Yogurts: alive or not so much?
Bacterial strains come in different varieties
This is the first and main reason for such discrepancies. Strains of the same bacterial species can indeed have quite different characteristics. They are — a bit like people: have different talents and capabilities. Behind every successful, strong, truly effective strain — a HUGE amount of costly scientific work — isolation, identification, safety studies, the ability to synthesize certain beneficial substances and exert a positive influence on our body. And, in addition — a whole bunch of studies on the ability to survive in simulated gastrointestinal tract conditions (resistance to acidic stomach conditions, the action of enzymes and bile acids) and, of course, storage conditions. And from thousands of studied strains, researchers select, in the best case, a few strains that truly have the necessary characteristics and are stable under production conditions.
The degree of bacterial survival in yogurt depends on the strain itself, the amount of dissolved oxygen in the environment and hydrogen peroxide (don’t be scared, we’re talking about hydrogen peroxide produced by the lactic acid bacteria themselves), on how intensively the environment acidifies and how different strains find a common language while sitting in one jar. To reduce the intensity of oxidation processes and increase survivability, technologists may sometimes add a little ascorbic acid (and this will be clearly indicated on the packaging and... aren’t we not afraid of ascorbic acid?).
The question of how long the strains survive for the maximum possible time is very relevant, because this direction determines the potential shelf life, stability, and, of course, the usefulness of the product.
It should be said that such strains cost quite pricey and not every production can afford them. But such an investment really eases the technological process and opens up a number of possibilities: from a longer shelf life to a wider geographic spread of their product (time spent on transportation).
What is shelf life and what does it depend on?
In simple terms — it is the period during which the manufacturer is legally prepared to guarantee all declared product characteristics under proper storage conditions. The better and more sterile the production conditions, the higher the quality of the raw materials, the more qualified the staff, and the more stable the strains, the easier it is to ensure proper quality over a longer period.
Modern rapid progress, technical innovations and hardy strains allow us to see a really stable picture for nearly two months! But it would also be fair to say that with such a very long storage fats can oxidize and sensory properties of the products may deteriorate, in simple terms — it may stop being as tasty.
Therefore the producer finds his golden mean — an optimal period during which the number of lactic acid bacteria does not fall below 10 million per ml (107), and microbiological purity and organoleptic indicators remain normal. Then he writes his TU (technical specification), which is coordinated with state authorities, and it truly allows declaring the shelf life, for example, one month.
...And just in case our text doesn’t look convincing enough (and critical perception of any information is sacred!), we provide a small overview of scientific publications where they studied the survival of lactic acid bacteria and bifidobacteria in yogurts during proper storage at 4°C.
Let’s go!
The famous probiotic strain Bifidobacterium lactis hn019, which is included in some fermented dairy products on our shelves, consistently maintains its population for seven weeks. The amount of Lactobacillus pentosus KCA1 in yogurt over 35 days decreased from 109^ to the required minimum 107^ (although in some scientific works it is mentioned that living cells of lactic acid bacteria exert probiotic action when there are at least 106). And even on the 63rd day of the study, the number of living cells of this strain was a little more than 104.
In studies L. acidophilus, B. bifidum over 21 days reduced their numbers by two orders of magnitude (from 108^ to 106). And in this study it’s shown that some strains of L. acidophilus remain stable at 107, while other strains of the same species reduced their numbers by 3–4 orders. Lactobacillus casei PRA205 [held at 108] for 28 days in this study. Some strains of lactobacilli and bifidobacteria were present in products at amounts of 107-108^ after 45 days of storage!
It should be noted that all these results were obtained with proper storage of the product — at 4°C.
Overall, as we can see, yogurt shelf life of about a month is really quite feasible if you have strong, surviving strains. And if you want to learn more specifically about your favorite yogurt, you can always try to contact the manufacturer directly with this question. It is highly likely they will even provide the protocols of study of their product at different storage durations.
Therefore bacteria in yogurts are alive and eagerly waiting to join your gut microbiome!
ps: just in case, we remind you of the importance of choosing a product with lower sugar content; we’ve written more about this here [shcho-strashnoho-v-iohurtakh.html].
Enjoy your meal and it’s healthy! :)
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