Microparticulated whey protein (MWP) are colloidal particles usually formed by combined heating
and shearing of whey protein concentrates (WPC), and typically have particle sizes ranging from
1.0 to 10 μm. Nanoparticulated whey protein (NWP) have a smaller particle size (100 to 990 nm).
Previous research in our group shown that, both MWP and NWP can give a higher viscosity and
denser microstructure compared to WPC when used as fat replacer in low-fat yoghurt. In the thesis,
we investigated how these two types of commercial whey protein particles interact with other milk
components and how these interactions affect final acidified milk products.
By detecting the properties of the whey protein aggregates, MWP and NWP showed low native
whey protein content, low free thiol content and high surface hydrophobicity and were relatively
stable at high temperature in the 5 % pure dispersions. When MWP and NWP were added to non-fat
milk model systems (5% protein in total) and processed into chemically (glucono-delta-lactone)
acidified milk gels, the formation of disulfide-linked structures was closely related to the increased
particle size of heated milk model systems and the rheological behavior of the acidified gels. MWP
enriched systems produced weak protein networks during acidification and required the addition of
whey protein isolate (WPI) to increase gel strength. However, systems containing NWP exhibited
pronounced increase in particle size and higher firmness of acidified gels through both covalent and
non-covalent interactions. NWP could self-associate above pH 5.5 and then further interactions
between caseins, NWP or casein/whey protein complexes took place at lower pH. Not only decline
of electrostatic repulsion but other interactions, such as hydrophobic interaction, play an important
role in contributing to the early self-association of NWP.
For the textural properties, rheology and microstructure of final acidified gels, NWP provided acid
gels with higher firmness and viscosity, lower syneresis and a denser microstructure. On the
contrary, MWP appeared to only weakly interact with other proteins present and resulted in a
protein network with low connectivity in the resulting gels. Increasing the casein/whey protein ratio
did not decrease the gel strength in the acidified milk model systems with added whey protein
aggregates.
The results of this study highlighted the influences of interactions between added whey protein
ingredients and other milk components on final acidified dairy products. The properties and the
interactions of whey protein aggregates with other milk proteins during processing are crucial for
final texture and structure of acidified milk gels. The knowledge obtained from these results is
expected to provide input for producing tailor-made whey protein aggregates to achieve a desired
functionality in dairy products, especially in acidified milk products