Influencing Factors And Prevention Measures Of Mildew Tobacco Leaf During Flue Curing

In order to prevent tobacco leaf mildew during baking,the middle leaf(9th-11th)of Yunyan 85 was used as material.The content of starch in tobacco leaves was determined by the method of iodine coloration.The total sugar content and reducing sugar content in tobacco leaves were measured by using a flow analyzer(API).The CS-C3S-52 FR fluorite camera and the MIK-TH702 type temperature and humidity recorder recorded the state of tobacco,the temperature and relative humidity in the baking process.FEI Quanta 200 scanning electron microscope was used to observe the ultrastructure of the midrib pulse.The self designed wind turbine wind direction variable control system and the air separation system were used to prevent and control the mildew of the flue cured tobacco.The main results are as follows:1.The results of tobacco leaf mildew study showed that tobacco leaves from different parts had the highest incidence of tobacco leaf mildew in the following areas,followed by the middle tobacco leaves,and the lowest rate of mildew in the upper leaf tobacco leaves.The incidence of tobacco leaf mildew had the first decline and then increase with the increase of tobacco maturity,the mildew incidence of proper ripe leaves was the lowest,and the mildew incidence of over ripe leaves was the highest.The impact of parts and maturity of tobacco leaves on the mildew of tobacco leaf had a greater proportion of maturity.The content of starch content,starch / total sugar,starch / reducing sugar content in tobacco leaves had a significant correlation with the leaf mildew.2.The results of studies on the ultrastructure of midribs in mildew tobacco leaves show that,at 0 to 12 hours,the midvein port of the leaf was damaged and some crystals were produced.When 12-24 hours,the crystal cracked and appeared hyphae in tobacco midvein.When 48-60 hours,the mold rapidly grew and propagated,and the growth of fungi was in epidermis > cortex > middle column.The width of epidermal cells in the midrib of tobacco slowly contracted from 0 to 12 hours,and there was a slight amount of fungal spores sprouting.The degree of contraction rapidly increased after 12 hours.Mycelia appeared at 12-24 hours,and the rapid growth and propagation period of fungi was between 48-60 hours.Epidermal gland hairs were shrivelled at 60 hours.The time of outbreak of tobacco leaf mildew was in the mid-yellow period.The breakage of midrib tissue of tobacco leaves was mutually promoting with mold growth and propagation on tobacco leaves.The midrib of tobacco was easily infected with mold.Therefore,it is necessary to reduce the injury of tobacco leaves to the midrib tissue during picking and baking.3.The incidence of mildew in tobacco leaves was changed by S-type during the baking process.The start time of mildew from one layer to four layers of tobacco in a four-story densely-baked barn was 30.3,28.7,23.2,and 22.3 hours;the one to four layers of mildew eruption were 49.29,46.97,44.70 and 43.47 hours;the one-fourth-grade mildew termination time was about 63.3,62.7,57.3 and 56.7 hours.Except for the mildew changes of the first and second floors and the third and fourth floors of the four-story air-flow rising dense barn,there were extremely significant differences.With the increase of tobacco level in the barn,the temperature gradually decreased,the relative humidity increased gradually,and the longer the low temperature and high humidity time,the mildew was more serious.The trend of tobacco leaf mildew was S-type,and it was related to the temperature and humidity during baking.In order to prevent mildew during the baking period,the temperature of the high temperature layer must be equal to or higher than 41.5°C and the relative humidity is equal to or less than 77.8% before 43.4 hours.4.The wind direction variable control system reduced the temperature difference in the baking room during the baking process,between 12-48 hours,and the temperature difference of the barn room was controlled below 1.5 °C.Compared with the conventional,reduced the temperature in the barn was about 1.5 °C.In addition,it was able to reduce the condensation water content in the low-temperature zone,between 12-48 h,reduced the average value of condensed water content in low temperature area was 22.2%,and then effectively alleviate tobacco mildew in baking.The device of air separation controlled the temperature difference in the baking process within a reasonable range,so that the temperature difference in the baking room in the early yellowing period and the middle yellowing period was between 1.0-1.5 °C,made the temperature difference of the baking room was between 1.5 and 2.0 °C in the late yellowing period,which reduces the mildew of the tobacco during the baking process.Improved barn tobacco mildew incidence compared with the conventional barn,there was a significant difference.