Abstract:
In order to clarify the quality and their formation mechanism of the upper leaves harvested with stalks, Yunyan 87 was used as a test material to analyze the quality characteristics of the upper leaves harvested and cured with stalks and the upper leaves harvested and cured leaf by leaf and the differences in the microstructure, antioxidant capacity and dry bulb temperature of the leaves at the key temperature points during the curing stage. The results showed that: 1) Compared to the leaves without stalks, the appearance quality of the leaves with stalks was significantly better, the area with characteristic yellow color was larger, the
L* and
b* values were higher, and the
a* value was lower. 2) As the curing process progressed, the tissue and cell morphology of the upper leaves with stalks were destroyed by ablation, and the degree of shrinkage lagged behind that of the upper leaves harvested without stalks at various critical temperature points. 3) As the curing process progressed, the mass fractions of lipid peroxide (LPO) and malondialdehyde (MDA) in the leaves generally increased and peaked at the end of the 46 ℃ interval in the color fixing stage, and those in leaves with stalks were 21.02% and 32.01% lower than those in leaves without stalks. The mass fraction of hydrogen peroxide (H
2O
2) and the production rate of superoxide anion (O
2-·) in leaves increased gradually, which were lower in the yellowing stage and higher at the end of the 46 ℃ interval in the color fixing stage in leaves with stalks than in leaves without stalks. 4) As the curing process progressed, the activities of superoxide dismutase (SOD) and catalase (CAT) in leaves with stalks were higher than those in leaves without stalks. The activity of glutathione reductase (GR) in leaves with stalks first increased gradually, then decreased and peaked at the end of the 42 ℃ interval in the yellowing stage; while that of leaves with stalks slowly and gradually increased, and then rapidly and slowly, before peaked at the end of the 46 ℃ interval in the color fixing stage, and the GR activity of leaves with stalks was higher than that of leaves without stalks in the yellowing stage. The total antioxidant capacity (T-AOC) of tobacco leaves generally showed a gradual upward trend, that of leaves with stalks was higher than that of leaves without stalks, and the difference reached a significant level at the end of the 40 ℃ interval in the yellowing stage and at the end of the 46 ℃ interval in the color fixing stage. In conclusion, the appearance quality of the upper leaves harvested and cured with stalks was better, which was closely related to the delayed destruction of the tissue cells and the strong antioxidant capacity of the leaves during the curing process.