Abstract:

The new flue-cured tobacco variety ‘YM2020’ is a mutant of ‘Yunyan 87’. To explore the optimal curing process for the middle leaves of ‘YM2020’, its curing characteristics were systematically evaluated and compared with those of ‘Yunyan 87’. A suitable curing process was also developed. Through dark-box and dynamic curing experiments, the yellowing/browning characteristics, moisture loss patterns, chlorophyll degradation dynamics, polyphenol oxidase (PPO) activity changes, and shrinkage rates of the tobacco leaves were determined. The results showed that ‘YM2020’ and ‘Yunyan 87’ had comparable ease of curing, with similar yellowing rates (complete yellowing within 72 hours). However, ‘YM2020’ had moderate curing tolerance [average PPO activity of 0.3-0.4 U/(g·FW)], which was lower than that of ‘Yunyan 87’ [PPO activity< 0.3 U/(g·FW)]. During the curing process, ‘YM2020’ exhibited a ‘slow-fast-slow’ moisture loss pattern, with a 12.6% slower chlorophyll degradation rate in the first 48 hours compared to ‘Yunyan 87’. Additionally, its shrinkage rates (length 19.61%, width 37.35%) were significantly higher than those of the control. Based on these characteristics, a phased temperature and humidity control process was proposed: during the yellowing stage (37-43℃), a gradual temperature increase to promote chlorophyll degradation; during the coloring stage (45-54℃), precise temperature control to balance material conversion and drying rate; and during the dry vein stage (54-62℃), a staged temperature increase to ensure complete drying of the main vein.

Key words: flue-cured tobacco, moisture content, dehydration pattern, chlorophyll degradation rate, polyphenol oxidase, curing characteristics, curing process