To overcome problems of browning and crusting during the pretreatment process and provide theoretical guidance for cantaloupe convection drying at 80°C, the effects of blanching (BL) and ultrasonic (US) treatments were examined. The effects of various BL (5, 10, and 15 s) and US (10, 20, 30, and 40 min) durations on convection drying were tested. The moisture ratio, drying rate, moisture effective diffusivity, color, browning, nuclear magnetic resonance characteristics, and texture were assessed. Compared with the control group, the maximal decreases in the drying time of BL and US pretreatment groups were 40% and 33.3%, respectively. BL and US pretreatments significantly increased the effective diffusion coefficient and shortened the drying time because of the destruction of the cell structure. Low-field nuclear magnetic resonance analysis showed that free water is mainly lost during the initial drying stage, while solidified water is mainly lost during middle and late stages. According to the results of magnetic resonance imaging, the moisture distribution shows that cavitation from US acts on internal tissue, while BL disrupts the structure of external tissue. Texture data define the area enclosed by SC-D as uniform. After BL and US pretreatment, the hardness of dried cantaloupe decreased and the uniformity increased significantly. The best pretreatment process for cantaloupe at 80°C was 10 min of US. These findings provide a reference for testing in the industrial production of dried cantaloupe and are deeply relevant for practice.
Keywords: browning; crusting; moisture migration; pretreatment; uniformity.
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