Thermophilic spore formers: Impact on dairy powder production, contamination pathways and potential of reduction

The microbiological quality of powdered milk products is mostly dependent from the aerobic thermophilic spore count. Milk powder producers worldwide face the challenge to produce powdered milk products with a low spore count. Therefore, the aim of this thesis was to study survival strategies and potential contamination pathways of thermophilic spore formers during single steps of powder production.

To reach those aims, the thermal resistance of thermophilic spore formers was determined. It was demonstrated, that some strains can survive a common high-temperature-short-time pasteurization in their vegetative form. To lower the risk of downstream contamination, heat treatment of milk concentrates would be of advantage. It was proven that spores can be reduced in concentrated milk products in the range of 3-log units.

In the second part the resistance of spores against cleaning solutions under laboratory conditions was examined. Moreover, the potential to protect spores during cleaning in a thermally induced fouling layer was researched. It was confirmed, that insufficient cleaning marks a problem. The spores can survive and transmit in the next production run.