Influence of Drying by Convective Air Dryer or Power Ultrasound on the Vitamin C and β-Carotene Content of Carrots

Convective air drying and power ultrasound effects on vitamin C and beta-carotene contents in carrots were studied. For convective air drying, a central composite face-centered design fitting temperature between 40 and 65 degrees C and air flow rate between 2 and 6 x 10(-1) m/s were used; previously, carrots were blanched. Likewise, ultrasound drying was performed on both unblanched and blanched carrots at 20, 40, and 60 degrees C for 120, 90, and 75 min, respectively. Blanching had a sharp effect on vitamin C and beta-carotene degradation (80-92% retentions, respectively), and convective air drying led to further losses (32-50% and 73-90% retentions, respectively). According to the response surface model, a combination of 40 degrees C and 6 x 10(-1) m/s will maximize vitamin C retention in dried carrots, whereas 40 degrees C and 3.3 x 10(-1) m/s will ensure the highest beta-carotene content. Ultrasound drying caused higher vitamin C and beta-carotene retention (82-92% and 96-98%, respectively) than convective air drying. Blanched carrots dehydrated by ultrasound showed retentions of 55% and 88% of vitamin C and beta-carotene, respectively. Ultrasound drying at 20 degrees C for 120 min caused the maximum vitamin C and beta-carotene contents. Therefore, power ultrasound may be considered a valuable tool to obtain high nutritive dehydrated carrots.