Model infant milk formula systems (5.5% protein) were formulated to contain alpha-lactalbumin:beta-lactoglo bulin ratios of 0.1, 0.5, 1.3, 2.1 or 4.6 and assessed for heat stability and heat-induced changes. 'Humanising' the model formulas by increasing alpha-lactalbumin:beta-lactoglobulin enhanced heat stability at 140 degrees C in the pH range 6.6-6.9. The model formulas were analysed after lab-scale high-temperature short-time heating at pH 6.8. Gel electrophoresis indicated that increased heat stability in high alpha-lactal bumin:beta-lactoglobulin samples was due to decreased covalent interactions between proteins. In low alpha-lactalbumin:beta-lactoglobulin formulas, protein-protein interactions caused marked increases in protein particle size and viscosity of the heated systems; conversely, covalent interactions between proteins were minimal in high alpha-lactalbumin:beta-lactoglobulin formulas. Reduced protein-protein interactions with increasing alpha-lactalbumin:beta-lactoglobulin has important implications for subsequent processing; for example, lower viscosity post-heating may affect bulk density in spray-dried products or physical stability in ready-to-feed products. (C) 2015 Elsevier Ltd. All rights reserved.Model infant milk formula systems (5.5% protein) were formulated to contain alpha-lactalbumin:beta-lactoglo bulin ratios of 0.1, 0.5, 1.3, 2.1 or 4.6 and assessed for heat stability and heat-induced changes. 'Humanising' the model formulas by increasing alpha-lactalbumin:beta-lactoglobulin enhanced heat stability at 140 degrees C in the pH range 6.6-6.9. The model formulas were analysed after lab-scale high-temperature short-time heating at pH 6.8. Gel electrophoresis indicated that increased heat stability in high alpha-lactal bumin:beta-lactoglobulin samples was due to decreased covalent interactions between proteins. In low alpha-lactalbumin:beta-lactoglobulin formulas, protein-protein interactions caused marked increases in protein particle size and viscosity of the heated systems; conversely, covalent interactions between proteins were minimal in high alpha-lactalbumin:beta-lactoglobulin formulas. Reduced protein-protein interactions with increasing alpha-lactalbumin:beta-lactoglobulin has important implications for subsequent processing; for example, lower viscosity post-heating may affect bulk density in spray-dried products or physical stability in ready-to-feed products. (C) 2015 Elsevier Ltd. All rights reserved.