Rheological and microstructural characterization of batters and sponge cakes fortified with pea proteins

The effect of pea protein fortification on the rheological properties of sponge-cake batters and their continuous phases, as well as their relationship with the final product properties were studied. Foams made out of whole egg and sugar were prepared in a planetary mixer; wheat flour (WF) was added to form a typical sponge-cake batter. Pea protein isolates (PP) were added in substitution to WF to form five batters with various PP concentrations expressed as the percentage of WF substitution: 0, 10, 20, 30 and 40%. The batter air volume fraction decreased when increasing PP concentration, which led to an increase in the cake density and apparent Young modulus. All batters and their respective continuous liquid phases showed shear-thinning behavior, which was modeled by a power law. They showed a predominant elastic behavior at intermediate frequencies, and a cross-over point at high frequencies. All of the rheological properties increased by a factor of about 10 when the PP concentration increased from 0 to 40%. Free-drainage experiments showed that batter stability increased with increasing PP concentration. PP had larger particles than WF, and showed a higher water binding capacity than WF, but no significant difference in solubility. Observations of the batter and cake microstructure revealed PP formed a network of interconnected ``bridged'' particles in the continuous phase. These results suggest that PP first acted as fillers that swelled and connected to each other in the continuous phase, and were the main driver for the increase of rheological properties.