Georgofili World

Newsletter of the Georgofili Academy

Sourdough ecophysiology to better guide the industrial processing

Sourdough fermentation is one of oldest examples of a traditional biotechnology. Its use has been recently rediscovered for producing baked goods. A number of studies have used innovative techniques to focus on the ecophysiology of the sourdough lactic-acid bacteria. First, the lactic-acid bacteria of eighteen sourdoughs used for the manufacture of some traditional Italian leavened sweet baked goods were studied through culture-dependent methods and pyrosequencing. Although some species were identified in most of the products, a large diversity was highlighted as well as positive correlations found between some technology parameters and cell density and the main metabolites of lactic-acid bacteria (Lattanzi et al. 2013 Intern. J. Food Microbiol. 163:71-79). Bacterial ecology during rye and wheat sourdough preparation was described by a 16S rRNA gene pyrosequencing. The permutation analysis based on biochemical and microbial features, the number of operational taxonomic units, and the diversity indices all together demonstrated the maturity of the sourdoughs during 5 to 7 days of propagation (Ercolini et al. 2013 Appl. Environ. Microbiol. 79:7827-7836). A comparison was made of the microbiotas of the seven mature type-I sourdoughs back-slopped (80 days) at artisanal bakery and laboratory levels using constant technology parameters. The cell density of the lactic-acid bacteria and related biochemical features were not affected by the environment of propagation but the species and, especially, the strain diversity were affected. The number of yeasts markedly decreased from the artisanal bakery to the laboratory propagation, Saccharomyces cerevisiae was no longer detectable in several sourdoughs. The propagation environment had an undoubted influence on the composition of sourdough microbiotas (Minervini et al., 2012 Appl. Environ. Microbiol. 78:5328-5340). A comparison was made of four traditional type-I sourdoughs propagated (28 days) in firm and liquid conditions to mimic the alternative technology options frequently used for producing baked goods. The liquid sourdoughs showed simplified microbial diversity and harbored a low number of strains, which were persistent. The use of liquid fermentation would change the main microbial and biochemical features of traditional baked goods, which have been manufactured under firm conditions for a long time (Di Cagno et al., 2012 Appl. Environ. Microbiol. 80:3161-3172). These studies allowed a better understanding of the sourdough microbial dynamics as affected by environmental and technology parameters to better control the industrial fermentation process and they were used to establish the first worldwide library on sourdough (St. Vith, Belgium), where typical sourdoughs are stored, together with strains, ingredients, recipes and their main historical data.  

Marco Gobbetti, Dipartimento di Scienze del Suolo, della Pianta e degli Alimenti, Università di Bari-