Production of mannitol under different culture conditions and mannitol dehydrogenase activity in Lactobacilus coryniformis subsp. coryniformis CRL 1001

MARÍA JOSÉ FORNAGUERA; CECILIA RODRÍGUEZ; GINO VRANCKEN; TOM RIMAUX; GRACIELA FONT DE VALDEZ; RAÚL RAYA; LUC DE VUYST; FERNANDA MOZZI

San Miguel de Tucumán, Argentina

Simposio; III Simposio Internacional de Bacterias Lácticas. Segundo Encuentro Red BAL Argentina.; 2009

Centro de Referencia para Lactobacilos

Mannitol is a sugar alcohol that is produced by certain bacteria, fungi, yeasts, and plants. This polyol has several applications in the food, pharmaceutical, chemical, and medical industries; however, the main application of this low-calorie sugar is as a food additive because of its sweetening power and it is also applicable in diabetic food products. At present, it is industrially produced by catalytic hydrogenation of fructose/glucose mixtures yielding mannitol in addition to sorbitol. In recent years, the production of mannitol by fermentation has gained much attention, especially involving food-grade microorganisms such as lactic acid bacteria. The purpose of this work was to evaluate mannitol production by the strain Lactobacillus coryniformis subsp. coryniformis CRL1001 under different culture conditions (pH-free and pH-controlled batch fermentations) and to correlate mannitol dehydrogenase activity (MDH) with optimum mannitol production. Bacterial cells were grown in modified MRS medium, containing 7.5% (w/v) of sugar cane molasses, at free or constant pH (6.0, 5.0, and 4.0) and 37°C for 24 h. Cell viability, sugar consumption, and organic acid and mannitol production were determined throughout the fermentations. Maximum mannitol production (40.5 g/l; Yp/s of 91.6%) was found with pH-free fermentations after 24 h, while mannitol production was not improved at the constant pH values assayed (33.1 and 28.9 g/l at pH 6.0 and 5.0, respectively). No cell growth was observed at pH 4.0 Therefore, MDH activity was measured during pH-free fermentations at different time points up to 48 h into fermentation; a positive correlation between MDH activity and mannitol production was observed, the highest specific activity (1.19 U/mg protein) being obtained after 48 h. The mannitol production values obtained here evidence that strain L. coryniformis subsp. coryniformis CRL1001 is an excellent candidate, as a starter or adjunct culture, for the microbial synthesis of mannitol to be produced as additive or for in situ production in mannitol-enriched foods.