Recent Advances in Rare Sugars and Potential Applications

摘要

Carbohydrates are not only an important source of energy but also mediate a variety of physiological processes in human health and disease. However, increasing the consumption of sugars (such as glucose, fructose, sucrose) added to foods and drinks in the modern diet has been viewed as a major contributor to obesity and health problems. In addition, low caloric alternatives to the present dominant sweeteners such as Aspartame and HFCS have also been questioned about the effects on human health. Therefore, in recent years, rare sugars which taste similar to sucrose but have almost zero-calories and high bioactivities such as scavenging free radical, anticancer, and neuroprotective function have attracted great attention for their applications in many areas ranging from health foods to pharmaceutical and nutrition industry. Unfortunately, rare sugars rarely exist in nature which restrict their utilizations and chemical synthesis does not satisfy the incresing demand. Nowadays, microbial and enzymatic transformation have become a very powerful tool for the synthesis of rare sugars. 'Izumoring tree' developed by Prof. Kan Izumori from Kagawa University illustrates the strategy to design the production processes of all rare sugars (e.g., D-psicose, D-allose, D-tagatose) from readily available materials such as glucose or fructose. This method is more controllable and scalable. Until now, two rare sugars, D-tagatose and D-psicose, have been approved by FDA as food additives in 2003 and 2014, respectively. Moreover, various novel physiological functions of rare sugars have also been discovered, including reduction of body fat and potent inhibitory effect on the production of reactive oxygen species, and thus, may be used for medical purposes. Combined with new fermentation systems and robust biocatalysts for industrial-scale applications, rare sugars are potential game-changers to be the next-generation sweeteners.