The Relationship Between Color Change Of Tobacco Leaves Based On Chroma And Moisture And Chemical Composition During Flue-Curing

To study the relationship between color,moisture content and main chemical components in tobacco leaf during curing qualitatively and quantitatively.Exploration of intelligent monitoring indicators for tobacco flue-curing.The flue-cured tobacco variety K326 was used as test material.Quantification of leaf and main vein color in curing process by chromatometer.Detection of moisture content and main chemical components in tobacco leaves.Changes of color parameters,moisture content and main chemical components in tobacco leaves during curing were analyzed.And based on the color parameters of leaf and main vein(L*?a*?b*??E),the relationship between leaf color and water content and main chemical components was explored.The main results are as follows:(1)Variation of leaf color parameters during curing:Variation regularity of color parameters on front and back of blade is basically the same.They all rise rapidly before 42 C and then tend to be stable gradually.The color change of upper leaves lagged behind that of middle and lower leaves.During the curing period,During the curing period,a*,b*,?E values on the front of leaves were always higher than those on the back,while L*values were lower than those on the back of leaves.The results showed that the change rate of leaf front color was faster than that of leaf back color.(2)Variation of midrib color parameters during tobacco curing:The variation law of tobacco leaves in different parts is basically similar.Among them,the L*value increased slowly from the beginning of baking to 48?,decreased slowly from 48?54?,and then decreased sharply.The values of a*and ?E increased during curing.The growth rate of a*value of lower leaves was faster than that of middle and upper leaves after 45?.The value of b*decreases before 42?,and then increases with the advance of curing.Overall,the midrib color of lower leaves changed faster,while that of upper leaves lagged behind.(3)Correlation analysis of color parameters of tobacco leaves in curing process:The change of color parameters on the front and back of tobacco leaves is basically synchronized.Significant or extremely significant positive correlations were found between ?E values on the front and back of leaves and various color parameters.The correlation between front and back color parameters of middle leaves was the best among different parts of tobacco leaves,and there was a significant or extremely significant positive correlation between the front and back color parameters.The correlation between main vein and leaf color parameters was poor,while the correlation between L*,b*and leaf color parameters was not significant.The value of a*was only positively correlated with the value of a*in the upper leaves,while the value of ?E was positively correlated with the color parameters of the leaves.(4)Changes of moisture content index in tobacco leaf during curing:The total moisture content of tobacco leaves showed a decreasing trend.The total moisture content of leaves and whole leaves decreased slowly before 42?,the rate of moisture loss increased gradually during 42?54?,and slowed down again after 54?.The total moisture content in the main veins of the middle and lower leaves decreased significantly after 48?,while that in the upper leaves lagged behind that of the leaves after 54?.Free moisture content of leaves and main veins decreased with curing.Free moisture content of leaves decreased rapidly before 38?,and that of main veins decreased rapidly after 48?.The moisture loss of upper leaves and main veins was slower than that of middle and lower leaves.The bound moisture content of leaves and main veins increased first and then decreased.The bound moisture content of leaves increased before 38?,and the decreasing rate increased gradually with the increase of curing temperature.After 54?,the decreasing rate slowed down obviously.The bound moisture content in the main veins of middle and upper leaves increased slowly before 48?,while that in the lower leaves increased gradually after reaching the highest value before 42?,and the decrease was the most significant after 54?.(5)Changes of main chemical components in tobacco leaf during curing:The content of total sugar and reducing sugar increased rapidly before 42?,then the growth rate slowed down and tended to be stable.Starch and protein content decreased rapidly before 42?.Total nitrogen content of middle and lower tobacco leaves decreased continuously during curing.The contents of nicotine,chlorophyll a,chlorophyll b,total chlorophyll and carotenoids all showed a decreasing trend,but the degradation of nicotine was lower during curing period.The contents of chlorophyll a,chlorophyll b and total chlorophyll decreased sharply before 38?,and basically degraded completely after 42?.Carotenoid content in middle and lower leaves decreased slowly before 48?,then stabilized.Carotenoid content in upper leaves decreased continuously before 54?.Carotenoid residues were significantly higher than chlorophyll after curing.(6)Analysis of the relationship between color parameters,moisture content and main chemical components in curing process:The values of a*,b*,?E of main veins were correlated well with total water of leaves,total water of main veins,total water of whole leaves,free water of leaves,free water of main veins and bound water content of leaves,while the lower leaves were significantly or very significantly negatively correlated.There is a good correlation between the leaf color parameters of middle and lower leaves and the free water content of leaves.The correlation between leaf color parameters and main chemical components in different parts of tobacco leaves was significant,but chlorophyll a,chlorophyll b and total chlorophyll contents in different parts of tobacco leaves were significantly or very significantly negatively correlated with leaf color parameters on both sides.The correlation between reducing sugar,total sugar and total nitrogen content and color parameters was the best in the middle leaves.The correlation of color parameters with nicotine and protein content was best in upper and lower leaves,respectively.Regression equation of moisture and main chemical components content in different parts of flue-cured tobacco leaves based on color parameters of front,back and midrib of flue-cured tobacco leaves showed good fitness.The change of color parameters in curing can be used to quantitatively predict the change of moisture content and main chemical composition content.