CONICET | Buscador de Institutos y Recursos Humanos

Mannitol is an interesting polyol with several industrial applications mainly employed as low-calorie sweetener in the food industry. Mannitol production by lactic acid bacteria represents an interesting alternative to its current chemical synthesis, which is obtained at high temperatures and pressures and after expensive purification. The genus Fructobacillus is a recently reclassified group of lactic acid bacteria that requires fructose as an alternative electron acceptor for growth and thereby reducing fructose to mannitol. High fructose corn syrup (HFCS) is the main source of fructose in the food industry, and is widely used in a variety of foods and drinks. Nevertheless, fructose syrup consumption is related to obesity, and its replacement for another sweetener is of great interest. We aimed to evaluate mannitol production as well as mannitol dehydrogenase (MDH) activity by Fructobacillus durionis H1-167 and Fructobacillus tropaeoli FYP-H3-450 using a culture medium (FYP without sugars) supplemented with HFCS (provided by Arcor Tucumán) or with a mixture of glucose and fructose (1:2) at 9 % (w/v) final concentration. Strains were inoculated at initial OD600= 0,05 and incubated in both media at 30 °C for 24 h. Samples were taken at different time points (4, 8 and 24 h) for cell growth determinations and MDH activity, whereas supernatants were collected at 24 h for mannitol quantification by HPLC. Microbial growth parameters (Δlog UFC/ml, μmax, and ΔpH) were similar for both strains in the assayed media. High mannitol production (32,10 and 30,43 g/L) by the F. durionis and F. tropaeoli strains, respectively, was detected in the syrup-supplemented medium while mannitol values comprised between 28,95 and 34,91 g/L were obtained using the fructose and glucose mixture. The highest specific MDH activity value (3,88 ± 0,42 ? 5,91 ± 1,58 U/mg prot.) was detected in cell extracts of F. tropaeoli FYP-H3-450 while values of 1,51 ± 0,15 ? 3,20 ± 0,87 U/mg prot. were found in F. durionis H1-167 using the syrup-supplemented medium; in both cases, the highest activity values were observed at 4 h of fermentation. These studies show that the fruit origin strains F. durionis H1-167 and F. tropaeoli FYP-H3-450 are promising candidates for mannitol production and more interestingly, HFCS represents an interesting carbon substrate to be used to produce mannitol by lactic acid bacteria.