Lactobacillus reuteri CRL 1101 highly produces mannitol from sugarcane molasses as carbon source.

Mannitol is a natural polyol extensively used in the food industry as low-calorie sugar being applicable for diabetic food products. We aimed to evaluate mannitol production by Lactobacillus reuteri CRL 1101 using sugarcane molasses as low-cost energy source. Mannitol formation was studied in free-pH batch cultures using 3-10% (w/v) molasses concentrations at 37 °C and 30 °C under static and agitated conditions during 48 h. L. reuteri CRL 1101 grew well in all assayed media and heterofermentatively converted glucose into lactic and acetic acids and ethanol. Fructose was used as an alternative electron acceptor and reduced it to mannitol in all media assayed. Maximum mannitol concentrations of 177.7 ± 26.6 and 184.5 ± 22.5 mM were found using 7.5% and 10% molasses, respectively, at 37 °C after 24-h incubation. Increasing the molasses concentration from 7.5% up to 10% (w/v) and the fermentation period up to 48 h did not significantly improve mannitol production. In agitated cultures, high mannitol values (144.8 ± 39.7 mM) were attained at 8 h of fermentation as compared to static ones (5.6 ± 2.9 mM), the highest mannitol concentration value (211.3 ± 15.5 mM) being found after 24 h. Mannitol 2-dehydrogenase (MDH) activity was measured during growth in all fermentations assayed; the highest MDH values were obtained during the log growth phase, and no correlation between MDH activities and mannitol production was observed in the fermentations performed. L. reuteri CRL 1101 successfully produced mannitol from sugarcane molasses being a promising candidate for microbial mannitol synthesis using low-cost substrate.

Mannitol production by heterofermentative Lactobacillus reuteri CRL 1101 and Lactobacillus fermentum CRL 573 in free and controlled pH batch fermentations.

Certain lactic acid bacteria, especially heterofermentative strains, are capable to produce mannitol under adequate culture conditions. In this study, mannitol production by Lactobacillus reuteri CRL 1101 and Lactobacillus fermentum CRL 573 in modified MRS medium containing a mixture of fructose and glucose in a 6.5:1.0 ratio was investigated during batch fermentations with free pH and constant pH 6.0 and 5.0. Mannitol production and yields were higher under constant pH conditions compared with fermentations with free pH, the increase being more pronounced in the case of the L. fermentum strain. Maximum mannitol production and yields from fructose for L. reuteri CRL 1101 (122 mM and 75.7 mol%, respectively) and L. fermentum CRL 573 (312 mM and 93.5 mol%, respectively) were found at pH 5.0. Interestingly, depending on the pH conditions, fructose was used only as an alternative external electron acceptor or as both electron acceptor and energy source in the case of the L. reuteri strain. In contrast, L. fermentum CRL 573 used fructose both as electron acceptor and carbon source simultaneously, independently of the pH value, which strongly affected mannitol production by this strain. Studies on the metabolism of these relevant mannitol-producing lactobacilli provide important knowledge to either produce mannitol to be used as food additive or to produce it in situ during fermented food production.