Abstract
The choice of a culture media to proceed a mycological analysis of food is extremely important to guarantee the reliability of the analysis. The medium should allow an excellent recovery of fungal species present in the food at the same time that it is necessary to avoid bacterial development. Thus the real microbial ecology will be reflected in the results. The efficacy of three media for fungal isolation and quantification (potato dextrose agar, dichloran rose of bengal and chloramphenicol agar and dichloran glycerol 18% agar) was compared for analysis of 54 samples of dry commercial pet food (34 for dogs and 20 for cats). Fungi were present in 74% of samples and 23 genera were isolated and identified. Aspergillus sp. and Aspergillus niger were respectively the most frequent genera and species isolated, whatever the culture medium selected to proceed the analysis. Dichloran glycerol 18% agar was the medium that presented the best results considering both the quantity and variety of isolated fungi. Comparing the results obtained in different media, it was observed that the fungi recovered can vary according to the selected culture medium. Eurotium was the genus that presented the biggest difference in occurrence among the media where samples were cultivated to enumeration in this study. Therefore, the utilization of specific media, selected according to the characteristics of the food to be analyzed (specially water activity) allow a better visualization of the presence of food spoilage fungi.
Highlights
A microbiological analysis of foods is carried out to guaran tee the quality and safety of the industrialized products
The analysis permitted the classification of 23 genera, besides the detection of fungi identified only as Mycelia sterilia and yeasts in 40 (74%) of the 54 samples of feeds (26 for dogs and 14 for cats)
dichloran glycerol 18% agar (DG18) presented the better results both in the quantity as much as in the variety of fungi isolated from the evaluated pet food
Summary
A microbiological analysis of foods is carried out to guaran tee the quality and safety of the industrialized products. Potato dextrose agar has been used for a general quantification of fungi This medium does not present an adequate nutritive source and can inhibit the recovering of damaged cells due to its low pH (3.5) [15]. Media supplemented with antibiotics and dye, as the dichloran rose of bengal and chloramphenicol [10], emerged as a more efficient alternative. These media show a less toxic effect to the damaged cells, are more effective to inhibit the bacterial development and use to induce a smaller amount of food particles precipitation due its higher pH (5-6) [15]. Media with reduced activity of water (Aw) were introduced, as the dichloran glycerol agar 18% (Aw 0.95), for a general quantification of moderately xerophilic fungi, those with fastidious growth, which in a medium with traditional activity of water (Aw 0.99) may have their growth inhibited due to the rapid development of other species [9]
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