Inflection point controlled intermittent drying shows improved quality retention in carrots.
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Interruption of the drying process at the correct moisture level and tempering period have a significant impact on the resulting quality.
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Intermittent heat supply has beneficial effects on energy efficiency improvement with a great potential for improving sustainability in drying processes.
Abstract
The objective of this research was to investigate the effect of intermittent drying on drying kinetics, moisture diffusivity and quality of organic carrot. The intermittent drying was conducted at 60 °C and 70 °C with a constant air velocity of 0.6 m/s. The drying process was paused at 30% moisture levels at which the inflection point for degradation of total carotenoids lies in this region and also at 40% moisture level in order to investigate the possibility of increasing the retention by changing the settings at slightly higher moisture content. Tempering was performed for 1 and 3 h under ambient condition and the results showed a significant effect on drying time and effective moisture diffusivity. Specific energy consumption reduced by 17.0% to 25.5% after tempering at 1 and 3 h for both moisture levels. Drying at 60 °C and tempering at a moisture level of 30% shortened the effective drying time by 24.5% compared to that of 18.2% when tempering at 40% moisture level. Moisture diffusivity for both moisture levels and tempering periods increased when drying was conducted at 70 °C as compared with 60 °C. The ideal drying condition was found to be at 60 °C with the tempering time of 3 h at 30% moisture level (wb) resulted in the best retention of total carotenoids (76.9% ± 2.42), total color change (8.1 ± 1.67) and rehydration ratio (0.4 ± 0.01).
