The combination of sucrose analogues as novel substrates (substrate engineering) and highly active recombinant beta-fructofuranosidase from A. niger (genetic engineering) provides a new powerful tool for the efficient preparative synthesis of tailor-made saccharides of the important 1-kestose and 1-nystose type headed with different monosaccharides of interest. These novel compounds have been isolated. They did not display toxic effects or suppress cell growth in initial studies, making these new compounds potential candidates for prebiotics.