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Natural yeast: monumental analysis over 30 years of studies

Research conducted by scientists of Micro4Food Laboratories of University of Bolzano/Annex

A team of researchers from Micro4Food laboratories of University of Bolzano, led by prof. Marco Gobbetti , reviewed the main studies dedicated to mother yeast published in over 50 countries in the last three decades. The resulting article represents the sum of all scientific knowledge on the subject and highlights the sensory, rheological, nutritional, nutraceutical and commercial potential of mother yeast. The mother yeast comes from the mixing of flour and water, and from preparation methods that favor the presence of lactic bacteria and yeasts coming from the environment or from flour. Probably appeared for the first time in Egypt, it has spread to every corner of the planet and in many different cultures: for example, UNESCO has included it the Maltese ftira, bread made with sourdough, in the list of intangible cultural heritage.

The authors of the paper "Thirty years of knowledge on sourdough fermentation: A systematic review", published by Trends in Food Science and Technology, probed the four most important databases into which scientific papers are loaded: Google Scholar, Scopus, PubMed and ScienceDirect . After the purification of duplicates, reviews, degree theses and book chapters, the final number of 1230 studies arrived with the term "Sourdough" as the main descriptor.

The first advantage given by the use of natural yeast concerns the possibility of applying it to a large variety of both sweet and savory baked goods (bread and substitutes). In Europe, it is Italy that leads the ranking of products based on mother yeast (with over 30 traditional varieties) but its use characterizes typical products both from northern Europe (especially based on rye bread), and from Asian countries, African (Balady, Egyptian bread) or Latin American (Central American tortillas). The potential of natural leavening is underlined by the variety of types of flours and food by-products that can be fermented with this technology: flours obtained from 23 species of cereals, 10 from pseudo-cereals, 19 from legumes and 25 from other types of vegetables . This is particularly interesting for the development of gluten-free products.

Many articles have focused on the rheology (texture), sensory attributes and shelf life of sourdough products. Also, from this point of view, natural leavening has shown its superiority compared to leavening based on brewer's yeast: various studies have shown that, for example, the volume, cohesion and persistence of the dough over time were superior. Other attributes such as flavor, aroma, color of the rind are unquestionably better in products from mother yeast, as well as their increased shelf life thanks to the ability to inhibit the production of mushrooms without the addition of preservatives of chemical origin.

From 2015 to 2019, research on mother yeast sought to identify its nutritional and nutraceutical qualities, i.e. curative or preventive of pathologies. The availability of minerals (zinc, calcium, iron, sodium and magnesium) naturally present in cereals, pseudo-cereals and legumes from which the flours have been obtained is maintained to a much higher extent. In the same way, naturally leavened products allow for the fortification of products with additional fibers without compromising their flavor or texture. Furthermore, fermentation with mother yeast and the addition of fibers generally lowers the glycemic index of bread from "high" to "moderate". The same was observed in the case of gluten-free products. Finally, the available scientific literature confirms that natural yeast increases the digestibility of the product and the degradation of so-called anti-nutritional factors present in cereals, pseudocereals and legumes such as raffinose, a trisaccharide contained in legumes that causes swelling and pain in the intestine.

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