Microbial Ecology of Cereal Fermentations

Rudi F. Vogel

Lehrstuhl für Technische Mikrobiologie, Technische Universität München, 8535 Freising-Weihenstephan, Germany

Article history:
Received: February 14,1997 
Accepted: March 21, 1997

Key words:
sourdough, lactobacilli, yeasts, ecology, metabolism

Summary:
Fermented cereal preparations are used to initiate and perform the essential acidification of rye flour containing doughs and also have a tradition in wheat doughs and various cereal batters. Starters containing living bacteria and also dried preparations are produced non-aseptically; their hygienical safety and high quality must be ensured by employing well defined, traditional process conditions which control the microbial ecology. The main flora of a traditional sourdough preparation consists of strains of Lactobacillus sanfrancisco, and L. pontis. Whereas these organisms exhibit a specialized and effective maltose utilization by using maltose Phosphorylase, typical sourdough yeasts as Candida milleri are maltose negative. The sourdough lactobacilli furthermore can excrete glucose and use electron acceptors as the fructose present in the flour to gain additional energy. These special metabolic features and internal parameters as the redox potential affect the composition of the metabolites formed and thus the composition of the microflora. Other effects on the microbial ecology result from external parameters. The increased temperature often used with cereal batters results in changes in the microflora. Such batters are used for the production of sour mashes for beer brewing or dried sourdough preparations. Additional lactobacilli are found which may even dominate including L. amylovorus, L. reuteri, L. johnsonii and L. acidophilus. These strains are furthermore adapted to the high acid content of such habitats. The knowledge of the intrinsic microbial capabilities helps set up formula and technology in cereal fermentations and control microbial ecology, the metabolites and thus the quality of the product.