Dynamic changes of volatile compounds and water distribution in microwave freeze-dried dumplings: Governed by endpoint moisture control

This study aimed to determine the optimal moisture endpoint for enhancing the quality of dumplings processed via microwave freeze-drying (MFD). Dumplings were dried at a microwave power density of 0.25 W/g to different semi-dried moisture levels (350, 300, 250, 200, 150 g/kg (w.b.)). Their quality attributes and volatile flavor compounds were then analyzed. The results showed that as the moisture content of the semi-dried dumplings decreased, the total peak area in low-field nuclear magnetic resonance (LF-NMR) analysis significantly decreased, and water transitioned from high to low degrees of freedom. Moderate dehydration improved the whiteness of the dumplings, with the whiteness of the 350 g/kg (w.b.) sample (81.12) being 13.19% higher than that of the fresh sample (71.67). The hardness of the semi-dried dumplings increased as the moisture content decreased, while their rehydration ratio decreased. Gas chromatography-mass spectrometry (GC-MS) analysis detected 50 volatile compounds in the dumpling wrapper and 62 in the filling. Among these, total of 19 and 25 key volatile compounds were identified in the wrapper and filling, respectively. Moisture control at 250 g/kg (w.b.) enhanced flavor retention and reduced undesirable flavors. These findings may provide a targeted strategy for controlling the flavor quality of dumplings during MFD. • Combining LF-NMR spectra with linear equations can predict dumpling moisture. • GC-MS identified 19 key volatile compounds in the wrapper and 25 in the filling. • Physical properties, microstructure, and flavor of semi-dried dumplings interact.