Template-Type: ReDIF-Article 1.0 Author-Name: V. Stejskal Title: Non-linear relationship between food resource exploitation and population density of stored-product pests Abstract: The main current strategies (IPM, HACCP) to control pests in stored food products are based on critical thresholds derived from pest population density. These thresholds usually do not consider cumulative effects of earlier pest infestation although injuries caused by biotic pest organisms to stored food commodities are irreversible. We present conceptual and illustrative models showing that population size indices, in contrast to cumulative (population history) indices, could (i) underestimate critical thresholds if pest population can grow exponentially and (ii) provide incorrect information about the level of stored food damage if pest population density can fluctuate. The importance of entomological food microanalysis and continual "cumulative monitoring" based on trapping is discussed with respect to HACCP and IPM programmes in stored food products. Keywords: pest populations dynamics, population history, cumulative population indices, thresholds, decision making Journal: Czech Journal of Food Sciences Pages: 81-85 Volume: 18 Issue: 3 Year: 2000 DOI: 10.17221/8315-CJFS File-URL: http://cjfs.agriculturejournals.cz/doi/10.17221/8315-CJFS.html File-Format: text/html Handle: RePEc:caa:jnlcjf:v:18:y:2000:i:3:id:8315-CJFS Template-Type: ReDIF-Article 1.0 Author-Name: N.D. Menkov Author-Name: D.I. Gelyazkov Title: Moisture sorption isotherms of millet seeds Abstract: The equilibrium moisture contents were determined for millet seeds of two cultivars using the gravimetric static method at 10, 25 and 40°C over a range of relative humidities from 0.112 to 0.868. The sorption capacity of the seeds decreased with an increase in temperature at constant relative humidity. The hysteresis effect is not distinctly expressed but statistically significant. The differences between equilibrium moisture contents of the cultivars are small. Four models were applied for analyzing the experimental data using the following equations: modified Chung-Pfost, modified Halsey, modified Oswin, and modified Henderson. The modified Chung-Pfost model was found to be the most suitable for describing the relationship between equilibrium moisture content, relative humidity and temperature. Keywords: millet, equilibrium, sorption, model Journal: Czech Journal of Food Sciences Pages: 86-90 Volume: 18 Issue: 3 Year: 2000 DOI: 10.17221/8316-CJFS File-URL: http://cjfs.agriculturejournals.cz/doi/10.17221/8316-CJFS.html File-Format: text/html Handle: RePEc:caa:jnlcjf:v:18:y:2000:i:3:id:8316-CJFS Template-Type: ReDIF-Article 1.0 Author-Name: N.A. Olasupo Title: Phenotypic features and enzymatic profile of a Lactococcus lactis strain isolated from wara, an indigenous cheese product from Nigeria Abstract: A lactic strain coded NA 1300, isolated from wara, a Nigerian cheese product, was identified as Lactoccus lactis, on the basis of sugar fermentation pattern, and other physiological and biochemical characteristics and by DNA-DNA hybridization. The enzytmatic profile of strain NA 1300 indicated the presence of a wide spectrum of enzymes. The organism exhibited relatively weak esterase and lipase activities as compared with peptidases. The strain showed no proteinase activity. The results are discussed in relation to the role of enzymes in starter selection for cheese production. Keywords: phenotypic features, enzymatic profile, Lactococcus lactis, wara Journal: Czech Journal of Food Sciences Pages: 91-94 Volume: 18 Issue: 3 Year: 2000 DOI: 10.17221/8317-CJFS File-URL: http://cjfs.agriculturejournals.cz/doi/10.17221/8317-CJFS.html File-Format: text/html Handle: RePEc:caa:jnlcjf:v:18:y:2000:i:3:id:8317-CJFS Template-Type: ReDIF-Article 1.0 Author-Name: A. Mohsen Title: Molecular detection of Brucella in milk using polymerase chain reaction Abstract: Brucellosis is a highly contagious disease affecting a wide variety of farm animals. It is also an important zoonosis, and man is often infected following contact with infected animals or the consumption of contaminated milk and milk products. At present, mainly bacteriological and serological detection methods are used. A bacteriological method takes days to weeks to grow the organism besides its health hazard. Serological tests are faster but antigen-antibody interactions can be faulted by non-specific interactions. A method for direct detection of Brucella melitensis in 1 ml of milk was developed on the basis of enzymatic treatment of milk components and subsequent PCR and line probe assay (LPA). After PCR, 3 × 104 CFU/ml sensitivity was obtained by agarose gel electrophoresis and LPA. The safety and sensitivity of LPA combined with its speed suggests the potential of this technique for diagnosis of brucellosis in milk rather than the time consuming classical methods. Keywords: Brucella melitensis, milk, polymerase chain reaction Journal: Czech Journal of Food Sciences Pages: 95-97 Volume: 18 Issue: 3 Year: 2000 DOI: 10.17221/8318-CJFS File-URL: http://cjfs.agriculturejournals.cz/doi/10.17221/8318-CJFS.html File-Format: text/html Handle: RePEc:caa:jnlcjf:v:18:y:2000:i:3:id:8318-CJFS Template-Type: ReDIF-Article 1.0 Author-Name: A. Hejtmánková Author-Name: J. Dolejšková Author-Name: V. Horák Author-Name: H. Dragounová Author-Name: F. Louda Title: Benzoic acid in some milk products from the market in the Czech Republic Abstract: Benzoic acid is a natural component of fermented milk products. The level of benzoic acid depends on the level of hippuric acid in used milk and on the process of dairy product manufacture, especially on the technologically used microorganisms. A hygienic limit 30 mg/kg of benzoic acid in milk products was laid down in the Czech Republic in 1997. In our study we determined the levels of benzoic acid in model yoghurts and in some milk products from Czech market. The benzoic acid content was determined by HPLC, by the use of our modification of the provisional IDF standard 139(1987). All samples of model yoghurts and all samples of milk products from the market showed levels of benzoic acid below the newly set hygienic limit. Highest level of benzoic acid was determined in the sample of white cheese (22.85 mg/kg), all other products based on white cheese showed average levels. Cottage cheese products (sample P), which belongs to the family of milk products for children, showed a very low level of benzoic acid, which is considered as a very positive result. Keywords: benzoic acid, fermented milk products, cheese, HPLC, hygienic limit Journal: Czech Journal of Food Sciences Pages: 99-102 Volume: 18 Issue: 3 Year: 2000 DOI: 10.17221/8320-CJFS File-URL: http://cjfs.agriculturejournals.cz/doi/10.17221/8320-CJFS.html File-Format: text/html Handle: RePEc:caa:jnlcjf:v:18:y:2000:i:3:id:8320-CJFS Template-Type: ReDIF-Article 1.0 Author-Name: K. Zdeňková Author-Name: K. Demnerová Author-Name: G. Jeníková Author-Name: J. Pazlarová Title: A new method for rapid detection of Listeria monocytogenes in food Abstract: Listeria monocytogenes represents serious danger for human health. Thus detection of this pathogen in food, which represents its main means of entry into the organism, is a topic of special importance. The original classic methods for the determination of Listeria monocytogenes are in general laborious and time-consuming procedures. In order to address this issue we developed a new rapid method for specific detection of Listeria monocytogenes in food samples. The method consists of three steps: i) enrichment of food microflora (16 h), ii) selective isolation of Listeria sp. exploiting immunomagnetic separation (2-3 h) followed by iii) precise identification of Listeria sp. and Listeria monocytogenes using duplex PCR. PCR primers specific to part of 16S rRNA were used in order to identify the members of Listeria genus. The specific identification of Listeria monocytogenes was accomplished exploiting a pair of primers specific to gene encoding invasion-associated protein - iap (4-5 h). Amplification products, 1003 bp and 593 bp respectively, were separated by electrophoresis and visualized by UV detection. The optimized IMS-PCR method was used to test the presence of Listeria sp. and Listeria monocytogenes in food samples (ground meat, low-fat milk and cheese [olomoucké tvarůžky]). A comparison of the efficiency of the bacteria enrichment step by IMS and centrifugation was also performed. The analysis time including enrichment is less than 24 h. The detection limit for Listeria monocytogenes was found between 101-102 cfu per 25 g of food sample. Keywords: Listeria monocytogenes, food sample, immunomagnetic separation (IMS), polymerase chain reaction (PCR) Journal: Czech Journal of Food Sciences Pages: 103-109 Volume: 18 Issue: 3 Year: 2000 DOI: 10.17221/8319-CJFS File-URL: http://cjfs.agriculturejournals.cz/doi/10.17221/8319-CJFS.html File-Format: text/html Handle: RePEc:caa:jnlcjf:v:18:y:2000:i:3:id:8319-CJFS Template-Type: ReDIF-Article 1.0 Author-Name: J. Čermák Author-Name: M. Rychtera Author-Name: P. Nechvíle Author-Name: J. Náhlík Author-Name: K. Melzoch Author-Name: J. Šindelář Author-Name: J. Vovsík Author-Name: J. Votruba Title: Influence of the specific growth rate on formation of sterols in yeast Saccharomyces cerevisiae during fed-batch cultivation Abstract: Ergosterol is a major sterol in yeast cells. Intermediates of ergosterol biosynthesis or products of ergosterol biotransformation occur in cells too. Sterols mainly form components of cell membranes. Fluidity of membranes is affected by sterols. The amount of sterols in cells can be influenced above all by cultivation conditions and by the yeast genotype. Specific growth rate is an important factor which affects the amount of sterols present in yeast cells. We carried out a series of 24-hour cultivations to find out the impact of specific growth rate on sterol biosynthesis. Inflow of synthetic medium to the bioreactor was controlled by means of a profile of carbon dioxide concentration in the outlet gases. This profile was acquired by simulation according to a mathematical model of cultivation. Profile of carbon dioxide concentration corresponded to a precalculated profile of specific growth rate. Cultivation was divided into two phases with different growth rate values. A constant value of the specific growth rate was maintained in the 1st phase. The specific growth rate value decreased by controlling the inflow in the 2nd phase (beginning at 12th hour of cultivation). Other cultivations were carried out using so-called physiological control which consisted in determining the immediate physiological state (e.g., RQ) and the choice of control strategy according to the metabolic state. Selected control strategy ensures an immediate action (inflow of the medium). If the specific growth rate decreased in the 1st phase, the amount of total sterols in yeast dry biomass increased (to 2.7% in yeast dry biomass). But the purity of ergosterol decreased (amount of sterol contaminants increased up to 23.3% in the sterol fraction). If a constant value of respiratory quotient was maintained (at about 1.1), the amount of total sterols in yeast dry biomass and the purity of ergosterol were constant. If the value of respiratory quotient was changed in the growth and final phase of cultivation, the amount of total sterols in yeast dry biomass increased (to 2.83% in yeast dry biomass). However, the purity of ergosterol decreased (amount of sterol contaminants increased up to 21.2% in sterol fraction). Keywords: sterols, Saccharomyces cerevisiae, effect on growth rate, fed-batch cultivation, control of feeding Journal: Czech Journal of Food Sciences Pages: 110-114 Volume: 18 Issue: 3 Year: 2000 DOI: 10.17221/8321-CJFS File-URL: http://cjfs.agriculturejournals.cz/doi/10.17221/8321-CJFS.html File-Format: text/html Handle: RePEc:caa:jnlcjf:v:18:y:2000:i:3:id:8321-CJFS Template-Type: ReDIF-Article 1.0 Author-Name: P. Kalač Author-Name: J. Moudrý Title: Composition and nutritinal value of quinoa (Chenopodium quinoa) - a review Abstract: Literature data on proteins, lipids, starch, minerals, vitamins and saponins contents and composition and their distribution within whole quinoa seeds, hulls, bran and flour are reviewed. An information on effects of quinoa processing on nutritional value and food applications is also given. Keywords: Chenopodium quinoa, quinoa seeds, composition, nutritional value Journal: Czech Journal of Food Sciences Pages: 115-119 Volume: 18 Issue: 3 Year: 2000 DOI: 10.17221/8322-CJFS File-URL: http://cjfs.agriculturejournals.cz/doi/10.17221/8322-CJFS.html File-Format: text/html Handle: RePEc:caa:jnlcjf:v:18:y:2000:i:3:id:8322-CJFS