Kombucha's versatility makes it usable in the kitchen. While it's an ideal ingredient for sauces or cold dishes, it's also a perfect substitute in main courses, standing in for wine or beer, for example. Lately we've been publishing plenty of recipes that use kombucha for cooking: mussels marinière, Swedish meatballs… And the question you ask us most often is: doesn't heating kombucha destroy the probiotic effect?

The short answer is YES, but that doesn't have to be a bad thing. This is where zombie probiotics come in — that is, dead probiotics. And although the name isn't remotely appealing, we have good news: they're just as beneficial for the body.

We all know that eating probiotics, or foods rich in probiotics, helps keep our microbiota in good shape. In fact, it's one of our favourite tricks! They're easy to work into your day and they're in many more foods than you think. Not just yoghurt, kefir or sauerkraut. Also raw cheese, pickles, olives, apple cider vinegar, kimchi — and our beloved kombucha. All of them unpasteurised, of course.

The potential benefits of dead probiotics and their metabolites began to be recognised, to some extent, in the early 1980s. That was when studies started appearing on a heat-killed strain of Lactobacillus acidophilus derived from the human gut, showing its pronounced effect in treating a range of digestive problems. But it wasn't until roughly a decade ago that enough research had been done for scientists to recognise that the dead cells released by certain bacterial species after heat inactivation secreted bacterial components. These were found to have beneficial immunomodulatory effects and antagonistic action against pathogens. This work went largely unnoticed until, in 2015, Nestlé published its research on the subject in the Journal of Allergy and Clinical Immunology, and NutraIngredients picked it up with a summary titled "Working dead? Nestlé scientists find heat-treated zombie probiotics may boost immunity beyond the grave".

Probiotics: looking for them alive or dead

Over the past five years, research into the benefits of these elusive "unprobiotics" (by definition, probiotics are live) has increased rapidly as scientists try to understand how they differ in performance from their living counterparts.

The bacteria that have been most extensively studied for their human health benefits and are most commonly found in probiotic products are derived from Lactobacillus and Bifidobacteria species, both inherently abundant in the human gastrointestinal tract. Research has shown that these probiotics work by producing antimicrobial compounds and lactic acid , as well as through competition with pathogens for attachment and colonization, nutrients, and other growth factors. Probiotic bacteria have also been shown to have immunomodulatory properties and can regulate inflammation in the gut and systemically.

However, there are disadvantages to using live bacteria . It seems that, perhaps, bacteria that function from "beyond the grave" can overcome most, if not all, of the disadvantages of live bacteria, since they retain - and in some cases improve - some of the good characteristics of living bacteria. their living forms. For example, there is a small risk that the live bacteria in probiotics will be absorbed through the intestinal wall into the bloodstream, especially in newborns and vulnerable subjects, whose intestinal mucosal layer may not function as an adequate barrier. Heat-killed bacteria, however, do not pose this risk. There is also no risk of acquiring or transferring antibiotic-resistant genes, and in newborns there is no risk of interfering with normal colonization of the gut microbiota. Stability , a common concern with live bacteria, is another advantage of non-living bacteria, both in stability and stability through the harsh environment of the gastrointestinal tract.

And although live spore-forming bacteria are much more stable than non-spore-forming bacteria, they can present a cleaning challenge for manufacturers.

After pasteurization, are probiotics really dead?

There are several ways to inactivate probiotic bacteria. The most common is heat treatment: pasteurization in which high temperatures, up to 100° C, are used.

So, yes, the bacteria are really dead; But like our favorite movie zombie, they have abilities beyond the reach of their living forms. Breakdown of cell walls releases cell contents such as DNA and cell wall components such as peptidoglycans and lipoteichoic acids, which are known to exert immunomodulatory effects .

Are zombie probiotics good?

There is still much to learn about how heat-killed bacteria exert their effects on the human body. It is thought that one of the main ways these bacterial fragments may work is through their effects on the mucosal lining of the intestine. Most of our indigenous gut bacteria are found in the lumen of the colon. They are separated from the epithelial layer of the intestine (the barrier) by dual mucosal layers. Although the bacteria themselves remain within the intestinal lumen, they release metabolites that can pass through the mucosa and exert an anti-inflammatory effect on the epithelial layer.

Probiotic bacteria work in a similar way. If the mucosal layer is damaged, both metabolites and probiotic bacteria can reach the epithelial layer for a more direct effect, although this also increases the risk that live bacteria can pass through the layer and into the systemic circulation. Introducing probiotic bacteria products without the live bacteria themselves provides a direct source of these anti-inflammatory and immunomodulatory products, without the potential risk that live bacteria present .

Most of the research on heat-killed probiotic bacteria has focused on digestive health, and they have been shown to be beneficial in a wide variety of digestive challenges, such as bloating , common infant colic , and diarrhea . More recently, research has expanded to include the management of some skin conditions (e.g. atopic dermatitis ) that are caused by gastrointestinal dysbiosis. Additionally, they may have benefits in more diverse areas, such as stress and anxiety management .

Is zombie probiotics the best name for these dead probiotics?

“ Zombie probiotics ” may not be the best nomenclature to refer to these beneficial remnants of a probiotic life, especially if you imagine visions of decaying human flesh when taken as supplements. As a result, current terminology tends to use postbiotic or parabiotic as more acceptable ways to identify them. But regardless of the name, let's hope they have a long "life" within the world of living dietary supplements.

Of course cooking with kombucha is a good idea! Although kombucha loses its probiotic effect when heated, dead or "zombie" probiotics have beneficial effects on health and wellbeing. Studies have shown that dead probiotics can have beneficial immunomodulatory effects and antagonistic action against pathogens, and they don't carry the risks that live probiotics can.

What's more, organic acids are one of kombucha's key components and are responsible for much of its distinctive taste and its health benefits. Common organic acids in kombucha include acetic acid, lactic acid, glucuronic acid and butyric acid. One benefit of the organic acids in kombucha is that they're heat-resistant, meaning they don't break down when the drink is heated. So you can use kombucha as a cooking ingredient without losing its nutritional and flavour properties.

Popular recipes that use kombucha as an ingredient include salad dressings, meat marinades and sauces for stews. Adding kombucha to your recipes brings a unique, complex flavour to your dishes, as well as some of the health benefits associated with this fermented drink.

In short…
If you cook with kombucha, the heat will kill the probiotics but leave the organic acids intact. And recent studies suggest dead probiotics still have benefits. So kombucha is an alternative for dishes traditionally seasoned with wine or vinegar.