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Baker's yeast (Saccharomyces cerevisiae-Sz1) enriched in chromium, iron, selenium or zinc was prepared by shaken cultivation and laboratory fermentation. Determination of the cellular distribution of microelements indicated that a considerable portion (68-88%) was bound to the cell constituents, a very little part was solved only in the cytosol and vacuole. More than half of the original vitamins B content has been lost during the general guarantee time (12 months) and the microelements had only little influence on it. Enrichment of yeast cells with iron was accompanied by considerable increase in vitamin B2

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Fruits and vegetables can be transmission vehicles of human opportunistic and obligate pathogenic bacteria, persisting in inner tissues for shorter or longer periods or colonizing the plants as facultative endophytes. In this study we investigated the ability of commensal E. coli and pathogenic L. monocytogenes strains to internalize sweet pepper seedlings via seed bacterization, as germinating seeds and roots are important infiltration sites for entry of enteric bacteria. By combining cultivation dependent and independent (PCR and FISH-CLSM) techniques we could not detect stably or transiently colonized inoculated bacteria in 6–7 weeks old pepper seedlings, suggesting that there is low risk associated with internalized enteric or human pathogenic bacteria via germinating seeds in sweet pepper.

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Endophytic microorganisms living inside plant tissues might have numerous positive effects on the host plants. Endophytes can promote the growth and yield of the plant, help to remove contaminants from the tissues, and can suppress growth of pathogens; however, some enteric human pathogenic bacteria have also been isolated as endophytes. The aims of our study were the characterisation and identification of endophytic coliform bacteria isolated from different cultivars of sweet pepper (Capsicum annuum var. grossum) using a selective (VRBL) agar medium, and determination of antagonistic interactions between these endophytes and Listeria monocytogenes. The bacterial isolates showed heterogeneity based on their phenotypic and genotypic properties. Results of identification by molecular biological methods also confirmed the presence of different genera/species. When the antagonistic effect of the isolated endophytic bacteria was tested it was found that one isolate — identified as Pseudomonas putida — showed significant inhibition on the growth of Listeria monocytogenes.

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Acta Alimentaria
Authors:
M. Tóth-Markus
,
I. Magyar
,
K. Kardos
,
L. Bánszky
, and
A. Maráz

In this study the role of different yeast strains in the production of volatile flavour components of Tokaji Aszú wine was tested. The effect of a Saccharomyces cerevisiae starter and that of the typical endogenous Candida stellata strain as well as spontaneous fermentation were studied and compared. For the fast comparison of aroma profile, a solid phase microextraction (SPME) sampling and a GC-MS separation and identification were used. Thirty of the present compounds were selected to characterise the changes of flavour. Significant differences were found between wines fermented with different yeast strains. Application of a Saccharomyces cerevisiae starter alone accelerated the fermentation but this caused only little change in the aroma profile and content. Candida stellata contributed weakly to the production of aroma, especially to that of the longer carbon chain ethyl esters. Characteristic compounds of aged wine were detected in bottle aged Tokaji Aszú. The change of aroma profile as a function of bottle storage time was studied. The concentrations of vitispirane, trimethyl dihydronaphtalene, 2-phenylethanol and diethyl succinate increased in the course of ageing time, while those of 3-methyl-butyl acetate, ethyl hexanoate, ethyl octanoate, ethyl decanoate and ethyl dodecanoate decreased.

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Psychrotrophic Pseudomonas species P. fluorescens, P. fragi and P. lundensis were found as predominant bacteria of chicken meat stored at chill temperature, which showed high level of molecular diversity, while isolates of the psychrotrophic yeasts Candida zeylanoides, Metschnikowia pulcherrima, Rhodotorula glutinis and Rhodotorula mucilaginosa formed clusters of high level similarity within the different species as revealed by RAPD-PCR analysis.Combination of multiplex PCR and sequencing of the rpoB gene resulted correct identification of the Pseudomas isolates, while the routine diagnostic tests led to improper identification in case of half of the isolates, which indicated the extended biochemical and physiological heterogeneity of the food-borne pseudomonads. Majority of P. fluorescens and P. lundensis isolates were strong protease and lipase producers, while P. fragi strains were week or negative from this respect. Proteolytic and lipolytic activities of the isolated yeast strains were species specific and protease production was less frequent than lipolytic activities.

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Abstract

The aim of our research was to study the water and ethanol extractable polyphenols of stinging nettle (Urtica dioica L.) harvested in different seasons and to determine their antimicrobial activity against certain human pathogenic and food spoiling bacteria and yeasts.

Our results indicate that the spring leaf extracts had higher polyphenol contents than the root one; however, close to the end of the vegetation period these values decreased considerably in both leaves and roots. Detection and quantification of the most abundant phenolic compounds in the spring extracts by HPLC revealed the occurrence of 12 different phenol carboxylic acids and flavonoids. Flavonoid compounds were more abundant than phenol carboxylic acids in the leaves; however, their proportion was equal in the case of the roots. Nettle leaf extracts had remarkable antimicrobial activity, the spring extracts were more efficient than the autumn ones. Escherichia coli and Staphylococcus aureus were sensitive to every leaf extract, while Listeria monocytogenes and Pseudomonas aeruginosa had reduced but remarkable sensitivity patterns. Among the yeasts, Candida glabrata was strongly inhibited by the aqueous leaf extracts. Most of the strains were insensitive to the root extracts, although Enterococcus faecalis was inhibited by the root and not the leaf extracts.

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