cold and warm water (4 and 45 °C, 120 s) prior to and after shredding, respectively. Throughout refrigerated storage (4 °C, 12 days), O2 and CO2 levels in the modified atmosphere of the consumer-sized sample bags were monitored, and fresh-cut products and process water were subjected to microbiological analysis. As further quality parameters, phenylalanine ammonia lyase (PAL) activity as well as levels of chlorophyll a and b, β-carotene and cyanidin 3-O-(6”-O-malonyl)-glucoside were determined by HPLC with diode array detection (HPLC-DAD) and HPLC coupled with diode array detection and tandem mass spectrometry (HPLC-DAD-MSn) throughout storage. Additionally, visual appearance and cut edge browning were assessed by sensorial evaluation and stereo microscopy on storage day 8. Microbiological quality throughout commercial shelf life was best retained by warm water washing of shredded lettuce. Furthermore, moderate heat treatment significantly reduced PAL activity and cut edge browning without affecting pigment contents and vitality of the lettuce tissue. Additionally, warm water treatment significantly lowered the microbial load in the process water. Throughout storage, water jet cutting did not affect the microbial, physiological and sensorial fresh-cut lettuce quality compared to blade cutting using a newly sharpened blade, thus indicating a similar degree of wounding due to the cutting techniques applied. The application of a pre-washing step prior to shredding was found to be suitable to reduce the risk of cross-contamination in subsequent process steps.

Mechanisms of enterohemorrhagic Escherichia coli spread along the food-chain and precautionary measures

Enterohemorrhagic Escherichia coli (EHEC) are food-borne pathogens implicated in large outbreaks and sporadic cases of bloody diarrhea and the hemolytic uremic syndrome. The main reservoir of EHEC is the intestinal tract of ruminants, in particular cattle. Feces containing these bacteria may act as a source of contamination for the environment and particularly for a variety of foods. E. coli O157:H7 as well as other EHEC-serotypes have been isolated from domestic ruminants and non-ruminant farm animals as well as products produced from them, but also from drinking water, vegetables and dairy products. The main transmission pathway of the pathogens is the ingestion of raw or undercooked contaminated food but human infection can also occur by person-to-person transmission. This article will focus on the prevalence and spread of EHEC by vegetable foods, especially the less common EHEC transmission sources sprouts and leafy greens. It will discuss precautionary measures against the spread of EHEC in food at all stages of the food chain: the primary production, the industrial processing, the retailing as well as the consumer.ZusammenfassungEnterohämorrhagische Escherichia coli (EHEC) sind durch Lebensmittel übertragbare Krankheitserreger, die sowohl für sporadische Fälle als auch Krankheitsausbrüche von hämorrhagischer Kolitis und des hämolytisch-urämischen Syndroms (HUS) verantwortlich sind. Als Hauptreservoir für EHEC gelten Wiederkäuer, vor allem Rinder. Über Fäzes ausgeschieden, gelangen diese pathogenen Mikroorganismen in die Umwelt und können eine Vielzahl von Lebensmitteln kontaminieren. Sowohl E. coli O157:H7 als auch weitere EHEC-Serotypen wurden aus Wiederkäuern und Nicht-Wiederkäuern sowie aus ihrem Fleisch und Fleischprodukten isoliert, des Weiteren aus Trinkwasser, Gemüse sowie Rohmilch und Rohmilcherzeugnissen. Die Übertragung auf den Menschen erfolgt hauptsächlich durch die Aufnahme von kontaminierten, rohen bzw. unzureichend erhitzten Lebensmitteln, aber auch durch Schmierinfektionen (Mensch-zu-Mensch). Dieser Artikel beschreibt die Verbreitung und Übertragungsmechanismen von EHEC durch pflanzliche Lebensmittel, wobei vor allem die weniger bekannten EHEC-Übertragungsvehikel Sprossen und Blattgemüse in den Focus gestellt wurden. Ebenfalls werden präventive Maßnahmen gegen die Übertragung von EHEC auf verschiedenen Stufen der Lebensmittel(herstellungs)-kette erörtert: der Primärproduktion, der Verarbeitung, dem Einzelhandel sowie dem Verbraucher.

Modified Bacteriophage S16 Long Tail Fiber Proteins for Rapid and Specific Immobilization and Detection of Salmonella Cells

ABSTRACT Bacteriophage-based assays and biosensors rival traditional antibody-based immunoassays for detection of low-level Salmonella contaminations. In this study, we harnessed the binding specificity of the long tail fiber (LTF) from bacteriophage S16 as an affinity molecule for the immobilization, enrichment, and detection of Salmonella. We demonstrate that paramagnetic beads (MBs) coated with recombinant gp37-gp38 LTF complexes (LTF-MBs) are highly effective tools for rapid affinity magnetic separation and enrichment of Salmonella. Within 45 min, the LTF-MBs consistently captured over 95% of Salmonella enterica serovar Typhimurium cells from suspensions containing from 10 to 105 CFU · ml−1, and they yielded equivalent recovery rates (93% ± 5%, n = 10) for other Salmonella strains tested. LTF-MBs also captured Salmonella cells from various food sample preenrichments, allowing the detection of initial contaminations of 1 to 10 CFU per 25 g or ml. While plating of bead-captured cells allowed ultrasensitive but time-consuming detection, the integration of LTF-based enrichment into a sandwich assay with horseradish peroxidase-conjugated LTF (HRP-LTF) as a detection probe produced a rapid and easy-to-use Salmonella detection assay. The novel enzyme-linked LTF assay (ELLTA) uses HRP-LTF to label bead-captured Salmonella cells for subsequent identification by HRP-catalyzed conversion of chromogenic 3,3′,5,5′-tetramethylbenzidine substrate. The color development was proportional for Salmonella concentrations between 102 and 107 CFU · ml−1 as determined by spectrophotometric quantification. The ELLTA assay took 2 h to complete and detected as few as 102 CFU · ml−1S. Typhimurium cells. It positively identified 21 different Salmonella strains, with no cross-reactivity for other bacteria. In conclusion, the phage-based ELLTA represents a rapid, sensitive, and specific diagnostic assay that appears to be superior to other currently available tests. IMPORTANCE The incidence of foodborne diseases has increased over the years, resulting in major global public health issues. Conventional methods for pathogen detection can be laborious and expensive, and they require lengthy preenrichment steps. Rapid enrichment-based diagnostic assays, such as immunomagnetic separation, can reduce detection times while also remaining sensitive and specific. A critical component in these tests is implementing affinity molecules that retain the ability to specifically capture target pathogens over a wide range of in situ applications. The protein complex that forms the distal tip of the bacteriophage S16 long tail fiber is shown here to represent a highly sensitive affinity molecule for the specific enrichment and detection of Salmonella. Phage-encoded long tail fibers have huge potential for development as novel affinity molecules for robust and specific diagnostics of a vast spectrum of bacteria.

Recent advances in cured raw ham manufacture

ABSTRACT Cured raw hams are a valuable and popular group of meat products. The consumption and international trade have increased during the last years, therefore new technologies to accelerate the production process and to increase product quality and safety are needed. In the current review, an overview of European protected cured raw hams is presented. Furthermore, traditional methods for cured raw ham production together with recent advantages in the techniques for pretreatment (trimming, blade tenderization, and freeze-thawing), curing/salting (tumbling, vacuum impregnation, pulsed pressure, ultrasound, pulsed electric fields, simultaneous thawing/salting), drying/ripening (Quick-Dry-Slice-process, oil drop application, high temperature short time process) and postprocessing (vacuum and modified atmosphere packaging, high hydrostatic pressure, high pressure carbon dioxide, high pressure carbon dioxide with ultrasound) are described. Moreover, application techniques and effects of protective cultures and starter cultures, such as molds, yeasts, coagulase-negative staphylococci and lactic acid bacteria, on cured raw ham quality and safety are reviewed.

Draft Genome Sequence of Staphylococcus carnosus subsp. utilis LTH 7013, Isolated from South Tyrolean Ham.

ABSTRACT Staphylococcus carnosus is used as a starter culture in meat fermentation, where it contributes to color formation and produces aromatic compounds. Here, we report the first draft genome sequence of an S. carnosus subsp. utilis strain, LTH 7013, isolated from South Tyrolean ham, with potential application as a starter culture.

Variation of the Pseudomonas community structure on oak leaf lettuce during storage detected by culture-dependent and -independent methods

The genus Pseudomonas plays an important role in the lettuce leaf microbiota and certain species can induce spoilage. The aim of this study was to investigate the occurrence and diversity of Pseudomonas spp. on oak leaf lettuce and to follow their community shift during a six day cold storage with culture-dependent and culture-independent methods. In total, 21 analysed partial Pseudomonas 16S rRNA gene sequences matched closely (> 98.3%) to the different reference strain sequences, which were distributed among 13 different phylogenetic groups or subgroups within the genus Pseudomonas. It could be shown that all detected Pseudomonas species belonged to the P. fluorescens lineage. In the culture-dependent analysis, 73% of the isolates at day 0 and 79% of the isolates at day 6 belonged to the P. fluorescens subgroup. The second most frequent group, with 12% of the isolates, was the P. koreensis subgroup. This subgroup was only detected at day 0. In the culture-independent analysis the P. fluorescens subgroup and P. extremaustralis could not be differentiated by RFLP. Both groups were most abundant and amounted to approximately 46% at day 0 and 79% at day 6. The phytopathogenic species P. salmonii, P. viridiflava and P. marginalis increased during storage. Both approaches identified the P. fluorescens group as the main phylogenetic group. The results of the present study suggest that pseudomonads found by plating methods indeed represent the most abundant part of the Pseudomonas community on oak leaf lettuce.

Complete Genome Sequence of Staphylococcus carnosus LTH 3730

ABSTRACT Specific strains of the apathogenic coagulase-negative species Staphylococcus carnosus are frequently used as meat starter cultures, as they contribute to color formation and the production of aroma compounds. Here, we report the complete genome sequence of S. carnosus LTH 3730, a strain isolated from a fermented fish product.

Adherence factors of enterohemorrhagic Escherichia coli O157:H7 strain Sakai influence its uptake into the roots of Valerianella locusta grown in soil

Increasing numbers of outbreaks caused by enterohemorrhagic Escherichia coli (EHEC) are associated with the consumption of contaminated fresh produce. The contamination of the plants may occur directly on the field via irrigation water, surface water, manure or fecal contamination. Suggesting a low infectious dose of 10 to 102 cells, internalization of EHEC into plant tissue presents a serious public health threat. Therefore, the ability of EHEC O157:H7 strain Sakai to adhere to and internalize into root tissues of the lambs lettuce Valerianella locusta was investigated under the environmental conditions of a greenhouse. Moreover, the influence of the two adherence and colonization associated genes hcpA and iha was surveyed regarding their role for attachment and invasion. Upon soil contamination, the number of root-internalized cells of EHEC O157:H7 strain Sakai exceeded 102 cfu/g roots. Deletion of one or both of the adherence factor genes did not alter the overall attachment of EHEC O157:H7 strain Sakai to the roots, but significantly reduced the numbers of internalized bacteria by a factor of between 10 and 30, indicating their importance for invasion of EHEC O157:H7 strain Sakai into plant roots. This study identified intrinsic bacterial factors that play a crucial role during the internalization of EHEC O157:H7 strain Sakai into the roots of Valerianella locusta grown under the growth conditions in a greenhouse.