Studies On Suitable Maturity Index And Precise Curing Technology Of Tobacco Leaves In Gansu Growing Area

In order to explore suitable maturity index and precise curing process of Gansu tobacco area leaves, Qinyan96 was used in the experiments. The SPAD value(chlorophyll meter reading) of fresh tobacco leaves with different maturity and chemical composition of tobacco leaves with different maturity in the curing process was measured. And then the influence on the quality of flue-cured tobacco leaves with different maturity was studied. The appearance features of maturity that its quality of flue-cured tobacco leaves was the best and corresponding SPAD value was combined to act as the suitable maturity index in Gansu tobacco area. The tests of different yellowing degree in yellowing stage and different wet-bulb temperature in dense curing process were also set on the basis of local conventional curing process. The best treatments were chosen by comparing the quality of flue-cured tobacco leaves, aming to optimize the precise curing technology. The experiment aimed to provide theoretical basis and technical support for local tobacco leaf production. The main results were as follows:1. Study on the suitable maturity index of tobacco leavesSPAD value of fresh tobacco leaves with different maturity was different.The SPAD value of fresh tobacco leaves decreased with the increase of maturity and correlation was significant negative between tobacco maturity and SPAD value; The change trend of chemical composition of tobacco leaves in the curing process was basically consistent,but the speed of change was not same. In the curing process, the content of total sugar and reducing sugar of tobacco leaves with different maturity increased first and then decreased on the whole. However, the maximum of total sugar content and reducing sugar content of tobacco leaves with different maturity emerged at different temperature, lower-maturity tobacco leaves at the ending of 38℃and higher-maturity tobacco leaves at the ending of 47℃. Starch content of tobacco leaves with different maturity showed a trend of decline from high to low. Starch content decreased fast from the beginning of curing to the ending of 42℃, and then decreased slowly. Protein content of tobacco leaves with different maturity decreased fast from the beginning of curing to the ending of 38℃,and then its change range was not big. Different maturity had a certain influence on the quality of flue-cured tobacco leaves. With the improvement of maturity, the quality of tobacco leaves improved. So the highest maturity was suitable maturity in Gansu tobacco growing area. It was yellow green area of tobacco leaves was 70 to 80 percent, and main vein was half white, and SPAD value was 8.6~11.4 in lower leaves; yellow green area of tobacco leaves was 80 to 90 percent, and main vein was white about 66.7 percent, and SPAD value was 17.9~18.6 in middle leaves; yellow green area of tobacco leaves was 90 to 100 percent, and main vein was all white, and SPAD value was 13.2~20.3 in upper leaves.2. Study on the precise process of dense curingThe comprehensive quality of flue-cured tobacco leaves with the treatment of 38℃turning yellow fifty to sixty percent,40℃turning yellow seventy to eighty percent,42℃turning yellow ninety to a hundred percent was at a high level. The proportion of high-class and middle-class tobacco leaves of bottom leaves,middle leaves and upper leaves was highest and it was 83.04%,94.98%,78.92% respectively, increasing 4.82 percentage points, 16.07 percentage points and 3.06 percentage points respectively compared with the contrast treatment. The total score of evaluation results of bottom leaves,middle leaves and upper leaves was highest in three parts. And it was 74.10, 72.90 and 73.20 respectively, better than that of contrast treatment obviously. Of the test of different wet-bulb temperature in the dense curing process,the treatment of high-low-high humidity(wet-bulb temperature was 38℃in leaves yellowing stage, wet-bulb temperature was 36℃in leaves withering stage, wet-bulb temperature was 35℃in vein yellowing stage, wet-bulb temperature was 39℃in leaves drying stage, wet-bulb temperature was 42℃in vein drying stage)had better economic benefits, and its average price of bottom leaves,middle leaves and upper leaves was 19.70 yuan per kg, 23.67 yuan per kg and 17.78 yuan per kg, better than other treatments obviously. The evaluation results of the treatment was best. And its total score of bottom leaves,middle leaves and upper leaves was 74.90, 74.40 and 73.40 respectly, higher 1.00, 1.00 and 1.30 than contrast treatment. The two tests were integrated to optimize the precise curing processes. They were in the yellowing stage, when dry-bulb temperature was 38℃ and wet-bulb temperature was 36 to 37℃,tobacco leaves became yellow 50 to 60 percent, and when dry-bulb temperature was 40℃ and wet-bulb temperature was 38℃,tobacco leaves became yellow 70 to 80 percent; In the fixed-color stage, when dry-bulb temperature was 45 to 47℃ and wet-bulb temperature was 35℃,tobacco leaves and their vein all became yellow and leaves became dry about 33.3 percent,and when dry-bulb temperature was 52 to 54 ℃ and wet-bulb temperature was 39℃,tobacco leaves all dried;In the dry reinforcement stage, when dry-bulb temperature was 65 to 68℃ and wet-bulb temperature was 42℃,the vein of tobacco leaves all dried.