Predictive modelling of the individual and combined effect of water activity and temperature on the radial growth of Fusarium verticilliodes and F-proliferatum on corn

The major objective of this study was to develop validated models to describe the effect of a, and temperature on the radial growth on corn of the two major famonisin producing Fusaria, namely Fusarium verticilliodes and F. proliferatum. The growth of these two isolates on corn was therefore studied at water activities between 0.810-0.985 and temperatures between 15 and 30 degrees C. Minimum a(w) for growth was 0.869 and 0.854 for F. verticilliodes and F. proliferatum, respectively. No growth took place at aw values equal to 0.831 and 0.838 for F. verticilliodes and F. proliferation, respectively. The colony growth rates, g (mm d(-1)) were determined by fitting a flexible growth model describing the change in colony diameter (mm) with respect to time (days). Secondary models, relating the colony growth rate with a(w) or a(w) and temperature were developed. A third order polynomial equation and the linear Arrhenius-Davey model were used to describe the combined effect of temperature and a(w) on g. The combined modelling approaches, predicting g (mm d(-1)) at any a(w) and/or temperature were validated on independently collected data. All models proved to be good predictors of the growth rates of both isolates on maize within the experimental conditions. The third order polynomial equation had bias factors of 1.042 and 1.054 and accuracy factors of 1.128 and 1.380 for F verticilliodes and F proliferatum, respectively. The linear Arrhenius-Davey model had bias factors of 0.978 and 1.002 and accuracy factors of 1.098 and 1.122 for F. verticilliodes and F. proliferatum, respectively. The results confirm the general finding that a, has a greater influence on fungal growth than temperature. The developed models can be applied for the prevention of Fusarium growth on maize and the development of models that incorporate other factors important to mould growth on maize, (c) 2005 Elsevier B.V. All rights reserved.[*]status: publishe

Inter- and intra-species variability in heat resistance and the effect of heat treatment intensity on subsequent growth of Byssochlamys fulva and Byssochlamys nivea

The major aims of this study were to assess inter- and intra-species variability of heat resistant moulds (HRMs), Byssochlamys fulva and Byssochlamys nivea, with regards to (i) heat resistance and (ii) effect of heat treatment intensity on subsequent outgrowth. Four-week-old ascospores were suspended in buffered glucose solution (13 degrees Brix, pH 3.5) and heat treated in a thermal cycler adjusted at 85 degrees C, 90 degrees C and 93 degrees C. Two variants of the Weibull model were fitted to the survival data and the following inactivation parameters estimated: b (inactivation rate, min(-1)), n (curve shape) and delta (the time taken for first decimal reduction, min). In addition to the assessment of heat resistance, outgrowth of Byssochlamys sp. from ascospores heated at 70 degrees C, 75 degrees C, 80 degrees C 85 degrees C and 90 degrees C for 10 min and at 93 degrees C for 30 and 70 s was determined at 22 degrees C for up to 30 days. The Baranyi and Roberts model was fitted to the growth data to estimate the radial growth rates (mu(max), mm.day(-1)) and lag times (lambda, days). Inter species variability and significant differences (p < 0.05) were observed for both inactivation and growth estimated parameters among B. fulva and B. nivea strains. The effect of heat treatment intensity on outgrowth of B. fulva strains was more apparent at the most intense heat treatment evaluated (90 degrees C/10 min), which was also the condition in which greater dispersion of the estimated kinetic parameters was observed. On the other hand, B. nivea strains were more affected by heating, resulting in greater variability of growth parameters estimated at different heating intensities and in very long lag phases (up to 25 days). The results show that inter- and intraspecies variability in the kinetic parameters of Byssochlamys sp. needs to be taken into account for more accurate spoilage prediction. Furthermore, the effect of thermal treatments on subsequent outgrowth from ascospores should be explored in combination with other relevant factors such as degrees Brix and oxygen to develop thermal processes and storage conditions which can prevent the growth of HRMs and spoilage of heat treated food products

Effect of sugar concentration (degrees Brix) and storage temperature on the time to visible growth of individual ascospores of six heat-resistant moulds isolated from fruit products

Heat-resistant moulds (HRMs) pose great challenges to processors of fruit-based products due to their thermal resistance and ability to grow across a broad range of conditions. Therefore, the quantification of the effect of inhibitory factors (conditions) on the growth of HRMs is very important to be used to prevent spoilage during shelf-life. This study assessed the minimum temperature and maximum sugar content (degrees Brix) for the growth of six HRMs (Byssochlamys spp. and Neosartorya spp.) previously isolated from fruit products. In addition, the time to form a visible colony (t(v), days) was determined to assess biological variability of individual ascospores within same population. Heat activated ascospores (10 min at 80 degrees C) were spread plated (+/- 100 spores) on acidified Potato Dextrose Agar (aPDA, pH 3.5) plates from which the degrees Brix was adjusted with fructose-glucose (1:1) to levels between 44 and 59 degrees Brix followed by incubation at 30 degrees C. To assess the effect of temperature, inoculated plates of aPDA were incubated at 4, 7, 8, 10, 12 and 14 degrees C. Three replicates (= 3 aPDA plates) were prepared per condition evaluated. The number of visible colonies were counted daily for up to two months. Probability distribution functions were then fitted in @Risk to the cumulative t(v)'s. With regards to cold tolerance, B. nivea was the most cold sensitive as it had the least ability to germinate and form visible colonies at low temperatures (no growth when T = 7 degrees C. Likewise, B. nivea was the most sensitive to increased degrees Brix values, whilst N. udagawae was able to grow out at the highest degrees Brix evaluated (59 degrees/a(w) = 0.86). The tolerance of potential spoilage HRMs to high sugar levels and their ability to grow under chilled conditions represent a challenge for the microbial stability of high-sugar fruit products. Differences in individual t(v)'s were mostly observed under conditions at the growth/no growth regions. For instance, individual t(v)'s of B. nivea ascospores ranged from 24 to 46 days at 12 degrees C and those of N. udagawae ranged from 20 to 45 days at 59 degrees Brix. The t(v)'s data from each HRM and condition evaluated were then fitted to different statistical distributions (Exponential, Normal, Lognormal, Weibull, Logistic or Pareto) to allow the use of the obtained data in further Quantitative Microbial Spoilage Risk Assessment work for pasteurized fruit products

Occurrence, distribution and contamination levels of heat-resistant moulds throughout the processing of pasteurized high-acid fruit products.

Heat-resistant moulds (HRMs) are well known for their ability to survive pasteurization and spoil high-acid food products, which is of great concern for processors of fruit-based products worldwide. Whilst the majority of the studies on HRMs over the last decades have addressed their inactivation, few data are currently available regarding their contamination levels in fruit and fruit-based products. Thus, this study aimed to quantify and identify heat-resistant fungal ascospores from samples collected throughout the processing of pasteurized high-acid fruit products. In addition, an assessment on the effect of processing on the contamination levels of HRMs in these products was carried out. A total of 332 samples from 111 batches were analyzed from three processing plants (=three processing lines): strawberry puree (n = 88, Belgium), concentrated orange juice (n = 90, Brazil) and apple puree (n = 154, the Netherlands). HRMs were detected in 96.4% (107/111) of the batches and 59.3% (197/332) of the analyzed samples. HRMs were present in 90.9% of the samples from the strawberry puree processing line (1-215 ascospores/100 g), 46.7% of the samples from the orange juice processing line (1-200 ascospores/100 g) and 48.7% of samples from the apple puree processing line (1-84 ascospores/100 g). Despite the high occurrence, the majority (76.8%, 255/332) of the samples were either not contaminated or presented low levels of HRMs ( 0.05). On the contrary, a significant reduction (p < 0.05) in HRMs levels was observed during the processing of apple puree. Twelve species were identified belonging to four genera - Byssochlamys, Aspergillus with Neosartorya-type ascospores, Talaromyces and Rasamsonia. N. fumigata (23.6%), N. fischeri (19.1%) and B. nivea (5.5%) were the predominant species in pasteurized products. The quantitative data (contamination levels of HRMs) were fitted to exponential distributions and will ultimately be included as input to spoilage risk assessment models which would allow better control of the spoilage of heat treated fruit products caused by heat-resistant moulds

Assessment of minimum oxygen concentrations for the growth of heat-resistant moulds

This study evaluated the effect of both gaseous and dissolved oxygen (O-2) concentration (0 - 21%) on the growth of six heat-resistant moulds (HRMs) (Neosartorya and Byssochlamys spp.) previously isolated from high-acid fruit products. The study was performed in acidified potato dextrose agar (aPDA) with all six HRMs and with B. fulva and N. fischeri in strawberry, apple and orange juice-based media. At >= 0.15% O-2, visible growth of the HRMs occurred within 3-6 days. Complete inhibition on aPDA did not occur even at very low levels of dissolved O-2 (ca. 0.01% O-2). With the exception of B. fulva, decrease of the O-2 concentration to = 0.15%. Significantly slower (p < 0.05) growth was observed for N. fischeri in orange juice medium. Strategies to inhibit the growth of HRMs should therefore not be based entirely on establishing low headspace O-2 levels. With this in mind, the effect of low O-2 concentrations ( < 1%) should be studied in combination with other factors (hurdles) such as antioxidants, organic acids, sugars (a(w)), storage temperature and pasteurization intensity, in order to predict the growth inhibition of the HRMs

Effect of O₂ - CO₂ enriched atmospheres on microbiological growth and volatile metabolite production in packaged cooked peeled gray shrimp (<i>Crangon crangon</i>)

This study evaluated the effect of modified atmospheres (MAs) with different O2 concentrations on microbial growth and volatile metabolite production in gray shrimp (Crangon crangon) during storage at 4 °C. Eight MAs were evaluated in total. Four of the MAs evaluated were without CO2: 0/0/100, 0/10/90, 0/30/70, 0/50/50 (% CO2/O2/N2) whilst the other four MAs all contained 50% CO2: 50/0/50, 50/10/40, 50/30/20, 50/50/0 (% CO2/O2/N2). Volatile spoilage metabolites were identified by thermal desorption GC-MS and quantified during storage by selective ion flow tube mass spectrometry (SIFT-MS). In comparison to microbial growth observed with an atmosphere of 100% N2, microbial growth was stimulated by the addition of O2 in the MAP in the absence of CO2. Under these conditions the total psychrotrophic counts exceeded 7 log cfu g- 1 after just 3 days of storage. However, in the presence of 50% CO2 the total psychrotrophic count exceeded 7 log cfu g- 1 after 5 days of storage. The combination of 50% CO2 and 50% O2 significantly inhibited microbial growth. For this MA condition, a diminishing effect on the production of metabolites was also observed, especially for amines and sulfur compounds, which constituted the major fraction of components causing the offensive odor