Hygienic quality of milk and cheese from local producers in Norway

Hygienic quality of milk and cheese from local producers in Norway Lisbeth Mehli, Anita N. Jakobsen, Hanne Karlsen Production of food in close proximity to farm animals and often also wild animals as birds and rodents, represents a challenge to hygienic practice and on-farm logistics. Cheese from unpasteurised milk and soft cheeses with high aw and pH are especially demanding in this respect. Elevated coliform counts in milk and dairy products suggest unsanitary conditions during processing. The presence of E.coli and Staphylococcus aureus may indicate poor raw milk quality, inadequate pasteurisation, post-pasteurisation contamination, poor hygiene conditions during processing, maturing or packaging. Raw milk, pasteurised milk, whey and cheese were analysed from three cheese makings at 5 different farms, over a period of 2 winter months (2009). Sampling was performed by the participants themselves. They were given written sampling instructions and supplied with test-tubes, refrigerant packs and styrofoam boxes for the return of samples. The samples arrived within 30 hours after sampling and the temperature on arrival was 0-6 °C, all samples (milk, whey and cheese) included. Coliforms were analysed using the traditional NMKL 44-method. E.coli was analysed using the NMKL125-method. (NMKL: Nordic Committee On Food Analysis). S. aureus was analysed using NMKL 66. Colonies from plates with possible S. aureus were sampled, propagated to pure cultures and subsequently frozen at -80°C for later verification. S. aureus pure cultures were later typed using Pulsed field Gel Electrophoresis (PFGE) with Sma1 as the digesting enzyme and the resulting gels were analysed with Bionumerics software E.coli and coliforms were not detected in the majority of the milk and cheese samples (Table 1). The remaining samples were positive of either E. coli or coliforms or both, but well within the compliance limits of Norwegian legislation. E. coli was detected in a few samples of raw milk for pasteurised production, but not in pasteurised milk, whey or cheese. Coagulase-positive staphylococci were detected in a couple of raw milk samples and in cheese, but well within the compliance limits of 103-104 bacteria pr ml. The level of S. aureus reaches a peak 1-3 days after production and then declines significantly during maturing. No sample reached the critical toxin production level of about 106 bacteria pr. ml. When analysing the S. aureus pure cultures, the results indicated that there were strains of both animal and human origin present in the samples. Both inadequate pasteurisation and a possible contamination caused by manual handling of the cheese were detected at five of the participating farms. Keywords: cheese, farm producers, pathogens, PFGE.