Evaluation of the probiotic properties of lactic acid bacteria isolated from fermented plant-based beverages

In the quiet corners of food science, researchers often look to the past to find the future. For centuries, people have relied on fermentation to preserve food and create new flavors, a process driven by tiny, invisible workers known as lactic acid bacteria. These microorganisms are the engine behind yogurt, sauerkraut, and sourdough, transforming simple ingredients into complex, stable products. Beyond just making food taste good, some of these bacteria are considered "probiotics," meaning they can survive the journey through the human digestive system and offer health benefits by helping to balance the gut's natural community of microbes. While scientists have long studied these bacteria in dairy products like milk and cheese, there is a growing curiosity about whether they can be found thriving in plant-based drinks. These plant ferments, made from vegetables, grains, and fruits, might harbor unique strains of bacteria that are naturally adapted to harsh environments, potentially offering new tools for creating healthier, functional foods.

A team of researchers in Ukraine set out to explore this potential by turning their attention to three traditional fermented drinks: beet kvass, oat kvass, and a complex "monastic" kvass made from rye, malt, and fruits. Their goal was not just to find bacteria, but to see if the specific strains living in these drinks could survive the tough conditions of the human body and fight off harmful germs. They began by collecting samples of these beverages and growing the bacteria in a laboratory setting. From the beet kvass, they isolated thirteen distinct bacterial colonies; the oat kvass yielded fifteen; and the monastic kvass provided eight. In total, they gathered thirty-six unique bacterial isolates to study. Under a microscope, these bacteria appeared as short, rod-shaped cells, some standing alone and others linked in short chains, a shape typical of the lactic acid family.

To understand who these bacteria were, the researchers tested how they behaved under different conditions. They checked if the bacteria could grow in salty water, at high temperatures, or in acidic environments. They also watched to see if the bacteria could turn sugars into gas or break down specific proteins. Using these behavioral clues, they identified the strains. The bacteria from the beet kvass, which they named strain BK, belonged to a group known as Lactiplantibacillus plantarum. The bacteria from the oat and monastic kvasses, strains OK and MK, were identified as Limosilactobacillus fermentum. This distinction was important because different types of bacteria have different strengths. For instance, the beet-derived strain was unable to grow at very high temperatures and did not produce gas from sugar, while the strains from the grain-based drinks could do both.

The next step was to see if these bacteria could survive the journey through a human stomach and intestines, which is the first test for any potential probiotic. The researchers simulated the harsh environment of the stomach by exposing the bacteria to a highly acidic liquid with a pH of 2.0, similar to strong gastric juice. They found that all the bacteria struggled, but the strain from the beet kvass was the toughest survivor. After three hours in this acidic bath, it still had a healthy population of living cells, whereas the strains from the oat and monastic kvasses saw their numbers drop significantly. The researchers then tested their ability to survive in the presence of bile salts, a digestive fluid that breaks down fats and can be toxic to many bacteria. Again, the beet-derived strain showed the highest resilience, though all three types managed to stay alive. They also tested how the bacteria handled ethanol, the alcohol found in fermented drinks. While high concentrations of alcohol slowed down the growth of all the bacteria, the beet strain held up better than the others, suggesting it is well-adapted to the environment of fermented beverages.

Beyond survival, the researchers wanted to know if these bacteria could actively protect the body by fighting off harmful invaders. They placed the beneficial bacteria next to several known pathogens, including Staphylococcus aureus, a common cause of skin and wound infections, and Pseudomonas aeruginosa, a bacterium often found in hospital settings. The results showed that the bacteria were indeed capable of defense. The strain from the beet kvass was particularly effective, creating a clear zone around itself where the harmful Staphylococcus could not grow, with a diameter of just over ten millimeters. The other strains also showed some ability to inhibit harmful bacteria, though their effects were less pronounced. Interestingly, none of the bacteria showed any ability to break down proteins or starches, nor did they possess the ability to break down bile salts, a trait sometimes used to lower cholesterol. This lack of certain enzymatic activities suggests they are specialized for other roles.

Finally, the team checked the safety of these bacteria by testing their reaction to common antibiotics. A safe probiotic should not carry resistance to antibiotics that doctors use to treat serious infections, as this could potentially pass that resistance to harmful bacteria in the gut. The study found that the bacteria were naturally resistant to a few specific types of antibiotics, such as penicillin and vancomycin, which is a normal characteristic for this family of bacteria due to their cell structure. However, they remained sensitive to most other antibiotics, including those used to treat a wide range of infections. This profile suggests they are safe for use in food. The researchers also observed how the bacteria behaved when left to sit in a liquid; they clumped together, a process called autoaggregation. This ability to stick to themselves is often a sign that they can also stick to the walls of the human intestine, a key step in establishing a healthy presence in the gut. The strain from the monastic kvass showed the strongest tendency to clump together.

The study concludes that these traditional plant-based drinks are a rich source of hardy, beneficial bacteria. While the strain from the beet kvass emerged as the most robust survivor against acid and alcohol, all the strains showed promise for future use in functional foods. They can survive the digestive tract, fight off harmful germs, and stick together effectively. The researchers suggest that these naturally occurring bacteria, adapted over time to their specific plant environments, could be valuable tools for developing new foods that support human health, bridging the gap between ancient fermentation traditions and modern nutritional science.