Biocontrol of aflatoxigenic Aspergillus parasiticus by native Debaryomyces hansenii in dry-cured meat products.

Dry-cured meat products, such as dry-cured ham or dry-fermented sausages, are characterized by their particular ripening process, where a mould population grows on their surface. Some of these moulds are hazardous to the consumers because of their ability to produce mycotoxins including aflatoxins (AFs). The use of native yeasts could be considered a potential strategy for controlling the presence of AFs in dry-cured meat products. The aim of this work was to evaluate the antagonistic activity of two native Debaryomyces hansenii strains on the relative growth rate and the AFs production in Aspergillus parasiticus. Both D. hansenii strains significantly reduced the growth rates of A. parasiticus when grown in a meat-model system at different water activity (aw) conditions. The presence of D. hansenii strains caused a stimulation of AFs production by A. parasiticus at 0.99 aw. However, at 0.92 aw the yeasts significantly reduced the AFs concentration in the meat-model system. The relative expression levels of the aflR and aflS genes involved in the AFs biosynthetic pathway were also repressed at 0.92 aw in the presence of both D. hansenii strains. These satisfactory results were confirmed in dry-cured ham and dry-fermented sausage slices inoculated with A. parasiticus, since both D. hansenii strains significantly reduced AFs amounts in these matrices. Therefore, both tested D. hansenii strains could be proposed as biocontrol agents within a HACCP framework to minimize the hazard associated with the presence of AFs in dry-cured meat products.

Mechanisms involved in reduction of ochratoxin A produced by Aspergillus westerdijkiae using Debaryomyces hansenii CYC 1244.

Aspergillus westerdijkiae is one of the most relevant ochratoxin A (OTA) producing species within the Section Circumdati contaminating a number of agroproducts. The yeast Debaryomyces hansenii CYC 1244 was previously reported to be able to reduce growth and extracellular OTA produced by A. westerdijkiae. In this work, we examined several mechanisms possibly involved in this OTA reduction in in vitro experiments. OTA biosynthesis was evaluated by quantitation of expression levels of pks (polyketide synthase) and p450-B03 (cytochrome p450 monooxygenase) genes using newly developed and specific real time RT-PCR protocols. Both genes showed significant lower levels in presence of D. hansenii CYC 1244 suggesting an effect on regulation of OTA biosynthesis at transcriptional level. High levels of removal of extracellular OTA were observed by adsorption to yeast cell walls, particularly at low pH (98% at pH 3). On the contrary, no evidences were obtained of absorption of OTA into yeast cells or the production of constitutively expressed enzymes that degrade OTA by D. hansenii CYC 1244. These results described the potential of this yeast strain as a safe and efficient biocontrol agent to decrease OTA in A. westerdijkiae and two important mechanisms involved which may permit its application at different points of the food chain.

The effects of 2,4-dichlorophenoxyacetic acid on respiration, nitrogen and carbohydrate metabolism of Aspergillus terreus Thom.

The effects of 2,4-D on respiration, carbohydrate and nitrogen metabolism have excited much interest in relation to higher plants (Hansen 1946, Hseuth and Lou 1946, SMITH et al. 1947, and Said and Naguib 1955). But the effects of 2,4-D on dungi have been tackled to a much less extent (Guiscafre-Arrilaga 1948, Bever and Slife 1948, Wei and Ling 1948, and Manil and Strazewska 1950). These investigators studied the effects exerted on fungal growth. Said and Naguib (1962) studied the effect of 2,4-D on the carbohydrate metabolism of Fusarium moniliforme. They showed that both sucrose inversion and absorption were retarded in the presence of 2,4-D. In the present investigation, a trial was carried out in order to elucidate the effect of 2,4-D on growth, nitrogen and carbohydrate metabolism of Aspergillus terreus when grown on two different nitrogen sources, namely sodium nitrate and ammonium phosphate.