an insoluble glucan forming enzyme obtained from a supernatant liquid recovered from the cultivation broth of s mutans was reacted with palatinose insoluble glucan was not formed and also when sucrose and palatinose existed together the formation of insoluble glucan was remarkably prevented by the inhibiting action of palatinose the above experiment was enzymatically performed since in a reaction system containing cells the separation of insoluble glucan from the cells is difficult and thence the product cannot accurately be determined this phenomenon confirmed by the enzyme reaction will as a matter of course occur in an oral cavity of human being therefore it is presumed that when palatinose is eaten at the same time in the case of eating sucrose the formation of an insoluble glucan from sucrose remaining in the oral cavity by the action of s mutans is controlled by palatinose existing together with sucrose and the formation of plaque which causes dental caries is reduced as shown in experiment 3 in regard to mixtures of sucrose and palatinose capable of giving a same sweetness as sucrose the formation of insoluble glucan is controlled to about 50 by the mixing ratio of 20 parts of palatinose and 100 parts of sucrose therefore the case of mixing more than 20 parts of palatinose with 200 parts of sucrose is particularly.