Towards low-spore milk powders: A review on microbiological challenges of dairy powder production with focus on aerobic mesophilic and thermophilic spores

Powdered milk products, such as skim milk powder or whey protein powder, represent a large fraction of the dairy sector, especially with respect to export. In the past years, the contamination with aerobic endospore-forming bacteria has become one of the main factors to evaluate microbial powder quality. Besides mesophilic spore formers, thermophilic and thermoresistant species have been isolated all over the world. During production of powdered commodities, milk or intermediate products go through several process steps. This review highlights and discusses individual production steps and their effect on the microbiota and the spore count. The plant cleaning and its influence on spore resistance are discussed in detail, since this is the most important step in controlling recontamination and persistence. Finally, future technologies to reduce spore counts during powder production are presented. The contribution on ‘non-thermal’ and novel technologies towards low-spore milk powders are discussed critically.