The presence of yeasts in milk may cause physical and chemical changes limiting the durability and compromising the quality of the product. Moreover, milk and dairy products contaminated by yeasts may be a potential means of transmission of these microorganisms to man and animals causing several kinds of infections. This study aimed to determine whether different species of yeasts isolated from bovine raw milk had the ability to develop at 37°C and/or under refrigeration temperature. Proteinase and phospholipase activities resulting from these yeasts were also monitored at different temperatures. Five genera of yeasts (Aureobasidium sp., Candida spp., Geotrichum spp., Trichosporon spp. and Rhodotorula spp.) isolated from bovine raw milk samples were evaluated. All strains showed one or a combination of characteristics: growth at 37°C (99·09% of the strains), psychrotrophic behaviour (50·9%), proteinase production (16·81% of the strains at 37°C and 4·09% under refrigeration) and phospholipase production (36·36% of the isolates at 37°C and 10·9% under refrigeration), and all these factors may compromise the quality of the product. Proteinase production was similar for strains incubated at 37°C (16·81% of the isolates) and room temperature (17·27%) but there was less amount of phospholipase-producing strains at room temperature (15·45% of the isolates were positive) when compared with incubation at 37°C (36·36%). Enzymes production at 37°C by yeasts isolated from milk confirmed their pathogenic potential. The refrigeration temperature was found to be most efficient to inhibit enzymes production and consequently ensure better quality of milk. The viability of yeasts and the activity of their enzymes at different temperatures are worrying because this can compromise the quality of dairy products at all stages of production and/or storage, and represent a risk to the consumer.

RESUMO Os fungos filamentosos e leveduras podem estar associados a diferentes patologias no homem e animais. O leite e seus derivados contaminados com estes microrganismos podem constituir potenciais vias de transmissão de zoonoses a eles relacionadas. Foram analisadas 70 amostras de leite, sendo 50 de tanques de refrigeração, 10 de latões de propriedades de exploração leiteira e 10 de latões de distribuidores que comercializam leite informal, visando a comparação da qualidade destes produtos quanto à presença e quantidade de fungos. Foram isolados, em diferentes percentagens, fungos filamentosos e leveduras a partir de todas as amostras de leite das diferentes procedências: Candida spp. (C. krusei, C. guilliermondii, C. tropicalis, C. kefyr, dentreoutras), Geotrichum spp., Rhodotorula spp., Trichosporon spp., Aureobasidium spp., Penicillium spp., Acremonium spp., Chrysosporium spp., Mucor spp. e Aspergillus spp. Não houve diferença estatisticamente significante entre as medianas das quantidades de unidades formadoras de colônias de fungos/ mL de leite das diferentes procedências, indicando que o nível de contaminação por fungos nas amostras destas três origens foi similar. Pode-se verificar que em todas as amostras de leite cru havia a presença de fungos, todos passíveis agentes de micoses oportunísticas.

RUZ-PERES, M. Evaluation of the presence of fungi in samples of raw milk and study of the susceptibility of these microorganisms to the temperature/time rates employed in pasteurization and boiling processes. [Avaliação da presença de fungos em amostras de leite cru e estudo da susceptibilidade destes microrganismos às relações temperatura/tempo empregadas nos processos de pasteurização e fervura]. 2005.92 f. Dissertação (Mestrado em Medicina Veterinária)