Single-Step Production of Mannitol From Yacon Fructo-Oligosaccharides Using Fructophilic Lactic Acid Bacteria

Mannitol is a naturally occurring sugar alcohol with several applications in the food and pharmaceutical industries, with special interest as a low-calorie sweetener. While mannitol can be synthesized chemically, synthesis by bacterial fermentation is an attractive means of production due to its low cost, mild (near-ambient) conditions for synthesis and high yield. Bacterial production also allows the possibility of using low-cost, second-generation feedstocks to produce mannitol in a sustainable manner. In this work, we describe the feasibility of producing mannitol from yacon (Smallanthus sonchifolius) tuber using Leuconostoc mesenteroides and Fructobacillus fructophilus previously isolated from floral sources. The tuber contains over 50% fructooligosaccharides (FOS) which was found to be bioavailable for mannitol production without prior hydrolysis or saccharifying pretreatments. Initial screening of several fructose-tolerant lactic acid bacteria (LAB) led to the selection of the most robust mannitol-producing strains for optimizing culture conditions and scale-up. We ultimately demonstrated the successful production of up to 7 g/L mannitol using L. mesenteroides with 2% yacon root powder in 200 mL bioreactors, achieving a yield greater than 0.6 g mannitol/g FOS with no significant decrease in titers as the scale of culture is increased. Our study demonstrates that yacon powder is a suitable and cheap substrate for the sustainable and economical production of an important sugar alcohol by biotransformation. Finally, we discuss future approaches to increase the scale and purity of production.