Implication of water state on glass transition temperature in hot air-dried carrot slices

摘要

This study assessed and correlated the water state and the glass transition temperature (T-g) of carrots treated by hot air drying at 50, 60, and 70 degrees C. Results showed that within carrots with high moisture content (X-w, 4.15 >= X-w >= 1.01 g water/g dry matter), free water in vacuoles dominated in tissues and the Tg remained practically constant (-48.4 +/- 1.04 degrees C). And when the X-w of carrots was = 0.41 g water/g dry matter, the T-g was increased by 6.79 and 22.7 degrees C with the relaxation time (T-22) of the immobilized water in the cytoplasm/extracellular space decreasing by 12.4 and 11.8 m, respectively. Moreover, correlation equations indicated that the T-g had a negatively linear relationship with the T-22 in dried carrots. These results suggested that the T-g were elevated appreciably by reducing the relaxation behavior of immobilized water in hot air-dried carrots. The more pronounced variation of the microstructure (e.g., vacuole disruption, cell wall dissociation, and turgidity loss) of tissues could be responsible for these results. (C) 2017 Elsevier Ltd. All rights reserved.