Fructo-oligosaccharides (FOS) are new food ingredients that are able to beneficially affect the host by selectively stimulating the growth and/or activity of colonic bifidobacteria (concept of prebiotics). A commercial enzyme preparation was found to possess a high fructosyltransferase activity and could be used as a biocatalyst for the industrial production of FOS from sucrose. Under optimum conditions (pH: 5.5, temperature: 55 degrees C and 7 units of fructosyltransferase activity per gram sucrose), in presence of glucose (competitive inhibitor) the actual yield reached the theoretical value (up to 50%). Actually, FOS that are commercially available for their prebiotic properties belong to inulin type with low degree of polymerisation (DP:3 to 10). Our FOS were identified by both HPLC and 13C-NMR spectrometry as neo-FOS type (neo-kestose, neo-nystose and neo-fructofuranosylnystose), a new structure which is very close to inulin type (same linkage between fructosyl units). The neo-FOS may act as a prebiotic factor due to their structural similarity with inulin type.