Whey protein concentrate (WPC) solutions containing
10, 30, 60 and
120 g dry powder/kg were heated at 75°C and whey
protein aggregation was studied
by following the changes in the distribution of
β-lactoglobulin, α-lactalbumin and
bovine serum albumin, using one dimensional and two
dimensional PAGE. The one
dimensional PAGE results showed that a minimal quantity
of large aggregates was
formed when 10 g WPC/kg solutions were heated at
75°C for up to 16 min whereas
appreciable quantities were formed when 30, 60 and 120 g
WPC/kg solutions were
similarly treated. The two dimensional PAGE analysis
showed that some disulphide-linked β-lactoglobulin
dimers were present in heated 10 g WPC/kg solution, but very
little was present in heated 120 g WPC/kg solution.
By contrast, SDS was able to
dissociate monomeric protein from high molecular mass
aggregates in heated WPC
solution of 120 g/kg but not in 10 g WPC/kg solution
heated for 30 min. The rates
of loss of native-like and SDS-monomeric β-lactoglobulin,
α-lactalbumin and bovine
serum albumin during heating increased as the WPC
concentration was increased
from 10 to 120 g/kg. In 120 g WPC/kg solution
heated at 75°C, the amounts of SDS-monomeric
β-lactoglobulin in each sample were greater than
the quantities of native-like protein. However, in WPC
solutions of 10, 30 and 60 g/kg, the differences
between the amounts of native-like and SDS-monomeric proteins
were slight. The
loss of the native-like or SDS-monomeric proteins was
consistent with a first or
second order reaction. In each case, the apparent reaction
rate constant appeared to
be concentration-dependent, suggesting a change of
aggregation mechanism in the
more concentrated solutions. Overall, these results
indicate that in addition to
disulphide-linked aggregates, hydrophobic aggregates
involving β-lactoglobulin, α-lactalbumin and
bovine serum albumin were formed in heated WPC solution at high
protein concentration, as suggested by model studies
using binary mixtures of these proteins.
Purification of β-Lactoglobulin from Whey Protein Concentrate by Pepsin Treatment
