Comparison of physicochemical properties of radish powder by different drying methods using radish by-products

Radish powder was prepared using radish and by-products of radish processing by three different drying methods, such as hot air drying, freeze drying, and microwave vacuum drying. The radish powder was characterized by measuring moisture content, color change, particle size, particle shape, and antioxidant activity. The moisture contents of the standard radish powder under the hot air drying, freeze drying, and microwave vacuum drying conditions were 5.15%, 5.22%, and 4.62%, respectively, while the moisture contents of the non-standard radish powder were 5.57%, 5.51%, and 4.85%, respectively. The smallest particle size of the non-standard radish powder was 9.5±0.10 μm observed by the microwave vacuum drying, and the largest particle size of the non-standard radish powder was 12.2±0.08 μm observed by hot air drying. The DPPH and ABTS radical scavenging activities were the highest in the hot-air-dried standard radish powder of 79.0% and 83.4%, respectively, and the lowest in the microwave vacuum-dried non-standard radish powder of 50.0% and 16.7%, respectively. Therefore, when manufacturing radish powder using non-standard radish waste discarded during radish processing, freeze-drying is considered the most suitable drying method because it could minimize color change of the radish powder and show high antioxidant activity.