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Naresh Magan

Publications and source records attributed to Naresh Magan.

At least 19 recordsLinked to original sources
PubMed2006

Mould germination: data treatment and modelling.

The objectives of this study were i/ to examine germination data sets over a range of environmental conditions (water activity, temperature) for eight food spoilage moulds, ii/ to compare the ability of the Gompertz equation and logistic function to fit the experimental plots, iii/ to simulate germination by assessing various distributions of the latent period for germination amongst a population of spores. Data sets (percentage germination, P (%), versus time, t) of Aspergillus carbonarius, Aspergillus ochraceus, Fusarium verticillioides, Fusarium proliferatum, Gibberella zeae, Mucor racemosus, Penicillium chrysogenum and Penicillium verrucosum were analysed. No correlation, or relationship between the mean percentage [mean (P)] and the variance [var (P)] was found. Therefore no transformation of the germination data was required. Experimental data were fitted by using the Gompertz equation P = A exp (-exp [mu(m) e/A (delta - t) + 1]) and the logistic function P = Pmax/(1 + exp (k (tau - t))). Based on the residual mean square error (RMSE), no model performed better than the other one. However, model parameters were generally determined more precisely with the logistic model than with the Gompertz one. The time course of fungal spore germination curves was simulated assuming different distributions of the latent period for germination, lag, amongst a population of spores. The growth rate of germ tubes was calculated by means of the relationship: lag x rate = k. For normal Gaussian distributions, germination curves were symmetrical with respect to the inflection point and should be modelled with the logistic function. Skewed distributions were capable of simulating an asymmetric germination curve that was fitted by the Gompertz model. Future studies should be conducted for assessing whether the distributions assumed in this paper are in accordance with the experimental distributions that are still unknown.

Colony Count, Microbial↗
PubMed2006

Mycotoxin contamination of food in Europe: early detection and prevention strategies.

This paper reviews the early detection and prevention strategies which have been employed in Europe for the control of mycotoxin contamination of food in the context of a hazard analysis critical control point (HACCP) framework. The critical control points (CCPs) in the whole food chain where mycotoxins such as trichothecenes and ochratoxins are important have been identified. Ecological studies on the effect of environmental factors which are marginal for growth and mycotoxin production have been identified for Fusarium culmorum and F. graminearum (deoxynivlenol production), and for Penicillium verrucosum and Aspergillus ochraceus (ochratoxin production) in relation to cereal production and for A. carbonarius in relation to grapes and wine production (ochratoxin formation). To minimise the entry of these mycotoxins into the food chain, effective and rapid diagnostic tools are required to monitor the CCPs effectively. To this end the potential use of molecular imprinted polymers, lateral flow devices and molecular-based techniques for the rapid detection and quantification of the mycotoxigenic moulds or their toxins have also been developed.

Aspergillus ochraceus↗
PubMed2005

Temperature and water activity effects on growth and temporal deoxynivalenol production by two Argentinean strains of Fusarium graminearum on irradiated wheat grain.

The objective of this study was to determine the effects of water activity (a(W); 0.900-0.995), temperature (5, 15, 25 and 30 degrees C), time of incubation (7-49 days) and their interactions on mycelial growth and deoxynivalenol (DON) production on irradiated wheat grain by two strains of Fusarium graminearum isolated from wheat ears in Argentina. Optimal a(W) levels for growth were in the range 0.950-0.995 with a temperature optima of 25 degrees C. Maximum growth rates were obtained at the highest a(W) (0.995) and 25 degrees C for both strains. No growth was observed at 5 degrees C regardless of the a(W) levels assayed. Both strains were able to growth at the lowest a(W) assayed (0.900), although the temperature ranges allowing growth at this minimal a(W) was 15-25 degrees C. DON was produced the most rapidly (7 days) when incubated at 25 degrees C and 0.995 a(W). All other conditions required 7-14 days before DON was produced on grain. Maximum amounts of DON for both strains were produced at the highest a(W) treatment (0.995) after 6 weeks at 30 degrees C. The range of DON concentrations varied considerably (5 to 140,000 ng g(-1)) depending on a(W) and temperature interaction treatments. Production of DON occurred over a narrower range of a(W) (0.995-0.95) than that for growth (0.995-0.90). DON was more rapidly produced at 25 degrees C but the maximum amount produced was at 30 degrees C. Two-dimensional profiles of a(W) x temperature were developed from these data to identify areas where conditions indicate a significant risk from DON accumulation.

Consumer Product Safety↗
PubMed2005

Environmental factors and weak organic acid interactions have differential effects on control of growth and ochratoxin A production by Penicillium verrucosum isolates in bread.

Studies were conducted to examine the effect of water activity (a(w), 0.97, 0.95, 0.93), pH (4.5, 6.0) and preservative type and concentration (potassium sorbate (KS), calcium propionate (CaP), 300 and 3000 ppm) on colonisation and ochratoxin A (OTA) production by three strains of Penicillium verrucosum on bread analogues. At 25 degrees C, colony extension from a point source was similar for all three strains at the different environmental treatments examined, with optimum growth at 0.97 and 0.96 a(w) and pH 6. Temporal OTA production over 36 days varied significantly with strain, pH and a(w) level. Maximum OTA was produced at approximately 28-36 days for two of the strains with an optimum at 0.93 a(w) at pH 6.0. One strain produced 75-80 microg g(-1) analogue under these conditions. However, at pH 4.5, optimum OTA was produced at 0.95 a(w) after a similar time period on bread analogues, with maximum amounts of about 25-35 microg g(-1) bread. KS and CaP incorporation inhibited growth completely at pH 4.5 and 3000 ppm at all three a(w) levels. However, at suboptimal concentration, little growth inhibition occurred. At pH 6, even with 3000 ppm, growth of all three strains occurred. Where effective inhibition of growth was achieved (3000 ppm/pH 4.5, all a(w) levels), no OTA was detected. However, when 300 ppm was used, up to 7 microg g(-1) was detected in bread analogues at pH 4.5. At pH 6, OTA was produced at all treatment conditions by all three strains, although preservative-treated bread had less present. Statistical analysis showed that many of the one-, two- and three-way interactions had a significant effect on growth and OTA production. These results suggest that there is a significant risk from OTA contamination if lower concentrations of existing preservatives are used in wheat-based bakery products contaminated by spoilage mycotoxigenic moulds such as P. verrucosum.

Bread↗
PubMed2005

Conditions of formation of ochratoxin A in drying, transport and in different commodities.

The major species of fungi responsible for ochratoxin production (OTA) in a range of commodities are Penicillium verrucosum, Aspergillus ochraceus and Aspergillus section Nigri, especially A. carbonarius. P. verrucosum is particularly important in northern Europe where damp cooler conditions occur and where drying regimes need to be efficient and effective for preventing post-harvest contamination with OTA. A. ochraceus can infect cereals including barley, maize, coffee, cocoa and edible nuts. A. carbonarius has been identified as the key species responsible for OTA contamination of grapes, wine and vine fruits. Recent studies have identified the environmental regimes, especially of temperature and humidity, which are conducive to growth and OTA production by these species pre- and post-harvest and during transport. The optimum and marginal interacting conditions for growth and OTA contamination often vary considerably. This has to be borne in mind when effective preventative management strategies are being implemented. Recent studies with cereals have suggested that isolation frequency can be related to OTA contamination of cereals. A logistical model has been developed and identified that 1000 CFUs g(-1) grain of P. verrucosum (CFUs) is the threshold limit at which the probability of exceeding the EU legislative limit of 5 microg kg(-1) in cereal grain can be predicted under different storage regimes. Controlled atmospheres >50% CO(2) is required to effectively prevent OTA accumulation in damp cereals. With regard to grapes, preharvest contamination with A. carbonarius has been shown to be a good indicator for regional risk in southern Europe from OTA contamination. The ecological conditions for optimum growth and OTA production have been shown to differ with the optima being 30-35 degrees C and 15-25 degrees C and 0.98-0.99 and 0.93-0.95 water activity, respectively. Studies on vine fruits (drying currants) suggest that OTA contamination and increase contamination levels occur during this drying process of 7-14 days. This will be influenced by prevailing weather conditions and drying rates. Minimizing OTA contamination in these and other commodities including coffee and cocoa require clear guidelines on safe moisture and temperature regimes pre- and post-harvest for the development of effective management strategies based on ecological criteria.

Cacao↗
PubMed2005

Enzymatic activity, osmotic stress and degradation of pesticide mixtures in soil extract liquid broth inoculated with Phanerochaete chrysosporium and Trametes versicolor.

In this study we examined the extracellular enzymatic activity of two white rot fungi (Phanerochaete chrysosporium and Trametes versicolor) in a soil extract broth in relation to differential degradation of a mixture of different concentrations (0-30 p.p.m.) of simazine, dieldrin and trifluralin under different osmotic stress (-0.7 and -2.8 MPa) and quantified enzyme production, relevant to P and N release (phosphomonoesterase, protease), carbon cycling (beta-glucosidase, cellulase) and laccase activity, involved in lignin degradation. Our results suggest that T. versicolor and P. chrysosporium have the ability to degrade different groups of pesticides, supported by the capacity for expression of a range of extracellular enzymes at both -0.7 and -2.8 MPa water potential. Phanerochaete chrysosporium was able to degrade this mixture of pesticides independently of laccase activity. In soil extract, T. versicolor was able to produce the same range of enzymes as P. chrysoporium plus laccase, even in the presence of 30 p.p.m. of the pesticide mixture. Complete degradation of dieldrin and trifluralin was observed, while about 80% of the simazine was degraded regardless of osmotic stress treatment in a nutritionally poor soil extract broth. The capacity of tolerance and degradation of high concentrations of mixtures of pesticides and production of a range of enzymes, even under osmotic stress, suggest potential bioremediation applications.

Basidiomycota↗
PubMed2004

Effect of the solvent on recognition properties of molecularly imprinted polymer specific for ochratoxin A.

A molecularly imprinted polymer specific for the mycotoxin ochratoxin A has been synthesised using a non-covalent approach. The polymer has shown an excellent affinity and specificity for the target template in aqueous solutions. The binding experiments, NMR study and molecular modelling have proven that the template recognition by polymer originates from the shape complementarity of binding sites. The binding mechanism is critically depended on factors that affect the polymer conformation. Thus the variation in buffer concentration, pH and presence of organic solvent, which affect the polymer swelling or shrinking, had a profound effect on the polymer recognition properties.

Binding Sites↗
PubMed2004

Detection of Mycobacterium tuberculosis (TB) in vitro and in situ using an electronic nose in combination with a neural network system.

The use of volatile production patterns produced by Mycobacterium tuberculosis and associated bacterial infections from sputum samples were examined in vitro and in situ using an electronic nose based on a 14 sensor conducting polymer array. In vitro, it was possible to successfully discriminate between M. tuberculosis (TB) and control media, and between M. tuberculosis and M. avium, M. scrofulaceum and Pseudomonas aeruginosa cultures in the stationary phase after 5-6h incubation at 37 degrees C based on 35 samples. Using neural network (NN) analysis and cross-validation it was possible to successfully identify 100% of the TB cultures from others. A second in vitro study with 61 samples all four groups were successfully discriminated with 14 of 15 unknowns within each of the four groups successfully identified using cross-validation and discriminant function analysis. Subsequently, lipase enzymes were added to 46 sputum samples directly obtained from patients and the head space analysed. Parallel measurements of bacterial contamination were also carried out for confirmation using agar media. NN analysis was carried out using some of the samples as a training set. Based on the NN and genetic algorithms of up to 10 generations it was possible to successfully cross-validate 9 of 10 unknown samples. PCA was able to discriminate between TB infection alone, the controls, M. avium, P. aeruginosa and a mixed infection. These findings will have significant implications for the development of rapid qualitative systems for screening of patient samples and clinical diagnosis of tuberculosis.

Algorithms↗
PubMed2004

Prevention strategies for trichothecenes.

Contamination of cereal commodities with mycotoxins represents a significant hazard to consumer health and has thus received increasing attention from food safety authorities and legislators. For trichothecenes, and deoxynivalenol (DON) in particular, the imminent implementation of legislative limits has focused attention on ways to prevent entry of such mycotoxin contaminants into the food and feed chains. Knowledge of the pre- and post-harvest stages in the cereal production chain and in particular information on where prevention strategies can be implemented is being used to develop quality assurance systems for improving food safety. Information on the ecology of Fusarium species, breeding for resistance, more effective fungicides, potential for biological control and effective drying and storage and preservation systems, are all helping to develop effective preventative strategies for minimising consumer exposure to trichothecenes and other mycotoxins.

Agriculture↗
PubMed2004

A novel immobilised design for the production of the heterologous protein lysozyme by a genetically engineered Aspergillus niger strain.

A novel immobilisation design for increasing the final concentration of the heterologous protein lysozyme by a genetically engineered fungus, Aspergillus niger B1, was developed. A central composition design was used to investigate different immobilised polymer types (alginate and pectate), polymer concentration [24% and 4% (w/v)], inoculum support ratios (1:2 and 1:4) and gel-inducing agent concentration [CaCl(2), 2% and 3.5% (w/v)]. Studies of the kinetics of production showed that optimum lysozyme productivity occurred after 10 days. Lysozyme production was significantly affected by polymer type, polymer concentration, and inoculum support ratio. Overall, immobilisation in Ca-pectate resulted in higher lysozyme production compared to that in Ca-alginate. Similar effects were observed when the polymer concentration was reduced. Regardless of polymer type and concentration, increasing the fungal inoculum level increased lysozyme production. A significantly higher lysozyme yield was achieved with Ca-pectate in comparison to Ca-alginate (approximately 20-23 mg l(-1) and 0.5-2 mg l(-1), respectively). The maximum lysozyme yield achieved was about 23 mg l(-1) by immobilisation in Ca-pectate 2% (w/v) with 33% (v/v) mycelium and 3.5% (w/v) gel-inducing agent (CaCl(2)). Response surface methodology was used to investigate the effect of pH and water activity (a(w)). The best medium pH was 4.5-5.0, and bead a(w) for optimum lysozyme yield was 0.94, regardless of polymer type.

Alginates↗
PubMed2004

Impact of water-stress and washing treatments on production, synthesis and retention of endogenous sugar alcohols and germinability of Metarhizium anisopliae blastospores.

The entomopathogenic fungus Metarhizium anisopliae was physiologically manipulated by culturing in liquid culture under a range of water-stress conditions (0.98, 0.97 and 0.96 water activity, a(w)) imposed by either PEG 200, KCl or NaCl at 25 degrees C to optimise blastospore production and quality in terms of accumulation of endogenous compatible solutes and germinability. Optimum spore yield occurred at 0.98a(w), when PEG 200 was the solute. Blastospores produced under different water-stress levels were subjected to hypo-osmotic and iso-osmotic washing treatments before quantification of endogenous sugar alcohols (polyols) and germinability studies. Endogenous amounts of the low molecular weight polyol erythritol were greatly affected by culture age, water-stress and hypotonic or isotonic washing treatment. Endogenous erythritol in blastospores produced under 0.98 and 0.97a(w) increased with culture age. Osmoprotection (washing with isotonic PEG 200 solution) of blastospores produced under all water-stress conditions resulted in retention of higher amounts of erythritol. Increased endogenous retention of the high molecular weight polyol mannitol was also observed with an isotonic washing treatment but only in blastospores produced under intermediate water-stress (0.98 and 0.97a(w)). Germination of all treatments was > 90 % on a medium with freely available water. Under water-stress conditions (0.96a(w)) only 10 % of unmodified blastospores washed with water germinated. However, those grown under modified water availability conditions (0.98a(w)) and washed with isotonic solutions had significantly improved germination (38-90 %). Blastospores produced at < or = 0.97a(w) washed with isotonic solutions had decreased germination. These results could have significant implications for conserving ecophysiological quality of fungal biocontrol propagules during harvesting and have an impact on storage and formulation.

Ascomycota↗
PubMed2004

Electronic noses and disease diagnostics.

Rapid developments in sensor technology have facilitated the production of devices--known as electronic noses--that can detect and discriminate the production profiles of volatile compounds from microbial infections in situ. Such qualitative and semi-quantitative approaches could have a significant role in the early diagnosis and detection of microbial diseases. Using artificial intelligence and web-based knowledge systems, electronic noses might also have a valuable role in monitoring disease epidemiology.

Biosensing Techniques↗
PubMed2004

Chemical composition and in vitro antimicrobial activities of the essential oils from endemic Psiadia species growing in mauritius.

The composition of the leaf oils, obtained by hydrodistillation, of five endemic Psiadia species of the Asteraceae family were studied by GC/MS on both polar and non-polar columns. The analysis showed that the volatile components of the oils were made up essentially of monoterpenes, sesquiterpenes, aliphatics and other shikimic acid derivatives. With respect to the non-volatile components, great variations were observed: P. lithospermifolia contained (E)-isoasarone (51.5%); P. penninervia: eugenol (5.1%); P. terebinthina: eugenyl-acetate (4.0%); P. viscosa: pentyl-4-(1-methylethyl benzoate) (25.8%); P. arguta: isoeugenol (56.5%). In vitro antimicrobial assays using the agar-well diffusion method, revealed that most of the oils were not very active against the tested microorganisms except for that of P. lithospermifolia, which significantly inhibited the growth of Bacillus cereus, Staphylococcus aureus and Pseudomonas aureofaciens, Aspergillus ochraceus, Candida pseudotropicalis, Kluyveromyces lactis and Fusarium moniliforme. This activity has been attributed to the presence of delta-elemene, (E)-farnesene, alpha-curcumene, selina-4,7(11)-diene, (E,Z)-alpha-farnesene, beta-bisabolene some of which have established antimicrobial profiles. Likewise, the fungi toxic action of the oil of P. arguta against Aspergillus ochraceus, Candida pseudotropicalis, and Fusarium moniliforme, may be attributed to the presence of isoeugenol, eugenol being known to be mycotoxic especially against Aspergillus species.

Anti-Bacterial Agents↗
PubMed2004

Fumonisin-producing strains of Fusarium: a review of their ecophysiology.

This review focuses on the fumonisin-producing Fusarium species and the ecophysiology of these species. The effects of environmental biotic and abiotic factors on germination, growth, and fumonisin B1 production by Fusarium verticillioides and Fusarium proliferatum have been investigated under laboratory, field, and storage conditions. An understanding of the factors involved in production of fumonisins is the first step in preventing accumulation of these toxins.

Consumer Product Safety↗
PubMed2003

Potential for detection of microorganisms and heavy metals in potable water using electronic nose technology.

Studies have been carried out to determine the potential for the detection of different microbial species (Enterobacter aerogenes, Escherichia coli, Pseudomonas aeruginosa), alone and in the presence of low concentrations of different heavy metals (As, Cd, Pb and Zn) in bottled, reverse osmosis (RO) and tap water, using an electronic nose. Studies show that it is possible to discriminate control water samples from water contaminated with 0.5 ppm of a mixture of metals. The presence of heavy metals may modify the activity of microorganisms and thus the volatile production patterns. Bacterial species at 10(2)-10(4) colony forming units (CFUs) ml(-1) could be detected after 24 h of incubation. Work is in progress to identify the limits of detection for a range of other microorganisms, including, fungi and cyanobacteria, and chlorinated phenols using electronic nose technology.

Biomimetics↗