A process for the demineralization and fractionation of cheese whey or raw milk comprising the steps of: a) subjecting the whey or raw milk to ultrafiltration to provide a retentate fraction and a permeate fraction; b) concentrating the permeate fraction by means of nanofiltration; c) subjecting the nanofiltration retentate to ion permeation chromatography at elevated temperatures of between 50° C. and 80° C. using an appropriate resin; and d) eluting the nanofiltration retentate with water in various fractions to obtain fractions which may be low in mineral content and/or high in 3′-sialyl lactose content and/or high in other desirable components.