Optimization of mannitol production by Fructobacillus tropaeoli CRL 2034 applying statistical central composite experimental designing

BRU, E.; MOZZI, F.; ALLER, K.; HEBERT, E.M.; RUIZ RODRIGUEZ, L.; DE VUYST, L.

San Miguel de Tucuman

Simposio; SIBAL 2016. V International Symposium on Lactic Acid Bacteria. Benefitting from Lactic Acid Bacteria. Progress in Health and Food.; 2016

Mannitol is a natural polyol mainly found in plants, but is also produced by yeast, fungi, and certain bacteria. This sugar alcohol is widely used in the chemical, pharmaceutical, medical, and food industries due to its versatile properties. The microbial production of mannitol has become an attractive challenge from a biotechnological standpoint as an alternative to the high-cost chemical hydrogenation method currently used. Among lactic acid bacteria (LAB), heterofermentative strains are excellent mannitol producers. These LAB convert fructose into mannitol with high yields from a 1:2 glucose:fructose mixture, using the mannitol 2-dehydrogenase enzyme. To achieve an efficient mannitol production process using a specific LAB strain, optimized production conditions are needed. In this work, we aimed to improve mannitol production and yield by Fructobacillus tropaeoli CRL 2034 using the Central Composite Design (CCD) response surface method as experimental optimization strategy. The effect of total sugar content [glucose + fructose (1:2)] in the medium (75, 100, 150, 200 and 225 g/L) and stirring (50, 100, 200, 300 and 350 rpm) on mannitol production and yield were evaluated. The levels of these 2 independent variables were defined according to a 22 full-factorial CCD with 4 axial points (a = 1.5) and 4 replications of the center point leading to 12 randomexperimental runs. All fermentations were carried out at 30 °C and pH 5.0, using a slightly modified FYP medium (adjusted for mannitol production by F. tropaeoli CRL 2034). Mannitol production was expressed as g of mannitol produced/L of culture after 24 h of fermentation quantified by HPLC, whereas mannitol yield was expressed as (g of mannitol produced/g of fructose consumed) x 100. The Minitab-15 statistical package was used for both experimental design and data analysis. Values of independent variables and their interactions displayed different levels of significance. The multiple response prediction analysis established 165 g/L of total sugar content and 200 rpm of stirring as optimal conditions to reach 85.03 g/L [95% CI (78.68, 91.39)] of mannitol and a yield value of 82.02 % [95 % CI (71.98, 92.06)]. To confirm the adequacy of the model, one verification experiment was conducted at the predicted optimum levels. The results obtained were 81.91 g /L of mannitol with 77.47 % yield, in outstanding agreement with the expected values. To conclude, F. tropaeoli CRL 2034 produced high amounts of mannitol from fructose, being an excellent candidate for this polyol production as food ingredient.