Dielectric behavior of frozen dough during thawing: Insights into phase transition, mobility, and migration of water

Abstract

Microwave heating may serve as a viable alternative to traditional thawing processes in the frozen dough industry owing to its rapid heating, strong penetration, and high efficiency. Water, a polar component, undergoes state changes during thawing, which may influence its dielectric properties and microwave absorption. Consequently, these alterations may affect the quality of frozen dough products. In this study, the microwave properties of frozen dough with different moisture contents (35, 40, 45, 50, and 55%) were investigated during thawing from −18 °C to 20 °C. The dielectric constant and dielectric loss factor of frozen dough with 35% moisture content exhibited an opposite trend to that of dough with a moisture content of ≥40% with increasing temperature. The penetration depth of the frozen dough with 35% moisture content was significantly higher than that of the other samples, whereas its reflection loss showed minimal variation during thawing. Differential scanning calorimetry, synchrotron X-ray microcomputed tomography, and low-field nuclear magnetic resonance analyses were conducted to elucidate these results from the perspective of water. Minimal changes were observed in both the size and quantity of ice crystals in frozen dough with 35% moisture content at subzero temperatures. Most of the water in frozen dough with 35% moisture content was absorbed and bound to starch or glutenins, resulting in low volume of water participating in the dielectric response above zero. This study reveals the relationship between the dielectric response of frozen dough and water, thereby advancing the application of microwave thawing in frozen dough technology.