Optimization of mannitol production by Lactobacillus reuteri CRL1101 using mollasses-based culture medium at controlled-pH fermentations

M. E. ORTIZ; R. R. RAYA; F. MOZZI

San Miguel de Tucumán

Simposio; IV Simposio Internacional de Bacterias Lácticas (SIBAL). Alimentos, Salud y Aplicaciones; 2013

CERELA-CONICET

Mannitol is a natural sugar alcohol found in bacteria, fungi and plants. This polyol is widely applied in the chemical and pharmaceutical industries and it is used as low-calorie sweetener in food production, being applicable in food products for obese and diabetic patients. Biotechnological production of mannitol using lactic acid bacteria (LAB) is being investigated as an alternative approach to the current chemical synthesis at industrial scale. Among LAB, heterofermentative lactobacilli are efficient mannitol producers from fructose using the mannitol 2-dehydrogenase enzyme. To achieve an efficient and competitive mannitol productive process, low-cost culture media and optimized culture conditions are needed. In this work we aimed to improve mannitol production by L. reuteri CRL1101 using a molasses-based medium at constant pH. Controlled-pH fermentations were performed in 2 l fermentor at 37°C with agitation (100 rpm) for 24 h; the assayed pH values were in a range between 4.8 and 6.0. Free-pH fermentations were used as control. Cell growth (log CFU/ml), sugar (sucrose, glucose and fructose) consumption and mannitol production (HPLC) were determined at 0, 4, 8 and 24 h of incubation. Mannitol yield (YMtl), expressed as fructose conversion into mannitol, was calculated in all assays. Microbial growth patterns obtained under controlled-pH were similar to those in free-pH fermentations being the maximum cell growth (log CFU/ml: 9.51±0.21) slightly higher at constant pH (5.4-5.2). All sugars present in the culture medium were almost depleted after 24 h at all assayed pH values. In all cases, fructose consumption and the concomitant mannitol production started after 4 h of incubation. Interestingly, mannitol production was markedly improved (228.2±6.3 mM; YMtl: 105±11%) under constant-pH of 5.0 as compared to free-pH cultures (148.4±6.9 mM, YMtl: 103±14%). Depending on the pH value, fructose was used only as an alternative external electron acceptor for mannitol synthesis (pH 5.0) or as both electron acceptor and substrate fermentation for biomass formation (pH 6.0). The optimization of the culture conditions using a low-cost medium for mannitol production by L. reuteri CRL1101 represents a relevant approach for the biotechnological semi-pilot scale production of this polyol.