From these experiments it appears that ultrasonication does no
cause changes to the protein secondary structure that can be
detected by CD spectroscopy. Other methods, such as IR spectroscopy,
could be applied in order to further investigate the
impact of ultrasonication on whey protein secondary structure.
The forces associated with ultrasonication are sufficient to disrupt
non-covalent as well as covalent bonds, leading to unfolding
and new inter- and intramolecular interactions. The enhancement
of the gelling properties caused by HIU has been described (Zisu
et al., 2011), but the underlying molecular changes conferring this
effect are not well-established.
The development of the gel described by G0 values recorded
during a thermal program, were similar for control, HIU and heat
samples. Again, NTC treatment resulted in significantly different
behavior; gelling was initiated in NTC samples already during
ultrasonication, whereas for the other samples gelling was not
observed until during the subsequent heating of the samples.
Hence, this could be a consequence of unfolding of the proteins
mediated by heat and ultrasonication, thereby exposing hydrophobic
patches. Disulfide bonds could be disrupted and the free thiol
group of b-Lg would be directed towards the exterior of the protein,
thereby initiating aggregation. All of which, in a short time
scale, could generate an environment that was indeed favorable
for establishing new interactions, and the gelation process was
accelerated.