Comparison of d-gluconic acid production in selected strains of acetic acid bacteria

The oxidative metabolism of acetic acid bacteria (AAB) can be exploited for the production of several compounds, including d-gluconic acid. The production of d-gluconic acid in fermented beverages could be useful for the development of new products without glucose. In the present study, we analyzed nineteen strains belonging to eight different species of AAB to select those that could produce d-gluconic acid from d-glucose without consuming d-fructose. We tested their performance in three different media and analyzed the changes in the levels of d-glucose, d-fructose, d-gluconic acid and the derived gluconates. d-Glucose and d-fructose consumption and d-gluconic acid production were heavily dependent on the strain and the media. The most suitable strains for our purpose were Gluconobacter japonicus CECT 8443 and Gluconobacter oxydans Po5. The strawberry isolate Acetobacter malorum (CECT 7749) also produced d-gluconic acid; however, it further oxidized d-gluconic acid to keto-d-gluconates.