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Vacuum drying (VD) and heat pump drying (HPD) are widely used in the food industry. However, their application is limited due to low drying efficiency and the resultant poor quality of dried products. Additionally, varying drying durations in combined drying can markedly impact the physical and chemical properties as well as the nutritional content of the dried product. To achieve the highest quality dried products, VD + HPD was initially compared and identified as the most suitable drying method. This paper investigates the impact of the first stage drying duration on the physical characteristics (color, microstructure, texture, volume shrinkage rate (VSR), rehydration rate (RR)) and bioactive components (total phenolic content (TPC), total flavonoid content (TFC), Polysaccharides) of pineapple. The results indicated that VD + HPD necessitated lower energy consumption and markedly enhanced the physical properties of dried products. The brightness, rehydration rate (RR), color difference, volume shrinkage rate (VSR), and surface microstructure of pineapple dried by VD 5h + HPD 5.5h were all optimal. In comparison with other tested drying methods, the textural properties (hardness, chewiness, viscosity) and bioactive components (TPC, Polysaccharides) exhibited significant improvement. Overall, these results indicate that VD5h + HPD5.5h can be viewed as a valuable technology for improving the quality of dried pineapples.
Han et al. (Mon,) studied this question.