The demand for healthier and low-calorie foods is increasing worldwide. Galactooligosaccharides and fructooligosaccharides are considered to be naturally-occuring prebiotics because they can selectively stimulate the growth of beneficial bacteria in the colon, and thus, improve host health. These oligosaccharides (OS) also have excellent technological properties regarding to viscosity, stability, solubility, and taste. A common weakness of the current OS production technologies is the incomplete bioconversion that results in a carbohydrate mixture consisting of a considerable amount of residual disaccharides and monosaccharides. Further purification of this mixture involves complex, high-cost and low-yield technologies that restricts the application of OS in low-calorie food formulations.This 4-year research project is devoted to the development of a novel technology for manufacturing low-calorie, value-added beverages that have beneficial health effects. The proposed technology has two key steps. First, the sugars present in cheap and abundant feedstocks available within the EU, such as whey and molasses, are partially converted into valuable OS. Then, the obtained saccharide mixtures are further processed in a selective fermentation step using appropriate microorganisms that are capable of utilizing mono- and disaccharides but lack the power to hydrolyze OS to a higher extent. The utilized carbon source is not wasted but required for giving rise to odour and taste constituents. The resulting mildly sweet product has a prebiotic function due to the presence of remaining OS.This highly multi-disciplinary research gathers new experimental data, involves 'state of the art' experimental and theoretical analysis on fundamental phenomena and their implications to real-life systems, and attempts to identify process designs, that have promising potential for industrial implementation, taking into account technical, economical and environmental impact tradeoffs.