This study[1. A. Homayouni, M.R. Ehsani, A. Azizi, S.H. Razavi and M.S. Yarmand, 2008. Growth and Survival of Some Probiotic Strains in Simulated Ice Cream Conditions. Journal of Applied Sciences, 8: 379-382. DOI: 10.3923/jas.2008.379.382, http://scialert.net/abstract/?doi=jas.2008.379.382] was presumably to see if developing a probiotic ice-cream was going to work in real life – can lactobacilli really survive a normal freezer experience? Turns out, sorta.
Four probiotic strains of bacteria were put into simulated ice-cream conditions and then examined after 1, 2 and 3 months to see how many actually survived. The temperatures ranged from between 4 and -20°C.
Bacteria studied
- Lactobacillus acidophilus
- Lactobacillus casei
- Bifidobacterium bifidum
- Bifidobacterium longum
Results of the lactobacilli freezing study
Lactobacilli strains are highly resistant compared to bifidobacteria strains. Lactobacilli casei reacted differently with different conditions, and won the survival of the fittest competition.
The study details
Lactobacillus and bifidobacterium are the most common type of bacteria used in probiotics, particularly in fermented dairy products like yoghurt. Studies are being undertaken to evaluate the survival of bacteria in certain conditions, like bile, stomach acid, production, and so on, with temperature another research area. It seems important to keep the bacteria alive as long as possible throughout the preparation and ingestion of probiotics.
Survival rates depend on the type of food product – some resistant strains tolerate the variable conditions better than others, but production is important for preserving probiotic count. Freezing is being investigated as one such method.
The study looked at several areas of the bacteria: the growth rates in high sucrose conditions, the effect of oxygen scavenging on survival rates, and the impact of low temperature. All of these factors make a difference, but since we’re just concerned with temperature, we’ll only discuss that.
Low temperatures do significantly affect survival rates of probiotic bacteria. L. casei and Bifidobacterium bifidum were deemed suitable bacteria to use in probiotic ice-cream, with Lactobacillus outperforming Bifidobacteria in the presence of sucrose, oxygen and low temperatures.
Moral of the story? If you are using milk kefir or other probiotics, it’s best not to freeze them, but if you do, some strains will survive better than others.
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