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Thermophilic spore‐forming bacteria in milk
powders
Background
• Bacteria involved – Bacillus, Geobacillus, Anoxybacillus – found everywhere, thermophilic ‐ spoilage
• Produce spores under stressful conditions which can withstand extreme conditions (temperature, lack of water, radiation and chemicals)
Background
• Biofilms
Knight et al. 2004
Background
• Not primarily coming from milk• Persistent population within system• Can achieve runs of 16 to 24 hrs before spore counts too high – value loss in millions
• Cleaning reduces but doesn’t eliminate• Not much known on limits of growth in milk
Background
• Spoilage on rehydrated products
• Powder buyers assess quality on spore counts
• So high counts = lower value
• Extending run times would save $$$$
Dairy powder processing plant• Temperature ranges ‐ 45 to 70°C, changes• Water activity decreases through the system
Aims
• Determine rates and limits of growth for 16 Geobacillus stearothermophilus strains –temperature, water activity in model and milk growth system– Use mathematical models tosummarise growth rates at defined conditions
Developing a model system
• Simulated milk broth for optical density measurements
– As close to milk as possible – casein, calcium, lactose
Results
‐0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 10 20 30 40 50 60
Log O
D600
Time (hrs)
W14
55C
52C
‐0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 10 20 30 40 50 60
log OD6
00
time (hrs)
W5D
55C
52C
Milk system
• Milk – cell and spore counts• Determine cell stages over time
Results
0
1
2
3
4
5
6
7
8
0 5 10 15 20 25
W14
log TVC
log Spores
pH
Aims• Replicate processing system at lab scale to determine best conditions for biofilm growth and spore formation to pin point spots in evaporators where they are growing to high numbers
Control• Sporulation and biofilm formation is a complex genetic process and are not mutually exclusive – can they be disrupted?
http://www.scripps.edu
Control
• What triggers sporulation and biofilmformation in the dairy system?
• Can it be disrupted or cells “tricked” into forming other cell types instead of spores?– Modifying processes– Chemicals
Relevance to TIA• Program 4 –managing risks and opportunities
Goal: Identify and extend management options for more reliable and sustainablesystems of food production to maximise their economic value.
• Program 5 – creating valueGoal: Assist agri‐businesses to capture value through optimal use of resources in the production of products demanded and valued by consumers.
Goals• Identify microbiological impact on product value• Microbiological expertise to help achieve low spore count milk powders (high
quality) which receive highest dollar value• Expanding industry (Murray‐Goulburn $200M on new processing plants including
Edith Creek) can adopt/implement control measures across the board
Acknowledgments
• Gardiner Foundation• Dairy Innovation Australia Ltd• Brent Seale ‐ UQ• Mark Tamplin• Tom Ross• Michelle Williams• Putri Tuflikha ‐ PhD