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Praca dotyczyła badań nad możliwościami regeneracji komórek E. coli uszkodzonych subletalnie w procesie utrwalania ditlenkiem węgla w podwyższonym ciśnieniu (HPCD). Do regeneracji zastosowano płytki dwuwarstwowe TAL (Thin Agar Layer). Dodatkowo podjęto próbę oceny przydatności metody płytek dwuwarstwowych do rutynowej kontroli jakości mikrobiologicznej w odniesieniu do znormalizowanej metody oznaczania E. coli. Bakterie zawieszone w roztworach modelowych o pH 4 i pH 7 poddawano działaniu HPCD pod ciśnieniem 40 MPa, w temperaturze 55°C, w czasie od 10 do 20 minut. Odzysk uszkodzonych komórek na pożywce TAL był wyższy niż na pożywce TBX zalecanej w obowiązującej normie. Różnice na pożywkach TAL i TBX wynosiły od 0,6 do 1,2 log w buforze pH 4 i od 0,8 do 1,2 log w buforze pH 7. Pożywka TAL umożliwiła wzrost bakterii w postaci charakterystycznych niebieskich kolonii.
The aim of this study was literature overview of polish and foreign literature relevant application of pulse electric field (PEF) to inactivate microorganisms occurring in fruit and vegetable juices. This paper presents the rule and mechanisms of PEF methods and compare its efficiency for particular groups of microorganisms concerning applied electric field parameters. Application of pulsed electric field in juice industry preserves desirable sensory properties of products, e.g. color or specific taste, and health-promoting compounds, e.g. vitamins.
High hydrostatic pressure (HHP) is a well known method currently used for food preservation. Nevertheless this treatment can also cause sublethal injury of foodborne pathogen cells, which could repair and become potentially dangerous for consumers. The survival of Listeria innocua CIP80.11T, Escherichia coli ATCC 8739 and the wild strains isolated from beetroot juice after HHP treatment (200 MPA, 300 MPa and 400 MPa) as well as the level of sublethal injuries in the surviving cells were investigated in this study. Lethal effect was reported after treatment at 400 MPa for the most of strains. The maximum level of sublethal injuries was reported after 5 minutes under pressure 300 MPa (L. innocua) and 400 MPa (E.coli).
The inactivation and sublethal injury of two strains of Listeria innocua (one collection strain and one wild strain isolated from beetroot juice) suspended in beetroot juice and in model solutions, after high hydrostatic pressure (HHP) were investigated. Changes within the population assessed by plating count methods of both L. innocua strains suspended in a buffer pH 4.0 were more noticeable than in the natural beetroot juice environment. In beetroot juice the lethal effect was reported after 1 min of pressure treatment at 400 MPa for the collection strain. In the case of the wild type strain, exposure to the maximal parameters of the compression process (400 MPa, 10 min) decreased the population number below 1 log (CFU/mL) but did not cause complete injury. The collection strain of L. innocua was easier to inactivate in beetroot juice than the strain isolated from this environment. The maximum level of sublethal injury was observed when the cells were suspended in a buffer pH 7.0. Structural damage in cell membranes after HHP processing was observed using a transmission electron microscope (TEM).
Commercially available unpasteurized, freshly-squeezed beetroot juice with a 24–72 hour shelf-life in cold storage, retains its natural flavour and nutritional value but can be a source of undesirable microflora. In this paper, the suitability of high pressure carbon dioxide (at 20 and 60 MPa, and a temperature of: 20, 35 and 60°C) to inactivate the native microflora in this juice has been studied. The results show that high pressure carbon dioxide was effective in the inactivation of the studied groups of microorganisms only when combined with increased temperature. The reduction in the total count of spoilage microorganisms and lactic acid bacteria was 5–6 log when 20 or 60 MPa and 60°C for at least 30 min were used. Yeasts treated with carbon dioxide at 20 MPa and 60°C were totally (>6 log) inactivated. The reduction in moulds count above 3 log, was observed in this conditions.
Alicyclobacillus spp. is an important thermoacidophilic, spore-forming spoilage bacterium that is a major concern for beverage and juice industries. This study was undertaken to: (i) estimate the incidence of Alicyclobacillus spp. and A. acidoterrestris in Polish apple and dark berry juice concentrates, and (ii) evaluate the ability of isolated A. acidoterrestris strains to spoilage of these juices after dilution to single strength. Polish apple and berry juice concentrates were screened for the presence of Alicyclobacillus spp. between 2002 and 2015. Incidence of Alicyclobacillus spp. in apple juice concentrates (n=1164) range from 27.3 to 86.8%, depending on the year. The species A. acidoterrestris accounted, depending on the year, from 12.7 to 100.0% of all isolated strains. Among the dark berry juice concentrates (n=146), approximately 60.0% were contaminated by Alicyclobacillus spp. Incidence of A. acidoterrestris strains in dark berry juice concentrates range from 4.2% in blackcurrant up to 40.0% in raspberry. Single strength apple juice promoted the growth of eight of the tested A. acidoterrestris strains (> 7 log cfu/ml) when was incubated at 45°C. No A. acidoterrestris growth was observed in single strength chokeberry, raspberry, strawberry, cherry and blackcurrant juices during 28 days incubation at 45ºC.
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