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Competition between a bacteriocinogenic and a non-bacteriocinogenic Lactococcus lactis strain, respectively, and a Listeria monocytogenes strain was studied in two semi-synthetic liquid media at various temperatures. The media used for the study were ST I and modified ST I broth (ST I broth + 1 g l-1 Tween 80). In both media, at 30 °C, a significant cell count reduction (5 log) of L. monocytogenes occurred only when the cell concentration of the bacteriocinogenic competitor reached the level of at least 107 CFU ml-1 required for the production of sufficient concentration of nisin-like bacteriocin. The same phenomenon was also observed when the initial level of the lactic acid bacteria (LAB) was one log higher or lower than that of the Listeria, however, the reduction of Listeria cell count occurred earlier with the higher initial concentration of the LAB. Incubation of the mixed cultures at 20 °C gave similar results but the bacteriocinogenic activity resulted in only a three log decline of the cell count of L. monocytogenes. At 10 °C Lactococcus lactis produced much less bacteriocin than at 30 °C, therefore, a drastic decrease of the Listeria cell count was not observed. Suppression of the Listeria growth was expressed in its decreased maximum population level (i.e. in an earlier appearance of the stationary phase). When the non-bacteriocinogenic Lac. lactis and Listeria were present at the same initial level (approx. 105 CFU ml-1), the Lactococcus did not affect the growth of L. monocytogenes at 30 °C in modified ST I broth.

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Conductimetry as an alternative data capture method for following microbial growth has a great potential as a research tool of predictive microbiology. In spite of this fact there is only a limited number of applications using conductimetric data for model generation. In this study the growth of single strains of Listeria monocytogenes and Lactococcus lactis was tested in 5 media using a RABITinstrument. The goal of the work was to find selective growth media for Listeria and Lactococcus, respectively, in order to study their interaction in mixed-culture using the conductimetric technique. Whitley Anaerobic broth, Whitley Impedance broth and modified Whitely Impedance broth (Whitley Impedance broth + Chloramphenicol 7 mg l &1) were not suitable for following selectively the growth of Lactococcus lactis or Listeria monocytogenes in a mixed culture of the two bacteria. BiMedia 630 A for Lactococcus lactis and Bimedia 403 A for Listeria monocytogenes satisfied the demands raised by conductance measurement. Linear correlations were established between the graphically estimated TTD values of the conductance curves and the logarithmic numbers of colony forming units (CFU). The correlations were very strong in each case (determination coefficients (R 2) of the linear regression were higher than 0.98 at both medium-strain combinations). However, in BiMedia 630 Listeria monocytogenes was capable of slow growth, therefore, this medium would be feasible for studying microbial interactions if only low concentrations of Listeria (less than 10 6 CFU ml &1) were present in the mixed culture.

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From the age of 9 weeks, 90-90 Kolos, Gourmaud and Babati goose breeds were force fed with 2 different types of technology and 3 types of feedstuff. Force feeding technologies were the traditional Hungarian and Israeli soft groats quick methods. In the case of the latter, feedstuff was fed both in a pre-fermented (Lactobacillus plantarumlactic acid bacteria) form and without fermentation. Frequency of daily force feeding was gradually increased from 2 to 6 until the 21st day of force feeding. Live weight before and after fattening and liver weight were measured in the case of each breed and treatment. Liver quality was also determined. On the basis of our results, differences in liver weight average were significantly influenced only by the genetic property of the breed. Liver quality was also influenced by the method of force feeding of one breed (Babati). Feedstuff tested did not result in significant differences in liver weight or in liver quality. Independently of the breed very close correlation was found between „fattening weight” and liver weight (r=0.98) and between „fattening weight” and liver quality grade (r=–0.97).

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Acta Alimentaria
Authors:
M. Szalai
,
J. Szigeti
,
L. Farkas
,
L. Varga
,
A. Réti
, and
E. Zukál

The shelf-lives of major commercial cooked meat products (i.e., Bologna sausage, Italian-type cooked sausage, and cooked ham) packaged under vacuum or modified atmospheres were tested in this study. Samples were taken from commercial meat processing lines, sliced to 1.2 mm thickness and placed overlapped into polypropylene trays sealed with plastic films. The headspace of modified atmosphere packaged formulations consisted of 30% CO2 and 70% N2 or 60% CO2 and 40% N2. The samples thus produced were stored under refrigerated conditions. The values of microbiological, chemical, physical or sensory properties were plotted against storage time, and Gompertz curves were fitted to all time series that changed from an initial to a final value during any period of storage. The influence of headspace CO2 concentration on the properties of sliced cooked meat products varied considerably and, therefore, it was not possible to specify general rules. However, the presence of CO2 in the packaging atmosphere slowed down the rate of microbial growth, thereby delaying the spoilage of meat products. A CO2 level of 60% had beneficial effects on both the microbiological and sensory properties of sliced sausages and cooked ham. It was concluded that cooked meat products packaged under modified atmospheres had a shelf-life of 20 days.

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Acta Agronomica Hungarica
Authors:
J. Pintér
,
E. Kósa
,
G. Hadi
,
Z. Hegyi
,
T. Spitkó
,
Z. Tóth
,
Z. Szigeti
,
E. Páldi
, and
L. Marton

The level of UV-B radiation reaching the surface of the earth is increasing due to the thinning of the ozone layer in the stratosphere over recent decades. This has numerous negative effects on living organisms.Some of the Hungarian inbred maize lines examined under the climatic conditions in Chile exhibited an unusually high proportion of pollen mortality, flowering asynchrony and barrenness. The evidence suggests that this can be attributed to the approx. 30% greater UV-B radiation in Chile.The investigation of this problem within the framework of abiotic stress breeding programmes is extremely important in the light of the global rise in UV-B radiation, which may make it necessary to elaborate a selection programme to develop inbred lines with better tolerance of this type of radiation.In the course of the experiment the same ten inbred lines, having different maturity dates and genetic backgrounds, were tested for five years in Chile and Hungary. The tests focussed on anthocyanin, a flavonoid derivative involved in the absorption of damaging UV-B radiation.Averaged over years and varieties, the total anthocyanin content in the leaf samples was significantly higher in Chile than in Hungary. This was presumably a response at the metabolic level to the negative stress represented by higher UV-B radiation.In the five early-maturing flint lines the anthocyanin contents were more than 45% greater than those recorded in Hungary. This suggests that these genotypes, originating from northern regions, were not sufficiently adapted to the higher radiation level. In these samples higher UV-B caused a sharp rise in the quantity of anthocyanin, which absorbs the dangerous radiation. In late-maturing genotypes the initial content of the protective compound anthocyanin was higher at both locations, so in these types the high radiation level was not a problem and did not cause any substantial change.Similar conclusions were drawn from the results of fluorescence imaging. The F440/F690 ratio indicative of the stress level was higher in late lines with a high anthocyanin content, good tolerance and good adaptability.

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The work was aimed at investigating short-term metabolic changes caused by S-methylmethionine (SMM) and at clarifying the gene expression background of these changes in order to gain a better understanding of the protective effect of SMM against stress. When examining the expression of genes coding for the enzymes responsible for the biosynthesis of polyamines, which play an important role in responses to low temperature stress, and that of the C-repeat binding transcription factor (CBF1) gene, it was found that both SMM and cold treatment increased the expression of genes responsible for the polyamine synthesis pathway starting from arginine. It caused only a slight increase when applied alone, but when SMM pre-treatment was followed by cold stress, it resulted in a considerable extent of up-regulation. SMM caused a similar increase in the expression of CBF1. The changes in the expression of genes responsible for the polyamine synthesis were clearly reflected in changes in the putrescine and agmatine contents, while the greater increase in the spermidine content was indicative of the role of SMM as a direct precursor in spermidine biosynthesis. The results demonstrated that, in addition to its direct effect on the sulphur metabolism and on polyamine biosynthesis, the protective effect of exogenous SMM was chiefly manifested in its influence on the expression of genes responsible for the biosynthesis of the polyamines important for stress responses and on the CBF1 transcription factor gene that acts as a regulator in cold stress.

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