Mechanism Underlying Quality Changes during Frozen Storage of Leavened Pancake Cooked by Different Cooking Methods

Leavened pancake plays an important role in the traditional Chinese diet. It has good taste and fermented flavor, making it popular with consumers. However, the quality of leavened pancake will decrease and the mouthfeel and flavor deteriorate as it is stored for a long time. Therefore, the quality deterioration of leavened pancake during storage is always a bottleneck restricting its industrial production and circulation. In this work, the changes of water mobility, starch crystallinity, starch thermal properties and microstructure in steamed or baked leavened pancake during frozen storage were evaluated by nuclear magnetic resonance (NMR), X-ray diffractometry (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM), in order to reveal the mechanism underlying the quality changes of leavened pancake cooked by different methods during frozen storage. The results showed that the moisture contents of the two cooked samples decreased gradually during frozen storage, a higher level being observed in steamed leavened pancake compared to baked one. For both samples, the relaxation peak area of weakly bound water decreased, while the relaxation peak area of free water increased gradually during frozen storage; the extent of starch crystallinity increased during frozen storage, being higher in steamed leavened pancake than in baked one, and the extent of starch crystallinity in baked leavened pancake gradually decreased with baking time. The gelatinization onset temperature, peak temperature and conclusion temperature and gelatinization enthalpy did not obviously change during frozen storage and the microstructure of steamed and baked leavened pancake changed from a continuous matrix to a thin broken state.