Scientists identify plant-based lactic acid bacteria for gut-friendly soy yogurt

Researchers have identified three new strains of lactic acid bacteria, isolated from vegetables and fermented foods, which are effective for making soy-based yogurt alternatives to dairy. They also highlight the soy yogurt’s desirable sensory characteristics and enzymatic activities relevant to digestibility for enhanced nutritional value. Ultimately, the new strains might help develop new functional plant-based foods. 

These bacteria are also often found in human and non-human intestines, prompting the scientists to think they might be more suitable than dairy. The researchers point out that consumer interest in naturally occurring antimicrobials in foods for preservation is growing, as they are concerned about the development of microbial resistance to conventional preservatives.

The team comprised experts from the Technical University of Denmark (DTU), Chalmers University of Technology, Sweden, and the University of Cambridge, UK. Although they highlight the promising results when using the new strains for fermentations, they call for further research and regulatory approval from the European Food Safety Authority before they can be commercially used.

“The bacteria did more than simply ferment the soy drink. They were also able to suppress undesirable bacteria, break down unwanted sugars, and reduce phytic acid, which makes it difficult for the body to absorb minerals such as iron, zinc, magnesium, and calcium,” says postdoctoral researcher Belay Tilahun Tadesse of the DTU National Food Institute.

Digestive comfort

The study in the Journal of Food Protection lauds the three plant-isolated Enterococci species — E. faecium BT0194, E. lactis BT0173_2, and E. lactis BT0167 — for being highly suitable for making soy yogurt. 

Tadesse and Solem in the lab at the DTU National Food Institute (Image credit: Lene Hundborg Koss).Soy milk contains sugars, α-galactosides, that are hard for humans to digest, such as raffinose, stachyose, and verbascose, as the human gut lacks the α-galactosidase enzyme. Without this enzyme, gut bacteria ferment these sugars and produce excess gas, causing bloating.

However, the study found that four tested bacterial strains, including the three plant-based ones, had genes for α-galactosidase. 

Some strains actively produced the enzyme, with BT0173_2 and BT0167_2 showing the highest activity in a test.

These strains were noted to metabolize raffinose, making them ideal for fermenting soy milk compared to most commercial starters, such as dairy-like YoFlex, cheese-like Choozit, and vegan-like Jo Vegan. Most starters, with the exception of the vegan option Veggi, do not have this ability.

Antimicrobial properties

Plant-based yogurts are often made using bacterial cultures used in dairy yogurt production, even though plant-based raw materials are significantly different from milk.

The lactic acid bacteria grew effectively, lowering the pH and making the yogurt acidic. But especially the promising candidates acidified the soy milk rapidly without requiring sugar.

Moreover, the bacteria were able to ferment at a relatively high temperature where undesirable microorganisms like pathogens cannot thrive. The researchers point out that this aspect can help extend its shelf life and improve food safety.

The promising Enterococci strains showed a broad antimicrobial effect against pathogens, such as Listeria and Escherichia coli.

“We have shown that the lactic acid bacteria tested are safe. However, further research is needed, for example, to determine how flavor is affected and whether plant raw materials other than soy can be used,” says associate professor Christian Solem of the DTU National Food Institute.

The paper suggests: “It would be relevant to look into behavior in mixed-culture fermentations, to determine performance in other plant substrates besides soymilk, investigating their effect on bioavailability of micronutrients and reduction of antinutritional factors, and determine the effect on organoleptic properties.”