|M.Sc Student||Richter Hadas|
|Subject||Ultra High Temperature (UHT) Aggregation of Hydrolyzed Soy|
Protein Isolates (SPI)
|Department||Department of Biotechnology and Food Engineering||Supervisor||Dr. Eyal Shimoni|
|Full Thesis text|
Soy based Ready to Drink (RTD) beverages are increasingly being consumed worldwide due to their functional and nutritional properties. RTD beverages manufacturing involves thermal processes, such as Ultra High Temperature (UHT) technology. One of the biggest challenges in the food industry is to incorporate soy proteins into homogenous shelf-stable RTD beverages. Partially hydrolyzed soy protein isolates (SPI) form macro aggregates when dispersed in water at neutral pH at 8°C. SDS-PAGE analysis of the sediments indicated a big variety of both hydrolyzed and intact peptides, but glycinin basic subunits precipitated at higher ratios. UHT treatment of hydrolyzed SPI at 145°C for 6 seconds resulted in smaller, denser and more ordered aggregates, as was examined by scanning electron microscopy and laser diffraction. A steep increase in solubility was observed at heating temperature in the range of 90-118°C and was related to endothermic enthalpy change, as was determined by differential scanning calorimetry (DSC). The phenomenon observed in protein aggregation following UHT treatment was sensitive to mineral composition and concentration. This was examined in relation to the Hofmeister series with the addition of NaCl and NaClO4 at concentrations in the range of 0.01-0.25M. DSC results indicated that the temperature at which endothermic enthalpy change occurred was increased with the addition of NaCl, and was accompanied by a reduction in the increase in solubility and in the decrease in particle size. NaClO4 added to hydrolyzed SPI showed a similar effect on protein aggregation but to a lesser extent in comparison with NaCl at the same concentrations. No effect of NaCl and NaClO4 on hydrolyzed SPI stability was observed prior to heat treatment, although zeta potential was reduced significantly. Anionic surfactants' molecular structure played an important role in protein aggregation. Spectroscopic analysis showed that anionic surfactants with a longer alkyl chain and a more polar head group increased protein solubility at lower concentrations. The results obtained in this study led to the assumption that hydrophobic interactions played a major role in hydrolyzed SPI aggregation and that electrostatic interactions were also involved. This research provides important insights for the development of highly soluble hydrolyzed SPI products for beverages and other food applications.