Improved fermentation processes were developed for the production of mannitol by a heterofermentative lactic acid bacterium (Lactobacillus intermedius NRRL B-3693). A fed-batch fermentation protocol overcame limitations caused by high substrate concentrations. The process was developed using corn steep liquor and glucose as inexpensive industrial nutrient sources, supplemented with a small amount of soy peptone and manganese. The fed-batch process resulted in a concentration of 176 +/- 0.5 g mannitol from 184 +/- 0 g fructose and 92 +/- 0.1 g glucose per L of final fermentation broth in 30 h with a volumetric productivity of 5.9 g/(L h). Further increases in volumetric productivity of mannitol were obtained in a continuous cell-recycle fermentation process that reached more than 40 g/(L h), despite reduced mannitol levels of 78-98 g/L and residual substrate of 10-20 g/L. This is the first report of such a high volumetric productivity of mannitol by a heterofermentative lactic acid bacterium. (c) 2007 Elsevier Ltd. All rights reserved.