The invention provides variants of the Aspergillus japonicus β-fructofuranosidase enzyme which have been modified so as to improve synthesis of inulin-type fructooligosaccharides (FOS) from sucrose. One or more substitutions may be made to the parent β-fructofuranosidase polypeptide at amino acid positions 121, 159, 302 and/or 471 of the mature peptide (SEQ ID NO: 3), corresponding to crystal positions 140, 178, 321 and 490. A method of synthesizing FOS using the variants is also claimed.