Objective This project aims to explore the effect of hot water blanching pretreatment combined with segmented heat pump variable temperature drying process on the drying characteristics and quality of plum.
Methods In this study, different temperatures (60, 80, 100 ℃) and different blanching times (30, 60, 90, 120 s) were used to treat the prunes. The anthocyanin content, vitamin C content, polyphenol oxidase and peroxidase activity were measured to screen out the best blanching conditions and then the heat pump drying experiment was carried out. The initial temperature of heat pump drying was set to 40, 45, 50 ℃, and increased at a gradient of 5 ℃. Drying for 6 h at each temperature stage, the experiment was stopped until the water ratio was 0.21 The drying rate, titratable acid content, color, total phenol content, flavonoid content, DPPH free radical scavenging ability, ABTS free radical scavenging ability and texture characteristics of prune were determined, and the results were analyzed.
Results Blanching temperature at 80 ℃ for 90 s was the best. The relative enzyme activities of polyphenol oxidase and peroxidase were 12.71% and 33.78%, respectively. The anthocyanin content was (31.63 ± 3.19) mg/100 g, and the vitamin C content was (2.45 ± 0.18) mg/100 g. Under the conditions of initial temperature of 45 ℃ and drying time of 36 h, the sensory quality characteristics of dried prunes could be significantly maintained, the loss of antioxidant capacity could be reduced, and the better taste could be maintained.
Conclusion In this study, the optimum blanching conditions of Prunus mume are determined to be 80 ℃ and 90 s. The optimum variable temperature drying parameters of segmented heat pump is initial temperature of 45 ℃ and drying time of 36 hours. The process parameters provide technical support for the drying process of Prunus mume, which is helpful to improve the processing efficiency and product quality.
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