Influence of interfacial characteristics and dielectric properties on foam structure preservation during microwave-assisted vacuum drying of whey protein isolate-maltodextrin dispersions

This study aimed at assessing the correlation between interfacial and dielectric properties of whey protein isolate (WPI)-maltodextrin (MD) dispersions and their foam structure stability during conventional vacuum drying (CVD) and microwave-assisted vacuum drying (MWVD). Interestingly, the presence of MD clearly increased the surface activity of WPI, whereas the surface dilatational properties were rather unaffected. Besides, loss factor and resonant frequency linearly increased with MD concentration, while the dielectric constant decreased. Regarding drying, foam structure preservation during CVD was mainly correlated with the dilatational elasticity. Thereby, all samples remained stable throughout the drying process. Compared to CVD, MWVD required ≥20% MD to avoid foam collapse. In addition, MWVD-dried samples exhibited larger bubble sizes, which was linked to the volumetric heating and higher mechanical stress as compared to CVD. Overall, high surface dilatational elasticity and bulk viscosity were identified as key parameters to ensure foam structure preservation during vacuum drying.