Chemical Changes in Tobacco during FIue-Cu ring Flue-cured tobacco, widely used for cigarette manufacture, represents over half of all tobacco produced in this country where climatic and soil conditions have proved to be especially suitable. Using a special heat-curing process the green tobacco leaf i s changed in about 5 days to the yellow “bright” leaf o f commerce. The results of tests reported here show that during curing, starch changed to sugars, resulting in the high sugar content characteristic of this type. Slight losses of total nitrogen and nicotine and a decrease in protein nitrogen occurred. Also, small losses of resins, oxalic, and pectinic acids were found. No significant changes in crude fiber, ash, malic and citric acids, and pH occurred. Sucrose was largely changed to reducing sugars during bulking subsequent to curing.
C. W. BACON, RAYMOND WENGERl, Bureuu o f Plunf
AND JAMES F. BULLOCK Indurfry, U. S . D e p a r f m e n t of Agriculture, Belfsville, Md.
HE flue-curing process is the method of curing tobacco by artificial heat in the relatively short time of about 5 days as contrasted to the older air-curing process, a t prevailing temperature, requiring 1 or 2 months. By proper regulation of temperature and ventilation a yellow colored product is obtained, very different in composition from the brown leaf produced by air curing with essentially only ventilation control. The development of the flue-curing process and the economic situation arising from its widespread use are reported by Tilley (24). Formerly, wood-burning furnaces, with metal flues inside the curing barn, and an outside smoke pipe were used. At present, however, a variety of heating systems are employed. Studies of the process itself were made by Cooper, Delamar, and Smith (7‘) working with conditioned air; Moss and Teter (16) studied the conduct of the process as ordinarily carried out using wood, oil, and coal as fuels. Since flue-cured tobacco can be obtained only by use of its special curing procedure information on the process is desirable for an understanding of the chemical changes involved. As ordinarily carried out the process is empirical and, to a large degree, its success depends on,the experience of the curer with the tobacco being processed. The flue-cured types do not ’lave identical characteristics, and various agronomic conditions affect the tobacco produced, and consequently its optimal, curing procedure. Fortunately the leaf itself affords a good index, to experienced persons, of the progress and for the regulation of the curing. Control is based on observation of leaf color, moisture content, and on temperature and humidity of the air within and outside the barn. While the ranges of temperature and humidity will not vary materially in a series of cures, the duration of the several phases and associated conditions for each and time of their application will be subject to considerable variation. During the process the brittle harvested leaf of greenish-yellow color is transformed into the pliant, yellow, flue-cured tobacco leaf. The changes taking place depend on the controlled action of the leaf enzymes to bring about the desired biochemical changes. If the temperature that the enzymes can tolerate is exceeded too early in the process the transformations are abruptly ended and a less desirable product, still containing green color, will result. Also, if the leaf dries too soon to such an extent that the enzymes are unable to function the cure will be unsatisfactory. With the limitations applying to any particular set of curing conditions in mind the record of a normal curing of South Carolina tobacco has been charted in Figure 1.
T
* Present
address, R. J. Reynolds Tobacco Co., Winston-Salem, N. C .
292
The desired high humidity and moderate temperature during the “yellowing” stage are shown as well as the loss of original green weight, mostly moisture, of about 30%. This loss is desirable in order that too much moisture will not remain in the leaf when the temperature is increased and the moisture comes off more rapidly. The thickness and state of ripeness of the leaf largely determine the temperature that can be used without causing the leaf tips to dry when still containing some green color and alsn the length of time required to complete the yellowing. Although 2 days may be required for yellowing, the fuel consumption during the period will be only a small percentage of the total. The “drying of the leaf” stage follows, and the loss of original weight is rapid as the temperature is raised. In about 3a/4 days a temperature of about 130’ F. and a relative humidity of about 30% is reached. At this time approximately 70% of the original green weight has been lost and about 50% of the fuel consumption used. The drying of the leaf tissue is frequently completed a t this temperature. The final, or “stem drying stage,” during which the leaf stems, which still contain a large amount of water, are dried, is carried out a t 175’ F. or considerably higher. A final weight loss of 82% of the original green leaf is shown, a t which time the humidity is reduced to about 12y0 The large difference in rate of loss of water from the lamina and midrib greatly extends the curing t i e . Using North Carolina tobacco, the moisture content of the two parts of the leaf were determined a t several stages of the curing. When the lamina contained only l6Y0 of moisture, the midrib contained 78%. At the end of the curing the moisture content of the former was 5.5% and the latter 7%. Previous Investigations
The biochemical changes in a number of constituents of tobacco during air curing were early studied by Garner, Bacon, and Foubert (13). Later, Garner, Bacon, and Bowling (12)reported on the relationship of production conditions to the chemical and physical characteristics of cigarette tobaccos (flue cured and other types) and of cigar tobaccos. The most extensive studies on the chemical composition of flue-cured tobacco were made by Darkis, Dixon, and coworkers (8-11). Despite the great commercial importance of flue-cured tobacco for cigarette manufacture, it was not until the past decade that chemical changes associated with its special curing process were investigated. The color of flue-cured tobacco serves as an index of its maturity
February 1952
I N D U S T R I A L A N D E N G I N E E R I N G CHEM‘ISTRY
293
has always been used as the most important guide Table 1. Chemical Changes during Flue Curing (Second Primings)for ita curing, and plays a leading role in its quality evaluation. Weybrew and Stinson (87) Data of Sastry (23) Chemical Changes, Grams/100 Grama Fresh Leaf first studied the progressive changes inBtotal green and total yellow pigments a t intervals during the Yellowing, hours Fixing, hours Drying, hours 0 29 54 ‘ 65 76 102 128 curing process. 0 29.37 31.53 46.48 53.39. 78.43 80.01 Loss in weight Observations of the tobacco and later pigment LOSS due t o water 0 27.81 30.44 45.39 51.26 75.84 77.41 2.59 2.60 1.56 1.09 1.09 2.13 Total loss-water 108s 0 analysis indicated that the leaf had “yellowed” Total solids 21.74 20.18 20.65 20.65 19.61 19.15 19.14 3.59 3.69 3.34 3.91 3.39 3.30 3.66 in a satisfactory manner when chlorophyll had Organic Inorganio solids solids 18.35 16.88 ‘16.99 17.06 15.92 15.81 15.23 been reduced to 10 mg. or less per square meter Bastry’s Data Recalculated to Initial Dry-Weight Basis, 70 of leaf surface. Using this figure as a measure of 26.22 3.86 1.66 1.43 ~ ~ ~ ~ glucose $ i1.98 ~ 11.73 5.24 ~ ~6.35 9.66 ~ 10.63 ~ 10.76 a2.30 s 7.08 6.39 the time required for yellowing, OVematUre leaf Suorose as invert sugar 0 0 0.51 0.28 0.32 6.76 6.39 yellowed in 36 hours and normal leaf in 48 hours. 1.98 6.24 10.17 10.90 11.09 13.85 12.79 Total sugars The immature leaf, however, still retained more ~ o t a carbohydrates l 28.20 16.97 16.51 14.77 13.39 15.50 14.21 1.674 1.670 1.647 1.725 1.665 1.587 1.711 Total N than the 10 mg. chlorophyll value after 84 hours, Soluble N 0.662 1.132 1.256 1.398 1.325 1.297 1.329 Insoluble N 1.012 0.492 0.391 0.327 0.340 0.290 0.382 the end of the curing process. When “yellowed” 0.198 0.179 0.179 0,198 0.198 0.198 0.207 Nicotine N after 36 hours, there had been a loss of about 73% Ammonia N 0.012 0.011 0.012 0.018 0.014 0.028 0.032 0.147 0.083 0.074 0,074 0.120 0.133 0.120 of chlorophyll and 21% of yellow pigments. At 0.368 0.869 0.989 1.063 0.980 0.952 0.943 the end of the curing the corresponding losses were about 95 and 45%. Studies of composition changes during curing green leaf basis or 12 to 16% on the original dry weight basis. have been made in several countries on the tobacco produced unWeight losses due to water were from 77.4 to 79.5%. Inorganic der their prevailing climatic and existing soil conditions. Ward solids remained unchanged during the process and losses in (86)working with Canadian tobacco was the first to study the organic solids (fresh leaf basis) averaged 1.6% during YelloWing, changes in carbohydrates a t intervals. Shortly after the to0.86% during color fixing (leaf drying), and 0.51% during stem bacco entered the kiln the sugars began to increase and the drying; 76 to 90% of the starch disappeared during yellowing, starch to decrease rapidly. During the process initial total sugar
kgpNN
0
1
0
1 I
Figure 1.
I
I
I
I
I
2
I
DAYS
l.6J
19.y
I
1
’
Jeo
4
6
57.0.1
W.7J
37.u
3sn 7.y
100.0 #J
TOTAL FUEL CONSUMPTION (PERCENT)
I6.U
1.6 I
CONSUMPTION (PERCENT)
Temperature and Humidity Conditions Percentage of Original Weight of Tobacco, and Fuel Consumption during Flue Curing
values of around 9% increased to maximum values of about 30%, whereas there was a decrease in starch from an original value of about 20% to less than 1%. Bastry’s (8.9) extensive work in India included studies on the changes in gross weight, carbohydrate, and nitrogen fractions during flue curing. The data of one of four curings made is given in Table I. Loss of solids ranged from 2.5 to 3.25% on the
followed by a reduced rate of loss during leaf drying with only insignificant change during stem drying. Reducing sugars increased progressively during yellowing, remained steady in the “fixing” period, and decreased during stem drying. A small quantity of sucrose in the fresh leaf increased to about 6% a t the end of the process. Total nitrogen did not change significantly during curing, but
294
INDUSTRIAL AND ENGINEERING CHEMISTRY
the water-insoluble nitrogen fraction decreased rapidly during yellowing, when from 76 to 98% of the total loss during the entire process occurred, and only slowly afterwards. Change in nicotine content in the first two curings were not significant although a small quantity of nicotine appeared to have been lost during the last two curing& Askew and Blick studied changes in weight, energy relationships, carbohydrate (%)and protein content ( 1 ) in New Zealand flue-cured tobacco during its curing. Carbohydrate changes found were similar to those previously reported. Breakdown of protein occurred a t a rapid rate and could be detected in about 12 hours. By the time the yellowing of the tobacco was completed the changes had stopped when from 18 to 35% of the protein had been broken down to substances not precipitable by the copper hydroxide in the Barnstein method used, The p H of the tobacco ranged from 5.55 to 5.70. The loss of about 14% of dry matter observed in previous studies by the same authors was confirmed. Experimental Methods
Flue-curing tests have been made for several years a t the Pee Dee Experiment Station a t Florence, S. C . , in cooperation with the South Carolina Agricultural Experiment Station. Changes in carbohydrates and 12 other constituents during the flue-curing process and in carbohydrates during bulking were investigated. Detailed results and associated tests are given in a technical publication (4). The curing tests were made in a specially constructed barn, divided into four separate units each 9 X 9 X 18 feet, or approximately one fourth the size of a regular barn. Each unit was complete with an electric heating and forced-air distributing system, recording thermometer, and psychrometer. A number of uniform 50-leaf samples were cured, with similar tobacco, in the normal manner. In each test a green control sample was prepared by drying in a large forced-air ventilated oven a t 60' to 65" C. Samples removed a t the yellowed stage were similarly dried, and the cured samples were removed dry and never allowed to regain moisture. Methods of the Association of Official Agricultural Chemists (3) were used for some of the determinations: Starch. After extracting the sugars (p. 138), the procedure in the presence of interfering polysaccharides (p. 360) was used and the hydrolysis effected by malt amylase (Wallerstein). The reducing sugar was then determined by Phillips' (16, 17) method. Sugars. Extracted as in starch method. Phillips' (16) method was used to determine all reducing sugar fractions. Levulose was determined, after removing dextrose, by oxidizing with iodine in potassium iodide solution by a modification of the van der Plank (18)method. Sucrose. Inverted by invertase (Wallerstein) (p. 139). Crude Fiber. (p.'357). Nitrogen. Total, Kjeldahl to include nitrates (p. 26, 27). Protein, determined by boiling with 0.570 acetic acid according to method of Mohr (14). Nicotine. Siliootungstic acid m e t h d (p. 64). Ash. Ignite a t about 550' C. for 2 hours; lixiviate ash, etc. Sand. (p. 125). Calcium. Macromethod (p. 127). Oxalic, Citric, and Malic Acids. Extraction in presence of sulfuric acid with ether, according to Pucher, Vickery, and Wakeman (?O). . For oxalic the water solution was treated with hydrochloric acid to remove interfering organic matter and a double precipitation made with calcium chloride. Citric acid was determined by pentabromo acetate method of Pucher, Vickery, and Leavenworth ( 1 9 ) . Malic acid was determined by the dinitrophenylhydrazine colorimetric method of Pucher, Vickery, and Wakeman (21)*
Resins. Extraction with ethyl alcohol and washing, according to procedure of Pyriki (82). Pectinic Acid. Method of Balabuha-Popzova (6). The carbon dioxide liberated by the decomposition of pectin materials, under prescribed conditions, was determined.
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pH. Determined electrometrically by a glass electrode on a water extract prepared accarding to Briickner (6). Moisture. Powdered tobacco (2 grams) dried in an aluminum moisture dish for 4 hours a t 100' C. Changes in Composition during Curing
Curing tests were made on each of two primings of tobacco from the lower-middle portion of the plant, representing leaf usually used in cigarette manufacture, each year for 3 years. The composition of the makrial varied to a certain extent, but the nature of the changes during the curing process were the same; the results of the six tests, as averages, are shown in Table 11. The values a t the yellowed and cured stages have been corrected to an original dry-weight basis in order to show the real changes in composition. The calcium in the leaf is unchanged during the curing and served, in most cases, as the basis for making the corrections. The average loss of dry weight was approximately 8.8% a t the yellowed and 13.3% at the cured stage. The outstanding changes in composition found during the flue-curing process were in the carbohydrate group. The initial starch value of approximately 29% was reduced to about 12y0 when the leaf was yellowed and to about 5.5% when cured. Reducing sugars increased 10% and levulose about 4'%. Sucrose had increased by about 3.5y0 a t the end of the yellowing and continued to increase by about 5.6% a t the end of the curing. The green tobacco was low in these sugars, and their origin was evidently associated with the large loss of starch. The final total sugar content of 24% characterizes good flue-cured tobacco and stands in marked contrast with that of the air-cured types, where these components are practically absent.
Table 11.
Changes in Composition of Tobacco during the Flue-Curing Process-Florence, S. C,
Constituents
(Averages of 6 curings) Changes (Water- and Sand-Free Basis), % Difference, Difference, green to green to Green Yelloweda yellowed Cured" cured
Starch 29.30 Free reducing sugars6 6.68 Levulose 2.87 Sucrose 1.73 Crude fiber 7.28 Total nitrogen 1.08 Protein nitrogen 0.65 Nicotine 1.10 Ash 9.23 Calcium0 1.37 Oxalic acid 0.96 Citric acid 0.40 Malic acid 8.62 Resins 7.05 Pectinic acid 10.99 pH value 5.55 a c
12.40 15.92 7.06 6.22 7.16 1.04 0.56 1.02 9.24 1.37 0.92 0.37 9.85 6.53 10.22 5.64
-16.90 +9.24 +4.19 +3.49 -0.12 -0.04 -0.09 -0.08 fO.O1 0 -0.04 -0.03 i-1.23 -0.52 -0.77
.....
5.52 16.47 7.06 7.30 7.34 1.05 0.51 0.97 9.25 1.37 0.85 0.38 8.73 6.61 8.48 5.55
-23.78 +9.79 4-4.19 4-5,57 4-0.06 -0.03 -0.14 -0.13 $0.02 0 -0. l a -0.02 +o. 11 -0.44 -2.51
.....
Yellowed and cured samples calculated to original dry-weight basis. Calculated as dextrose. Average of four curings.
The origin of the increase in sucrose, averaging about 5.6%, is of interest from the standpoint of plant physiology. Although the increases were accompanied by loss of starch, there is apparently no known direct change from starch to sucrose. This interesting transformation has been considered by Weiss ( 2 6 ) who reviewed previous work on other planh, where phosphorylation as well as enzymatic action is considered as playing a part. The quantity of sucrose found is also higher than most published results since many analyses were made on tobacco that had been held for a considerable time in bulks in a packing house. Under such conditions it has been found that a reduction of sucrose content occurs, as considered later. Content of crude fiber, essentially cellulose, was about 7.2% a t all stages of curing.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
February 1952 Table 111.
295
Sugars in Flue-Cured Tobacco of Several Types before and after Bulking (Water-free basis)
Sample No.
Treatment
34-1 36-1 36-2 36-3 37-A 37-B 374 39-1 39-2 39-3 37-D 37-E 37-F
Cured only Cured on1 Cured anblbulked 84 days Cured imd bulked 158 days Cured on1 Cured, regied, and bulked 116 days Cured and bulked 118 days Cured only Cured, redried, and bulked 120 days Cured bulked 120 days Originh green leaf Cured only Air cured 42 days
36-1 36-2 39-2 39-1 39-4 39-3
Cured only Cured bulked 17 days Cured'onl Cured, bu%ed 40 days Cured on1 Cured, bu%ed 38 days
37-1 37-2
Cured only Cured, bulked 26 days
Reducing Su arsa,
Total Sugars after Invertase Inversionn, % &ford, N. C., Type l l ( b )
k
Reducing Sugars, Sucrose,
%
%
Levulose Dextrose
Levuloae in Reducing Sugars, %
6.49 12.82 4.96 Y; 62 7.11 2.72 0.62 9.70 1.93 2.21 1.09 7.20 0.26
5.21 7.68 12.22 12.62 4.22 6.78 8.15 6.27 10.30 9.64
3.80 9.47 11.20 12.48 4.22 4.93 6.24 4.56 7.89 7.61
57.8 44.8 52.2 50.8 50.0 57.9 56.6 57.9 56.6 55.9
7.70
7.48
50.7
9.68 7.72 8.20 1.50 8.48 1.75
6.28 8.80 8.07 11.34 7.65 11.05
6.49 7.96 8.07 11.53 7.33 10.44
49.2 52.5 50.0 49.6 51.1 51.4
9.48 2.68
8.61 12.04
8.40 11.65
50.6 50.8 Average 52.4
Florence, 8. C., Type 13
a
17.01 23.69
Calculated as invert sugar.
The carbohydrate content of the tobacco studied was high and the nitrogen compounds correspondingly low, The leaf was of a light yellow color, thin, and of the type generally considered as having a high carbohydrate and low nitrogen content. Small losses of a few hundredths of 1% of. nitrogen were found, and the total quantity present was about 1%. Corresponding to the low total nitrogen content the protein nitrogen was also low. Although the change in this component was small, a consistent loss of about 0.15% was found between the green and the cured material. The total amount present was about 0.65% and the loss represents about 20% of that originally present. The nicotine content of the samples was low and averaged about l . l O % , and there was an indicated loss of about O.13y0during the curing process. The highest temperatures used in the curing were about 180' F.and a t no stage of the process was there an indication of an ammoniacal or similar odor. Ash constituents in flue-cured tobacco are low compared to other types, About 9.25% was present in the original material, and while some changes in curing were found in separate tests, as an average no difference was found. The calcium content was used as the basis for making the correction for the loss of dry weight occurring. On this basis all calcium values would be the same as that of the original material, which averaged about 1.4%. Oxalic, citric, and malic acids, frequently determined together as total organic acids, represented approximately 10% of the weight of the original leaf. Greater attention would be given them except that the method for their extraction (continuous long-time extraction with ether) and the uncertainties of the method for the determination of malic acid make their study difficult. About 1% of oxalic acid was found in the green leaf and there was an indicated reduction of about 0.10% during the curing. Oxalic acid is a constituent of all types of tobacco and is little changed by any method of curing. About 0.4070 of citric acid was present in the original leaf and no real change was indicated during the curing process. About 8.670 of malic acid was found in the green tobacco, and there was an apparent average increase of about 1% during yellowing. The resins include various related compounds and made up about 7% of the original tobacco, and a decrease of about 0.50% was found. Included in the pectinic acid determination are various components of the cell wall of the leaf in which a reduction of about 2.5% was found, from an initial value of about 11%. The acidity of the flue-cured type of tobacco is higher than that
26.99 26.51
of any of the other types and is an important factor in ita smoking properties. The pH values of the tobacco as harvested were around 5.5 and the greatest differences found were only about 0.2 PH. Changes in Carbohydrates during Bulking Flue-cured tobacco is customarily removed from the curing barn as soon as the brittle-dry leaves have taken up sufficient moisture to allow handling without breakage. Exposure of the hygroscopic leaves in the barn with the doors open overnight will usually cause them to soften enough to handle. The leaves, still attached to the sticks on which they were cured, are then packed, in a special manner, in large piles or bulks in a pack house where they remain for varying periods of time until marketed. The moisture content of the tobacco during that time varies greatly, and may be relatively dry and contain only about 10% of moisture; in good handling condition with about 20% of moisture; or so moist that spoilage occurs. The color of the leaf becomes more uniform, and any moderate amount of green color that remains in the leaf veins, a t the end of the curing, usually disappears. Bulking tests were made on flue-cured tobaccos of several types. Special lots of 50 paired-le8f samples were selected in the fields and cured in the regular barns with other similar leaves. Following the curing the sample representing the original cured leaf was placed in a sealed container without permitting moisture regain. Other samples that were to undergo the bulking process were left in the barn and bulked with the other tobacco in the regular manner. Carbohydrate analyses of the samples were made by methods of the Association of Official Agricultural Chemists (3): The reducing sugars were extracted by the method for grain and cattle feed (p. 358), and the determination carried out by the Quisumbing and Thomas (p. 138)procedure. The sugar solution was inverted (p. 139) by the use of a preparation of invertase (Wallerstein), and the sucrose calculated from the increase in reducing sugars. The Jackson-Mathews (p. 504) modification of Nyns selective method for levulose was used. The dextrose values were obtained as the difference between the reducing sugars and levulose. The quantity of sugars in the different types of flue-cured leaf immediately a t the end of their curing and after they had been kept in bulks for different ueriods of time are shown in
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Table 111. In the leaves that were cured only, the free-reducing sugars ranged from about 8.5 to 17y0, which is on the low side for these tobaccos. The tobaccos were selected to represent cigarette grades that as a rule show higher values (8). When the sugars were inverted, however, using the enzyme invertase, there was a very considerable increase in total reducing sugars, the value of which then ranged from about 16 to 31%. The average increase on invertase inversion was 9.25%, equivalent to 8.870 of sucrose. The total sugar values were then in agreement with the values usually given for these types (8). The increase in reducing sugars on acid hydrolysis is usually given as only about 1 or 2%. In the samples that had been bulked (with the exception of one that had been in the packhouse only 17 days), the observed increase in reducing sugars, on inversion, as sucrose averaged about 2.5%. The large increase on inversion in the samples that were cured only is probably due to the fact that the changes usually taking place in the packhouse had not occurred. Confirmation of the large increase in reducing sugars on hydrolysis is given by Ward ( 2 5 ) and others, who reported increases, calculated as sucrose, averaging about 10%. In that work the material was analyzed a t the end of the curing process proper, and any possible bulking changes had not been allowed to take place. Change of some of the sucrose present in tobacco that had not been bulked was brought about in the laboratory in a similar manner to the bulking process. Powdered tobacco exposed for a week in a desiccator a t a humidity of about 72% showed a reduction in sucrose content from 8.7 to about 3.7% and an accompanying increase in free reducing sugars. The difference in composition of tobacco brought about by the curing method used is shown in Table III,37 D-F. When fluecured, the sugar content was about 2370, but when air-cured, only about O.4y0 sugar was present. Also, the flue-cured leaves were yellow and the air-cured the usual brown color. Although carbohydrates are present in large amounts and different forms in flue-cured tobacco their complete study and identification have not been carried out. The sugars are usually hydrolyzed by a mineral acid or one of the stronger organic acids, and the increase in reducing sugars is calculated as sucrose. However, their action is more or less general and not restricted to any particular compound, while that of the enzyme invertase is essentially specific for sucrose linkages. Also, the hydrolysis of sucrose results, theoretically, in the formation of equal parts of dextrose and levulose, and special analysis for the levulose component showed that it made up, on the average, about 5270 of the free-reducing sugar fraction. Further evidence of the identity of sucrose was given by a polarimetric test of the reducing sugar in one sample before and after invertase treatment, when over 10% of sucrose was found. In two of the series of samples the effects of redrying the tobacco in a commercial redrying plant, before putting into the packhouse, was tested. Decreases in sucrose were found to take place in very much the same amounts as in the corresponding samples that had not been redried. When the leaf remained in the bulks for periods of from 17 to 158 days there was an average increase of reducing sugars of 6.l2yO. This increase apparently was obtained a t the expense of the sucrose, which showed an average decrease of 6.54%, indicating that in addition to color changes during the bulking process, chemical changes were also taking place. The increases in reducing sugar result in a moderate increase in the hygroscopic property of the tobacco since levulose is much more hygroscopic than sucrose. Summary
Flue-cured tobacco is cured by a special process employing heat (90’ to 180” F.) in about 5 days. Only comparatively recently have the process and the associated chemical changes in
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the tobacco been studied. In previous work major changes found were the loss of starch and increase in reducing sugars. Total nitrogen values did not change significantly; there was a considerable decrease in protein nitrogen, an increase in soluble nitrogen, and small losses of nicotine or changes not significant. Chlorophyll was almost completely destroyed as well as about one half of the yellow pigments. In curing studies on South Carolina tobacco carbohydrate changes followed previous findings. Loss of a few hundredths of 1%of nitrogen and a reduction in protein nitrogen and nicotine of about 0.10% was found. Ash and crude fiber values remained essentially unchanged. A small loss of oxalic acid was observed, and the low citric acid value appeared to be unchanged. Malic acid was present in considerable quantity and some changes observed were not considered significant. Resins showed a small decrease and pectinic acid was reduced about 2.5%. pH values were near 5.5 with a range of 0.2. When cured, three U. S. flue-cured types were found to contain considerable sucrose but after the usual bulking process the quantity had been greatly reduced and there was a corresponding increase in reducing sugars. literature Cited (1) Askew, H. O., New Zealand J . Sci. and Technol., 29 (Sec. A), 312-16 (1948). (2) Askew, H. O., and Blick, R. T. J., Ibid., 28 (Sec. A), 338-44 (1947). (3) Assoc. Official Agr. Chemists, “Official and Tentative Methods of Analysis,” 5th ed., 1940. (4) Bacon, C. W., Wenger, Raymond, and Bullock, James P., U. S. Dept. Agr., Tech. Bull. 1032 (1951). (5) Balabuha-PoDzova. V.. (Krasnodar) Gosud. Inst. Tabakoved. (State Ins; Tobacco Invest.) (in Russian, English summary) Bull. 69, 55-64 (1930). Briickner, H., “Die Biochemie des Tabaks,” Berlin, Paul Parey, 1936. Cooper, A. H., Delamar, C. D., and Smith, H. B., Virginia Polytech. Inst. Eng. Expt. Sta. Ser., Bull. 37 (1939). Darkis, F. R., Dixon, L. F., and Gross, P. M., IND.ENG.CHEM., 27, 1152-7 (1935). Darkis, F. R., Dixon, L. F., Wolf, F. A., and Gross, P, M., Ibid. 28, 1214-23 (1936). Ibid., 29, 1030-9 (1937). Dixon, L. F., Darkis, F. R., Wolf, F. A., Hall, J. A., Jones, E. P., and Gross, P. M., Ibid., 28, 180-9 (1936). Garner, W. W., Bacon, C. W., and Bowling, J. D., Jr., Ibid., 26, 9 7 0 4 (1934). Garner, W. W., Bacon, C. W., and Foubert, C. L., U. S. Dept. Agr., Bull. 79 (1914). Mohr, E. C. J., L a d w . Vers. Eta., 59, 253-92 (1903-04). Moss, E. G., and Teter; N. C., Nbrth Carolina (State) Agr. Expt. Sta., Bull. 346 (1944). Phillips, T. G., J. Assoc. Oj%. Agr. Chemists, 24, 181-3 (1941). Phillips, T. G., J. Biol. Chem., 95, 735-42 (1932). Plank, J. E. van der, Biochem. J., 30, 457-83 (1936). Pucher, G. W., Vickery, H. B., and Leavenworth, C. S., IND. ENO.CHEM.,ANAL.ED.,6, 190-2 (1934). Pucher, G . W., Vickery, H. B., and Wakeman, A. J., Ibid., 6, 140-3 (1934). Ibid., pp. 288-91. Pyriki, C., Z. Untersuch. Lebensm., 84, 225-30 (1942). Sastry, A. S., unpublished thesis for M.S. degree, Bombay University (Central Tobacco Research Inst., Rajahmundry, India), (1946). . (24) Tilley, Nannie May, “The Bright-Tobacco Industry-18601929,” Chapel Hill, N. C., University of N. C. Press, 1948. (25) Ward, G. M., Canada Dept. Agr., Tech. Bull. 37 (1942). (26) Weiss, Francis Joseph, Sugar Research Foundation, Inc.. Member Rept. 22 (1950). (27) Weybrew, J. A., and Stinson, F. A., North Carolina Agr. Expt, Sta., Special Tobacco Issue (July 1949). I
RECEIYED August 8,1951.
