Utilization of mildly fractionated pea proteins for the development of thermally stable beverage emulsions
Mild fractionation is a non-invasive protein extraction technique that can be used to retain protein fractions of high purity and functionality. The overall aim of this research was to develop beverage emulsions using mild-fractionated soluble pea proteins with improved stability against thermal processing initially, soluble pea proteins were retained from a pea protein concentrate dispersion via mild fractionation using simple aqueous centrifugation. Later, high-pressure homogenized (20,000 psi for 6 cycles) 5 wt% oil-in-water emulsions were made using different concentrations of soluble proteins as the aqueous phase. After various emulsion characterization tests were carried out, 2.5 wt% of protein in the aqueous phase was concluded to be the ideal concentration of protein for optimum emulsion stability. All the emulsions for further characterization were made using 2.5 wt% of mildly fractionated soluble proteins in the aqueous phase. It was important to test the stability of pea protein-stabilized emulsions against various environmental stresses: heat treatment at 90°C for 30 minutes, addition of 0.1M-1M salt, and the effect of two different pH (2 and 7). Heating caused extensive emulsion destabilization due to droplet and protein aggregation at both the pH values. The emulsions at pH 2 showed destabilization even without heating. The problem of aggregation could be due to the denaturation of proteins during heat-treatment which caused the exposure of hydrophobic groups, in turn causing emulsion destabilization. To overcome the problem, it was hypothesized that partial denaturation of the soluble proteins by pre-heating and thereafter making the emulsions with the heated protein solutions could solve the problem of protein aggregation in emulsions after heat treatment. Therefore, emulsions were prepared at heated conditions using heat-treated (75°C) partially denatured soluble pea proteins. From the characterization tests, it was found that the heat-treated protein-stabilized emulsions at pH 7 had superior stability at all salt concentrations without any sign of extensive droplet and protein aggregation even after heating the emulsion to 90°C for 30 minutes. A similar improvement in stability was, however, not observed for the pH 2 emulsions prepared under comparable conditions. The effect of protein pre-heat treatment on the emulsion lipid digestibility was also determined by in-vitro digestion tests, which showed that the unheated protein unheated emulsion showed the maximum lipid digestion of 97.51%, followed by 73.47% and 56.06% lipid digestibility for heat-treated protein heated emulsion and heat-treated protein unheated emulsion, respectively. Overall, this research showed that the pre-treatment of mildly fractionated soluble proteins could significantly improve the stability of beverage emulsions and also influence the protein structure to reduce the lipid digestibility of the emulsions.
mild fractionation, pea protein, beverage emulsion, soluble protein
Master of Science (M.Sc.)
Food and Bioproduct Sciences