The evolution of dielectric properties of starch-based food pellets with different moisture contents was measured during microwave expansion to determine the effect of water content on the expansion dynamics.Dynamic dielectric measurements were found to be an excellent procedure to in situ monitor and characterize the different stages in the material transformation of food pellets during microwave expansion.Although the maximum bulk expansion of pellets was achieved at a moisture content of approximately 8% (wet basis), comparative analysis showed that a moisture content 10–11% produced the best results considering the tradeoff between the foaming and expansion temperature. This was due to the high expansion index and an expansion temperature that was sufficiently lower than the onset temperature for pellet scorching, which provides an operating window to maximize expansion and minimize the likelihood of burning.Dielectric measurements during microwave heating in short on/off cycles prior to pellet expansion suggested that the water was not as dielectrically bound for high moisture content pellets.

The relationship between structural and foaming properties of two tryptic and two peptic wheat gluten hydrolysates was studied at different pH conditions. The impact of pH on foam stability (FS) of the samples heavily depended on the peptidase used and the degree of hydrolysis reached. Surface dilatational moduli were in most, but not all, instances related to FS, implying that, although the formation of a viscoelastic protein hydrolysate film is certainly important, this is not the only phenomenon that determines FS. In contrast to what might be expected, surface charge was not a major factor contributing to FS, except when close to the point-of-zero-charge. Surface hydrophobicity and intrinsic fluorescence measurements suggested that changes in protein conformation take place when the pH is varied, which can in turn influence foaming. Finally, hydrolyzed gluten proteins formed relatively large particles, suggesting that protein hydrolysate aggregation probably influences its foaming properties.