Abstract
Organic acids such as fumaric, malic and lactic acids are produced by associative growth of fermentative microorganisms and contribute largely to flavor of fermented foods. In the present study, the effect of cultural conditions on the fumarate metabolism was tested for three strains of Lactobacillus delbrueckii possessing an ability in conversion of fumarate to L-malate, and an attempt was undertaken as preliminary studies for the flavor improvement of fumaric acid forming-mold starter foods in combination with lactic acid bacteria. These strains were incubated in the basal medium (glucose-yeast extract-peptone) containing 1% sodium fumarate at 34°C under stand and shaking cultures and the cell growth and organic acid compositions during the incubation were tested. The effects of medium compositions and inorganic salts on the fumarate metabolism were investigated as well. Fumarate consumptions and the uptake of glucose by three strains were activated by the addition of fumarate to the basal medium. L-Malate production decreased after 24 to 28hours incubation under the stand culture, whereas the production showed a tendency to increase until 48hours incubation under the shaking culture. However, the productive ratio of fumarate to L-malate was nearly same in both stand and shaking cultures. On the other hand, stimlatory effects on the cell growth of three strains were observed in fumarate-added basal medium supplemented with magnesium ions. Their fumarate-hydrolyzing abilities were also stimulated, although the abilities were inhibited in the presence of copper ions.
