Migration Patterns of Moisture and Sugar in Honey Peach Slices during Vacuum Freeze-drying Combined with Puffing Drying

To investigate the migration mechanisms of water in different states and sugars in peach slices during drying, samples were unpretreated or pretreated with either 20% sucrose or 20% oligosaccharide solution impregnation. Each group was then processed using vacuum freeze-drying (FD) or vacuum freeze-drying combined with puffing drying (FP). The drying kinetics, water migration patterns, and sugar transport dynamics were systematically analyzed throughout the process. Results demonstrated that the T2 relaxation curve exhibited a leftward shift during drying, indicating progressive conversion of free water into immobilized and bound water in peach slices. Concurrently, intra-tissue moisture migrated outward, as evidenced by the decreasing free water content and evolving water state distribution. Compared to FD, FP significantly reduced drying duration while enhancing moisture removal efficiency. During FP treatment, initial moisture evaporation occurred preferentially from surface regions, while intracellular immobilized and bound water fractions progressively increased. During FP stage, accelerated accumulation of immobilized water in the peripheral tissue layers enhanced drying kinetics. In sugar-impregnated FP samples, a steep concentration gradient emerged: Sugar content exhibited a sharp decline in peripheral regions versus gradual depletion in medial zones, confirming unidirectional outward sugar migration. The sugar in the internal field of the peach slices presented with little migration change. In this study, migration from internal to external both happened to the water and sugar in the peach slices during the drying process, which was more prominent in the outer field of the peach slices and less prominent in the internal field. These findings can provide theoretical supports for the improvement of drying efficiency and quality control of the dried fruits and vegetables.