Ultra- and microfiltrations are industrially applied for the concentration and fractionation of whey proteins. Thereby, either high (similar to 50 degrees C) or low (< 10 degrees C) processing temperatures can be selected to avoid microbial spoilage of the product. Filtration performance at the two temperature ranges was found to be significantly different. For this reason, this study focusses on the impact of temperature on membrane fouling during both ultra- and microfiltration of whey and whey protein suspensions. We found significantly different deposit layer structures at the two pore sizes investigated. During microfiltration (full whey protein permeation), membrane fouling due to adsorption processes was Facilitated at temperatures <= 10 degrees C and >35 degrees C. For filtrations with fully retentive ultrafiltration membranes, an increase in processing temperature resulted in a decrease of specific fouling resistance, while deposit layer solid height increased. In cross-flow mode, fouling resistance was independent of temperature during acid whey microfiltration. A temperature increase during filtration of sweet whey resulted in a sharp increase of membrane fouling for temperatures above 40 degrees C. When increasing temperature, the stronger fouling reaction in neutral pH-range could be attributed to both, the acceleration of thiol/disulfide reaction speed and calcium based protein cross-linking. (C) 2015 Elsevier B.V. All rights reserved.