FLUE-CURED TOBACCO Chemical Composition of Rib and Blade Tissue This study gives comparative chemical analyses of the different portions of leaves of flue-cured tobacco after separation into midrib tissues, secondary veins, veinules, and blade tissues. In general, the results indicate that veinule tissues are most nearly like blade tissues, with secondary vein tissues next in similarity, and midrib tissues least like blade tissues. The midrib tissues were found to be significantly different from the laminar tissue. These chemical findings validate the practice of eliminating stem tissues from tobacco used in the manufacture of cigarettes.
F. R. DARKIS, L. A. BAISDEN, P. M. GROSS, AND
F. A. WOLF
Duke University, Durham, N. C.
then passing the flattened tissues through the cutting machines i t has been found possible to use a very limited portion of such material without physical difficulties in the actual process of manufacture of cigarettes. As a basis, however, for assaying the properties that might account for objectionable “burn” and flavor imparted by veinous tissues, a series of chemical analyses were made. These analyses involved the entire cured leaf in comparison with vein tissues alone, and with blade tissues alone. The account that follows contains the results of these analyses, in condensed tabular form, together with a discussion of certain of their outstanding features.
ROM previous investigations of flue-cured tobaccos, made in these laboratories ( 7 - I O ) , it has been established that differences in chemical composition of leaves may be attributed largely t o one or the other of several factors. These factors include locality or region where the crop is grown, seasonal differences in amount and distribution of rainfall, and position on the stalk a t which the leaf was borne. In all the foregoing studies entire cured leaves have constituted the material that was analyzed. The present study is concerned with comparative differences between the ribs or veins and the blade or laminar tissues. The results of such an investigation are of interest especially to manufacturers of cigarettes, since the major portion of the midrib (commonly called stem) is discarded during the process of preparing the leaf for use in cigarettes. The discarded portion usually approximates 20% of whole leaf and is therefore a n item of economic significance t o tobacco manufacturers and the industry as a whole. Cigarette manufacturers consider the removal of midribs to be essential for two reasons: The first has to do with the physical character of midrib material as produced by the cutting machines operating on unstemmed leaves. The midribs would remain as slivers and chunks or segments, which interfere with the rolling and cutting operations performed by the cigarette-making machines. I n consequence, the cigarettes may be imperfect in shape and the paper wrapping may be torn or perforated. The second reason relates to the chemical propertieq af the midribs when incorporated as chunks and slivers in the oigarette. It is believed t h a t the burning of the cigarette is impaired and that undesirable flavor is imparted by midrib tissues. To be sure, by compressing midribs between rollers, thus flattening them, and
F
Materials and Methods Samples of tobacco from a portion of three successive seasons’ crops from special ‘/na-acre plats were employed in making the analyses. These crops were grown on Durham sandy loam soil a t the Tobacco Experiment Station, Oxford, N. C., during the seasons of 1934,1935,and 1936. Cash was the variety of tobacco grown during each season. Such practices of cultivation and fertilization were followed as had proved from previous experience t o be most suitable in tobacco culture. Essential information regarding dates of transplanting and harvesting are contained in Table I. Table 1.
Year 1934 1935 1936
Time of Transplanting and Harvesting of the Tobaccos Analyzed
Traqsplanting Date M a y 25 M a y 24 May18
1 2 July30 Aug. 7 July29 Aug. 8 July27 Aug. 3
Successive Primings 3 4 6 Aug. 13 Aug. 20 Aug. 25 Aug. 12 Aug. I9 Aug. 26 Aug. 11 Aug. 17 Aug. 25
Percentage Distribution of Separated Blade and Vein Tissues on Basis of Primings % Midrib % Lateral % Veinules % Blade % Midrib 9 Lateral % Veinules % Total of Total Veins Veins of Total of Total Veins
6 Sept. 3 Aug. 31 Aug.31
Table II.
Year 1934
1935
lg3‘
Np. pf
Priming 1 and 2 3 and 4 5 and 6 Total 1 and2 3 and 4 5 and 6 Total 1 and 2 3alsd4 6 and 6 Total
of Total
Priming 66.14 67.26 65.73 66.34 68.54 66.47 67.15 67.31 67.55 66.11 67.69 66.88
of Total
Priming 23.69 22.84 23.01 23.16 23.93 25.84 22.05 23.91 23.52 23.10 22.35 22.90
Veins of Total Priming 7.12 6.54 6.92 6.85 5.27 5.47 6.37 5.74 6.58 5.95
5.44 6.72
of Total
Priming 3.05 3.36 4.34 3.66 2.26 2.22 4.43 3.04 3.35 4.84 4.62 4.41
297
Veins of Total Priming 33.86 32.74 34.27 33.66 31.46 33,53 32.85 32.69 32.45 33.89 32.31 33.12
of Total Priming 69.98 69.75 67. I6 68.70 76.06 77.07 67.10 73.15 72.48 68.17 69.18 69.40
Veins of Total Priming 21.02 19.98 20.18 20.36 16.74 16.31 19.40 17.56 17.19 17.56 16.82 17.27
of Total Priming 9.01 10.27 12.67 10.85 7.20 6.62 13.50 9.29 10.33 14.27 14.00 13.33
% Total Harvested Leaves by Primings 29.06 32.10 38.84 100.00 29.01 34.71 36.28 100.00 22.66 49.28 28.07 100.00
298
Vol. 44, No. 2
INDUSTRIAL AND ENGINEERING CHEMISTRY Table 111. No. p i Yea1 Priming
Total Vein Tissue
Lamina ~
1934 1 and 2 3 and 4 5 and 6
Total 1935 1 and 2 3 and 4 5 and 6 Total 1936 1 and 2 3 and 4 5 and 6 Total
7 -
1934 1 and 2 3 and 4 5 and 6 Total 1 and 3 and 5 and Total 1936 1 and 3 and 5 and Total
1935
2 4 6 2
4 6
Total
1935 1 and 2 3 and 4 5 and 6 Total
1936 1 and 2 3 and 4 5 and 6 Total
-~
2.11 2.37 2.76 2.44 2.15 3.74 4.17 3.43 1.91 2.26 3.48 2.53 r
1934 1 and 2 3 and 4 5 and 6
1.14 1.28 2.03 1.54 1.81 2.13 2.47 2.16 1.56 1.41 1.90 1.58
2.02 2.35 3.00 2.50 2.53 3.11 3.80 3.19 2.30 2.17 3.17 2 48
7.18 5.64 5.81 6.15 7.60 8.74 8.68 8.38 9.27 8.37 8.66 8.66
0.52 0.57 0.74 0.62 0.99 1.08 1.30 1.14 0.72 0.77 1.06 0.84
1935 1936
Total 1 and 3 and 5 and Total 1 and 3 and 5 and Total
2 4
6 2 4 6
10.71 8.49 8.47 9.13 14.33 10.31 9.22 11.10 14.26 9.09 10.73 10.74
1.48 1.59 1.30 1.42 1.06 1.10 1.63 1.28 1.35 1.86 2.06 1.80
%tal 1935 1 anct2 3 and 4 5 and 6 Total 1936 1 and 2 3 and 4 5 and 6 Total
-Nic
0.35 0.43 0.45 0.41 0.86 0.97 1.01 0.95 0.52 0.51 0.51 0.51
0.89 1.04 0.95 0.96 0.81 0.93 1.40 1.05 0.88 0.94 1.17 0.99
-Soluble
15.38 15.91 14.44 15.48 12.99 13.80 14.14 14.96 16.47 16.84 12.97 14.71 12.57 13 61 13.80 14.93 17.76 18.42 13.37 14.53 13.84 15.48 14.48 15.69
c -
1934 1 and 2 3 and 4 5 and 6
1.14 1.79 1.35 1.82 2.05 2.05 1.98 1.46 1.24 1.61 1.39
-Petroleum
r
1934 1 and 2 3 and 4 5 and 6
LatMideral Veinribs Veins ules -Total nitrogen, %1.01 1.31 1.79
1.41 0.64 0.70 0.88 2.49 0.54 0.47 1.09 1.88 1.20 0.56 1.17
1.18 0.58 0.60 0.76 1.28 0.41 0 43 0.66 2.12 1.09 0.61 1.19
-Silica
0.97 0.50 0.66 0.70 0.63 0.27 0.34 0.40
0.99 0.81 0.43
0.74
Stalk
Lamina
2.02 2.85 2.25 2.28 2.58 3.79 3.16 2.27 2.07 3.10 2.40
1.72 .. 1.99 .. 2.66 2.18 0:95 2.30 .. 2.78 3.36 2.85 l;i5 2.06 .. 1.91 2.76 2.18 0180
0.87 1.01 1.20 1.04
1.19 1.40 1.89 1.58 2.11 2.50 3.44 2.91 1.57 1.77 3.14 2.13
1.57 .. 1.78 .. 2.06 1.83 0133 1.78 2.85 .. 3.23 2.68 0:45 1.52 1.66 2.70 1.92 0133
1.53 2.51 1.85 1.80 2.29 2.90 2.41 1.68 1.56 2.25 1.83 :otine, %
0.66 0.73 0.96 0.80
1.19 1.63 1.67 1.53 1.00 0.92 1.58 1.11
ether extract, %
1.12 1.97 1.20 1.41 1.48 1.74 2.19 1.85 1.60 2.06 2.90 2.18
2.36 2.91 3.26 2.94 3.07 4.12 4.81 4.26 5.20 5.60 5.57 5.52
ash, %-
13.72 12.73 11.72 12.63 15.62 12.31 12.31 13.19 16.15 12.39 12.02 13.12
(SiOz), 1.41 0.66 0.62
0.87
0.85 0.83 0.58 0.73 2.08 1.23 0.69 1.27
9.75 9.11 8.36 8.92 14.46 8.74 8.74 10.10 14.35 9.75 8.68 10.23
I"
Entire Leaf
.. ..
--
.. ....
Total 1935 1 and 2 3 and 4 5 and 6 Total 1936 1 and 2 3 and 4 5 and 6 Total
--..
--. . .. ..
.. ..
15.31 17.44 12.73 15.00 6.70 11.59 7.17 8.57 9.11 13.65 5.62 10.37
8.84
14.91 5.18 10.76
Tobaoco--.
0.87
2.08
0.23
0.17 0.13 0.17 0.32
0.13
0.10 0.18 0.31 0.15 0.17 0.19
The plants were topped to a height of 16 to 18 leaves and were harvested by priming. After having been flue-cured, the leaves while still attached to the sticks were bulked in the usual way. They remained in the bulk for about a month after which the tobaccos were taken to the laboratory and ground in preparation for analyses. First of all, the midribs were separated manually from the remaining tissues. The remaining tissues were rubbed in a 20mesh sieve, using a pestle made from a rubber stopper. All veins not passing through the sieve were regarded as secondary or lateral veins. All material which passed through this 20-mesh
I .
.. ..
.. ..
.. ..
0 : i4
.. ..
o:i3
.. ..
0:05
...
... ...
0.57 ,..
... 0:67 ...
...
...
-
0.54
... ... , . .
4.70
... ...
...
2.35
...
. .. , . .
6.03
..
... .,. .. ...
3.87 2.93 2.27 2.95 6.29 3.62 3.32 4.26 3.47 2.44 3.21 2.88
-Calciu
7
0.44 0.54 0.62 0.54 0.56 0.69 0.72 0.63 0.65 0.69 1.09 0.80
Stalk
17.16 16.46 ..., 13.15 ... 15.37 9.97 24.37 17.50 17.49 . 19.51 9.71 19.18 12.37 ... 14.96 14.64 ii:&
0.63 0.61 0.58 0.60 0.63 0.54 0.53 0.56 0.40 0.32 0.65 0.43
1.33 0.62 .. 0.67 0.84 0 : 71 2.11 0.50 0.46 0.95 O:i6 1.96 1.16 0.58 1.18 0149
Entire Leaf
0.73 0.85 1.00 0.88 0.97 0.85 1.03 0.95 0.80 0.84 1.08 0.90
7
2.70 2.60 2.25 2.46 2.67 1.58 0.75 1.38 3.40 2.32
Veinules
17.10 19.69 12.93 16.34 5.75 9.29 5.51 6.88
4.04 2.72 2.44 3.00 7.22 4.13 3.05 4.65 4.92 2.53 2.67 3.11
.. .. 0:31 .. ..
Lateral Veins
---
12.29 10.43 10.01 10.81 4:34 15.00 10.32 .. 10.32 11.98 3178 15.40 10.54 11.84 12.00 5:37
0:33
Midribs
1.03 1.23 1.14 0.94 0.97 1.29 1.05
0:is
..
Total Vein Tissue
1.16
15.39 15.80 12.59 14.45 24.70 17.13 17.13 19.41 18.75 11.13 13.85 13.64
5.24 4.28 4.26 4.56 5.54 6.18 6.37 6.06 6.69 6.16 6.53 6.38
7
1934 1 and 2 3 and 4 5 and 6
Chemical Analyses of Separated Lamina and Veinous
0.82 0.99 1.08 0.98
0.70 0.83 1.11 0.90 0.99 1.16 1.48 1.21
3.94 2.98 2.64 3.13 6.51 3.64 3.63 4.47 3.56 2.85 3.77 3.27
m (CaO), %-
3.61 2.67 2.20 2.77 5.89 3.91 2.96 4.06 3.72 1.91 2.58 2.49
3.32 2.81 2.20 2.65 6.04 3.38 2.30 3.38 3.07 1.48 2.51 2.05
-Magnesium 0.62
0.60 0.61 0.61 0.62 0.53 0.00 0.58 0.39 0.40 0.70 0.48
0.66 (MgO), 0.56 %0.63 0.66 0.62 0.60 0.64 0.60 0.69 0.61 0.55 0.43 0.58 0.36 0.60 0.43 0.39 0.42 0.26 0.20 0.46 0.29 0.34 0.26
...
0.71
...
...
... 1.21
... 0:92
0.46 0.42 0.39 0.42 0.53 0.39 0.35 0.42 0.38 0.22 0.39 0.30
...
... ...
0.17
... ...
0.23
...
... ... 0.11
...
-Phosphorus 0.89 0.85 (PzOs).%-
0.99 1.13 1.01 0.67 0.83 1.12 0.88 1.03 1.22 1.52 1.26
1.14 1.29 1.11
0.77 0.94 1.35 1.06 1.00 1.22 1.54 1.26
... ... O.'$l 0.92 0.99 0.96 0.94 1.00 1.22 1.05
...
0.60
... ... 6:36 ... ... 0: 60
sieve was then rubbed, in a similar manner, in a 60-mesh sieve. The portion passing through was regarded as blade tissue and the part retained in the sieve as veinules. Each of the separated portions was then ground in a Wiley mill to a fineness to pass a 1mm. sieve, enclosed in Mason jars, and stored in a cold room a t 30" to 34" F. until analyzed. The official methods of chemical analyses employed previously in a series of studies involving the composition of flue-cured tobaccos (7-10)were used with the present materials. Each of the six primings was analyzed separately for each of the three crops. The data of the first and second primings were then
INDUSTRIAL AND ENGINEERING CHEMISTRY
February 1952
Tissues of Three Crops of Flue-Cured Tobacco Total Vein Tissue
Lamina
7
0.100 0.125 0.336 0.201 0.231 0.251 0.381 0.293 0.165 0.090 0.196 0.136
0.188 0.209 0.373 4.266 0.308 0.382 0.458 0.388 0.202 0.125 0.251 0.178
LatMidera1 Veinribs Veins ules -a-Amino b nitrogen, %--0,233 0.087 0.179 0.075 0.240 0.220 0.435 0.476 0.226 0.137 0.315 0.325 0.218 0.358 0.249 0.422 0.214 0.342 0.511 0.477 0.282 0.455 0.372 0.238 0.127 0.202 0.191 0.121 0.077 0.104 0.255 0.228 0.164 0.174 0.156 0.112
Toita1 sugars), %-
12.69 14.28 13.03 13.33 10.40 17.94 11.45 13.58 11.08 11.95 7.29 10.48 5.17 5.03 4.66 4.91 5.26 4.94 4.79 4.98 5.19 5.06 4.90 5.04
-
4.97 4.88 4.89 4.89 5.09 4.80 4.77 4.87 4.88 4.89 4.79 4.86
11.52 10.79 10.46 10.88 5.96 9.54 7.24 7.66 8.96 13.99 7.56 11.16
16.97 17.48 13.54 15.54 8.38 10.07 7.03 8.09 13.26 17.74 7.67 14.07
-Hydrogen ion 4.91 4.93 5.00 4 95 5.04 4.76 4.78 4.85 4.77 4.76 4.72 4.75
Entire Leaf 0.158 0.181 0.360 0.244 0.284 0.327 0.433 0.353 0.190 0.113 0.233 0.104 16.14 18.09 13.32 15 56 7.18 11.94 7.74 9.02 10.34 16.16 6.64 12.17 5.08 4.98 4.71 4.91 5.21 4.89 4.79 4.95 5.09 5.00 4.86 4.98
2.13 2.09 2.30 2.18 1.67 1.92 1.96 1.66 3.20 2.75 3.07 2.94
0.41 0.41 0.56 0.47 0.94 0.79 0.66 0.79 0.51 0.25 0.45 0.37
--
0.54 0.49 0.58 0.54 0.49 0.61 0.77 0.63 0.77 0.64 0.87 0.74
--...
Stslk
... ... ...
0 : ois
:...
0 Oi4
...
... 0 :os9
...
... ... .. .. ..
0.38 4.31
...
... ...
--...
7.71 I
.
.
... 4 46 ...
... ...
4 27
...
.
.
I
--... 5:io
... ... ...
1:ii
1:ii
...
...
... ... 2: 04
I
1.74 1.81 2.06 1.89 2.37 1.99 2.45
0.86
0.87 1.07 0.94 1.39 1.19 1.25 1.27 0.93 0.54 0.79 0.70
2.26
1.79 1.09 1.47 1.35 0.47 0.48 0.56 0.49 0.52 0.46 0.67 0.55 0.58 0.51 0.62 0.56
-Sulfur 0.52 0.51 0.55 0.53 0.64 0.49 0.59 0.54 0.57 0.53 0.62 0.56
(S), %-
0.53 0.52 0.52 0.52 0.47 0.51 0.70 0.58 0.62 0.46 0.57 0.53
... ... .. .. ..
0.63 0.63 0.73 0.68 0.72 0.51 0.72 0.61
0.52 0.49 0.57 0.53 0.50 0 56 0.74 0.61 0.71 0.60 0.79 0.68
... ... ...
0.49 o:i9
... ... ...
-
0.54
... ... ... 0.28 ... ... ... 0.61 .. ... ,
. ..
0.27
averaged on a weighted basis the data of the third and and sixth primings. The fourth primings and also of t combined data are presented in Table 111. Results and Discussion of Analyses As a basis for computations from the results of analyses, the weights of the entire selected portion of the harvested crop for each of the three years were assembled separately, to show the weights of leaf comprising the first and second primings, that of the third and fourth ones, and also the fifth and sixth ones. The corresponding weights of blade tissue alone, of total vein
299
tissues alone, and the weights of the three physically separated fractions of vein tissues ever used to calculate data in Table 11. In round numbers 5000 grams of cured leaf comprised the amount employed for analyses from the 1934 crop, 6750 grams from the 1935 crop, and 8600 grams from the 1936 crop. These amounts of leaf seem ample for the mechanical separations and chemical analyses. The proportions of blade tissue, veinous tissue, and rib tissue were quite alike each season. The data of Table I1 show that the ratio of total blade tissue to rib tissue in any of the three crops is approximately 2:l. The midrib tissue makes up on the average 23.35y0 of the total leaf, by weight, and 70.45% of the veinous tissue. The lateral veins make up on the average 6.10% of the total leaf and 18.40y0 of the veinous tissue. The veinules constitute on the average 3.70% of the total leaf and 11.16y0 of the veinous tissue. The proportion of veinous tissue varies slightly from priming to priming and from crop to crop as does the proportion of the three fractions of the veinous tissue. The variation in these proportions does not follow any consistent trend or pattern and it is believed that the slight variations arise primarily from limitations inherent in the method of separation. The data also show that the proportion of the harvested tobacco from each of the three sections of the plant varies from season to season. These variations are traceable to seasonable factors. These factors and their modifying influence werc, discussed a t length in a previous report (8). Chemical analyses were made of the following constituents: total nitrogen, protein nitrogen, a-amino nitrogen, nicotine, total sugars, reducing sugars, total acids, pH, petroleum,ether extractive, soluble ash, potassium, calcium, magnesium, phosphorus, sulfur, iron and aluminum, chlorine, and silicon. The amount of data amassed from these analyses is necessarily voluminous and only the averages obtained from the replications are assembled in Table 111. I n the discussion which follows attention will be directed only to those data in Table I11 which appear to be most significant. Differences also exist in the distribution of these materials in leaves borne a t three stalk positions-namely, the lower part of the stalk, the median region, and the upper portion of the stalk. The other data may be meaningful to the reader and therefore they are presented in the table. There are outstanding differences in the content of chemical components of laminar and veinous tissues. For clarity it seems best to isolate by means of histograms (Figures 1and 2) certain salient features from the data in Table 111. The greatest differences in components exist between midrib tissues and blade tissues, and the composition of secondary veins is intermediate between veinule tissues and midrib tissues. Perhaps next in importance are the differences in constituents as related to leaf position on the stalk. In general the results confirm those of a previous study (8). The four constituents, total nitrogen, protein nitrogen, nicotine, and petroleum ether extractive, occur in greatest abundance in the blade tissue and occur in decreasing abundance in the veinules, secondary veins, and midribs, respectively (Figure 1). Even though other investigators have not separated the leaf into portions prior to making analyses, as was done in the present study, yet their results, in a general way, may be interpreted to support the present findings. For example, Garner et al. ( 1 2 ) ‘found that the midribs of Maryland tobacco contain approximately half as much total nitrogen as do the laminar tissues. Askew ( 4 ) working with New Zealand tobaccos found that the midribs contained about three fourths as much total nitrogen as the laminar tissues. Vladescu (18)observed in Oriental tobaccos that the protein content progressively increased in amount from the base of the leaf toward the tip and from the midrib toward the lateral margins. He also showed ( 1 7 ) that the total nitrogen increased toward the periphery. Similarly Wenusch (19)noted that the lamina contains more soluble proteins than does the midrib. ,
300
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 44, No. 2
conceded that flue-cured tobaccos of go06 quality are high in sugar content. It is also an established fact that leaves produced in the median stalk region have a higher sugar content than the basal leaves or the tip leaves (8); the C R O P YEARS 1934,193581936 present findings are in agreement. A. L A M I N A Askew ( 4 ) found the sugar content of a VEINULES C. L A T E R A L V E I N S the lamina to be higher than that of the D. M I D R I B S midribs. From Figure 1it appears that the largest percentage of sugar is not consistently present in any one of the physical portions of the leaf. These inconsistencies are probably traceable in part to seasonal influences and in part to diffusion of sugars through the different portions of the leaf during the process of curing. However, the desirable properties of veinous tissue traceable to a high content of soluble sugars may be Figure 1. Percentage of Protein Nitrogen, Total Nitrogen, Nicotine, Petroleum Ether Extract, and Total Sugars in Parts of l e a f offset by undesirable characteristics traceable to other constituents. In connection with this work the The literature contains numerous data for nicotine (1-3, 6, 11, main stalk which supports the leaves of the plant was removed 19, 16, 18) which indicate that the nicotine content increases from the field a t the time the last priming was harvested. These from the base to the tip of the leaf and from the midrib to the stalks were dried and subjected to the same chemical analyses as the leaves. A check of the literature failed to disclose any periphery. The present results accord with those of Bacon (6) and Pyriki (16),who found that midribs contain much less nicocomplete analyses of tobacco stalks. Therefore, these data on tine than does the remainder of the leaf. The most elaborate and the chemical composition of the stalk are also presented in conclusive studies bearing on distribution of nicotine in the Table 111. With one exception they show that the stalk contobacco leaf are those of Andreadis and his coworkers (1, %). tains a smaller percentage of constituents determined than do They found that there is a definite pattern of distribution of nicothe tissues of the leaf. The stalk tissue, however, contains more chlorine than the laminar part of the leaf, and the content of tine. It is most abundant a t the leaf tip and near the lateral margins, and least abundant at the base and near the midrib. potassium in the stalk is relatively high. Also they show that there is a progressive increase in nicotine In the opinion of the authors flavor and taste of smoke from tobacco that is undergoing combustion are due to its component from the midribs through the veins of decreasing size to the organic constituents. The flavor of the smoke and the pleasing laminar part of the leaf. It is apparent from Figure 2 that potassium and chlorine occur qualities of the taste of the smoke are correlated directly ~ i t the h in greatest percentage in the midribs and in least percentage in content of nitrogenous constituents. If the content of these materials (especially nicotine) is very large, a pungent irritating the blade tissues. Askew (4) found the ash and potassium coneffect is imparted by the smoke, which the smoker generally tent to be greater in the midribs than in the lamina. There is the aame general relationship of total ash in the various parts of the terms strength of the smoke. If the content of nitrogenous leaf except that there is slightly less in the veinules than in the constituents is very small, as it is in the midribs, the smoke lacks blade tissues. Soluble ash, potassium, and chlcrine findings are in accord with those of Pyriki (16), Ridgway (16), and Pantea (14). Pyriki found that midribs contain mOre minerals than do the other portions of the leaf. Ridgway found that the total ash and potassium CROP Y E A R S 1 9 3 4 , 1 9 3 5 a 1 9 3 6 content of both the large veins and A LAMINA 8 VEINULES small veins exceeds that of the laminae. Pantea noted that midribs have the C. L A T E R A L VEINS D M I D RIBS greater chlorine content. Table I11 shows that the midrib t i s sue and the laminar tissue are quite alike in calcium content and that the veinules contain less calcium than any other portions of the leaf. Furthermore, the content of total acids is the least in the veinules. A previous report ( 9 ) showed that as the calcium content increases there is a concomitant increase in the content of total acids. CHLORINE CALCIUM POTASSIUM ASH TOTAL ACIDS Perhaps none of the constituents of flue-cured tobacco is of more signifiFigure 2. Percentage of Chlorine, Calcium Oxide, Potassium Oxide, Soluble cance than the sugars. It is generally Ash, and Total Acid (Cc. N/10 Alkali] Der Gram of Tobacco
February 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
pleasing qualities and flavor and the smoker usually regards the smoke as being flat and insipid. The smoker’s desires are not satiated by such a product. If flue-cured tobaccos are smoked alone, those which contain from 1.70 to 2.30y0 total nitrogen usually give the greatest satisfaction t o the smoker. Midribs from flue-cured tobaccos suitable for cigarette manufacture usually contain less than these amounts of nitrogen. This is confirmed by the data in Table 111 for the tobacco from the bottom and middle sections of the plant. Tobaccos which are very low in nitrogenous materials usually are high in content of insoluble carbohydrates, organic acids, and ash constituents. The analyses in Table I11 show that the midrib portion of the veinous material contains more total acids and soluble ash than the laminar material. Unpublished work from this laboratory indicates that as the content of organic acids increases in the tissue of flue-cured tobacco, the proporbion of oxalic acid in the aggregate of the acids becomes proportionally greater. On combustion tobacco tissue which is high in content of oxalates and insoluble carbohydrates imparts to the smoke a bitter irritating taste. Such a smoke is not pleasing and may impart a lasting aftertaste which is undesirable. The difference in petroleum ether extractive between laminar and vein tissues is very striking; however, the significance of this difference is not clear. The data in Table I11 are believed to contain evidence of a chemical nature that supports the validity of the practice of eliminating the major portion of the midribs of flue-cured tobaccos in the manufacture of cigarettes.
301
Literature Cited
Andreadis, T. B., andToole, E. J., Z . Untersuch. Lebenam., 68. 431 (1934).
Andreadis, T . B., Toole, E. J., and Binopoulos, J. T., Ibid., 77, 262 (1939).
Anon., Rev. Appl. Botan. Agr. Maurice, 2, 122 (1924). Askew, H. O.,Blick, R. T., Currie, K. E., and Joyce, W., New Zealand J . Sci., 30, 129 (1948). Bacon, C. W., J . Am. SOC.Agron., 21, 159 (1929). Cicerone, D., and Marocchi, G., Boll. tec. colt. tabacchi, 12, 119 (1935). Darkis, F. R., Dixon, L. F.,andGross, P. M., IND.ENQ.CHEM., 27, 1152 (1936). Darkis, F. R., Dixon, L. F., Wolf, F. A., and Gross, P. M., Ibid., 28, 1214 (1936). Zbid., 29, 1030 (1937). Darkis, F. R., Pederson, P. M., and Gross, P. M., Ibid.. 33, 1549 (1941). Dittmar, H., Pharm. Zentralhalle, 81, 169 (1940). Garner, W. W.,Bacon, C. W., Bowling, J. D., and Brown, D. E., U. 8. Dept. Agr., Tech. Bull. 414 (1934). Jehau, J. B., Mem. Manufactures etat (Pards), III, 21 (1898). Pantea, c., Bull. Facultat Stunte Agr. Chisinan. C m u n . Lab. Chim Agr., 3,194 (1940). Pyriki, C.,Z. Untermch. Lebensm., 83,221 (1942). Ridgway, C.W.,J . Agr. Research, 7 , 269 (1916). Vladescu. I. D.. Bull. Cult. Ferm. Tutunuli.. 29.. 307 (1940). . , ZbkZ., 30,’116(1941). Wenuech, A., Z . Untersuch. Lebensm., 79, 481 (1940). RECEIVED M a y 24, 1951. Papers 1, 2, 3, and 6 of this series appeared in IND. ENG.CEEM.,27, 1162 (1936): 28, 180 (1936); 29, 1030 (1937); 33, 1549 (1941). The fourth appeared in BUZZ. Torrey Boton. Club,64, 117 (1937).
Nitrogen Compounds in Fermented Cigar leaves A n essential step in the chain of industrial operations by which crude leaves of cigar tobacco are transformed into a good smoking product is the so-called fermentation. Substantial chemical changes occur during this phase of processing within the leaf tissues, including conversions of the nitrogenous leaf components. During the phases of processing thpt precede the fermentation, about half of the initial leaf protein is hydrolyzed by the leaf enzymes and yields considerable amounts of amino acids. A large part of these amino acids undergoes oxidative deamination with the formation of ammonia, which, after having reached a maximal concentration in the leaves, evaporates gradually during fermentation. The remain-
ing amino acids react with other constituents of the tobacco leaves, probably with polyphenolic substances, yielding Condensation products of increasing molecular size ond decreasing solubility in water. As a net result of these reactions, only very small amounts of amino ocids are left in the leaves after fermentation. The nitrates remain almost unaffected by the fermentation, but the contrary applies to nicotine and the related alkaloids of the leaves. These findings, in conjunction with studies of the catalytic and enzymic mechanism, have helped in replacing the traditional, purely empirical art of tobacco fermentation b y a catalytically controlled procedure which yields a mild and aromatic product of very low alkaloid content.
W. G. FRANKENBURG AND A. M. GOTTSCHO General Cigar Co., Inc., Lancasfer, Pa.
A
T H E end of the curing process the leaves of cigar tobacco are still unsuited for the manufacture of good smoking products. The cured leaves have t o undergo additional processes called sweat, fermentation, or resweat before they develop, on ignition, a mild and aromatic smoke. People, unfamiliar with the tobacco industry, are astonished t o learn t h a t these various processing operations take, as a rule, several years. We shall describe here briefly the processing operations as they are applied to the cured leaves of a typical cigar filler tobacco. For more detailed descriptions, see (7,18). Figure 1 illustratee the construction of a conventional cigar. As a rule, different types of tobacco are used for the filler, binder, and wrapper. Usually, the filler tobaccos undergo a more vigorous sweat and fermentation than the tobaccos used as binders, and partictdarly than tobaccos used as wrappem. I n the first phase called natural sweat the leaves, packed in tightly compressed units, undergo a prolonged storage in which
they are exposed t o the fluctuation of temperatures and humidities of at least one summer and one winter season. In the following process of fermentation, they are moistened with carefully controlled amounts of water, repacked, and kept in rooms at about 45’ C. and air humidity of about 60%. Periodically, the tobacco is withdrawn from these rooms, supplied with fresh air by unpacking and shaking the leaves, repacked, and returned to the heat rooms. These “cycles” are repeated four t o ten times, depending on the individual type and character of the tobacco. Concurrently, the periods in the heat room are increased from a few days t o many weeks. An aging process completes the treatment. Although it may sound ample enough, this processing is an art rather than a mechanical operation. No rigid schedule can be followed because of the extreme variability of the tobacco leaves which calls for a highly individualized treatment for every new crop and, within each crop, of every single unit of tobacco.
