Utilization of electron acceptors by lactobacilli isolated from sourdough

Abstract

The metabolism of maltose and the use of electron acceptors has been investigated in strains of lactobacilli which are known to be stable elements in sourdoughs, which, traditionally, have been used for a long time. The metabolic features ofLactobacillus sanfrancisco have been described by us in a previous communication. Similar principles have been detected for the competitiveness ofL. pontis, L. reuteri, L. fermentum andL. amylovorus, as well as species-specific characteristics. Based on these findings the metabolic key reactions have been identified and the use of electron acceptors present in sourdough are presented in a schematic overview. In contrast toL. sanfrancisco, these species can not use oxygen as an electron acceptor, and the length of their lag phase was not affected by agitation. Malate and fumarate were reduced to succinate, and fructose was used, depending on the species, as an electron acceptor, carbon source or both. All heterofermentative sourdough lactobacilli efficiently split maltose using maltose phosphorylase. Glucose was excreted, which induced glucose repression in competing indigenous micro-organisms, without affecting the maltose metabolism of sourdough lactobacilli. Lactobacilli generate additional adenosine 5′-triphosphate (ATP) from acetyl phosphate in the presence of electron acceptors. These special features are suggested to represent a general principle which accounts for the prevalence of specific heterofermentative lactobacilli which are propagated over long periods present in sourdough fermentations.