| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- Feng, X. M., et al.
(författare)
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Growth of lactic acid bacteria and Rhizopus oligosporus during barley tempeh fermentation
- 2005
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Ingår i: International Journal of Food Microbiology. - Amsterdam, Netherlands : Elsevier. - 0168-1605 .- 1879-3460. ; 104:3, s. 249-256
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Tidskriftsartikel (refereegranskat)abstract
- The zygomycete Rhizopus oligosporus is traditionally used to ferment soybean tempeh, but it is also possible to ferment other legumes and cereals to tempeh, The traditional soybean tempeh harbours a multitude of microorganisms with potentially beneficial or detrimental effects on quality. Lactic acid bacteria (LAB) have positive effects on the safety of soybean tempeh, but the effects of LAB on R. oligosporus growth have not been investigated. We have developed a cereal grain tempeh by fermenting pearled barley with R. oligosporus ATCC 64063. Four LAB species, Lactobacillus plantarum, Lactobacillus fermentum, Lactobacillus reuteri and Lactococcus lactis were assessed for their growth abilities and their effects on R. oligosporus growth during barley tempeh fermentation. Growth of LAB was assayed as colony forming units (cfu), while growth of R. oligosporus was measured as ergosterol content and hyphal length. The two fungal measurements highly correlated (r=0.83, P < 0.001, n = 90). The ergosterol content of fungal mycelia ranged from 11.7 to 30.1 mg/g fungal dry matter. L. plantarum multiplied from 4.8 to 7.4 log cfu/g dry tempeh and L. fermentum increased from 4.4 to 6.8 log cfu/g during 24 h incubation at 35 degrees C. L. reuteri and L. lactis had significantly slower growth, with increases from 4.8 to 5.6 log cfu/g and 5.0 to 5.4 log cfu/g, respectively. The growth of R. oligosporus and the final pH (4.9) in barley tempeh were not significantly influenced by any of the LAB investigated.
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| 6. |
- Feng, Xin Mei, et al.
(författare)
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Production of volatile compounds by Rhizopus oligosporus during soybean and barley tempeh fermentation
- 2007
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Ingår i: International Journal of Food Microbiology. - Amsterdam, Netherlands : Elsevier. - 0168-1605 .- 1879-3460. ; 113:2, s. 133-141
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Tidskriftsartikel (refereegranskat)abstract
- Rhizopus oligosporus Saito can ferment soybeans or cereal grains to tempeh, a sliceable cake with improved nutritional properties. Volatiles produced by different R. oligosporus strains grown on malt extract agar (MEA), barley and soybean were investigated. The effect of co-cultivation with Lactobacillus plantarum on the production of volatiles was also studied. Volatile compounds were collected in situ by headspace diffusion and identified by GC-MS. The ten R. oligosporus strains that had different colony morphologies on MEA produced very similar volatile profiles, except for slight variations among the minor volatile compounds (e.g. sesquiterpenes). Likewise, practically no differences in volatile profiles were observed between three of the strains grown on soybeans. In contrast, the R. oligosporus volatile profile on soybean was different from that on barley from the same strain. Co-cultivation with L. plantarum did not influence volatile production by R. oligosporus. The dominant compounds produced on all three Substrates were ethanol, acetone, ethyl acetate, 2-butanone, 2-methyl-1-propanol, 3-methyl-1-butanol and 2-methyl-1-butanol. Acetaldehyde and 2-methyl-propanal were also produced on MEA and barley, while 2-pentanone, methyl acetate, 2-butanol and 3-methyl-3-buten-1-ol were observed on soybeans. Ethanol, 2-methyl-1-butanol and 3-methyl-1-butanol were the most abundant volatile compounds produced on MEA and barley, while 2-butanone was the dominant volatile metabolite on soybean. The mushroom odour compounds, 3-octanone and 1-octen-3-ol, were only detected from soybean and soybean tempeh.
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| 7. |
- Leong, Su-lin L., et al.
(författare)
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The extreme xerophilic mould Xeromyces bisporus : Growth and competition at various water activities
- 2011
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Ingår i: International Journal of Food Microbiology. - Amsterdam, Netherlands : Elsevier. - 0168-1605 .- 1879-3460. ; 145:1, s. 57-63
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Tidskriftsartikel (refereegranskat)abstract
- Little is known about the mould, Xeromyces bisporus, unique in its strong xerophilicity and ability to grow at water activity (a(w)) 0.62, lower than for any other known organism. The linear growth rates of one fast and one slow-growing strain of X. bisporus were assessed at 20, 25, 30 and 37 degrees C on solid agar media containing a mixture of glucose and fructose to reduce a(w) to 0.94, 0.88, 0.84, 0.80, 0.76 and 0.66. Growth rates of xerophilic species closely related to X. bisporus, viz. Chrysosporium Mops, C. xerophilum and Monascus eremophilus, were also assessed. Optimal conditions for growth of both X. bisporus strains were approx. 0.84 a(w) and 30 degrees C, despite FRR 2347 growing two- to five-fold faster than CBS 185.75. X. bisporus FRR 2347 even grew well at 0.66 a(w) (0.48 mm/day). C. Mops and C xerophilurn were more tolerant of high a(w) than X. bisporus. and could be differentiated from each other based on: the faster growth of C. xerophilum; its preference for temperatures >= 30 degrees C and a(w) >= 0.94 (c.f. <= 25 degrees C and similar to 0.88 a(w) for C Mops); and its ability to grow at 0.66 a(w), which is the lowest a(w) reported to date for this species. M. eremophilus grew slowly (max. 0.4 mm/day) even in its optimal conditions of similar to 0.88 a(w) and 25 degrees C. To investigate the competitive characteristics of X. bisporus at low a(w), both X. bisporus strains were grown in dual-culture with xerotolerant species Aspergillus flavus and Penicillium roqueforti, and xerophilic species A. penicillioides, C. Mops, C. xerophilum and Eurotium chevalieri, on glucose-fructose agar plates at 0.94, 0.84, 0.80 and 0.76 a(w) and at 25 degrees C. Growth rates and types of interactions were assessed. Excretion of inhibitory substances acting over a long-range was not observed by any species; inhibitors acting over a short-range that temporarily slowed competitors' growth or produced a protective zone around the colony were occasionally observed for A. penicillioides, C. Mops and C. xerophilum. Instead, rapid growth relative to the competitor was the most common means of dominance. The xerotolerant species. A. flavus and P. roqueforti were dominant over X. bisporus at 0.94 a(w). E. chevalieri was often dominant due to its rapid growth over the entire a(w) range. At a(w) < 0.80, X. bisporus was competitive because it grew faster than the other species examined. This supports the concept that its ideal environmental niche is sugary foods with low a(w).
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| 8. |
- Lind, Helena, et al.
(författare)
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Antifungal effect of dairy propionibacteria - contribution of organic acids
- 2005
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Ingår i: International Journal of Food Microbiology. - : Elsevier. - 0168-1605 .- 1879-3460. ; 98:2, s. 157-165
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Tidskriftsartikel (refereegranskat)abstract
- Large amounts of food and feed are lost every year due to spoilage by moulds and yeasts. Biopreservation, i.e. the use of microorganisms as preservatives instead of chemicals, has gained increased interest. Lactic acid bacteria and propionibacteria might be particularly useful due to their important role in many food fermentations. Knowledge of the antifungal effects of the organic acids produced by these bacteria is necessary to understand their inhibitory activity. We evaluated the antifungal activity of the type strains of five dairy propionibacteria, Propionibacterium acidipropionici, P. jensenii, P. thoenii, P. freudenreichii subsp. freu denreichii and P. freudenreichii subsp. shermanii against eight food- and feedborne moulds and yeasts. A dual culture system assayed the inhibitory activity on three different agar media, sodium lactate (SL), de Man Rogosa Sharp (MRS) and MRS without acetate (MRS-ac). The amounts of organic acids produced during growth of propionibacteria in liquid SL, MRS and MRS-ac were also determined. The minimal inhibitory concentration (MIC) values of propionic, acetic and lactic acid were established for all fungi at pH 3, 5 and 7. Propionic acid, followed by acetic acid, was the most potent antifungal acid. Inhibition at pH 7 generally required concentrations above 500 mM for all three acids, at pH 5 the MIC values for propionic and acetic acids were 20-120 mM and above 500 mM for lactic acid. At pH 3, the MIC values were, with one exception, below 10 mM for both propionic and acetic acid and above 160 mM for lactic acid. The yeast Pichia anomala was the fungus most resistant to organic acids. The propionibacteria exhibited a pronounced species variation in antifungal activity on MRS (+/- acetate) agar, with P. thoenii being the most potent. Four of the five propionibacteria species produced more propionic and acetic acid in liquid SL medium than in MRS (+/- acetate) broth. However, when SL agar was used as the growth medium, none of the propionibacteria inhibited fungal growth.
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