Modeling the effect of ethanol vapor on the germination time of Penicillium chrysogenum

The influence of ethanol vapor on germination of Penicillium chrysogenum was determined on yeast nitrogen base plus glucose agar medium at 25°C. Ethanol vapors were generated by 0 to 6% (wt/wt) ethanol solutions at the bottom of hermetically closed petri dishes. The logistic equation was used to describe the data as the percentage of germination versus time and to estimate the germination time. The effect of ethanol concentration on germination time was described by a new reparameterized equation, resulting in an estimated limiting ethanol concentration of 4.3%. Up to 3% ethanol, all spores germinated, and the germination time increased with increasing ethanol concentration. At 3.5 and 4%, some spores formed abnormal germ tubes and others were inhibited at the swelling stage. The inhibiting effect of ethanol was reversible under these experimental conditions

Modelling the inhibitory effect of copper sulfate on the growth of Penicillium expansum and Botrytis cinerea

International audienceAims: This study aimed to investigate the effect of copper sulfate (from 0 to 8 mmol kg(-1)) on radial growth rate and lag time of two moulds responsible for vine grapes spoilage: Penicillium expansum strain 25.03 and Botrytis cinerea, strains BC1 and BC2. Methods and results: A new model was developed to describe tailing and shoulders in the inhibition curves. Because of tailing, the minimum inhibitory concentration (MIC), was not defined as the concentration at which no growth was observed, but as the concentration at which the lag time was infinite. The concentrations at which mu = mu(opt)/2, (Cu-50), were in the range of 2.2-2.6 mmol kg(-1). Radial growth rate of P. expansum and the reciprocal of the lag time were linearly correlated (r = 0.84). In contrast, in the range 0-4 mmol kg(-1), an inhibition of growth of B. cinerea was observed whereas germination remained unaffected (i.e. the lag time was constant). In the range 4-8 mmol kg(-1), the radial growth rate of B. cinerea was almost constant (c. 1 mm day(-1)), but germination was inhibited (i.e. the lag time was increased). Conclusions: The MIC values were 4.7 mmol kg(-1) for P. expansum, 8.2 and 7.3 mmol kg(-1) for B. cinerea strain BC1 and BC2, respectively, demonstrating that some isolates of these moulds are resistant to copper. Significance and Impact of the Study: Copper concentrations at 4 mmol kg(-1) would be sufficient to control the development of these isolates, but the toxicity of copper should be extended to other isolates and evaluated in vineyards

Modelling the effect of ethanol on growth rate of food spoilage moulds

The effect of ethanol (E) on the radial growth rate (¿) of food spoilage moulds (Aspergillus candidus, Aspergillus flavus, Aspergillus niger, Cladosporium cladosporioides, Eurotium herbariorum, Mucor circinelloides, Mucor racemosus, Paecilomyces variotii, Penicillium chrysogenum, Penicillium digitatum, Rhizopus oryzae and Trichoderma harzianum) was assessed in Potato Dextrose Agar (PDA) medium at aw 0.99, 25 °C. In order to model this effect, the Monod type equation described previously by Houtsma et al. (Houtsma, P.C., Kusters, B.J.M., de Wit, J.C., Rombouts, F.M., Zwietering, M.H., 1994. Modelling growth rates of Listeria monocytogenes as a function of lactate concentration. Int. J. Food. Microbiol. 24, 113-123.) was re-parameterised: ; Emax (%, wt/wt): ethanol concentration at which no growth occurs, K (%, wt/wt): ethanol concentration at which ¿=¿opt/2, ¿opt (mm day¿1): growth rate at 0% ethanol. The model was capable of describing curves, ¿ vs. E, with either a concave shape (KEmax/2) with a good accuracy (root mean square error (RMSE)¿0.136) with the notable exception of R. oryzae and T. harzianum. After growth rate data were square-root transformed to stabilise the variance, Emax was estimated in the range 3% to 5% for all moulds with the exception of T. harzianum (Emax 2.14%) and P. variotii (Emax 6.43%). Ethanol would appear an effective additional barrier to inhibit fungal growth in food products and would represent an interesting alternative to the use of preservatives

Use of a logistic model to assess spoilage by Byssochlamys fulva in clarified apple juice

The percentage P (%) of spoiled bottles (n = 40) of clarified apple juice due to Byssochlamys fulva, was modeled by using a logistic model: P = P(max)/1 + exp(k(tau-iota)) where P(max) (%) the maximum percentage of spoiled bottles, k (h(-1)) slope parameter and T (h) the time for P = P(max)/2. Bottles of pasteurized apple juice were inoculated with B.fulva IOC 4518 ascospores for low and high initial loads, 4.8 +/- 23 ascospores/100 mL and 19.3 +/- 4.6 ascospores/100 mL respectively and incubated at 21 degrees C and 30 degrees C. P(max) was not significantly different from 100% except for a low initial load at 21 degrees C. Model parameters were estimated with a good accuracy, RMSE in the range 3.89-7.50. Then the model was used to determine the time for 10% bottles spoiled, t(10%). This time was greater at low initial loads, 57.4 and 104 h at 30 and 21 degrees C respectively, than at high initial loads 23.9 and 75.1 h at 30 and 21 degrees C respectively. This study demonstrated that even at a very low initial contamination, clarified apple juice can be easily spoiled by B.fulva highlighting the importance of controlling critical control steps of fruit juice processing (i.e., fruit washing, juice filtration and pasteurization). (C) 2009 Elsevier B.V. All rights reserved.1374170029930