Fitting of colony diameter and ergosterol as indicators of food borne mould growth to known growth models in solid medium

Characterisation of the surface growth of Mucor circinelloides in cheese agar media using predictive mathematical models

The main objective of this work was to characterise the mycelial growth of Mucor circinelloides, one of the fungal contaminants that appear frequently in the artisan cheese production environment. The study uses primary Baranyi and Huang models to compare their parameters and predict M. circinelloides on cheese-based medium (CBA) under diverse environmental conditions (temperature range from 6 to 37 °C and 0 and 1 % NaCl concentration). However, the Baranyi model consistently estimated longer lag phases and higher surface growth rates (sgr) than the Huang model; both models showed adequate best-fit performance (exactly with the mean coefficient of determination R2 = (0.993 ± 0.020 × 10-1). The groups of primary growth parameters were analysed against temperature using the cardinal model (CM) with the following main outputs. The optimal surface growth rates (sgropt) on CBA were 6.8 and 6.5 mm/d calculated with the Baranyi and Huang models, respectively. They were reduced by approximately 46 % on the surface of the agar medium when 1 % NaCl was added. Topt was estimated in a very narrow range of 32.1-32.5 °C from both primary sgr data sets (0 % and 1 % NaCl). Similarly, Tmax values of 37.2 °C and 37.3 °C were estimated for the Baranyi and Huang models, respectively; however, they decreased at 2 °C in CBA with 1 % NaCl (Tmax = 35.1 °C). The application of CM for sgr provided an estimation of the parameter Tmin with negative values that are considered only as a theoretical output. The results provide insight into the modelling and prediction of fungi growth as a function of time and salt concentration, including the times to detect visible mycelial growth of Mucor circinelloides. The mere quantification of this phenomenon can be useful for practice. Adjusting the frequency of the cheese surface washing step with a salt solution at the early stage of ripening properly can prevent the growth of not only fast fungal growers.

Wine Microbiology and Predictive Microbiology: A Short Overview on Application, and Perspectives

Predictive microbiology (PM) is an essential element in food microbiology; its aims are the determination of the responses of a given microorganism combining mathematical models with experimental data under certain environmental conditions, and the simulation a priori of the growth/inactivation of a population based on the known traits of a food matrix. Today, a great variety of models exist to describe the behaviour of several pathogenic and spoilage microorganisms in foods. In winemaking, many mathematical models have been used for monitoring yeast growth in alcoholic fermentation as well as to predict the risk of contamination of grapes and grape products by mycotoxin producing fungi over the last years, but the potentialities of PM in wine microbiology are underestimated. Thus, the goals of this review are to show some applications and perspectives in the following fields: (1) kinetics of alcoholic and malolactic fermentation; (2) models and approaches for yeasts and bacteria growth/inactivation; (3) toxin production and removal.

A novel coconut-malt extract medium increases growth rate of morels in pure culture

Morels are gourmet wild edible mushrooms that can grow on several substrates with significant growth rate variations. Such variations have hindered the development of a standardized culture media to promote morel’s sustainable production. The aim of this study is developing a novel culture media that takes advantage of coconut water as a complementary component of culture media. Coconut water has been extensively used as a growth-promoting component for plant tissue cultures; however, its application as component of fungi cultivation medium has not been fully developed. This study confirms that coconut water can be efficiently used as culture media component for morels using a kinetic characterization. Morchella sp. kinetic growth is evaluated in different cultures: agar, malt extract agar (MEA), lactose, coconut water (15%) and combinations of them. Kinetic growth parameters (lag phase, λ and maximum specific growth rate, µ_max) are estimated using primary modeling methods. Among the selected models, the best fit is achieved using Baranyi’s model. A significant increase from 15.8% to 43.4% of the µ_max values was observed when culture media (agar, lactose, MEA) is supplemented with coconut water. The largest values of µ_max are obtained in MEA-coconut cultures (21.13 ± 0.43–22.57 ± 0.35). Micro-sclerotia and late sclerotia are observed in all cultures containing coconut water justifying the development of a feasible and cost-effective way of culturing morels. The results demonstrate that coconut water can be used for formulation of standard media for morel cultivation leading to a cheap alternative to produce dense mycelium and promote sclerotia formation.

Environmental Effects of Temperature and Water Potential on Mycelial Growth of Neocosmospora solani and Fusarium spp. Causing Dry Root Rot of Citrus

This study aimed at evaluating the effect of environmental factors temperature and water potential (Ψw) on the growth of Neocosmospora (Fusarium) solani and three Fusarium species (F. oxysporum, F. equiseti and F. brachygibbosum) associated with citrus dry root rot and to determine the optimum and marginal rate for their growth. The effects of incubation temperature (5-40 °C), water potentials (Ψw) (- 15.54; - 0.67 MPa) (0.89-0.995 a_w) and their interaction (5-30 °C) was evaluated on the in vitro radial growth rates of Fusarium spp. and on their lag phase. Secondary models were used to model the combined effect of these factors on radial growth rate. The results underlined a highly significant effects (P < 0.001) of Ψw and temperature and their interactions on radial growth rates and lag phases (λ). The Four studied species were shown tolerant to a temperature of 35 °C with an optimum mycelial growth at 30 for N. solani and F. oxysporum and at 25 °C for F. equiseti and F. brachygibbosum. However, no growth was observed at both temperatures 5 and 40 °C and at Ψw of - 9.68 MPa (0.93 a_w). The optimum water potential for growth was ≥- 2.69 MPA (>0.98 a_w). The results from the polynomial model and response surface showing good agreement between observed and predicted values. The external validation on citrus fruit indicated slight differences between predicted and observed values of radial growth. The results of this study will be beneficial for understanding the ecological knowledge of these species and thereby limited preventively their occurrence.

Modelling the Radial Growth of Geotrichum candidum: Effects of Temperature and Water Activity

Modelling the growth of microorganisms in relation to environmental factors provides quantitative knowledge that can be used to predict their behaviour in foods. For this reason, the effects of temperature and water activity (aw) adjusted with NaCl on the surface growth of two isolates and one culture strain of Geotrichum candidum were studied. A dataset of growth parameters obtained from almost 600 growth curves was employed for secondary modelling with cardinal models (CMs). The theoretical minimal temperature resulting from the modelling of the mycelium proliferation rate ranged from -5.2 to -0.4 °C. Optimal and maximal temperatures were calculated and found to have narrow ranges of 25.4 to 28.0 °C and 34.2 to 37.6 °C, respectively. Cardinal aw values associated with radial growth (awmin from 0.948-0.960 and awopt from 0.992-0.993) confirmed the salt sensitivity of the species. Model goodness-of-fit was evaluated by the coefficient of determination R2, which ranged from 0.954 to 0.985, and RMSE, which ranged from 0.28 to 0.42. Substantially higher variability accompanied the lag time for growth modelling than the radial growth rate modelling despite the square root transformation of the reciprocal lag phase data (R2 = 0.685 to 0.808). Nevertheless, the findings demonstrate that the outputs of growth modelling can be applied to the quantitative evaluation of the roles of G. candidum in fresh cheese spoilage as well as the ripening of Camembert-type cheeses or various artisanal cheeses. Along with validation, the interactions with lactic acid bacteria can be included to improve the predictions of G. candidum in the future.

Improving the storage stability of tomato paste by the addition of encapsulated olive leaf phenolics and experimental growth modeling of A. flavus

It is necessary to apply some preservatives for tomato paste since in the harvest season, a high load of tomatoes need to be processed as they are among highly perishable products. Application of antimicrobial extracts or essential oils, as natural preservatives, in their raw forms might reduce their efficiency when they are exposed to environmental conditions. However, microencapsulation is a well-known method to solve this problem. Our main goal was to restrict fungal growth rate in stored tomato paste and increase its storage stability by incorporating encapsulated olive leaf phenolic-rich extract. Total Soluble Solids (TSS), consistency, pH, color indices and diametrical growth rate of Aspergillus flavus were measured for different samples. The treatments designed in terms of considering two levels of non-encapsulated olive phenolics extract with 500 and 1000 ppm (NE₅₀₀ and NE₁₀₀₀), the same levels with encapsulated extract; i.e., 500 and 1000 ppm (ME₅₀₀ and ME₁₀₀₀), and similar levels of the common preservative of sodium benzoate with 500 and 1000 ppm (B₅₀₀ and B₁₀₀₀). Antifungal properties of NE samples were higher than ME ones during storage although ME samples could maintain diametrical growth rate of the fungus more stable than NE ones. NE samples justified lower maximum growth rate than ME samples while ME samples could extend lag phase of microbial growth compared with NE one and delay their internal deteriorative reactions. Among Baranyi, modified Baranyi, Modified Gompertz, and Logistic models, Modified Gompertz model represented the best model and could fit the growth factors of A. flavus on tomato paste with higher R² index as well as lower RMSE and SSE indices. Based on the results obtained, it could be concluded that usage of encapsulated olive leaf extract in tomato paste is an effective, natural and sustainable approach to improve the shelf life of tomato paste since this natural compound could perform as favourable as preservatives; also it could maintain physicochemical as well as microbial properties of tomato paste for a long term. Thus, it is strongly recommended that application of encapsulated olive leaf extract to be considered seriously by the tomato paste industry as it can effectively reduce the mold and fungal contaminations which are very common and prevalent in the plants. The future work in this regard should focus on sensory evaluations when incorporating encapsulated olive leaf extract into tomato paste.

Predictive Model for the Effect of Environmental Conditions on the Postharvest Development of Colletotrichum gloeosporioides Strains Isolated from Papaya (Carica papaya L.)

ABSTRACT

Colletotrichum species are the most important postharvest spoilage fungi of papaya fruit. The objective of this research was to evaluate the effect of temperature and relative humidity on growth rate and time for growth to become visible of five strains of Colletotrichum gloeosporioides isolated from papaya fruit in a complex medium. As a primary model, the radial growth rates were estimated using the Baranyi and Roberts model in papaya agar. The Solver MS Excel function was used to obtain the time to visible mycelium (tv). Secondary models obtained with the Rosso et al. cardinal model of inflection were applied to describe the effect of temperature on the growth rate (μ). The Arrhenius-Davey model was used to model tv. The obtained models seem to be satisfactory for describing both μ and tv. The relative humidity had an effect on μ and tv for all tested C. gloeosporioides isolates, but no model accurately described the behavior of the fungus. External validation of models was performed with papaya fruit. Growth models were developed with the same models used in vitro. The bias and the accuracy factors as indices for performance evaluation of predictive models in food microbiology as a function of temperature and RH were 1.22 and 1.33, respectively, for μ and 1.18 and 1.62, respectively, for tv, indicating accurate predictions. The supply chain of papaya is complex and requires constant conditions, and poor conditions can result in damage to the fruit. Knowledge of the behavior of C. gloeosporioides on papaya fruit and application of the developed models in the supply chain will help to establish transport control strategies to combat these fungi. This research has contributed to development of the first models of growth for C. gloeosporioides in Mexico.

HIGHLIGHTS

Three-Dimensional Study of F. graminearum Colonisation of Stored Wheat: Post-Harvest Growth Patterns, Dry Matter Losses and Mycotoxin Contamination

Fusarium causes significant post-harvest quality losses and mycotoxin contamination in stored wheat but the colonisation dynamics of the grain and how this may be affected by the initial inoculum position in the grain mass is poorly understood. This study examined the 3D growth kinetics and mycotoxin production (deoxynivalenol and zearalenone) by F. graminearum during hyphal colonisation from different initial inoculum positions in wheat microcosms (top-centre, bottom-centre, and bottom-side) maintained at two water activities (a_w; 0.95 and 0.97). Clear jars were used to visually follow the colonisation dynamics. Fungal respiration and associated dry matter loss (DML) and ergosterol were also quantified. Colonisation dynamics was shown to be affected by the inoculation position. At the end of the colonisation process, fungal respiration and DML were driven by the inoculation position, and the latter also by the prevailing a_w. Fungal biomass (ergosterol) was mainly affected by the a_w. The initial inoculum position did not affect the relative mycotoxin production. There was a positive correlation between respiration and ergosterol, and between mycotoxin production and colonisation indicators. We suggest that spatially explicit predictive models can be used to better understand the colonisation patterns and mycotoxin contamination of stored cereal commodities and to aid more effective post-harvest management.

The Use of Colors as an Alternative to Size in Fusarium graminearum Growth Studies

Size-based fungal growth studies have limitations. For example, the growth in size stops in closed systems once it reaches the borders and poorly describes metabolic status, especially in the stationary phase. This might lead mycotoxin studies to unrealistic results. Color change could be a viable alternative, as pigments result from a mold’s metabolic activity. This study aimed to verify the possibility of using gray values and the RGB system to analyze the growth of Fusarium graminearum. It consisted of color and area measurements using ImageJ software for specimens grown in yeast extract agar (YEA). The results suggest the utility of color and gray values as reliable tools to analyze the growth of F. graminearum.

Mycoflora assessment, growth and toxigenic features of patulin-producers in kiwifruit in China

BACKGROUND

Fungal development in agricultural products may cause mycotoxin contamination, which is a significant threat to food safety. Patulin (PAT) and PAT-producer contamination has been established as a worldwide problem. The present study aimed to investigate the mycoflora and PAT-producers present in kiwifruits and environmental samples collected from orchards and processing plants in Shaanxi Province, China.

RESULTS

Variations in mycoflora were observed in different samples, with penicillia and aspergilli as the predominant genera. Approximately 42.86% of dropped fruits were contaminated with PAT-producers, which harbored the 6-methylsalicylic acid synthase and the isoepoxydon dehydrogenase genes that are involved in PAT biosynthesis. The growth of Penicillium expansum, Penicillium griseofulvum and Penicillium paneum in kiwi puree agar (KPA) medium and kiwi juice well fitted the modified Gompertz and Baranyi and Roberts models (R² ≥ 0.95). A significant positive correlation between colony diameter and PAT content in KPA medium of P. expansum and P. griseofulvum was observed (P < 0.05).

CONCLUSIONS

The present study analyzed the mycofloral composition and the potential risk for PAT and PAT-producer contamination in kiwifruit, which may be utilized in the establishment of proper management practices in the kiwifruit industry. © 2017 Society of Chemical Industry.

Growth Modeling of Aspergillus niger Strains Isolated from Citrus Fruit as a Function of Temperature on a Synthetic Medium from Lime (Citrus latifolia T.) Pericarp

Molds are responsible for postharvest spoilage of citrus fruits. The objective of this study was to evaluate the effect of temperature on growth rate and the time to visible growth of Aspergillus niger strains isolated from citrus fruits. The growth of these strains was studied on agar lime medium (AL) at different temperatures, and growth rate was estimated using the Baranyi and Roberts model (Int. J. Food Microbiol. 23:277-294, 1994). The Rosso et al. cardinal model with inflexion (L. Rosso, J. R. Lobry, S. Bajard, and J. P. Flandrois, J. Theor. Biol. 162:447-463, 1993) was used as a secondary model to describe the effect of temperature on growth rate and the lag phase. We hypothesized that the same model could be used to calculate the time for the mycelium to become visible (t_v) by substituting the lag phase (1/λ and 1/λ_opt) with the time to visible colony (1/t_v-opt and 1/t_v), respectively, in the Rosso et al.

MODEL

High variability was observed at suboptimal conditions. Extremes of temperature of growth for A. niger seem to have a normal variability. For the growth rate and time t_v, the model was satisfactorily compared with results of previous studies. An external validation was performed in lime fruits; the bias and accuracy factors were 1.3 and 1.5, respectively, for growth rate and 0.24 and 3.72, respectively, for the appearance time. The discrepancy may be due to the influence of external factors. A. niger grows significantly more slowly on lime fruit than in culture medium, probably because the nutrients are more easily available in medium than in fruits, where the peel consistency may be a physical barrier. These findings will help researchers understand the postharvest behavior of mold on lime fruits, host-pathogen interactions, and environmental conditions infecting fruit and also help them develop guidelines for future work in the field of predictive mycology to improve models for control of postharvest fungi.

Single vs multiple-spore inoculum effect on growth kinetic parameters and modeled probabilities of growth and aflatoxin B1 production of Aspergillus flavus on pistachio extract agar

The objective of the present study was to assess the differences in modeled growth/AFB1 production probability and kinetic growth parameters for Aspergillus flavus inoculated as single spores or in a concentrated inoculation point (~500 spores). The experiment was carried out at 25°C and at two water activities (0.85 and 0.87) on pistachio extract agar (3%). Binary data obtained from growth and AFB1 studies were modeled using linear logistic regression analysis. The radial growth curve for each colony was fitted to a linear model for the estimation of the lag phase for growth and the mycelial growth rate. In general, radial growth rate and lag phase for growth were not normally distributed and both of them were affected by the inoculation type, with the lag phase for growth being more affected. Changing from the multiple spore to the single spore inoculation led to a delay of approximately 3-5days on the lag phase and higher growth rates for the multiple spore experiment were found. The same trend was observed on the probability models, with lower predicted probabilities when colonies came up from single spores, for both growth and AFB1 production probabilities. Comparing both types of models, it was concluded that a clear overestimation of the lag phase for growth occurred using the linear model, but only in the multiple spore experiment. Multiple spore inoculum gave very similar estimated time to reach some set probabilities (t10, t50 and t100) for growth or AFB1 production due to the abruptness of the logistic curve developed. The observed differences suggest that inoculum concentration greatly affects the outcome of the predictive models, the estimated times to growth/AFB1 production being much earlier for the concentrated inoculum than for a single spore colony (up to 9days). Thus the number of spores used to generate data in predictive mycology experiments should be carefully controlled in order to predict as accurately as possible the fungal behavior in a foodstuff.

Inhibitory effect of essential oils on growth and on aflatoxins production by Aspergillus parasiticus

The aim of this work was to assess the inhibitory effect of essential oils on the growth and aflatoxin production of Aspergillus parasiticus, as well as to correlate it with the chemical composition of the essential oils. Essential oils from six aromatic species (Cymbopogon citratus, Eucalyptus globulus, Origanum vulgare, Ruta graveolens, Salvia officinalis, Satureja montana) were characterised by gas chromatography and tested for their inhibitory effect against A. parasiticus strain MUM 92.02. Furthermore, the in vitro inhibitory effects of these essential oils on the production of aflatoxins were evaluated by HPLC. Results showed that all essential oils retarded the time for visible growth. Growth rate was affected differently depending on the essential oil. S. montana essential oil prevented growth in all cases. The essential oil of R. graveolens inhibited most of the aflatoxin production even though growth inhibition was low, while with C. citratus essential oil trace levels of aflatoxins were detected. Essential oils containing carvacrol and/or thymol (S. montana and O. vulgare) have the highest activity against fungal growth, while an essential oil (R. graveolens) containing 2-undecanone and 8-phenyl-2-octanone inhibited the synthesis of aflatoxins. Although the main component of this essential oil was 2-undecanone (91%), when pure 2-undecanone was tested, it did not inhibit aflatoxin production. Inhibition activity is probably due to the recently identified minor compound or to a synergistic effect. Essential oils seem to be a good alternative to fungicides not only because of environmental issues but also because they do not seem to enhance mycotoxin production as it has been reported for some fungicides.

Description of Aspergillus flavus growth under the influence of different factors (water activity, incubation temperature, protein and fat concentration, pH, and cinnamon essential oil concentration) by kinetic, probability of growth, and time-to-detection models

A Box-Behnken design was used to determine the effect of protein concentration (0, 5, or 10g of casein/100g), fat (0, 3, or 6g of corn oil/100g), a_w (0.900, 0.945, or 0.990), pH (3.5, 5.0, or 6.5), concentration of cinnamon essential oil (CEO, 0, 200, or 400μL/kg) and incubation temperature (15, 25, or 35°C) on the growth of Aspergillus flavus during 50days of incubation. Mold response under the evaluated conditions was modeled by the modified Gompertz equation, logistic regression, and time-to-detection model. The obtained polynomial regression models allow the significant coefficients (p<0.05) for linear, quadratic and interaction effects for the Gompertz equation's parameters to be identified, which adequately described (R²>0.967) the studied mold responses. After 50days of incubation, every tested model system was classified according to the observed response as 1 (growth) or 0 (no growth), then a binary logistic regression was utilized to model A. flavus growth interface, allowing to predict the probability of mold growth under selected combinations of tested factors. The time-to-detection model was utilized to estimate the time at which A. flavus visible growth begins. Water activity, temperature, and CEO concentration were the most important factors affecting fungal growth. It was observed that there is a range of possible combinations that may induce growth, such that incubation conditions and the amount of essential oil necessary for fungal growth inhibition strongly depend on protein and fat concentrations as well as on the pH of studied model systems. The probabilistic model and the time-to-detection models constitute another option to determine appropriate storage/processing conditions and accurately predict the probability and/or the time at which A. flavus growth occurs.

Comparative study of growth responses and screening of inter-specific OTA production kinetics by A. carbonarius isolated from grapes

The aim of this work was to assess OchratoxinA (OTA) production of different Aspergillus carbonarius isolates, evaluate their growth profile through different growth measurements, and reveal any underlying correlation between them. Ten different isolates of A. carbonarius isolated from Greek vineyards located in different geographical regions were examined in vitro for their OTA production potential after an incubation period of up to 11 days. All fungal isolates grew on a synthetic grape juice medium (SGM) similar to grape composition at optimum conditions of temperature and water activity (25°C and 0.98 a_w). Samples for OTA determination were removed at 3, 5, 7, 9, and 11 days of growth and analyzed by HPLC. Based on OTA measurements the isolates were characterized by diverse OTA production ranging from 50 to 2000 ppb at day 11. The different fungal growth responses (colony diameter, colony area, biomass, biomass dry weight, and colony density) have been measured and correlated with toxin production by means of principal components analysis (PCA), confirming satisfactory correlation and explained over 99% of data variability. Leudeking-Piret model was also used to study OTA production with time, revealing a mixed-growth associated trend and pointing a fail-safe model with slightly better prediction through colony area. This approach contributes to the assessment of correlation between mycotoxin production and different methods of fungal growth determination in relation to time.

The use of real-time PCR to study Penicillium chrysogenum growth kinetics on solid food at different water activities

Fungal growth on solid foods can make them unfit for human consumption, but certain specialty foods require fungi to produce their characteristic properties. In either case, a reliable way of measuring biomass is needed to study how various factors (e.g. water activity) affect fungal growth rates on these substrates. Biochemical markers such as chitin, glucosamine or ergosterol have been used to estimate fungal growth, but they cannot distinguish between individual species in mixed culture. In this study, a real-time polymerase chain reaction (rt-PCR) protocol specific for a target fungal species was used to quantify its DNA while growing on solid food. The measured amount of DNA was then related to the biomass present using an experimentally determined DNA-to-biomass ratio. The highly sensitive rt-PCR biomass assay was found to have a wide range, able to quantify the target DNA within a six orders-of-magnitude difference. The method was used to monitor germination and growth of Penicillium chrysogenum spores on a model porous food (cooked wheat flour) at 25°C and different water activities of 0.973, 0.936, and 0.843. No growth was observed at 0.843, but lag, exponential and stationary phases were identified in the growth curves for the higher water activities. The calculated specific growth rates (μ) during the exponential phase were almost identical, at 0.075/h and 0.076/h for aw=0.973 and 0.936, respectively. The specificity of the method was demonstrated by measuring the biomass of P. chrysogenum while growing together with Aspergillus niger on solid media at aw=0.973.

Predicting and preventing mold spoilage of food products

This article is a review of how to quantify mold spoilage and consequently shelf life of a food product. Mold spoilage results from having a product contaminated with fungal spores that germinate and form a visible mycelium before the end of the shelf life. The spoilage can be then expressed as the combination of the probability of having a product contaminated and the probability of mold growth (germination and proliferation) up to a visible mycelium before the end of the shelf life. For products packed before being distributed to the retailers, the probability of having a product contaminated is a function of factors strictly linked to the factory design, process, and environment. The in-factory fungal contamination of a product might be controlled by good manufacturing hygiene practices and reduced by particular processing practices such as an adequate air-renewal system. To determine the probability of mold growth, both germination and mycelium proliferation can be mathematically described by primary models. When mold contamination on the product is scarce, the spores are spread on the product and more than a few spores are unlikely to be found at the same spot. In such a case, models applicable for a single spore should be used. Secondary models can be used to describe the effect of intrinsic and extrinsic factors on either the germination or proliferation of molds. Several polynomial models and gamma-type models quantifying the effect of water activity and temperature on mold growth are available. To a lesser extent, the effect of pH, ethanol, heat treatment, addition of preservatives, and modified atmospheres on mold growth also have been quantified. However, mold species variability has not yet been properly addressed, and only a few secondary models have been validated for food products. Once the probability of having mold spoilage is calculated for various shelf lives and product formulations, the model can be implemented as part of a risk management decision tool.

Modeling kinetics of aflatoxin production by Aspergillus flavus in maize-based medium and maize grain

Predictive mycology has dealt mainly with germination, growth and inactivation of fungi while the issue of mycotoxin production remains relatively unexplored. Very few studies provide biomass dry weight/colony size data along with mycotoxin data for the same sample times, thus the ratio mycotoxin accumulation per fungal biomass dry weight/colony size has rarely been reported. For this reason, the objective of the present study was to model the kinetics of mycotoxin production under the assumption of existing both no-growth-associated and growth-associated production. Aspergillus flavus was chosen as a model mycotoxigenic microorganism, and it was grown in maize agar medium and maize grain at 0.90 and 0.99 aw at 25°C. A significant positive correlation (p<0.05) was observed among the biomass responses (colony radius and biomass dry weight) in agar medium and colony radius in maize at both aw levels assayed. The Luedeking-Piret model was used to model AFB1 production and reasonable percentages of variability were explained. Moreover, AFB1 production was in general slightly better predicted through colony area. As conclusion, aflatoxin production may follow a mixed-growth associated trend, confirming that toxin formation does not present a clear delay in relation to growth under certain conditions.

Relation between germination and mycelium growth of individual fungal spores

The relation between germination time and lag time of mycelium growth of individual spores was studied by combining microscopic and macroscopic techniques. The radial growth of a large number (100-200) of Penicillium expansum and Aspergillus niger mycelia originating from single spores was monitored macroscopically at isothermal conditions ranging from 0 to 30°C and 10 to 41.5°C, respectively. The radial growth curve for each mycelium was fitted to a linear model for the estimation of mycelium lag time. The results showed that the lag time varied significantly among single spores. The cumulative frequency distributions of the lag times were fitted to the modified Gompertz model and compared with the respective distributions for the germination time, which were obtained microscopically. The distributions of the measured mycelium lag time were found to be similar to the germination time distributions under the same conditions but shifted in time with the lag times showing a significant delay compared to germination times. A numerical comparison was also performed based on the distribution parameters λ(m) and λ(g), which indicate the time required from the spores to start the germination process and the completion of the lag phase, respectively. The relative differences %(λ(m)-λ(g))/λ(m) were not found to be significantly affected by temperatures tested with mean values of 72.5±5.1 and 60.7±2.1 for P. expansum for A. niger, respectively. In order to investigate the source of the above difference, a time-lapse microscopy method was developed providing videos with the behavior of single fungal spore from germination until mycelium formation. The distances of the apexes of the first germ tubes that emerged from the swollen spore were measured in each frame of the videos and these data were expressed as a function of time. The results showed that in the early hyphal development, the measured radii appear to increase exponentially, until a certain time, where growth becomes linear. The two phases of hyphal development can explain the difference between germination and lag time. Since the lag time is estimated from the extrapolation of the regression line of the linear part of the graph only, its value is significantly higher than the germination time, t(G). The relation of germination and lag time was further investigated by comparing their temperature dependence using the Cardinal Model with Inflection. The estimated values of the cardinal parameters (T(min), T(opt), and T(max)) for 1/λ(g) were found to be very close to the respective values for 1/λ(m), indicating similar temperature dependence between them.

The application of bioactive compounds from the food industry to control mold growth in indoor waterborne coatings

Microbial growth in indoor environments creates health problems, especially in people with asthma; approximately 80% of these patients are allergic to mold. Antimicrobial coatings are formulated to generate surfaces that are easy to clean and may also incorporate active agents, commonly called biocides, which inhibit microbial colonization, subsequent growth and bio-deterioration of the substrates. Some research lines seek to replace traditional organometallic and organochlorines biocides with environmentally acceptable ones. The aim of this research was, primarily, to explore the possible application of different compounds used in food industry like preservatives to be used as antimicrobial additives for antimicrobial coatings. Four biocides were tested against two different ambient molds isolated from an interior painted wall (Chaetomium globosum and Alternaria alternate). The selected biocides were zinc salicylate, zinc benzoate, calcium benzoate and potassium sorbate. The resulting paints were subjected to biological and physical tests (viscosity, hiding power, humidity absorption and biocides leaching rate). Bioassays revealed that zinc benzoate and zinc salicylate resulted active against both fungi.

Effects of storage condition factors on fungal invasion of Radix Ophiopogonis

Fungal invasion is a main factor leading to the loss of postharvest herbs during storage. To prevent fungal invasion and clarify the favorable conditions for the stability of herbs during the storage period, uniform design and three-dimensional response surfaces were applied to investigate the relationship of the mildew degree of Radix Ophiopogonis induced by prevalent fungal isolates and the storage factors including air relative humidity (X(1)), temperature (X(2)), and moisture content (X(3)), in laboratory studies. Mildew degree was evaluated by ergosterol assay of mold isolates through a high-performance liquid chromatography-diode array detector (HPLC-DAD) technique. As a result, storage conditions, which satisfied the following correlation equations established by the relationships between the storage factors and the biomass of mildew (Y), could effectively prevent fungal spoilage: Y = -0.2484084028 + 0.00030711966572 x X(3) x X(3) + 0.00018881361186 x X(1) x X(2) - 0.00029473040679 x X(2) x X(3) <or= 0; Y = -0.2697457586 + 0.004127756022 x X(1) - 0.000015977780492 x X(1) x X(1) + 0.00021906984606 x X(2) x X(3) <or= 0; Y = -0.325655811 + 0.015464432582 x X(2) + 0.00004779394354 x X(1) x X(1) - 0.00021743815482 x X(2) x X(2) <or= 0. This compositive methodology might be useful to predict the occurrence of fungal invasion.

Modelling of growth of aflatoxigenic A. flavus isolates from red chilli powder as a function of water availability

The aim of the present work was to apply mathematical models for the prediction of growth of aflatoxigenic moulds in powdered Capsicum fruits as a function of its water availability. As prevention of fungal growth effectively conduces to prevention of mycotoxin accumulation, the development of models for prediction of growth of mycotoxigenic fungi becomes a key step in risk management. Two aflatoxigenic A. flavus from chilli powder were grown on 3% chilli powder extract agar at different water activity levels and their growth was evaluated over time in terms of colony sizes and ergosterol accumulation. Both variables were modelled over time, and the resulting parameters (growth rates and lag phases) were modelled as a function of water availability using the Rosso cardinal model. Linear logistic regression was also applied to predict the probability of growth over storage time. Both isolates showed a similar pattern of behaviour, with decreasing growth rates and increasing lag phases with decreasing water activity level. While estimation of optimum a(w) for growth was consistently around 0.97-0.99, the minimum estimated a(w) varied from 0.82 to 0.88 depending on the isolate and on the parameters used for predictions. Comparing growth rates obtained for colony size and ergosterol accumulation, a linear relationship between them could be observed. The rate of root square ergosterol/colony diameter/unit of time was 0.25-0.27. Probabilities of growth before 10 days over 90% were estimated at a(w) 0.91, while the safe period could be extended to more than 20 days (22-29 days) if water activity was decreased to an a(w)=0.87. Finally, the probability of growth is always under 50% when water availability is under a(w) 0.85, and almost null for A. flavus UdLTA 3.147. It was concluded that for safe production, storage and transport, chillies and chilli powder must be kept under 31% mc (db) (probability of growth <50%). However, growth is unlikely to occur if chilli is kept at approx. 34% for less than 10 days, or at approx. 33% for less than 20 days. Careful hazard analysis and critical control point (HACCP) techniques during raw material production and the subsequent stages of drying, transportation, elaboration and storage are indispensable.