Shrinkage and Color Change during Microwave Vacuum Drying of Carrot

Abstract

Microwave vacuum drying (MVD) was applied to carrot slices and the radial shrinkage and changes in color and shape of its main tissues were evaluated. Tissue dimensions were obtained using computer vision; their visual color was quantified from Hunter Lab coordinates and their carotenoids contents were determined spectrophotometrically. The drying time varied from 24 to 42 min when the microwave power was changed from lower to higher values. MVD samples showed high rehydration capacity. The radial shrinkage values ranged from 36.2 ± 5.0 to 46.1 ± 4.6%, where higher values were seen in the core and under high microwave power. Circularity, solidity, and major and minor axes were shape descriptors of carrot slices that varied significantly during drying, changing from 0.58 to 44.3% of their initial values. In both fresh and dried products the cortex color exhibited superior color than that of the core. MVD incurred a significant whitening index and carotenoids losses.

Keywords:

• Carotenoids
• Carrot
• Color
• Core
• Cortex
• Shape
• Shrinkage
• Vacuum microwave drying

ACKNOWLEDGMENTS

Financial support for this study was provided by the China Scholarship Council. The authors acknowledge the assistance of Professor A.S. Mujumdar of the National University of Singapore in the preparation of this article.

Notes

^a β = ER/ER ₀; a, b, c, d, e are model parameters; X, X ₀ are instant and initial moisture contents.