PhD Defence by Maryam Maktabdar

Principal supervisor:

• Professor Paw Dalgaard, DTU Food

Co-supervisor:

• Professor Lisbeth Truelstrup Hansen, DTU Food

Examiners:

• Senior Researcher Tina Beck Hansen, DTU Food
• Senior Manager Mariem Ellouze, Ferrero, Italy
• Research Director Frédéric Carlin, INRAE, France

Chairperson at defence:

• Associate Professor Håkan Vigre

Resume
This research focused on Bacillus cereus, a group of bacteria that can cause food poisoning. B. cereus is commonly found in the environment and can sometimes contaminate food. While harmless at low concentrations, high concentration of B. cereus can cause food poisoning, leading to symptoms like nausea, vomiting, and diarrhea.

A key factor that makes B. cereus tricky to control is its ability to form spores (a dormant, resistant form). These spores allow the bacteria to withstand harsh conditions like heat, dryness, and even some cleaning processes. When conditions become favorable again, these spores can "wake up" and the bacteria can start growing and potentially producing toxins.

This study found that nearly half of the dairy products tested were contaminated with B. cereus, especially dairy powders, whey, and cheeses. Models then were developed to predict how these bacteria grow and form spores, under different conditions, such as temperature, acidity, and salt concentration. These models were tested extensively and proved to be accurate in predicting how fast B. cereus grows in various dairy products in different storage conditions. The models can help the dairy industry better predict and control B. cereus growth, ultimately improving food safety.

A copy of the PhD thesis is available for reading at the department.