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.

Exogenous trehalose enhanced the biocontrol efficacy of Hanseniaspora uvarum against grape berry rots caused by Aspergillus tubingensis and Penicillium commune.

BACKGROUND: Primarily, chemical pesticides are commonly used to control preharvest and postharvest diseases of fruits and vegetables. However, there is strong public concern regarding the human and environmental health problems that might emanate from the residues of these chemical pesticides. As a result, biocontrol is often preferred due to its safety for humans and animals. The microbial antagonists employed often encounter variable climatic conditions, which affect their efficacy. In this study, the biocontrol efficacy of Hanseniaspora uvarum enhanced with trehalose against Aspergillus tubingensis and Penicillium commune in grapes was investigated. RESULTS: H. uvarum Y3 pretreated with 2.0% w/v trehalose in nutrient yeast dextrose broth (NYDB) before used significantly inhibited the incidence of decay and lesion diameter without affecting the sensory qualities of the grapes stored at either 4 °C or 20 °C. There was also a significant (P < 0.05) increase in the population dynamics of H. uvarum that was pretreated with 2% trehalose compared to that of H. uvarum alone. The in vitro assay on spore germination revealed an inhibition of A. tubingensis and P. commune by 85.6% and 87.0% respectively. Scanning electron microscopy results showed that both untreated H. uvarum and H. uvarum pre-treated with the 2% w/v trehalose before use inhibited fungal mycelium and development of grape rot. CONCLUSION: The biocontrol efficacy of H. uvarum was enhanced against grape rot caused by A. tubingensis and P. commune. The findings indicate the potential applicability of trehalose in the enhancement of H. uvarum. © 2018 Society of Chemical Industry.

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.