烟叶采收成熟度对烘烤过程中酶促棕色化反应相关指标的影响

Effect of Different Harvesting Maturities of Flue-cured Tobacco on Related Indicators in Enzymatic Browning Reaction during Curing

以烤烟新品种‘豫烟11号’为试验材料,研究未熟、成熟和过熟烟叶在常规三段式烘烤过程中水分含量、多酚氧化酶（PPO）活性和多酚类物质含量的变化特征,以及指标间的关系,以明确烟叶采收成熟度对酶促棕色化反应的影响及各指标之间的内在联系.结果表明：（1）在烘烤过程中,3个成熟度烟叶的水分含量逐渐降低;其PPO活性先缓慢下降,再快速上升,最后急剧下降;而总酚与绿原酸含量先缓慢上升,再缓慢下降,最后快速上升.未熟和过熟烟叶的芸香苷含量变化与总酚类似,成熟烟叶芸香苷含量呈现缓慢‘降-升-降-升’趋势;3个成熟度烟叶莨菪亭含量变化总体呈波动上升趋势.（2）在酶促棕色化反应敏感期（烘烤48～66 h）,水分含量和PPO活性以未熟烟叶最高,成熟烟叶居中,过熟烟叶最低,总酚和绿原酸含量以成熟烟叶最高,过熟烟叶略低,而未熟烟叶最低;3个成熟度烟叶芸香苷和莨菪亭含量差异没有明显规律性.（3）在棕色化反应敏感期,不同成熟度烟叶PPO活性变化与多酚类物质积累速度均呈负相关关系,未熟与成熟烟烟叶分别达到了极显著和显著水平,而与过熟烟叶没有达到显著水平,未熟、成熟烟叶因过高的PPO活性明显降低了多酚类物质积累速度,而过熟烟叶因较低的PPO活性对多酚类物质的积累速度影响较小.研究认为,适当提高烟叶田间采收成熟度,能够有效地提高烘烤过程中烟叶的失水速率,降低PPO活性,有利于防止烟叶发生褐变,提高烤后烟叶的外观和内在品质.

Effects of different maturities（unripe, ripe and overripe）of tobacco on the changes in the content of water, PPO activity, polyphenols of ＇Yuyan 11＇ （a new kind of flue-cured tobacco） during baking process and the correlation between indexes were investigated. The results indicated that： （1）The tendency of the changes in the contents of water,PPO activity, total polyphenols in three maturity levels are similar：Water content of tobacco leaf gradually reduced;PPO activity slightly declined, then rapidly increased and finally sharply declined. The changes in the rutin content of unripe and overripe tobacco leaves were similar. The trend of rutin content in mature tobacco leaf was ＂decreasedqncreased-decreased-increased＂ slightly. The content of scopoletin in three maturities increased as a whole. （2）During the sensitive period in enzymatic browning reaction（48--66 h in the curing process）, overripe tobacco had the lowest content of water and PPO activity,the contents of total polyphenols and chlorogenie acid were slightly lower than that in mature tobacco. The water and PPO activity contents of mature tobacco leaf were lower than that in immature to- bacco leaf and higher than that in over mature tobacco leaf. The contents of total polyphenols and chloro genic acid in mature tobacco leaf were the highest. The water and PPO activity contents of immature tobac- co leaf were the highest ~ the contents of total polyphenols and chlorogenic acid in immature tobacco leaf were the lowest. The content differences of rutin and scopoletin among three maturities had no significant regularity. （3）During 48--66 h period, there was a significant negative correlation between the change of PPO activity and the accumulate speed of polyphenols..Unripe treatment reached an extremely significant level,mature treatment reached a significant level, and overripe treatment reached an insignificant level. It suggested that high PPO activity reduced the accumulation of polyphenols in immature and mature tobacco leaf significantly,and low PPO activity effected on the accumulation of polyphenols in overripe tobacco insignificantly. The result indicate that appropriately improving the maturity of harvested flue-cured tobacco, can promote the tobacco leaf water loss effectively, so as to reduce the PPO activity during the curing process,it is beneficial to prevent Browning in tobacco leaves,thus improve the appearance and intrinsic quality of cured tobacco leaf.