Improving thermal stability of hydrolysed whey protein-based infant formula emulsions by protein–carbohydrate conjugation

•Hydrolysed whey protein was conjugated with maltodextrin.•Intact, hydrolysed, preheated and conjugated whey protein ingredients were evaluated.•Preheating of hydrolysed whey protein improved thermal stability of emulsions.•Conjugation resulted in emulsions with greatest overall thermal stability.•Improved thermal stability was due mainly to enhanced steric stabilisation.

Whey protein hydrolysate (WPH) ingredients are commonly used in the manufacture of partially-hydrolysed infant formulae. The heat stability of these emulsion-based formulae is often poor, compared with those made using intact whey protein. The objective of this study was to improve the heat stability of WPH-based emulsions by conjugation of WPH with maltodextrin (MD) through wet heating. Emulsions stabilised by different protein ingredients, whey protein isolate (WPIE), whey protein hydrolysate (WPHE), heated WPH (WPH-HE), and WPH conjugated with MD (WPH-CE) were prepared and heat treated at 75 °C, 95 °C or 100 °C for 15 min. Changes in viscosity, fat globule size distribution (FGSD) and microstructure, evaluated using confocal laser scanning microscopy (CLSM), were used to monitor the effects of hydrolysis, pre-heating and conjugation on the heat stability of the emulsions. Heat stability increased in the order WPHE < WPIE << WPH-HE <<< WPH-CE; emulsions WPHE, WPIE and WPH-HE destabilised on heating at 75 °C, 95 °C or 100 °C, respectively. Flocculation and coalescence of oil droplets were mediated by protein aggregation (as evidenced by CLSM) on heat treatment of WPH-HE emulsion at 100 °C, while no changes in FGSD or microstructure were observed in WPH-CE emulsion on heat treatment at 100 °C, demonstrating the excellent thermal stability of emulsions prepared with the conjugated WPH ingredient, due principally to increased steric stabilisation as a result of conjugation.