Abstract:In order to protect the color of apple during the processing of freeze-dried, four groups were designed according to different pretreatments: the control group, the blanching group, the color protection liquid soaking group, and the blanching-color protection liquid soaking composite color protection group. The vacuum freeze-drying was applied to produce freeze-dried apple slices, and then the water content, vitamin C content, titer acidity, rehydration ratio, texture, color difference, sensory evaluation, microstructure and other quality of each group of products were compared. The results showed that the moisture content, the vitamin C content, the titer, the rehydration ratio, the hardness, the brittleness, the brightness values and sensory evaluation in four freeze-dried apple slices ranged from 5.13% to 5.47%, 9.56 to 17.06 mg/100 g, 2.22 to 2.37 g/100 g, 5.15 to 3.49, 9715.67 to 9384.67 g, 1762.50 g to 1989.00 g, 77.73 to 84.04, 5.82 to 8.02, respectively. Vitamin C content of the CK group was significantly (p<0.05) higher than those of the other three groups. The rehydration ratio of the BCP group was significantly (p<0.05) higher than that of the CK group. The color protection effect of the BCP group was best, with the brightness value 84.04 and the overall score 8.02. The results of the microstructure showed that the cells were disorganized and the structure was loose and broken after the combined treatment of pretreatments and vacuum freeze-drying. In general, although the four groups of freeze-dried apple slices had differences in nutrient composition and sensory evaluation, they all retain the typical flavor of apples. The better freeze-dried slice quality was found in the BCP group. This study could provide the theoretical and technical guidance for the industrial production of freeze-dried apple slices.
