Influence of stainless steel surface properties on whey protein fouling under industrial processing conditions

Abstract

Heat-induced fouling is a financial and environmental burden for food and dairy industries and its control is therefore desperately needed. A better understanding of the fouling mechanisms and their relation to stainless steel surface properties is thus of considerable interest. This work aims at studying the impact of stainless steel's surface morphology and surface free energy on fouling by a model dairy solution by a close examination of the deposit's growth and adhesion at the substrate-fluid interface. Pristine model surfaces of controlled roughness and surface energy, i.e. native, mirror polished and biomimetic femtosecond laser textured stainless steel surfaces, fluorosilanized or not, were tested under isothermal conditions in a pilot pasteurization facility fed with a model dairy fluid (whey protein and calcium solution). Multi-scale characterizations of those surfaces before and after fouling, using a wide range of analytical tools (goniometry, SEM, ToF-SIMS, EPMA X-Ray mappings) allowed for a better comprehension of the impact of surface energy and morphology modifications on the fouling behavior while highlighting their complex interactions in fouling governance. Lower surface energy was shown to be an asset against deposit growth, as fluorosilanization of native stainless steel allowed to reduce fouling by 72% (wt.%). The relative sizes of surface relief versus fouling agents has been found crucial, as it impacts interlocking phenomena. Textured surfaces have shown a tremendous increase in fouling (+391% for textured, +86% for fluorosilanized textured). However, interesting fouling performances were obtained on smooth, hydrophobic surfaces, as a reduction by 83% of fouling weight was achieved with fluorosilanized polished samples.