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Endospores of thermophilic bacilli are a major concern for producers of dairy powders. In this study, we heat treated 10 different spore suspensions at 110 °C in skim milk and skim milk concentrate (36% dry matter) of the species Geobacillus stearothermophilus (10 min) and Anoxybacillus flavithermus (5 min) in a new shear-heating device. The highest log reduction in skim milk concentrate was 3.5. The death behavior of the spores was strain dependent. Particle formation and Maillard reaction were observed. By increasing the shear-rate up to 1500 s −1 the particle size was reduced for both heating times (D90 reduction: 57.4 and 77.0%, respectively). The particle size was lessened by a reduction of dry matter of 27%, compared to 36%. This work emphasizes, that heat treatment of concentrated dairy products represents a technological option to reduce thermophilic spores in skim milk concentrate and powders produced thereof. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

During the last decades, thermophilic spore counts became a very important quality parameter for manufacturers with regard to powdered dairy products. Low-spore count powders are highly demanded but challenging to produce when high production volume and long process times are intended. In this study a detailed monitoring of microbial levels in three skim milk powder plants was conducted. Anoxybacillus flavithermus was found to be primarily responsible for increased spore levels with increasing spore numbers being detected after 6–8 h already during initial processing steps. Simultaneously, the species composition shifted from a diverse bulk tank milk microbiota where different Bacillus species represented around 90% of the thermophilic bacteria to a dominance of A. flavithermus in the end product. The analysis of A. flavithermus isolates from different powder batches with RAPD PCR revealed recurring patterns in each of the eight German manufacturers sampled over several months. The high relatedness of isolates exhibiting identical RAPD patterns was exemplified by cgMLST based on whole genome sequences. We assume that A. flavithermus strains persisted in production plants and were not eliminated by cleaning. It is concluded that such persisting strains recurrently recontaminated subsequent powder productions. The data highlight that a targeted optimization of cleaning and disinfection procedures is the most promising measure to effectively reduce thermophilic spore counts in German dairy powders. • Thermophilic spores persist in milk powder production plants. • Persisting strains form an in-house microbiota in the powder plant. • Growth of thermophiles occurs early in processing and leads to high spore loads. • Prevalence of obligate thermophilic bacilli in bulk tank raw milk is very low. [ABSTRACT FROM AUTHOR]

Internationally, there are no official guidelines for the quantification of thermophilic spores in dairy products, which leads to variations in applied methodology. In this study, we assess the heat sensitivity of thermophilic spores, vegetative cells grown under laboratory conditions and spores in German dairy powders to determine appropriate heating conditions for accurate quantification of total thermophilic spores. The heat inactivation effect (80–95 °C) is limited for spores of Anoxybacillus flavithermus and Geobacillus stearothermophilus grown under laboratory conditions. However, for spores originating from whey, whey powder and skimmed milk powder (mostly identified as A. flavithermus), a different trend was observed; spore counts continuously reduced when heating time and temperature increased (80–98 °C, 10–30 min). The results indicate that data obtained using laboratory cultures cannot be extrapolated to commercial powders, and in this case, applying temperatures above 80 °C leads to an underestimation of spore counts in dairy powders. [ABSTRACT FROM AUTHOR]