Pretreatment of Apple Slices using Coating-Ultrasound before Hot Air Drying to Enhance Drying Characteristics and Quality
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Abstract:
The experiment used apples as materials, in order to improve the hot air drying rate and quality of dried products. In this paper, carboxymethyl cellulose (CMC) coating film and pretreatment with different ultrasonic powers (0, 160, 320, 480 W) were used to study the hot air drying characteristic curve (water content of dry base and drying rate) and quality (total polyphenol and color difference, DPPH removal rate, rehydration rate and dried microstructure) of apple slices. Under the drying condition of 60~90 ℃, the increase of ultrasonic power led to the increases of drying rate, total polyphenol, DPPH removal rate and the rehydration ratio, while the drying time and color difference(ΔE) decreased with the increase of ultrasonic power. At 70 ℃ and 480 W, a higher drying rate and better drying quality could be obtained, the drying time of drying apple slices is 150 min, the total phenol content is 16.25 mg GAE /g DW, the ΔE is 8.13, the DPPH scavenging rate is 38.15%, and the rehydration ratio is 5.26. The microstructure of dried apple products after ultrasonic pretreatment could be observed by using an electron microscope, and it could be found that there are many folds and microspore channels. Overall, the combined application of ultrasonic and CMC coating pretreatments could shorten the drying time, improve the drying rate and total polyphenol content, DPPH scavenging rate, rehydration ratio of the products, and strengthen the quality of the dried apple slices.
