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Improve the Microbial Quality of Milk Powders by Controlling Thermally Resistant Spore Formers and Spores

Anand, Sanjeev; Metzger, Lloyd
South Dakota State University
Start date
End date
1. Analyze raw milk and milk powder samples from different sources for thermoduric spore forming Bacillus species. The isolates that resist pasteurization conditions in their vegetative forms will be identified using cultural and genetic characterization. 2. Combine power ultrasound treatment and hydrodynamic cavitation with pasteurization of milk inoculated with thermally resistant bacilli and their spores to study their resistance to combined treatments. 3. Trace the progression of Bacillus species by inoculating actively growing cells of the most resistant spore formers in skim milk at log 5 cfu/ml and expose to spray drying process using pilot scale milk spray. 4. Study the ability of thermoduric thermophiles to form biofilm under static and dynamic conditions using stainless steel (SS) coupons and SS tubes. 5. Analyze samples of mineral scale from evaporators for the presence of the spores and spore formers, and possible integration in to biofilm matrix. 6. Evaluate the modified clean-in-place (CIP) protocol for its efficacy in reducing biofilms in evaporators. 7. Determine if ultra-sonication increases the efficiency and yield of lactose crystallization when applied in a continuous process prior to crystallization. 8. Determine if application of direct steam injection and flash cooling prior to drying reduces the spore count without having a major impact on the flavor and functionality of skim milk powder (SMP).
More information
Endospore forming bacilli and their spores can resist thermal treatments and transfer into the end products where they cause spoilage and defects. Geobacillus stearotheimophilus (strain A), Anoxybacillus flavithermus (Strain B, C, D), Bacillus licheniformis (Strain F, G) and Bacillus subtilis are the seven most important Bacillis spp. that constitute about 92% of total bacterial counts of milk powders manufactured worldwide. During milk powder manufacture, thermophilic bacteria may grow within regeneration sections of heat exchangers and evaporators where the temperature is ideal (45 -60?C). Spore forming thermophiles can also form biofilms and sporulate within the biofilms in these sections. Previous studies by this researcher revealed that non thermal processes, such as ultrasonication, can reduce the thermal resistance of these spore formers and their spores. In the present study, researchers will track the progression of thermally resistant spore formers and their spores during the manufacture of milk powders (particularly evaporation and spray drying) and attempt to reduce their numbers by combining ultrasonication (US) with pasteurization. They will also conduct studies to determine if thermoduric thermophiles persist beyond regular clean-in-place (CIP) cycles and interact with organic mineral scales and fouling layers within evaporators. Researchers hypothesize that thermodurics can be eliminated (or reduced) in milk powders by integrating better clean-in-place (CIP) protocols with US and pasteurization processes. They also hypothesize that US will improve the efficiency and yield of lactose crystallization and can be applied in a continuous process to concentrate permeate prior to crystallization. The use of direct steam injection and flash cooling prior to drying can be used to produce a low spore count skim milk permeate (SMP) with minimal impact on flavor and functionality.
Funding Source
Dairy Research Inst.
Bacterial Pathogens