A process is described which uses whole cell preparations, immobilized or without immobilization, of a microorganism, including Aureobasidium pullulans, capable of forming enzymes of the group of fructosyltransferases, for catalyzing a reaction between sucrose and 6-O-protected glucose for formation of 6-O-protected sucrose, an intermediate in synthesis of trichlorogalactosucrose. 6-O-protected Sucrose is separated from high molecular weight by-products of the reaction having molecular weight of 500 daltons and more by reverse osmosis, and further purified by column chromatography.