Study On Mineral Element Content Change And Speciation Analysis Of Flue-cured Tobacco Leaf During Curing Process

Experiment on the Electric-type temperature and humidity-controlled intensive tobacco oven designed by Henan Agricultural University was conducted to study the trend of the major mineral elements content in curing process and the effects of mineral element contents in cured leaf in different baking conditions. In order to investigate the existing form of mineral elements in flue cured tobacco leaves, the elements speciation of calcium, magnesium, copper, iron, manganese and zinc in pre-baked and cured leaf were analyzed at different baking temperature and humidity, using gradual extraction method. The main conclusions as follows:1. In curing process, the variation trends of mineral element contents are similar in different regions and varieties of tobacco samples, but the content of different elements is not exactly the same. Among them, iron, manganese, sodium is basically stable in the curing process, no significant change; copper content has increased in yellowing stage and then decreased slowly; calcium, magnesium, boron, phosphorus and potassium content rose slowly in the whole curing process. Cured tobacco leaf compared with the fresh, iron, manganese, sodium content did not change; calcium, magnesium, boron content was significantly increased; phosphorus, potassium, copper content has increased slightly but not significantly; zinc content reduced.2. Different conditions of yellowing and color-fixing has little influence on calcium, phosphorus, copper, sodium, iron and manganese content in curing process, there was no obvious difference in all treatments; influence was significant on potassium, magnesium, boron and zinc content, There were significant differences in all treatments, potassium average content: T1 (15.35mg/g)> T2 (15.09 mg/g)> T4 (14.30 mg /g)> T3 (13.82 mg/g), low temperature in yellowing stage and slow heating in color-fixing stage were beneficial to increasing content of potassium; the maximum content of magnesium was reached at 4.55mg/g at high temperature in yellowing stage and slow heating in color-fixing stage; the lowest content of magnesium was reached at 4.04 mg/g at high temperature in yellowing stage and rapid heating in color-fixing stage; boron content: T1 (29.67μg/g)> T4 (29.66μg/g)> T2 (27.53μg/g)> T3 (26.80μg / g), the effects of increasing boron content was more obvious at low temperature treatment in yellowing stage; zinc content: T1 (36.68μg/g)> T3 (35.82μg/g)> T2 (32.09μg/g)> T4 (30.02μg/g). 3. The main existing form of the elements in tobacco leaves showed: deionized water extractable (36.84% ~ 49.67%) and NaCl extractable (15.50% ~ 26.13%) state were the main existing form of calcium in tobacco leaves; ethanol extractable (28.15% ~ 36.36%), deionized water extractable (28.13% ~ 48.01%) and residual state (15.56% ~ 32.97%) were the main existing form of magnesium;HAc extractable state (24.8% ~ 49.4%) was the main existing form of iron; deionized water extractable (21.07% to 31.43%) and HAc extractable state (31.36% ~ 35.27%) were the main existing form of zinc; the main existing form of manganese in fresh tobacco leaves is different from cured tobacco leaves, deionized water extractable(54.05%)and residual state(23.37%) were the main existing form of manganese in fresh tobacco leaves, deionized water extractable(38.6%～56.53%)and HAc extractable state (9.81% ~ 30.85%) were the main existing form of manganese in cured tobacco leaves.4.In different curing treatments, the general trend of various forms of mineral elements: residual state calcium species raised, which T1, T2 treatments, were significantly increased; NaCl extractable state calcium content was significantly decreased; ethanol extractable state raised, T2 treatment reached significant level; deionized water extractable, HAc extractable, NaCl extractable state had no significant changes.Ethanol extractable, HAc extractable and residual state magnesium Content rose significantly; deionized water extractable state did not change significantly; NaCl extractable state increased, T1 treatment reached significant level; HCl extractable state magnesium increased significantly in T1,T2 treatments.Ethanol extractable, deionized water extractable, HAc extractable, HCl extractable state Copper Content did not change significantly; residual state Copper Content increased significantly.Ethanol extractable, NaCl extractable, residual state iron Content increased, HCl extractable state iron Content decreased, HAc extractable state decreased significantly in T3,T4 treatments; deionized water extractable state did not change significantly.Ethanol extractable, deionized water extractable, HAc extractable, HCl extractable state Manganese Content increased, residual state decreased significantly; NaCl extractable state increased significantly in T1,T2 treatments.Ethanol extractable, deionized water extractable state Zinc Content decreased, HAc extractable state Zinc Content decreased significantly in T4, residual state decreased in T2,T4 treatments.