The effect of water activity and temperature on the production of some mycotoxins

Preventing mold from growing and producing mycotoxins requires knowledge of the conditions under which each of the toxinogenic molds becomes active. In this investigation the relation between fungal growth and mycotoxin formation and the factors water activity and temperature is studied. Various fungal species known to produce mycotoxin were tested. Optimal substrates for production of the particular mycotoxin were used to determine the lowest possible water activity and temperature at which mycotoxins may be produced.In article 1 a water activity measurement device is described which has been designed for accurate measurements. The first study encompasses the aflatoxin production by Aspergillus parasiticus at different conditions of water activity and temperature. Experience is gained with both liquid cultures and surface cultures. Because of its reproducibility and resemblance to mold growth in practice, the surface culture is preferred and used in the following investigations.In article 2 attention is paid to differences between Aspergillus flavus strains in their response to various conditions of water activity and temperature.In articles 3, 4 and 5 the results of similar investigations with patulin, penicillic acid and ochratoxin A, respectively, are described and discussed. The effect of water activity and temperature on mycotoxin production is studied with semi-synthetic agar media, but also with some natural substrates.In the last experimental section of the thesis the effect of water activity and temperature on the mycotoxin production rate and mycotoxin production lagtime of the four mycotoxins is described. For this a calculation model is developed to exclude the influence of mycelial weight and growth time on the outcome of the experiments.In the chapter Discussion the results of articles 1-5 are discussed in the light of the results described in the last experimental section. In a final discussion the practical implications of the results with respect to safeguarding of foods from mycotoxin contamination are considered.<p/

Contaminants and micro-organisms in organic and conventional food products

In the Netherlands we investigated animal and plant products on potentially hazardous contamination with heavy metals, mycotoxins, pesticide residues, patho-genic micro-organisms and nitrate. In most cases, the organically produced foods had equal or lower amounts of contaminants than conventionally pro-duced products. These results conflict with a common idea that organic farming theoretically increases food safety risks. For many contaminants organic food showed a large diversity in the amount of contamina-tion. Experience with organic farming, managing and manure use partly explain these differences. Understanding of these cultivation parameters can help in further improvement of organic cultivation practices

The use of quantitative risk assessment in HACCP

During the hazard analysis as part of the development of a HACCP-system, first the hazards (contaminants) have to be identified and then the risks have to be assessed. Often, this assessment is restricted to a qualitative analysis. By using elements of quantitative risk assessment (QRA) the hazard analysis can be transformed into a more meaningful managerial tool. In this way the effect of control measures can be quantified, so the occurrence of contaminants in the endproducts can be estimated. Also, the quantitative risk assessment is a tool to derive or validate control measures and critical limits at process steps (CCPs). The practical use of quantitative risk assessment is demonstrated by two examples: the risk of raw fermented sausages and the risk of a pressurized meat product. It can be concluded that quantitative risk assessment is a powerful combination of food microbiology, modelling and applied statistics. It is recommended as the input for managing food safety issues as an extension or validation of the HACCP-system. © 2001 Elsevier Science Ltd