Types of Bacillus endospores in milk protein concentrate and milk protein isolate

Document Type


Publication Date



American Dairy Science Association


Journal of Dairy Science




Suppl. 1






endospore, milk protein concentrates, milk protein isolates


Dairy powders and ingredients have an enormous market worldwide. Several studies indicate the presence of aerobic spore formers and bacterial endospores in dried milk powders. The present study investigates the types of Bacillus endospores present in milk protein concentrates (MPC) and milk protein isolates (MPI). Twenty-five samples each of MPC and MPI were obtained from commercial dairy plants and were enumerated for 3 types of endospores after heat treating at 80°C/12min for regular spores (SP), 100°C/30min for high-heat resistant spores (HHRS), and 106°C/30min for specially thermoresistant spores (STS). In all these cases, 11 g of the sample was reconstituted in 99 mL of phosphate buffer saline, and the desired serial dilutions were plated on tryptic soy agar. The plates were incubated under aerobic conditions for 24 h at 37°C for mesophiles, and 55°C for thermophiles. Colonies were differentiated based on J. Dairy Sci. 103 (Suppl. 1) 275 colony morphologies and the distinct isolates were identified using MALDI-TOF. All samples were tested in duplicates and means were compared using ANOVA. In MPC, the samples containing mesophilic spores were 39% SP, 23% HHRS, and 38% STS. Similarly, the samples containing thermophilic spores were 43% SP, 22% HHRS, and 35% STS. In MPI samples, the mesophilic spore pattern showed 39% SP, 29% HHRS, and 32% STS, while the samples with thermophilic spores were 54% SP, 31% HHRS, and 15% STS. Based on the percent distribution, SP was the most prominent heat treatment spore-category. The MALDI-TOF identification revealed Bacillus licheniformis to be the most predominant spore former species in both MPC (51%) and MPI (41%) samples. These findings will help design process interventions for controlling endospores in powders, and decide their utilization based on the types of spore-types encountered.