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28.08.2020 - Foods

MicrobiologicalSelf-InspectionsOfIceCreamBacillusCereusAnImportantTestParameter

Especially during the summer months, as temperatures rise, so does the demand for ice cream. Unfortunately, this popular product is also regularly subject to official complaints. Due to errors in personnel and operational hygiene, ice cream can be microbiologically contaminated. In 2019, over 6% of the sampled ice cream samples were criticized.

Microbiological self-checks are an essential part of quality control for food businesses in Germany and the EU. The German Society for Hygiene and Microbiology (DGHM) published guideline and warning values in 2013 for the examination of ice cream for consumer distribution.

Relevant bacteria for ice cream investigations are:

• Aerobic mesophilic bacteria count
• Enterobacteria
• Escherichia coli
• Coagulase positive staphylococci
• Presumptive Bacillus cereus
• Listeria monocytogenes
• Salmonella

Bacillus cereus is not very well known but plays an important role in practice. Elevated values of Bacillus cereus frequently lead to difficulties. Therefore, we would like to introduce you to this bacterium today:

General

Presumptive Bacillus cereus can form heat-resistant forms called spores. These are very heat-stable and can withstand heating processes. Furthermore, these bacteria can sometimes produce heat-stable toxins that are very resistant and can cause poisoning with vomiting and/or diarrhea.

Origin

These bacteria or their spores are widespread in our environment. They are found in the soil, dust, water, animals, and humans. Therefore, practically all raw plant and animal materials can be contaminated with this germ.

Importance

Spores often germinate in food after the cooking process and multiply there if not sufficiently cooled. To avoid high germ counts, it is important to pass through the critical temperature range between 10 °C – 60 °C as quickly as possible.

These bacteria are of particular importance as causative agents of diarrheal diseases. These illnesses are caused by the toxins that can be produced by some Bacillus cereus species. Therefore, these bacteria play a significant role as food poisoners in the gastronomy industry.

Important causes for elevated germ counts

• too low temperatures when keeping warm (usually holding temperatures of > + 60 °C are required)
• too long cooling phase. The critical temperature range between 10 °C and 60 °C must be passed through as quickly as possible (usually max. 3 h)
• insufficient cooling and/or overstock of food (shelf life exceeded)
• microbiologically contaminated raw materials

Growth conditions

• Temperature: growth at 4 - 50 °C, toxin production at 37 - 42 °C
• pH value: growth at 4.3 – 10.5, toxin production up to max. 10.0
• aw value: growth up to min. 0.92 – 0.95
• Salt tolerance: 0.5 – 9%
• Oxygen requirement: facultative anaerobic, preferably aerobic

At what temperatures do these microorganisms die?

Generally, it can be assumed that vegetative bacteria are killed when heated to +72 °C for at least two minutes or in an equally effective process. However, spores of these bacteria are often found in food. These are usually very heat-resistant and can even survive cooking processes.

In our laboratory, we regularly conduct these investigations. We provide you with fast and reliable results.
Our customer advisors are happy to assist you with any inquiries.