The 4 benefits of fermented foods

When a food is fermented, its properties are altered, affecting the physicochemical structure of the food matrix. The microorganisms present in the fermented food produce molecules, called metabolites, which can in some cases have health benefits, such as the production of vitamin C in sauerkraut. They can also act by enriching the diversity of microorganisms within the microbiota of the eater, an essential element of human health. The following is an overview of the benefits of fermented foods.

Some microorganisms produce compounds called bacteriocins that inhibit the growth of pathogenic bacteria.

The very principle of fermentation is as follows: when microorganisms break down the sugars in food, they release an acid (lactic, acetic, etc.), or alcohol in the case of alcoholic fermentation, which inhibits the growth of other pathogenic microorganisms that may develop in food. In addition, some microorganisms produce compounds called bacteriocins that inhibit the growth of pathogenic bacteria. They can also delay the development of microorganisms that spoil food and thus allow it to be preserved for longer. This is called bioprotection or biopreservation. “But we don’t always know how it works! This is the case for a strain of Afnia alvei that inhibits Echerichia coli, but we still haven’t managed to determine its mechanism of action”, explains Cécile Callon, a research engineer at the joint research unit on Cheese in Aurillac. Selected bacteria can also be added to certain foods to improve their preservation, without transforming them into another product. Or, during wine-making, we can select strains that produce less sulphite. All of this has the same objective: to do without synthetic additives or to limit the production of undesirable molecules.

The activity of the microorganisms in fermented foods can, in some cases, reduce their toxicity. One example is cyanogenic compounds, which are the source of cyanide. Present in cassava but degraded through a fermentation process, they are simply rendered harmless and edible. This is also true for the modification of certain compounds that were originally allergenic and become “inactive”.

Woody notes, red fruit notes, exotic fruit aromas… These descriptions of wines are not there ONLY to show off in company! These aromas are real, exist in the thousands, and we have yeast to thank for them. But how can this great diversity of aromas be explained? The diversity of the grape of course... but it doesn't end there.

“The production of aromas depends on the strain of yeast involved. Different strains produce different aromas with very different profiles”, explains Carole Camarasa, research director at the Sciences for Oenology (SPO) unit. Could there be a recipe for choosing the grape and the yeast to obtain the desired aromas? If only it were that simple. Fully 90% of wines are obtained by fermentation with the yeast Saccharomyces cerevisiae, but in the harvested grapes there are other microorganisms that intervene at the beginning of the process and whose growth is inhibited by the alcohol formed. Only Saccharomyces cerevisiae survives in the presence of ethanol and can thus complete the fermentation process. “This is why in the wine industry, the addition of this yeast is almost systematic to ensure complete fermentation, but its systematic use hinders the development of other yeasts that can contribute to the aromatic profile of wines”, explains Carole. The challenge for research is to test the introduction of other yeast species at the beginning of the process and to encourage their development. Torulaspora delbrueckii and Starmaerella bacillaris are good candidates. If exotic fruit or passion fruit aromas are desired, Metschnikowia pulcherrima yeast is the way to go, with its beta lyase enzymes that release the thiols responsible for these highly sought-after aromas in winemaking.

Another possibility is to look at the genetic profiles and make the link between genes and the production of a particular aroma. “By getting the right mix, we can succeed in obtaining the right genes in the yeast according to the desired aromatic profile.” In recent years, the SPO unit has identified several alleles (variants of a gene) that influence the production of metabolites, in particular esters, which contribute to the aroma of wines. The production of negative aromas can also be limited. The SPO unit has been working on the hydrogen sulphide responsible for the rotten egg smell. The scientists identified two genes responsible for this molecule. These results are used by yeast producers to select strains that lack these genes. But genetics is not everything; several parameters come into play in the formation of flavours. “We have identified three key factors: the amount of available nitrogen, oxygenation and the amount of lipids, fatty acids being precursors of aromatic compounds. Temperature also influences the process as well as the nutrition of the yeast during fermentation.” This will lead to many more years of research for the greater pleasure of our taste buds... and our noses!