Drying kinetics and quality characteristics of beetroot slices under hot air followed by microwave finish drying

Abstract

The experiments were conducted to evaluate the impact of air temperature and microwave power level on drying behavior and quality of beetroot. The osmotically pretreated samples in sugar-salt mixed solution were further dehydrated using convective tray drier upto a moisture content of 40 to 60% db (the point where drying rate became slow) followed by microwave drying to a moisture content of 6% (bone dry conditions) to overcome the slow removal of moisture content in the end. Three levels of air temperature 55, 65 and 75°C and microwave power 540,810 and 1080 W each were selected and readings on moisture content, rehydration ratio, color, total soluble solid, water activity and hardness were taken. The results showed that osmotic pretreatment prior to hot air microwave finish drying improved the final quality of dehydrated sample. The drying took place in the falling rate drying period regardless of the drying conditions. Drying at high air temperature (75°C) followed by high microwave power (1080 W) witnessed increased drying rates and substantial shortening of the drying time. Two term and logarithmic model successfully described the drying kinetics of convectively dehydrated and microwave finish dehydrated beetroot slices respectively. Rehydration characteristics of beetroot were improved for samples dehydrated at 55°C and 1080 W, which helped in reduction of shrinkage and case hardening. A greater change in color resulted due to decreased L and b values and increased 'a' value with increase in both air temperature and microwave power. Sample dehydrated at high air temperature followed by high microwave power exhibited high water activity, high total soluble solids (TSS) and improved hardness as compared to fresh sample.

Process optimization for dehydration of shelled peas by osmosis and three‐stage convective drying for enhanced quality

“…Water removal is based on the natural and nondestructive phenomenon of osmosis across cell membranes (Kar & Gupta, 2001;Kaur and Singh, 2014 ). The higher osmotic pressure of the hypertonic solution acts as the driving force for the diffusion of water from the tissue into the solution with concomitant counter diffusion of solutes from the osmotic solution into the tissue.…”

Drying of peaches by a combination of convective and microwave methods

“…The Henderson & Pabis model has also been used successfully to describe the drying kinetics of ginger (Thorat et al, 2012), strawberry (Doymaz, 2008), beetroot (Figiel, 2010), and oregano (Figiel et al, 2010). On the other hand, the logarithmic model was found to be suitable for peach slices (Kingsly et al, 2007) and beetroot slices (Kaur & Singh, 2014), while for the description of drying behavior of garlic using vacuum, the modified Page model was proposed (Calin‐Sanchez et al, 2014).…”

“…Comparable observations have been reported for apples and carrots by Funebo and Ohlsson (1998), who found that the finishing method gave better rehydration results. However, Drouzas and Schubert (1996) observed that banana slices dried in vacuum absorbed twice as much moisture as the product of the conventional method, while Kaur and Singh (2014) reported that the microwave finish method helped in reducing shrinkage and avoiding surface hardening of beets.…”

Effect of Drying Methods on Physicochemical Parameters of Different Red Beetroots (Beta vulgaris L.) Species

“…5, which shows the differences between the each drying methods. Based on the drying curve of the different beetroot and according to other scientific results [21][22][23] the microwave drying resulted faster drying compared to the traditional method and it is effective on lower temperature except the MV40 method, where the pre-drying was longer because of the low temperature.…”