Influence of Different Drying Methods on the Quality of Crispy Plum Preserved Fruits

To explore a drying technique tailored to the characteristics of crisp plum preserves, this study systematically compared the effects of four drying methods—hot-air drying at constant temperature (HD), hot-air drying with variable temperature (VHD), hot-air-vacuum-hot-air drying (CD), and vacuum freeze drying (VFD)—on the drying characteristics, sensory quality, physicochemical properties, and antioxidant activity of the preserves. Additionally, a comprehensive analysis of the correlations between various indicators was conducted. The results indicated that all drying rates followed a pattern of initial increase followed by decrease, with the drying durations for the HD, VHD, CD, and VFD groups being 15, 17, 16 and 23 h, respectively. Within the first 9 h, the drying rate of the VFD group was lower than that of the HD, VHD, and CD groups. However, from 11 h onwards, the drying rate of the VFD group exceeded that of the other three groups. In sensory evaluation, the VHD group achieved the highest score (79.60 points), while the VFD group obtained the lowest (73.20 points). The L*, a*, and b* values of the VFD group were significantly higher than those of the other treatment groups (PP>0.05). Regarding physicochemical properties, the VHD group contained the highest level of free amino acids (0.7105 g/100 g). Its contents of total sugar, total phenols, flavonoids and vitamin C were significantly higher than those in other hot-air drying groups (P2+/g, a hydroxyl radical scavenging rate of 45.04%, and both ABTS+ and DPPH free radical scavenging rates exceeded 80%. The VHD group ranked second, with the corresponding indicators being 35.73 μmol Fe2+/g (FRAP), 41.75% (hydroxyl radical scavenging rate), 77.29% (ABTS+ free radical scavenging rates), and 67.37% (DPPH free radical scavenging rates), respectively. Correlation analysis demonstrated that the total sensory evaluation score was significantly negatively correlated with L*, a*, and b* values (PPPa* (r=−0.58, Pr=−0.70, P<0.05). Considering comprehensive indicators and economic costs, VHD would be more suitable for the production of crisp plum preserves, providing a reference for enhancing their industrial efficiency and quality.