Rare sugar bioproduction: advantages as sweeteners, enzymatic innovation, and fermentative frontiers

The demand for alternative sweeteners remains high in an increasingly health-conscious society. Of the various sugar substitutes that have emerged, rare sugars may represent a promising ‘next generation’ option. Here, we discuss the advantages of rare sugars over other alternative sweeteners as well as current advancements in their production. Unique enzymatic pathways and wide substrate ranges make D-allulose and D-tagatose the most intensely researched rare sugars. For D-allulose, production via a novel phosphorylation–dephosphorylation pathway is particularly promising, while we currently favor the oxidoreductive pathway for D-tagatose production. In addition, microbial fermentation-based rare sugar production has great potential in unlocking cost-effective and scalable utilization of industrially relevant feedstocks.