Process for the successive production of calcium galactonate crystals by Gluconobacter oxydans

Galactonic acid and its salts can be potentially used in foodstuffs and as specialty chemicals. So far, the researches on microbial conversion of galactose to galactonate are still scarce. In this study, we initially used Gluconobacter oxydans strain NL 71 to convert galactose to galactonic acid via aerobic fermentation by fed-batch and product separation process in shaken flasks, finally 390 g/L galactonic acid could be obtained after 96 h fermentation. To harvest calcium galactonate product, an aeration-agitation bioreactor with product drain port was applied. The lower solubility of calcium galactonate aided its crystallization during fermentation and after 96 h fermentation, approximately 720 g calcium galactonate crystals were produced from 1 L broth. The results showed that successive production of calcium galactonate by a combination of fed-batch and natural crystallization in the process of fermentation was feasible.