Correlation of viscoelastic behavior with water state and ultrastructure in hot air-dried carrots

- Hot-air drying decreased Tp, Ce, He, T22, T23, M22, and M23 in carrots.
- PCA regression analysis was performed.
- Viscoelastic behavior was linked to water state and cell wall components.
- Elastic modulus decreased due to reduced free water and cell wall components.
- The pronounced changes in cell ultrastructure could explain the results obtained.

This study evaluated and correlated the viscoelastic behavior, water state and ultrastructure of hot air-dried carrots. The results revealed that with increasing time, hot air-drying increased loss tangent (Tan δ) and reduced storage (G′) and loss (G″) moduli, cell wall components including total pectin (Tp), hemicellulose (He), and cellulose (Ce), free water (reflected by relaxation time T23 and relative area M23) in vacuoles, and immobilized water (T22 and M22) in cytoplasm and extracellular space in carrots. Pearson's correlation analysis showed that G′ and G″ were positively correlated (p < 0.01) with T22, T23, M23, Tp, He, and Ce in dried carrots, whereas Tan δ was negatively with these indicators (p < 0.01). Principal component regression analysis revealed that the contribution rate of principal factor 1 and 2 (F1 and F2) was 72.7 and 21.9%, respectively. The Tp, He, Ce, T23, and M23 (42.3, 42.7, 42.5, 43.8 and 44.2% of the explained variance, respectively) were well explained by F1. The G′, G″, and Tan δ could be predicted by the following regression equation, G′ = 0.696 × F1, G″ = 0.680 × F1, and Tan δ = 0.341 − 0.652 × F1. These relationships were consistent with the more pronounced changes (plasmolysis of cytoplasm, disruption of plasmalemma and tonoplast, and degradation of cell walls and middle lamella) in the ultrastructure of dried carrots.