Interactions in heated milk model systems with different ratios of nanoparticulated whey protein at varying pH

To better understand the interactions between nanoparticulated whey protein (NWP) and other milk proteins during acidification, milk model systems were diluted to 0.5% protein concentration and adjusted to pH of 6.0-4.5 following homogenisation and heat treatment. The diluted systems with different concentrations of NWP (0-0.5%) were characterised in terms of particle size, viscosity, surface charge and hydrophobicity. When pH was adjusted to 5.5, aggregation was initiated at levels of NWP (0.25-0.5%) leading to significant increase in particle size and viscosity. Pure NWP (0.5%) showed largest initial surface charge (−27 mv) and higher surface hydrophobicity than the other systems. The results indicated that NWP could self-associate above pH 5.5 and not only the decrease of electrostatic repulsion but also other interactions, such as hydrophobic interaction, play an important role in contributing to the early self-association of NWP.