Ice cream is considered as one of the most popular foods around the world. It
is a complex food in which each component plays an important role in ensuring and
creating a quality product. Proteins are one of the most important components in ice
cream. The main source of proteins are milk proteins. Milk contains caseins as well as
whey proteins, which have several important structural roles in the production of quality
ice cream products. Therefore, it is important that manufacturers choose the appropriate
protein source of the final product.
In this thesis we wanted to semi-qualitatively determine the type of proteins present in
various dairy raw materials. Native polyacrylamide gel electrophoresis method was used
for the separation of whey proteins and native SDS polyacrylamide gel electrophoresis
was used to separate proteins from casein raw materials. We analysed several different
samples of dairy raw materials where we determined the appropriate concentration to
achieve the optimal separation resolution. We determined the following approximate
concentrations: 5 mg/mLforskimmed milk powder, 8 mg/mL for whey powder, 5 mg/mL
for milk substitute powder, 3 mg/mL for whole milk powder and 1 mg/mL for whey
protein concentrate 80, whey protein concentrate 80 with reduced lactose, whey protein
isolate 90 and micellar casein concentrate 80.
In addition to determining the optimized standard conditions for the separation of
individual proteins, we also analysed how the proteins behave during different periods of
exposure of high temperature and changes in the pH value of the protein environment.
Native polyacrylamide gel electrophoresis was used for analysis. Denaturation of whey
proteins increases with longer heat treatment. When exposed to 85 °C for longer than 5
minutes, most proteins are irreversibly denatured. Denaturation is observed in samples
that are not heat stable. In heat stable samples, denaturation is not noticeable. We also
analysed the influence of the change in pH value. When the protein environment is
acidified between pH values 5.0 and 4.0, protein precipitation occurs. Proteins precipitate
around the isoelectric point (around pH 4.6) and do not enter the gel.
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