The effect of high pressure homogenization on structural and functional propoties of sesame protein isolate

In order for plant based proteins to be a good alternative to animal based proteins, it is very important to have improved functional properties in addition to their nutritional properties in terms of better storage stability and better structure of the food product. Therefore, in this thesis, it was aimed to improve the functional properties of sesame protein isolate (SPI), which was obtained from sesame meal, which is a by-product of the oil industry, by providing modification with high pressure homogenization (HPH) technology. For this purpose, HPH was applied to the extracted sesame proteins at pressures of 0, 50, 100 and 150 MPa and some physicochemical, functional and rheological properties of both unprocessed and modified proteins were investigated. HPH did not cause a general change in the secondary structures and subfractions of the proteins. However, significant differences were determined in some basic physicochemical properties of SPIs. Sesame proteins had the smallest particle size and highest zeta potential at 100 MPa pressure, but a slight increase in particle size was observed as 150 MPa pressure caused partial aggregation of the protein. This was also supported by microstructure images. Likewise, with increasing homogenization pressure up to 100 MPa, the surface hydrophobicity, free/total –SH groups and water solubility of SPI also increased significantly. When the changes in functional properties were examined, the most developed water/oil binding capacity, foaming capacity and emulsification properties were achieved by homogenization at 100 MPa pressure. The emulsion activity value, which was 32,2 m2/g in the untreated SPI, was 64,63 m2/g with 100 MPa YBH. The emulsion stability value, which was 44,06 minutes, reached its maximum state as 59,84 minutes with 100 MPa pressure. Similarly, the foam capacity, which was 78,33% at the beginning, increased significantly to 191,66% with the application of 100 MPa pressure. The most stable foam formation was achieved with a pressure of 150 MPa. While the highest viscosity was observed in the protein suspension treated with 0 MPa, the lowest viscosity was determined in the treated with 50 MPa pressure. The analysis results of the flow properties of the SPI suspensions were well fitted to Oswalt-de-Waele model (R2=0,997-0,999). In all samples except 50 MPa pressure-treated proteins, the viscoelastic character became dominant with increasing frequency (Gʹ > Gʺ). Modification with YBH resulted in a decrease of about 15 ºC in the gelation temperature of SPI.