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1.
The ability of the direct epifluorescent filter technique (DEFT) to enumerate the viable numbers of various species of yeasts was evaluated. A DEFT count could be made in less than 10 min and the DEFT counts of non-heat-treated samples agreed well with plate counts. The DEFT was unsuitable for the enumeration of yeasts in heat-treated samples because non-viable cells fluoresced orange. A double staining technique using Janus Green B and acridine orange was developed to overcome this problem. The modified DEFT enabled viable and non-viable yeasts to be differentiated in heat-treated samples of pure cultures and improved the relationship between the DEFT count and plate count. The method proved to be of little value, however, for use with beverage products because of unreliable staining patterns.  相似文献   

2.
The ability of the direct epifluorescent filter technique (DEFT) to enumerate the viable numbers of various species of yeasts was evaluated. A DEFT count could be made in less than 10 min and the DEFT counts of non-heat-treated samples agreed well with plate counts. The DEFT was unsuitable for the enumeration of yeasts in heat-treated samples because non-viable cells fluoresced orange. A double staining technique using Janus Green B and acridine orange was developed to overcome this problem. The modified DEFT enabled viable and non-viable yeasts to be differentiated in heat-treated samples of pure cultures and improved the relationship between the DEFT count and plate count. The method proved to be of little value, however, for use with beverage products because of unreliable staining patterns.  相似文献   

3.
The keeping quality (KQ) of pasteurized milk stored at 5 degrees C and 11 degrees C was predicted within 24 h by pre-incubating samples and counting bacteria by the Direct Epifluorescent Filter Technique (DEFT). For samples from 5 degrees C storage, 0.03% (w/v) benzalkonium chloride and 0.002% (w/v) crystal violet (final concentration) were added to inhibit the growth of Gram positive bacteria during pre-incubation. The samples from milk stored at 11 degrees C were pre-incubated without the addition of inhibitors. After pre-incubation there was a satisfactory relationship between the DEFT count and the KQ of milks at both 5 degrees C and 11 degrees C. The DEFT count following pre-incubation correctly classified greater than 80% of pasteurized milks on the basis of KQ.  相似文献   

4.
The keeping quality (KQ) of pasteurized milk stored at 5°C and 11°C was predicted within 24 h by pre-incubating samples and counting bacteria by the Direct Epifluorescent Filter Technique (DEFT). For samples from 5°C storage, 0.03% (w/v) benzalkonium chloride and 0.002% (w/v) crystal violet (final concentration) were added to inhibit the growth of Gram positive bacteria during pre-incubation. The samples from milk stored at 11°C were pre-incubated without the addition of inhibitors. After pre-incubation there was a satisfactory relationship between the DEFT count and the KQ of milks at both 5°C and 11°C. The DEFT count following pre-incubation correctly classified > 80% of pasteurized milks on the basis of KQ.  相似文献   

5.
Filtration of "stomachered" food suspensions through nylon filters (pore size, 5 microns) removed most of the food debris without affecting the recovery of microorganisms. Two to ten milliliters of these prefiltered suspensions could be filtered in the direct epifluorescent filter technique (DEFT). The technique takes less than 30 min to complete and has a lower sensitivity of less than 60,000 microorganisms per g for all products examined. Vegetative bacterial cells, spores, fungal hyphae, and yeasts could be distinguished with the technique. For fresh meat and fish, the DEFT count of prefiltered suspensions agreed well with the plate count of unfiltered suspensions over the range of 10(4) to 10(10)/g (correlation coefficient of 0.91). For frozen meat and fish and frozen vegetables, the two counting methods had correlation coefficients of 0.87 and 0.66, respectively. The poor correlation for frozen vegetables was due to the inclusion in the DEFT count of nonviable bacteria killed by the blanching process used to inactivate enzymes. Good agreement was obtained between the prefiltered DEFT count and unfiltered plate count for cooked meats, cream doughnut, and whole peppers. Possible reasons for the poor agreement between the DEFT count and plate count for certain products are discussed.  相似文献   

6.
Of the bacteriostats tested, that comprising boric acid, glycerol, potassium sorbate and nystatin was the most suitable in preventing the multiplication of bacteria, yeasts and moulds in milk whilst causing least change in the Direct Epifluorescent Filter Technique (DEFT) count of bacteria and somatic cells. The DEFT and plate count of bacteria and the DEFT count of somatic cells were reduced after preservation and storage. The relationships between the plate count of fresh milk samples and the DEFT count and plate count of the same samples after preservation and storage for 3 d at room temperature (20–22°C) had correlation coefficients ( r ) of 0.80 and 0.85, respectively. The relationship between the Coulter count of somatic cells in fresh milk and the DEFT count of somatic cells in stored preserved milk had a correlation coefficient of 0.90. The addition of the bacteriostatic mixture to milk affected the determination of protein by the Milkoscan and lactose by the Infra Red Milk Analyser. It did not affect the estimation of the other milk components (fat, protein or lactose) by either instrument.  相似文献   

7.
A modified direct epifluorescent filter technique (DEFT) for the detection and enumeration of visible yeast in fruit-flavoured yoghurt is described. The method involves an initial enrichment in oxytetracycline glucose yeast peptone broth (OGYP, 30C/24, 48 h), prefiltration prior to DEFT and use of the vital stain Viablue 1. Additional yoghurt samples were subjected to prolonged incubation at 12C or spiked with Kluyveromyces fragilis . When DEFT was compared with the plate count, regression and correlation coefficients of 1.12 and 0.85 respectively were obtained for values above the sensitivity threshold of DEFT (103 cells/ml). The use of an enrichment stage (OGYP, 30C/24 h) enabled, by calculation, a theoretical minimum yeast contamination level of 7 yeast cells/g in the original yoghurt to be detected assuming the cells exhibit no lag phase of growth.  相似文献   

8.
Brine fermentation by osmophilic lactic acid bacteria and yeasts for long periods of time is essential to produce a good quality of shoyu (Japanese fermented soy sauce). It is well known that lactic acid fermentation by osmophilic lactic acid bacteria results in the depression of alcoholic fermentation by osmophilic yeasts, but the nature of the interaction between osmophilic lactic acid bacteria and yeasts in brine fermentation of shoyu has not been revealed. The inhibitory effect of osmophilic lactic acid bacteria on the growth of osmophilic yeasts was investigated. It was recognized that osmophilic shoyu yeasts such as Saccharomyces rouxii and Torulopsis versatilis were inhibited by a metabolite produced by osmophilic lactic acid bacteria (belonging to Pediococcus halophilus) in brine fermentation of shoyu. The primary inhibitor was considered to be acetic acid, although lactic acid was slightly inhibitory.  相似文献   

9.
An epifluorescent microscope fitted with a 'Chalnicon' closed circuit television camera linked to an Optomax System III image analyser was used to count bacteria and somatic cells on membrane filters prepared from milk by the direct epifluorescent filter technique (DEFT). For both bacteria and somatic cells, the semi-automated DEFT count of low count milk exceeded the visual DEFT count but this difference became proportionately less as the count increased. There was close agreement between the semi-automated and visual DEFT counts over the range 105-5 times 106/ml for bacteria and 3 times 105-5 times 106/ml for somatic cells. The semi-automated DEFT count of bacteria and somatic cells correlated well with the plate count and Coulter count respectively, with correlation coefficients of 0.83 and 0.81.  相似文献   

10.
A total of 1752 strains of osmophilic yeasts were isolated from honey and pollens. Forty-three strains of osmophilic yeasts produced polyols, among which 6 strains produced erythritol in good yields. On the other hand, 52 osmophilic yeasts converted sucrose to fructooligosaccharides, among which 8 strains produced both extra and intracellular β-fructofuranosidase, which converted sucrose to fructooligosaccharides. This investigation concluded that osmophilic yeasts converted sucrose not only to polyols, but also to fructooligosaccharides in good yields.  相似文献   

11.
Heat treatment at 80°C for 10 min effectively destroyed all vegetative cells (except for Gram-positive cocci) and made easier the counting of bacterial spores, which stained orange, green or rarely transparent/black with a dull green halo, in the direct epifluorescent filter technique. The numbers of both orange- or green-staining spores were lower than the plate count. A variety of physiological conditions were used to investigate the relationship of the different staining patterns with germination status. It was concluded that orange-staining spores had germinated and their number agreed with the plate count after incubation in yeast glucose broth at 30°C for 4 h. This observation was unreliable, however, but it was found that a total spore count in the DEFT gave a good agreement with the plate count.  相似文献   

12.
A method was evaluated which has the potential to detect a food sample which has been irradiated. The technique will give an indication of the total number of viable micro-organisms present before irradiation. It is based on the comparison of an aerobic plate count (APC) with a count obtained using the Direct Epifluorescent Filter Technique (DEFT). When the APC of an irradiated sample was compared with the DEFT count on the same sample, the APC was considerably lower than that obtained by DEFT. The count of orange fluorescing cells after irradiation, however, correlated well with an APC of the same sample before irradiation. For the samples examined the DEFT count determined the viable microbial population in the sample before irradiation. The difference between the APC and the DEFT count gave the number of organisms rendered non-viable by the process.  相似文献   

13.
A rapid direct epifluorescent filter technique (DEFT), taking ca. 20 min to complete, was used to enumerate bacteria in heat-treated milk and milk-products. The DEFT count could detect as few as 5750 bacteria/ml in pasteurized and skim milk, pasteurized cream, whey and sweet cream butter and was in agreement with the standard plate count. The technique was also used to determine the sterility of cartoned ultra heat-treated milk after incubation at 37°C. The agreement between the DEFT and plate count was poor for evaporated and condensed milks, some reconstituted skim milk powders, pasteurized whey and ripened cream butter. Possible reasons for this are discussed.  相似文献   

14.
A method was evaluated which has the potential to detect a food sample which has been irradiated. The technique will give an indication of the total number of viable micro-organisms present before irradiation. It is based on the comparison of an aerobic plate count (APC) with a count obtained using the Direct Epifluorescent Filter Technique (DEFT). When the APC of an irradiated sample was compared with the DEFT count on the same sample, the APC was considerably lower than that obtained by DEFT. The count of orange fluorescing cells after irradiation, however, correlated well with an APC of the same sample before irradiation. For the samples examined the DEFT count determined the viable microbial population in the sample before irradiation. The difference between the APC and the DEFT count gave the number of organisms rendered non-viable by the process.  相似文献   

15.
The direct epifluorescent filter technique (DEFT) is a new rapid method which uses membrane filtration and epifluorescent microscopy for counting bacteria in milk. A collaborative trial of the DEFT was conducted between six laboratories. Each laboratory obtained a highly significant relationship between the DEFT count and plate count with a correlation coefficient generally > 0.9 but there were significant differences between these relationships. The repeatability of the DEFT, although ca 1·5 times worse than that of the plate count, was of a level acceptable in practice. Reproducibility of the DEFT was ca 3 times that of the plate count. This poor reproducibility was probably mainly due to counting errors. Possible reasons for this and ways of reducing counting errors are discussed.  相似文献   

16.
Candida magnoliae and its mutants were analyzed to produce erythritol from glucose with high yield and productivity. One mutant, M2, showed higher erythritol conversion yield and productivity than the wild strain. The osmophilic mutant produced 25 g erythritol l–1 after 83 h of a flask culture in a medium containing 10% (w/v) glucose, corresponding to a 25% increase in erythritol and a 30% increase in erythritol productivity compared with the wild type. The fermentation properties were further improved by cultivating the osmophilic mutant in a fermenter containing 20% (w/v) glucose medium with 0.54 g l–1 h–1 of erythritol productivity and 43% of erythritol conversion yield based on glucose.  相似文献   

17.
A slow feed batch fermentation is described for the production of glycerol from sugar. The conversion efficiency was approximately 1 mole of glycerol produced per mole of glucose utilized after the cell growth phase. The glycerol production phase was extended several-fold by periodic glucose addition. The yeast cell count remained constant during this time as limited by phosphate, a deficiency required for an efficient glycerol fermentation. A small amount of phosphate was supplied during the extended fermentation, maintaining an active culture, by the normal autolysis of spent cells. Interfering or inhibitory by-products did not accumulate, and the osmophilic yeasts are tolerant of high glycerol concentrations. These factors combined to allow a particularly efficient fermentation well suited to product enrichment by supplying large quantities of substrate over an extended period.  相似文献   

18.
A simple, rapid, physicochemical treatment for the removal of viable bacteria from the surface of raw and cooked beef is described. The detachment method was linked to a differential centrifugation step which removed large amounts of particulate food matter and concentrated the detached bacteria. The method increased the numbers of bacteria released from beef surfaces and increased the numbers detected by at least one and a half orders of magnitude, when compared to the traditional 'stomaching' technique. This 1-h separation and concentration method produced cleaner suspensions of bacteria and improved the sensitivity of detection by DEFT and direct plate count.  相似文献   

19.
With the direct epifluorescent filter technique (DEFT), differentiation of bacteria was achieved by a modified Gram-staining procedure using acridine orange as the counterstain. The method enumerated viable Gram-negative and all Gram-positive bacteria. Counts of clumps of orange fluorescent cells (Gram-negative DEFT count) correlated well with colony counts of Gram-negative bacteria in samples of raw milk ( r = 0·94). The use of stainless steel membrane filter supports and the addition of citrate-NaOH buffer (0·1 M, pH 3·0) during filtration enabled 10 ml samples of milk to be filtered, thereby increasing the sensitivity of the DEFT five-fold. The relationship between colony and DEFT counts with 10 ml samples was better ( r = 0·90) than that using standard 2 ml samples ( r = 0·88). Alternatively, these modifications in procedure allowed the preincubation time for 2 ml milk samples to be reduced from 10 to 2 min. Sonication was successful in dispersing bacterial clumps in both pure cultures and in raw milk samples to yield a bacterial count by DEFT which should give a better indication of the hygienic status and keeping quality of a product, than counts of colony forming units.  相似文献   

20.
The suitability of a microbiological method based on the comparison of an aerobic plate count (APC) with a count obtained with the direct epifluorescent filter technique (DEFT) for the detection of irradiation of deep-frozen foodstuffs was evaluated. The study was carried out on parsley, mechanically deboned poultry meat (MDPM) and liquid egg white. The foodstuffs were stored at—18°C and examined after storage for 0, 4 and 12 months.
The results showed that this method is discriminating during the whole storage period. Nevertheless, it has been observed that for non-irradiated liquid egg white the difference between DEFT and APC tends to increase with the time of storage. This phenomenon which did not limit the interest of the test, was not observed for the other products tested.  相似文献   

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