Cycloisomaltooligosaccharides (CI) are cyclic sugars with a structure in which glucose is linked by α-1,6 glycosidic bonds, also known as cyclodextran. They are represented by CI-n (n = number of constituent glucose), and currently CI-7 to CI-20 and CI-4 have been structurally determined. They have been confirmed to be present in natural brown sugar. CI is tasteless and odorless, highly soluble in water, heat resistant, acid resistant, and alkali resistant. It has anti-plaque activity that strongly inhibits the glucosyltransferase (GTF) of cariogenic bacteria, and its inclusion ability, such as solubilization of insoluble substances and stabilization of unstable substances, has been reported. CI is synthesized from dextran or isomaltooligosaccharides with DP ≥4 by the action of cycloisomaltooligosaccharide glucanotransferase (CITase) [1] (Fig. 135.1a). CITase has only been reported in bacteria, and strains with a metabolic system that produces α-1,6 glucose polymers from starch or dextrin and converts them to CI have been discovered [2] (Fig. 135.1b).