A Comparative Study of Four Drying Methods on Drying Time and Quality Characteristics of Stem Lettuce Slices ( Lactuca sativa L.)

This article presents experimental results and analysis of four drying methods, viz. hot air drying (AD), hot air-assisted radio frequency drying (ARFD), infrared drying (IRD), and microwave-assisted hot air drying (MAD), on color, microstructure, density, rehydration capacity, and texture after rehydration of stem lettuce slices (Lactuca sativa L.). The drying time required for these drying protocols was also compared. These four drying tests were conducted at fixed air temperature (60 degrees C) and velocity (1m/s), as well as identical sample load (300g), bed depth (20mm), and the power level for ARFD, IRD, and MAD, which was fixed at 4W/g. The results showed that the drying time required for stem lettuce slices using ARFD was the shortest (120min), followed by MAD (140min) and IRD (180min); AD required the longest time (360min). Notably, ARFD yielded uniform drying and the quality of the dried samples using ARFD was also the best among these four drying methods.