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Shell eggs have been irradiated with increasing radiation doses in the 0.5-3.0 kGy dose range and various non-microbiological changes, important from the point of view of consumer quality, have been estimated. Dose-dependent changes in the flow behaviour of egg white and brittleness of the yolk membrane in broken eggs, sensorial parameters of the raw and soft-boiled eggs, whippability and foam stability of the egg white were observed. Considering that a minimal dose of 1.5 kGy would be required for radiation inactivation of salmonellae and other, non-pathogenic bacteria, the quality of irradiated eggs upon such gamma radiation dose would not be equal in all parameters to those of the fresh shell eggs, however, changes in sensorial and functional properties at this dose level may be still acceptable, mainly for risk population and some industrial use.

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The microbiological spoilage of foods depends on the initial microbiological contamination and some factors which influence the growth of microorganisms. Therefore, reducing the initial cell count is necessary for both extending shelf-life and improving food safety. Physical, chemical and combined treatments serve this purpose. In these experiments, the effect of trisodium phosphate dipping (0-15% solutions) was studied. Chicken wings were used, which after dipping (1 min) in the solution were packed in PE-PA-PE pouches and stored at 4 °C. Aerobic mesophilic (Nutrient Agar, Merck), pseudomonad (Pseudomonas Selective Agar, Oxoid), and Enterobacteriaceae counts (VRBD Agar, Merck) were determined by Spiral Plate Technique at 30 °C incubation temperature. Effect of 3.8, 5.7, 7.6% trisodium phosphate dipping solutions was studied as a function of storage time. Immediately after treatment, total colony count was reduced by maximum 1.5 log cycles. Pseudomonads were the most sensitive. One day after treatment with these low concentration solutions, the colony count was reduced by 2 log cycles. Na3PO4concentration higherthan 7.6% practically did not result in higher effectivity. The growth rate and maximum cell count of surviving fraction were estimated as a function of trisodium phosphate concentration. It can be concluded from fitted survival curves that immediately after treatment the initial viable cell count was reduced and the critical spoilage level (107g-1) has been reached 2-3 days later than in case of the untreated samples, i.e. the shelf-life was extended.

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Comparison of eleven selective media for detecting and enumerating foodborne yeasts in blue-veined cheese showed that rose bengal chloramphenicol agar (RBC), dichloran rose bengal chloramphenicol agar (DRBC), oxytetracycline gentamycin glucose yeast extract agar (OGGY) and dichloran 18% glycerol agar (DG18) were the most efficient. Other examined media failed to be suitable for either inhibiting bacteria and suppressing the spread of moulds or supporting the growth of all yeasts present. Significant differences (P≯0.05) were obtained on different media, however counts obtained were overlapping on three groups of media. Yeast extract eugenol agar (YEE) medium significantly differed from all others.

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A recombinant Bacillus subtilis strain containing a plasmid encoding a luxAB fusion, which gave bioluminescence upon addition of an exogenous long-chain aldehyde as substrate for the endogenous luciferase enzyme, was used as test organism. Its populations were treated with 300 MPa for 20 min, or 600 MPa for 20 min at around room temperature, and this treatment is foreseen as a quality-friendly, non-thermal pasteurisation of foods. Besides the estimation of viable cell counts, the extent of pressure-induced germination and post-process development were investigated by phase-contrast microscopy, turbidimetry and luminometry. Increased heat sensitivity of pressurized spore populations was observed both by viable cell counting during a linearly programmed elevation of temperature and a simultaneous differential scanning calorimetry. This was related to pressure-induced germination of spores, although a small fraction remained ungerminated. The luciferase pool built into the spores during their formation seemed to have withstood pressurization. Spore germination was accompanied by the emergence of bioluminescence which also indicated sensitively the characteristic changes of metabolic activity running parallel with the development of untreated cell populations and that of the survivors of the hydrostatic pressure treatments when the cells were incubated in a nutrient broth.

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The effect of high hydrostatic pressure (HHP) and nisin was studied on micro-organisms in minced chicken and beef meat. Pressure in the range of 0-800 MPa and nisin (670 IU g-1) were applied for vacuum packed minced meat. In chicken meat the total viable cell count decreased by 3 log cycles as an effect of HHP at 300 MPa and by 5 log cycles in combination with nisin. The D value is 35-39 MPa for pseudomonads in minced chicken meat. In case of inoculation with L. monocytogenes, the cell count in beef meat was reduced only by pressure higher than 200 MPa (“shoulder”) with a characteristic value of D=37-38 MPa. B. cereus spores, both dormant and heat activated, were very resistant (D=800 MPa) in beef. However, the survival of pressurised spores after chilled storage (for two weeks at 4 °C) was smaller for non-heat activated spores than for heat activated spores. Efficiency of HHP combined with nisin needs further research work.

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Laboratory batches of fresh tomato juices were treated in several experimental trials by high hydrostatic pressure alone or in combination with various concentrations of oregano, thyme or dill seed oils. Lactic acid bacteria formed the dominating component of the spoilage microbiota during post-processing storage at 15 °C causing spoilage of the untreated samples within 4 days. One tenth of a percent oregano or thyme oils at least doubled the microbiological shelf life, while their respective concentrations of 0.5% alone, or 400 MPa 5-20 min high hydrostatic pressure treatment alone resulted in microbial stability for at least two weeks. Two hundred MPa for 10 min resulted only in an approx. 3 days delay of spoilage, whereas 0.1% thyme oil increased the efficiency of this moderate UHP-treatment, resulting in a microbiologically stable product for at least 3 weeks at the storage temperature applied.

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Acta Alimentaria
Authors:
Á. Koncz
,
L. Mészáros
,
J. Farkas
,
K. Pásztor-Huszár
,
R. Helt
, and
N. Lechner

Thermal and HHP treatments were compared. We established that the applied HHP treatments reduced the total cell count more significantly than thermal treatments. For example, the 10 min 600 MPa/10 min HHP treatment was equivalent to about 10 min thermal treatment at 70 °C. This combination of temperature and time is not used in the pasteurisation practice of the dairy industry. The various thermal treatments reduce the phosphatase enzyme activity to between one-third and one-hundredth of the original activity. The HHP treatments yielded similar results. Six hundred MPa pressure caused 10 to 70% decrease in the enzyme activity, while 700 MPa pressure led to a decrease of one log cycle.In the second year we tried to investigate the kinetics of the effect of HHP treatment. The 5, 10, 20, 40 min holding times were systematically applied in the range of 400 to 700 MPa. According to the results, 600 and 700 MPa HHP treatments effectively assured a decrease in the total cell count and the alkaline phosphatase enzyme activity. No organoleptic changes occurred.

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Acta Alimentaria
Authors:
Y. Hassan
,
L. Mészáros
,
A. Simon
,
E. Tuboly
,
Cs. Mohácsi-Farkas
, and
J. Farkas

The total viable cell count of bacteria in vacuum-packaged chilled minced beef has been decreased equally, by approx. two log-cycles, as an effect of 1.5-2.0 kGy gamma radiation or 200-300 MPa high hydrostatic pressure (UHP) treatment for 20 min. Coliform bacteria could be eliminated to non-detectable levels by the same treatments. The shelf-life of both untreated and non-thermally pasteurised samples were limited mainly by growth of lactic acid bacteria. At about equal bactericidal effect, more drastic changes of texture and colour occurred in UHP-pasteurized minced beef samples than in the radiation-pasteurized ones. Whereas radiation pasteurisation caused minimal changes in appearance, texture and DSC-thermograms of minced beef, UHP-pasteurisation of the raw samples proved to be strongly discolouring by denaturing the muscle pigments and causing extensive denaturation of the myofibrillar proteins. The water holding capacity of irradiated samples decreased, while that of high pressure treated ones increased as compared to the untreated control. Near infrared spectrometry and electronic nose measurements gave promising results to make distinctions non-destructively on changes of various physical-chemical changes and quality parameters as a function of pasteurising treatments and/or storage.

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