a low cost process for producing concentrated fructose is described which involves selective , preferential biological utilization of glucose in mixtures of glucose and fructose , in order to thereby yield concentrated fructose . broadly speaking , the method involves contacting a mixture containing respective amounts of glucose and fructose with a microorganism which preferentially utilizes glucose as compared with fructose , incubating the mixture until the relative concentration of fructose is substantially in excess of that of glucose , and recovering concentrated fructose . in preferred forms , the microorganism is pullularia pullulans , and the starting material may be a mixture of gluctose and fructose , sucrose , a carbohydrate such as inulin or starch ; in the latter instances , the p . pullulans , by virtue of excretion of invertase , acts to degrade the starting material to give the desired glucose - fructose mixture . recovery procedures such as ion exchange , evaporation and / or crystallization give highly concentrated or essentially pure fructose . a biopolymer side product resulting from glucose utilization by the preferred microorganism can also be recovered if desired .