| 1. |
- Hedell, Ronny, 1985, et al.
(författare)
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Detection probability models for bacteria, and how to obtain them from heterogeneous spiking data. An application to Bacillus anthracis
- 2017
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Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 1879-3460 .- 0168-1605. ; 241, s. 78-88
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Tidskriftsartikel (refereegranskat)abstract
- © 2016 Elsevier B.V.Efficient and correct evaluation of sampling results with respect to hypotheses about the concentration or distribution of bacteria generally requires knowledge about the performance of the detection method. To assess the sensitivity of the detection method an experiment is usually performed where the target matrix is spiked (i.e. artificially contaminated) with different concentrations of the bacteria, followed by analyses of the samples using the pre-enrichment method and the analytical detection method of interest. For safety reasons or because of economic or time limits it is not always possible to perform exactly such an experiment, with the desired number of samples. In this paper, we show how heterogeneous data from diverse sources may be combined within a single model to obtain not only estimates of detection probabilities, but also, crucially, uncertainty estimates. We indicate how such results can then be used to obtain optimal conclusions about presence of bacteria, and illustrate how strongly the sampling results speak in favour of or against contamination. In our example, we consider the case when B. cereus is used as surrogate for B. anthracis, for safety reasons. The statistical modelling of the detection probabilities and of the growth characteristics of the bacteria types is based on data from four experiments where different matrices of food were spiked with B. anthracis or B. cereus and analysed using plate counts and qPCR. We show how flexible and complex Bayesian models, together with inference tools such as OpenBUGS, can be used to merge information about detection probability curves. Two different modelling approaches, differing in whether the pre-enrichment step and the PCR detection step are modelled separately or together, are applied. The relative importance on the detection curves for various existing data sets are evaluated and illustrated.
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| 2. |
- Hjortmo, Sofia, 1978, et al.
(författare)
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Biofortification of folates in white wheat bread by selection of yeast strain and process
- 2008
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Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 1879-3460 .- 0168-1605. ; 127:1-2, s. 32-36
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Tidskriftsartikel (refereegranskat)abstract
- We here demonstrate that folate content in yeast fermented food can be dramatically increased by using a proper (i) yeast strain and (ii) cultivation procedure for the selected strain prior to food fermentation. Folate levels were 3 to 5-fold higher in white wheat bread leavened with a Saccharomyces cerevisiae strain CBS7764, cultured in defined medium and harvested in the respiro-fermentative phase of growth prior to dough preparation (135-139 mu g/100 dry matter), compared to white wheat bread leavened with commercial Baker's yeast (27-43 mu g/100 g). The commercial Baker's yeast strain had been industrially produced, using a fedbatch process. thereafter compressed and stored in the refrigerator until bakings were initiated. This strategy is an attractive alternative to fortification of bread with synthetically produced folic acid. By using a high folate producing strain cultured a suitable way folate levels obtained were in accordance with folic acid content in fortified cereal products.
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| 3. |
- Berndtson, Eva, et al.
(författare)
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Campylobacter incidence on a chicken farm and the spread of Campylobacter during the slaughter process
- 1996
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Ingår i: International Journal of Food Microbiology. - : Elsevier. - 0168-1605 .- 1879-3460. ; 32:1-2, s. 35-47
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Tidskriftsartikel (refereegranskat)abstract
- To get a better understanding of the epidemiology of Campylobacter, a chicken farm was studied for 16 weeks with samplings in each flock weekly from input until the flock became colonized with Campylobacter or slaughtered. Samples were taken from fresh droppings and from drinkers during the rearing period, as well as from the environment in empty houses. The spread of Campylobacter during the slaughter process was also surveyed. No Campylobacter was found in samples from newly-hatched ol one-week-old chickens or their drinkers. All Hocks but one were colonized at two to five weeks of age. All Campylobacter isolates belonged to the same sero- and biotype; C. jejuni Penner 2. The spread of Campylobacter in the flock was rapid and usually all samples were positive once colonization had been proven. C. jejuni was isolated from flies in ante-rooms as well as from air in chicken units ill houses with positive chicken flocks. Samples were taken at slaughter when some of the Campylobacter positive Hocks from the farm were slaughtered. Campylobacter were isolated from all sampled equipment along the processing line, from the chicken transport crates to the chillers, as well as from the air.
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| 4. |
- Beuchat, L. R., et al.
(författare)
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Performance of mycological media in enumerating desiccated food spoilage yeasts : an interlaboratory study
- 2001
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Ingår i: International Journal of Food Microbiology. - : Elsevier. - 0168-1605 .- 1879-3460. ; 70:1-2, s. 89-96
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Tidskriftsartikel (refereegranskat)abstract
- Dichloran 18% glycerol agar (DG18) was originally formulated to enumerate nonfastidious xerophilic moulds in foods containing rapidly growing Eurotium species. Some laboratories are now using DG18 as a general purpose medium for enumerating yeasts and moulds, although its performance in recovering yeasts from dry foods has not been evaluated. An interlaboratory study compared DG18 with dichloran rose bengal chloramphenicol agar (DRBC), plate count agar supplemented with chloramphenicol (PCAC), tryptone glucose yeast extract chloramphenicol agar (TGYC), acidified potato dextrose agar (APDA), and orange serum agar (OSA) for their suitability to enumerate 14 species of lyophilized yeasts. The coefficient of variation for among-laboratories repeatability within yeast was 1.39% and reproducibility of counts among laboratories was 7.1%. The order of performance of media for recovering yeasts was TGYC > PCAC = OSA > APDA > DRBC > DG18. A second study was done to determine the combined effects of storage time and temperature on viability of yeasts and suitability of media for recovery. Higher viability was retained at - 18 degreesC than at 5 degreesC or 25 degreesC for up to 42 weeks, although the difference in mean counts of yeasts stored at - 18 degreesC and 25 degreesC was only 0.78 log(10) cfu/ml of rehydrated suspension. TGYC was equal to PCAC and superior to the other four media in recovering yeasts stored at - 18 degreesC, 5 degreesC, or 25 degreesC for up to 42 weeks. Results from both the interlaboratory study and the storage study support the use of TGYC for enumerating desiccated yeasts. DG18 is not recommended as a general purpose medium for recovering yeasts from a desiccated condition.
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| 5. |
- Hellström, Andreas, 1980, et al.
(författare)
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Biodiversity and phytase capacity of yeasts isolated from Tanzanian togwa
- 2010
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Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 1879-3460 .- 0168-1605. ; 136:3, s. 352-358
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Tidskriftsartikel (refereegranskat)abstract
- The focus of the present investigation was on the Tanzanian fermented food togwa as a source for dietary iron and zinc, and the potential for mineral availability improvements using selected yeasts. To establish the content of target minerals and main inhibitor for intestinal uptake, iron and zinc as well as the mineral chelating phytic acid, (IP6 or phytate) were determined in naturally fermented togwa. Yeasts were isolated from sorghum, maize and cassava based togwa, and identified by sequencing the D1/D2 region of the LSU rRNA gene. The isolated yeasts were subsequently screened for phytase activity.The total iron content in sorghum, maize and cassava based togwa were 41.5 (±7.2), 85.4 (±31.9) and 28.6 (±3.8) μg/g dw (dry weight) respectively. The zinc content was 12.3 (±3.1), 11.0 (±1.1) and 6.4 (±4.5) μg/g dw in sorghum, maize and cassava based togwa, and the phytate content in the three varieties were 2.6±1.2, 4.7±0.8 and 0.4±0.4 μmol/g dw respectively. The phytate levels in the sorghum and maize based togwa are expected to substantially reduce the availability of iron. The molar ratio phytate to iron for these two varieties were estimated to be 3.5:1 and 3.1:1 respectively. In general, a phytate to iron molar ratio below 1 is needed to increase the availability of iron.Among 26 isolates, 9 different species could be distinguished: Issatchenkia orientalis, Pichia anomala, Pichia norvegensis, Pichia burtonii, Pichia guilliermondii, Kluyveromyces marxianus, Saccharomyces cerevisiae, Hanseniaspora guilliermondii and Candida glabrata. The strains were screened for phytase activity in YPD supplemented with 0.5 mM IP6. Of 26 screened strains, the phytase activity was most prominent in strains of I. orientalis and H. guilliermondii. The strains and data constitute a basis for further improvements of iron andzinc bioavailability in togwa.
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| 6. |
- Jonsson, A., et al.
(författare)
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Electronic nose for microbial quality classification of grains
- 1997
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Ingår i: International Journal of Food Microbiology. - : Elsevier. - 0168-1605 .- 1879-3460. ; 35:2, s. 187-193
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Tidskriftsartikel (refereegranskat)abstract
- The odour of grains is in many countries the primary criterion of fitness for consumption. However, smelling of grain for quality grading should be avoided since inhalation of mould spores or toxins may be hazardous to the health and determinations of the off-odours are subjective. An electronic nose, i.e. a gas sensor array combined with a pattern recognition routine might serve as an alternative. We have used an electronic nose consisting of a sensor array with different types of sensors. The signal pattern from the sensors is collected by a computer and further processed by an artificial neural network (ANN) providing the pattern recognition system. Samples of oats, rye and barley with different odours and wheat with different levels of ergosterol, fungal and bacterial colony forming units (cfu) were heated in a chamber and the gas in the chamber was led over the sensory array. The ANN could predict the odour classes of good, mouldy, weakly and strongly musty oats with a high degree of accuracy. The ANN also indicated the percentage of mouldy barley or rye grains in mixtures with fresh grains. In wheat a high degree of correlation between ANN predictions and measured ergosterol as well as with fungal and bacterial cfu was observed. The electronic nose can be developed to provide a simple and fast method for quality classification of grain and is likely to find applications also in other areas of food mycology.
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| 7. |
- Karlsson, Ida, et al.
(författare)
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Agricultural factors affecting Fusarium communities in wheat kernels
- 2017
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Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 0168-1605 .- 1879-3460. ; 252, s. 53-60
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Tidskriftsartikel (refereegranskat)abstract
- Fusarium head blight (FHB) is a devastating disease of cereals caused by Fusarium fungi. The disease is of great economic importance especially owing to reduced grain quality due to contamination by a range of mycotoxins produced by Fusarium. Disease control and prediction is difficult because of the many Fusarium species associated with FHB. Different species may respond differently to control methods and can have both competitive and synergistic interactions. Therefore, it is important to understand how agricultural practices affect Fusarium at the community level.Lower levels of Fusariwn mycotoxin contamination of organically produced cereals compared with conventionally produced have been reported, but the causes of these differences are not well understood. The aim of our study was to investigate the effect of agricultural factors on Fusarium abundance and community composition in different cropping systems. Winter wheat kernels were collected from 18 organically and conventionally cultivated fields in Sweden, paired based on their geographical distance and the wheat cultivar grown. We characterised the Fusarium community in harvested wheat kernels using 454 sequencing of translation elongation factor 1-alpha amplicons. In addition, we quantified Fusariwn spp. using real-time PCR to reveal differences in biomass between fields.We identified 12 Fusariwn operational taxonomic units (OTUs) with a median of 4.5 OTUs per field. Fusarium graminearum was the most abundant species, while F. avenaceum had the highest occurrence. The abundance of Fusariwn spp. ranged two orders of magnitude between fields. Two pairs of Fusariurt species co-occurred between fields: F. poae with F. tricinctwn and F. culmorwn with F. sporofrichoides. We could not detect any difference in Fusariwn communities between the organic and conventional systems. However, agricultural intensity, measured as the number of pesticide applications and the amount of nitrogen fertiliser applied, had an impact on Fusariwn communities, specifically increasing the abundance of F. tricinctwn. There were geographical differences in the Fusarium community composition where F. graminearwn was more abundant in the western part of Sweden. The application of amplicon sequencing provided a comprehensive view of the Fusarium community in cereals. This gives us better opportunities to understand the ecology of Fusarium spp., which is important in order to limit FHB and mycotoxin contamination in cereals.
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| 8. |
- Lund, Bodil, et al.
(författare)
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Gastrointestinal transit survival of an Enterococcus faecium probiotic strain administered with or without vancomycin
- 2002
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Ingår i: International Journal of Food Microbiology. - 0168-1605 .- 1879-3460. ; 77:1-2, s. 109-115
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Tidskriftsartikel (refereegranskat)abstract
- The primary aim of this study was to evaluate if an ingested probiotic, containing viable Enterococcus faecium could survive gastrointestinal transit and if so, correlate the amount of the recovered probiotic strain with the host's own enterococci. The second aim was to investigate if simultaneous vancomycin intake influenced the survival and persistence of the probiotic strain and the stability of endogenous enterococci strains. Twenty healthy volunteers were given the probiotic product once daily for 10 days. Half of the subjects were simultaneously given vancomycin. Isolates of E. faecium strains were genotypically or phenotypically analysed with pulsed-field gel electrophoresis (PFGE) and the PhenePlate(TM) system, respectively. In eight of the ten volunteers given only the probiotic, the ingested E. faecium could be detected on day 10, while in none on day 31. From subjects given both probiotic and vancomycin no ingested E. faecium could be detected on day 10 or day 31. The estimated amount of ingested E. faecium recovered from faeces on day 10 ranged from 1.2 x 10(3) to 4.2 x 10(6) colony forming units per gram faeces, which in several cases were a substantial part of the total amount of E. faecium. The E. faecium isolated before probiotic plus vancomycin administration showed no close relationship to the ones isolated 3 weeks after ceased intake in any subjects. In conclusion, the ingested E. faecium strain can survive gastrointestinal transit. After intake, the E. faecium probiotic strain might become a large part of the total E, faecium population. The occurrence of the probiotic strain in the human gut seems to be transient after intake stop. Re-colonization of E. faecium after simultaneous probiotic plus vancomycin intake occurs mainly with strains without close genetic relationship to the strains harboured before treatment or to the ingested E. faecium strain.
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| 9. |
- Olsson, J., et al.
(författare)
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Detection and quantification of ochratoxin A and deoxynivalenol in barley grains by GC-MS and electronic nose
- 2002
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Ingår i: International Journal of Food Microbiology. - : Elsevier. - 0168-1605 .- 1879-3460. ; 72:3, s. 203-214
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Tidskriftsartikel (refereegranskat)abstract
- Mycotoxin contamination of cereal grains can be detected and quantified using complex extraction procedures and analytical techniques. Normally, the grain odour, i.e. the presence of non-grain volatile metabolites, is used for quality classification of grain. We have investigated the possibility of using fungal volatile metabolites as indicators of mycotoxins in grain. Ten barley samples with normal odour, and 30 with some kind of off-odour were selected from Swedish granaries. The samples were evaluated with regard to moisture content, fungal contamination, ergosterol content, and levels of ochratoxin A (OA) and deoxynivalenol (DON). Volatile compounds were also analysed using both an electronic nose and gas chromatography combined with mass spectrometry (GC-MS). Samples with normal odour had no detectable ochratoxin A and average DON contents of 16 mug kg(-1) (range 0-80), while samples with off-odour had average OA contents of 76 mug kg(-1) (range 0-934) and DON contents of 69 mug kg(-1) (range 0-857). Data were evaluated by multivariate data analysis using projection methods such as principal component analysis (PCA) and partial least squares (PLS). The results show that it was possible to classify the OA level as below or above the maximum limit of 5 mug kg(-1) cereal grain established by the Swedish National Food Administration, and that the DON level could be estimated using PLS. Samples with OA levels below 5 mug kg(-1) had higher concentration of aldehydes (nonanal, 2-hexenal) and alcohols (1-penten-3-ol, 1-octanol). Samples with OA levels above 5 mug kg(-1) had higher concentrations of ketones (2-hexanone, 3-octanone). The GC-MS system predicted OA concentrations with a higher accuracy than the electronic nose, since the GC-MS misclassified only 3 of 37 samples and the electronic nose 7 of 37 samples. No correlation was found between odour and OA level, as samples with pronounced or strong off-odours had OA levels both below and above 5 mug kg(-1). We were able to predict DON levels in the naturally contaminated barley samples using the volatile compounds detected and quantified by either GC-MS or the electronic nose. Pentane, methylpyrazine, 3-pentanone, 3-octene-2-ol and isooctylacetate showed a positive correlation with DON, while ethylhexanol, pentadecane, toluene, 1-octanol, 1-nonanol, and 1-heptanol showed a negative correlation with DON. The root mean square error of estimation values for prediction of DON based on GC-MS and electronic nose data were 16 and 25 mug kg(-1) respectively.
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| 10. |
- Olsson, J., et al.
(författare)
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Volatiles for mycological quality grading of barley grains : determinations using gas chromatography-mass spectrometry and electronic nose
- 2000
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Ingår i: International Journal of Food Microbiology. - : Elsevier. - 0168-1605 .- 1879-3460. ; 59:3, s. 167-178
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Tidskriftsartikel (refereegranskat)abstract
- The possibility of using an electronic nose or gas chromatography combined with mass spectrometry (GC-MS) to quantify ergosterol and colony forming units (CFU) of naturally contaminated barley samples was investigated. Each sample was split into three parts for (i) ergosterol and CFU analysis, (ii) measurements with the electronic nose and (iii) identification of volatiles collected on an adsorbent with a GC-MS system. Forty samples were selected after sensory analysis to obtain 10 samples with normal odour and 30 with some degree of off-odour. The data set of volatile compounds and the data collected from the electronic nose were evaluated by multivariate analyse techniques. SIMCA classification (soft independent modelling of class analogy) was used for objective evaluation of the usefulness of the data from the GC-MS or electronic nose measurements for classification of grain samples as normal or with off-odour. The main volatile compounds of grain with normal odour were 2-hexenal, benzaldehyde and nonanal, while 3-octanone, methylheptanone and trimethylbenzene were the main volatile compounds of grain with off-odours. Using data from the electronic nose three samples of 40 were misclassified, while data analysis of the volatile compounds detected with the GC-MS, led to six misclassified samples. Regression models (partial least-squares, PLS) were built to predict ergosterol- and CFU-levels with data from the GC-MS or electronic nose measurements. PLS models based on both GC-MS and electronic nose data could be used to predict the ergosterol levels with high accuracy and with low root mean square error of prediction (RMSEP). CFU values from naturally infected grain could not be predicted with the same degree of confidence.
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