烟叶烘烤过程中蛋白质的降解及相关酶活性的变化

  目的  明确不同成熟度烤烟烘烤过程中蛋白质降解规律。  方法  以K326为材料，分析烟叶蛋白质、游离氨基酸含量，内肽酶、氨肽酶和羧肽酶活性变化情况。  结果  1）烘烤过程中，烟叶蛋白质含量持续下降；2）蛋白质的降解幅度与内肽酶活性密切相关。与尚熟烟叶相比，适熟和过熟烟叶在变黄前期内肽酶活性最高，蛋白质含量降解幅度大。3）游离氨基酸含量升高幅度与氨肽酶和羧肽酶活性有关。与适熟和过熟烟叶相比，尚熟烟叶在变黄后期，氨肽酶和羧肽酶活性较高。  结论  适当延长变黄期（36~38℃）烘烤时间，有利于保持烟叶内肽酶的活性，减少不同成熟度烘烤烟叶中蛋白质的含量。 

Changes of protein degradation and related enzyme activity during flue-curing

  Objective  Explore the degradation rule of protein content in tobacco leaves with different maturity during flue-curing process.  Method  Flue-cured tobacco K326 was adopted as test material to study the dynamic changes of protein content, free amino acid content, the activities of endopeptidase, aminopeptidase and carboxypeptidase.  Result  (1) During flue-curing, the content of protein continued to decline, the content of free amino acids continued to rise in immature tobacco leaves, the content of free amino acids showed a "rise-down-rise" change in the proper-mature and over-mature tobacco leaves; (2) The protein degradation range was related to the activity of endopeptidase.The endopeptidase activity variation followed a double-peak curve of "rise-down-rise-down".Compared with immature tobacco leaves, the proper-mature and over-mature tobacco leaves (curing time 24~48 h) had the highest endopeptidase activity and faster protein degradation rate at the early yellowing stage.(3) The ascending range of free amino acid content was related to the aminopeptidase and carboxypeptidase activities.Compared with the proper-mature and over-mature tobacco leaves, the immature tobacco leaves (curing time 24~72 h) had higher aminopeptidase and carboxypeptidase activities and the content of free amino acid continued to rise in the curing process.The free amino acid content in the proper-mature and over-mature tobacco leaves presented a"rise-down-rise" trend, which indicated that proper-maturity had a certain effect on the conversion of free amino acids into maillard products.  Conclusion  This study reveals the relationship between content of protein and free amino acids and the activities of endopeptidase and exopeptidase in curing process.It is shown that appropriately extending curing time of yellowing period (36~38 ℃) will help maintain the activity of endopeptidase and reduce protein content in tobacco leaves with different maturity.