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Aw Levels (aw + level)
Selected AbstractsEfficacy of natamycin for control of growth and ochratoxin A production by Aspergillus carbonarius strains under different environmental conditionsJOURNAL OF APPLIED MICROBIOLOGY, Issue 6 2007Á. Medina Abstract Aims:, To examine the efficacy of natamycin produced by Streptomyces natalensis against strains of Aspergillus carbonarius growth and ochratoxin A (OTA) production under different environmental factors on a grape juice-based medium. Methods and Results:, Detailed studies in the range 0,20 ng ml,1 for control of growth and ochratoxin production by strains of A. carbonarius at 0·98, 0·96 and 0·94 water availabilities (aw) and 15,25°C on a fresh red grape extract medium were examined. Inhibition of growth was depending on temperature and aw level. At 15°C, 5,10 ng ml,1 natamycin was effective in reducing growth almost completely. However, at 20,25°C and all the three aw levels, growth was only slightly inhibited by 5,10 ng ml,1 natamycin. There were strain differences with regard to inhibition of OTA production. At 15°C and 0·98 aw, 10 ng ml,1 was required to inhibit production by >90%. However, at 0·96 and 0·94 aw, almost complete inhibition occurred. At 20°C, OTA production was only significantly inhibited by 10 ng ml,1 natamycin at 0·94 aw. At 0·96 and 0·98 aw, some inhibition occurred with 5,10 ng ml,1, but greater concentrations would be required for effective inhibition. At 25°C, 5 ng ml,1 was effective at all aw levels. However, at 15°C and 25°C and a wide range of aw levels, natamycin effectively controlled OTA production. Conclusions:, Natamycin appears to be a very effective for controlling growth and OTA production by strains of A. carbonarius over a range of aw and temperature conditions on grape-based media. Significance and Impact of the Study:, This is the first detailed study to demonstrate the impact of natamycin against A. carbonarius. This study suggests that use of natamycin at 50,100 ng ml,1 can give complete inhibition of growth of A. carbonarius and OTA production over a range of environmental conditions. Natamycin could be an important component of a system to prevent OTA contamination of wine as well during the drying and production of vine fruits. [source] Influence of water activity and temperature on conidial germination and mycelial growth of ochratoxigenic isolates of Aspergillus ochraceus on grape juice synthetic medium.JOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 10 2005Predictive models Abstract The first stages in the development of Aspergillus ochraceus, an ochratoxin A-producing fungus that infects grapes and may grow on them, have been studied on a synthetic nutrient medium similar to grape in composition. Spore germination and mycelial growth have been tested over a water activity (aw) and temperature range which could approximate to the real conditions of fungal development on grapes. Optimal germination and growth were observed at 30 °C for all three isolates tested. Maximal germination rates were detected at 0.96,0.99 aw at 20 °C, while at 10 and 30 °C the germination rates were significantly higher at 0.99 aw. Although this abiotic factor (aw) had no significant influence on mycelial growth, growth rates obtained at 0.98 aw were slight higher than those at other aw levels. Predictive models for the lag phase before spore germination as a function of water activity and temperature have been obtained by polynomial multiple linear regression, and the resulting response surface models have been plotted. Copyright © 2005 Society of Chemical Industry [source] Modulation of water activity on fungicide effect on Aspergillus niger growth in Sabouraud dextrose agar medium,LETTERS IN APPLIED MICROBIOLOGY, Issue 5 2005X. Ni Abstract Aims:, To examine whether water activity (aw) in combination with low concentration of fungicides can be used to effectively control Aspergillus niger van Tieghem growth in cultural medium, the Sabouraud dextrose agar (SDA). The data would be used as baseline information for reducing A. niger contamination in insect artificial diets. Methods and Results:,Aspergillus niger was isolated from an insect artificial diet. Four concentration levels (i.e. 0, 1, 10 and 20 ,mol) of two fungicides (i.e. amphotericin B and itraconazole) were tested against A. niger under four aw levels (i.e. 0·994, 0·961, 0·921 and 0·859) adjusted by including 0, 12·5, 25 and 38% of glycerol in the medium mixture. Aspergillus niger growth was significantly reduced at low fungicide concentration (1 ,mol), and at reduced aw. The spore germination was prevented with either higher fungicide concentration (>10 ,mol), or low aw in the medium (aw < 0·921). The two ecological determinants (fungicides and aw) showed a significant impact on A. niger survival in the medium (P < 0·0001). Itraconazole is more effective than amphotericin B in controlling A. niger contamination in the agar medium. Conclusion:, Adjustment of aw (with 12·5% of glycerol) in combination with 1 ,mol of itraconazole can effectively prevent A. niger growth in the SDA cultural medium. Significance and Impact of the Study:,Aspergillus niger contaminations have frequently affected the quality of insects produced from mass rearing facilities. Low aw in combination with low fungicide concentration has the potential to become one of the most cost-effective management strategies to prevent A. niger contamination in insect artificial diets. The effect of fungicides and low aw in artificial diets on insect biology needs to be further examined. [source] | ||||||||||