Mannitol production by fruit-origin Fructobacillus strains using a fructose-rich syrup-based medium

Abstract

Mannitol is a low-calorie sweetener used in the food and pharmaceutical industries. Fructobacillus species reduce fructose to mannitol thanks to their fructophilic metabolism. In this work, we aimed to study mannitol production by fruit-origin F. tropaeoli CRL2034 and Fructobacillus sp. CRL2054, using a minimized culture medium (FYP-based) containing fructose-rich syrup as carbon source under optimized culture conditions. Fermentations with a 2-L bioreactor were performed at pH 5.0 and 30 °C under stirring conditions (130 or 200 rpm for CRL2054 or CRL2034, respectively) for 24 h. Two different total saccharide contents (10 and 20%, m/v) were assessed for each strain. Mannitol yield (mannitol production/consumed fructose) was close to 100 % for both strains using a sugar concentration of 10 %; however, higher mannitol concentrations were achieved when 20 % sugar was used (77-79 g/L compared to 47-51 g/L with 10 % carbohydrates). Mannitol crystals were isolated from 24-h fermentation culture supernatants using 20 % sugar. For both producer strains, the physicochemical properties of the mannitol crystals were highly similar to those of high purity commercial mannitol. These results showed that fermentations of fructose-rich syrup-based medium by selected Fructobacillus strains at constant pH are an interesting alternative for mannitol production.