This study investigates the effects of various blanching methods (hot water blanching (HB) or steam blanching (SB)) and thawing methods (room temperature thawing (RT), running water thawing (WT), and microwave thawing (MT)) on the quality attributes of frozen potatoes and carrots. Blanched potatoes and carrots were frozen using individual quick freezing (−35°C), followed by applying various thawing methods. We observed increased thawing speed in the order of RT, WT, and MT. The MT method was about 24 to 70 times shorter than the other methods. The thawing losses were influenced by the blanching methods which affect the drip loss and moisture contents of potatoes and carrots. The blanching process reduced the browning of potatoes but did not affect color of the carrots. No change was obtained in the pH value when considering different blanching or thawing methods. The hardness of potatoes and carrots tended to be lowered by blanching treatment. SB treated potatoes and carrots had high DPPH radical scavenging ability and vitamin C content. Especially, the WT treated potatoes and carrots had the highest total polyphenol content. Our results confirmed that SB is an excellent pre-treatment for potatoes and carrots from the nutritional aspect, and blanching pre-treatment before the freezing process could suppress the quality changes that occur during the thawing processes. Furthermore, we propose that RT after SB treatment for potatoes and carrots is probably the most suitable method to maintain their nutritional quality.

Beet (Beta vulgaris L.) is a healthy food that has recently attracted the consumer's attention. However, beet has low storage stability due to the high moisture content. Therefore, a drying process is necessary to improve the beet quality. In this study, Jeju beet was dried by applying two processes: hot air drying (4.5 hours at 70°C, 6 hours at 60°C, 13 hours at 50°C) and combined drying (hot air and infrared radiation, 1 hour at 100°C). The effect of both processes was investigated on the physicochemical properties and antioxidant activity was investigated. The dried beets were compared for their appearance, drying yield, moisture content, water activity, pH value, color, rehydration ratio, betalain pigment content, total polyphenol content, DPPH radical scavenging activity, ABTS + radical scavenging activity, and FRAP assay. The beet subjected to combined drying was determined to have high storage properties due to its low moisture content and pH value. In addition, the combined dried beet showed the highest rehydration ratio and antioxidant activity. Taken together, our results indicate that an appropriate combination of hot air and infrared radiation is suitable to produce high-quality dried beet.