Effect of gum Arabic and ethanol pretreatments on drying kinetics and quality attributes of dried carrot slices

Carrot is an important root vegetable to the food industry and consumers due to its nutritional and health benefits. Given the high moisture content and low shelf life of fresh carrots, preserving this highly demanded vegetable is vital. This current research modelled the drying kinetics and evaluated the quality of ultrasonic-assisted gum Arabic and ethanol pretreated and oven-dried carrot slices. Fresh carrots were processed into thin slices and immersed in 3% gum Arabic (GA), ethanol (99.9%), and distilled water (control), followed by ultrasonication (frequency: 50 Hz, power: 500 W, temperature: 25 °C) for 10 min and drying in a hot air oven at 50 °C. The loss of moisture from the carrots was periodically recorded, converted to moisture ratio before fitted to eleven semi-theoretical thin layer drying mathematical models. The effects of the pretreatments on the retention of bioactive compounds and carrots' physical and chemical properties were also evaluated. From the tested models, the Diffusion, Modified Henderson and Pabis, and Two-term models showed the best fitting (R(2) = 0.9944–0.9985; RSME = 0.0103–0.0227) to the experimental data from 3% GA and ethanol pretreated carrots, while control samples followed the Aghbasho model (R(2) = 0.9999; RMSE = 0.0033). Overall, the 3% GA pretreated carrot slices exhibited better colour (yellowness: 25.82–34.50; total colour differences: 8.12–13.06), water activity (0.37–0.44), total phenolic content (1.34–2.99 mg GAE/100 g DM), β-carotene (7.63–13.07 mg/100 g DM), and DPPH radical scavenging activity (5.67–8.02 mM AAE/100 g DM) than ethanol pretreated carrot slices and control samples. At the same time, 3 % GA pretreatment did not affect the drying rate of the carrot slices. The total soluble solids/titratable acidity ratio, rehydration capacity, and shrinkage ratio did not significantly (p > 0.05) vary among the treatments. The findings of this study can be used to develop an optimal drying protocol for pretreated carrot slices and to produce shelf-stable carrot products that can be used dried, rehydrated, or in combination with other products.