Shrinkage in frozen desserts.

Shrinkage is a well-documented defect in frozen desserts, yet the root causes and mechanisms remain unknown. Characterized by the loss of volume during storage, shrinkage arose during the mid-twentieth century as production of frozen desserts grew to accommodate a larger market. Early research found that shrinkage was promoted by high protein, solids, and overrun, as well as postproduction factors such as fluctuations in external temperature and pressure. Rather than approaching shrinkage as a cause-and-effect defect as previous approaches have, we employ a physicochemical approach to characterize and understand shrinkage as collapse of the frozen foam caused by destabilization of the dispersed air phase. The interfacial composition and physical properties, as well as the kinetic stability of air cells within the frozen matrix ultimately affect product susceptibility to shrinkage. The mechanism of shrinkage remains unknown, as frozen desserts are highly complex, but is rooted in the physicochemical properties of the frozen foam. Functional ingredients and processing methods that optimize the formation and stabilization of the frozen foam are essential to preventing shrinkage in frozen desserts.

The microstructural, melting, rheological, and sensorial properties of high-overrun frozen desserts.

Air incorporated during dynamic freezing influences the development of the microstructure and the final texture of frozen desserts. Frozen desserts were manufactured with 100-175% overrun from a constant ice cream mix formulation. Microstructural elements (fat, air, and ice phases) of the frozen desserts were then investigated and related to the melting, rheological, and sensory properties of the product. Mean ice crystal and air cell size were found to decrease with increasing overrun, and the extent of fat destabilization increased. Frozen desserts manufactured with higher overrun had slower drip-through rate and better shape retention after melting at ambient conditions, demonstrating that fat destabilization and the interplay of fat, air, and serum phases affect the melting behavior. Structural elements also influenced the rheological behavior, as measured by oscillatory thermo-rheometry. Frozen desserts had similar rheological properties at temperatures below the freezing point due to the presence of ice, and the values of G' and G″ (solid-like and viscous-like character, respectively) increased with increasing overrun above the freezing point, corresponding to a more solid-like structure. Slight differences in sensory denseness and breakdown were detected, but sensory texture was not significantly different for the frozen desserts studied. This study provided insights into the role of air in ice cream and frozen desserts, and its influence on product texture.