D-Psicose

d-Psicose, a rare sugar is an epimer of d-fructose on the C-3 position and occurs in very minute quantity in nature. It is the substitute for sucrose having 70% of the sweetness of sucrose with zero calories. d-Psicose exhibits unique health and physiological benefits in the field of food, pharmaceutical, and agriculture. It is used against obesity, diabetes, hyperglycemia, hyperlipidemia, inflammatory actions, and glucose tolerance in the body. Due to its scary nature, the chemical synthesis of d-psicose is very difficult, expensive, and laborious. Therefore, its production is currently attained by enzymatic bioconversion, generally ketose-3-epimerase plays an important role from d-fructose to d-psicose. Recently, ketose-3-epimerases from different bacterial strains have been experimentally identified and characterized as well as their crystal structures and mechanism have been anticipated from different strains. However, the research on molecular modification is insufficient, which could improve the enzymatic activities and thermostability via directed evolution and mutagenesis of an enzyme. Herein, an outline of recent advances regarding the biological production and characterization of d-psicose, as well as their physiological, pharmaceutical, food, and agricultural uses is mentioned in this chapter. Moreover, the comparison of biochemical characteristics of epimerases has been overviewed.