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Freezing effects on the microbiological quality of goat cheese

Pereira, R.M.*1; Sales–Gomes, M.*1; Lima-Costa, E.*1; Cassinello, J.*2 and Dionísio, L.*1

*1Universidade do Algarve–FERN Campus de Gambelas 8005-139 Faro Portugal *2Direcção Regional de Agricultura do Algarve–DRAALG Patacão 8001-904 Faro Portugal. E-mail: ldionis@ualg.pt

Seasonal nature of goat milk production induces the cheese producers to keep some over production, under frozen storage (-20±2ºC). Traditional Portuguese cheesemaking uses flowers of Cynara cardunculus L., widely known by their coagulant properties. These flowers may also lead to microbiological contamination of the final product. The evaluation of the effects of frozen storage on microbiological quality of goat cheese was the aim of this study. In the present work we have determined the number of aerobic heterotrophic microorganisms that grows at 30ºC, Lactobacillus, total and fecal coliforms, on three batches of goat fresh cheese produced from raw milk. Staphylococus aureus, moulds and yeasts were also enumerated in two of the three bacthes. In order to monitor the microbiological quality of goat fresh cheese, submitted to frozen conditions the samples were kept at -20±2ºC and were taken weekly along 56 days. Decimal dilutions were prepared with sterile Ringer solution (Oxoid). The first dilution was homogenized for two minutes in a Stomacher Lab-Blender 400 (Seward Medical, London, UK). Aliquots were plated in triplicate on complex and selective media. Aerobic heterotrophic microorganisms were cultivated on Plate Count Agar (Merck) supplemented with skimming milk at 30±1ºC for 48 hours, by pour plate technique. Total and fecal coliforms were incorporated on Violet Red Bile Glucose Agar (Merck), and incubated in anaerobic conditions at 30±1ºC for 48 hours and at 44.5ºC for 24 hours, respectively. Lactobacilli were grown in Rogosa Agar (Biokar) at 36±1ºC for 48 hours. Staphylococcus aureus were enumerated in Baird-Parker Agar base supplemented with Rabbit Plasma Fibrinogen (Oxoid). Moulds and yeast were isolated by spreading on Cook Rose Bengal (Oxoid) at 25±1ºC for 5 days.

Along the freezing treatment, fecal coliforms, moulds and yeasts counting were reduced, being, at the end, two orders of magnitude less. Lactobacillus showed one order less. Staphylococcus aureus, total coliforms and aerobic heterotrophic microorganisms did not show significant reduction during frozen storage.

The present work was partially financed by the AGRO 281 Project (Ministério da Agricultura – Portugal.


Sales-Gomes, M., Lima-Costa, E., Dias, J., Dionísio, L. (2003) Microbiological Characterization of cardoon (Cynara cardunculus L.) Congresso Nacional de Microbiologia, Tomar. (Painel)

Tejada, L.; Sánchez, E.; Gómez, R.; Vioque, M.; Fernandez-Salguero, J. (2002) Effect of freezing and frozen storage o­n chemical and microbiological characteristics in sheep milk cheese. Food Chemistry and toxicology. 67:126-129.

Directiva 92/46/CEE do Conselho das Comunidades Europeias de 16 de Junho de 1992 do Jornal Oficial das Comunidades Europeias.


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