Volume 11 (1982): Edizione 3 (January 1982)

With a liquid displacement flow system, pressure drop and flow measurements were performed on filter rods, tobacco columns and multicapillary pressure drop standards. The purpose of these measurements was to determine the relative contributions of laminar or viscous flow, inertial flow, and entry and exit effects to pressure drop. Pressure drops were obtained both by forcing and drawing air through the article. No difference in pressure drop was obtained by either method provided that the flow was the same at a common point in the rod. This specification was necessary because of the change in flow rate due to gas expansion inside the rod. Pressure drop contributions from gas expansion, thermal effects and rod collapse were negligible. From regression equations, the major pressure drop component in all three types of article was viscous flow, ranging from 98 % of the total pressure drop in filter rods to 79 % in tobacco columns. Entry and exit effects were small in both filter rods and tobacco columns but were appreciable and the only other pressure drop contributor in multicapillaries. These measured entry and exit effects in multicapillaries agreed well with those estimated by flow theory. Inertial flow was found to contribute 1.5 % and 19 % of the total pressure drop in filter and tobacco rods, respectively. These contributions are reasonable from flow theory for packed columns.

To evaluate the effects of dilution and filtration on the particle size of tobacco smoke, a cyanoacrylate fixation technique has been applied directly to smoke issuing from a cigarette. This fresh, undiluted smoke has appreciable numbers of particles with diameters less than 0.1 and relatively few particles with diameters greater than 0.5 micrometer. For a middle puff on an unfiltered tobacco cigarette, the median and mass median diameters are 0.20 and 0.32 micrometer. The experimental method involves the injection of cyanoacrylate vapor directly into the issuing smoke stream, collecting a sample of fixed particles on a membrane filter, and the use of image analysis to separate, size and count individual particles. Aging of undiluted smoke for up to 1.4 seconds essentially doubles the number and mass median diameters and decreases the particulate concentration in line with coagulation theory. Different puffs on unfiltered cigarettes have little effect on the size distribution and particulate concentration. Addition of a filter removes both larger and smaller particles, and tends to skew the distribution to smaller sizes. The reduction in particulate concentration in filtered smoke is as expected from nicotine removal efficiencies. Filter dilution tends to skew the size distribution to larger sizes, while tobacco column dilution has no great effect. Particulate concentration correlates well with overall dilution levels.

Naphthalene and alkylnaphthalene were detected qualitatively and quantitatively for the first time in Latakia tobacco. 62 different alkylnaphthalenes were determined by means of GC-MS analysis, 22 of which were exactly allocated structurally by comparing the Kovats retention indices. Besides naphthalene, the following substances were also identified: 1-methylnaphthalene, 2-methylnaphthalene, 1-ethylnaphthalene, 2-ethylnaphthalene, 1-propylnaphthalene, 2-propylnaphthalene, all ten theoretically possible isomers of dimethylnaphthalene, four trimethylnaphthalenes, isobutylnaphthalene and five ethylmethylnaphthalenes. The concentration of the naphthalenes detected in Latakia tobacco is in the region of 1 ppm to 10 ppm, with the focus on 1 ppm to 3 ppm. Alkylnaphthalenes make an important contribution to the aroma of the Latakia tobacco. They clearly modify the burnt aroma of the Latakia phenols to mild, dusty, with earthy undertone.

Leaves from 8 stalk positions from four Burley tobaccos, the cultivars Burley 21, Ky 14 and Ky 12 and one breeding line of low-alkaloid Burley 21 (LA Burley 21), were tested in this study. A total of 116 variables, including leaf and smoke characteristics, were determined by collaborating scientists using established methods. Simple correlations and multiple regressions among selected variables were determined to examine the relationship among these variables. Generally, Burley tobaccos do not differ from bright tobaccos, in that the nitrogenous fractions and combustibility appear to be the major factors affecting nicotine and dry TPM (total particulate matter) delivery as well as other major smoke constituents. Stalk position and varieties also demonstrated significant differences in nicotine and dry TPM delivery. Benzo[a]pyrene content, however, did not show significant differences among these experimental Burley tobaccos or stalk positions.

Condensate deliveries from cigarettes can be reduced by manufacturers in various ways. Lines or cultivars of tobacco can also be developed whose cured leaf, upon pyrolysis, delivers less condensate in the smoke. Since there appears to be an association between condensate and nicotine in smoke, the condensate : nicotine ratio is important to the development of lines of tobacco that deliver low condensate levels. Experiments were conducted to evaluate the potential for genetically controlling condensate delivery in cigarette smoke and data are presented. In general, when comparing the condensate delivery potential for different classes of tobacco, Burley delivered higher condensate values followed by dark fire-cured, dark air-cured, flue-cured and Maryland cultivars. In selecting genotypes for lowering condensate deliveries, the condensate / g of tobacco smoked is a better index than condensate/cigarette. In evaluating low-alkaloid tobaccos, the condensate delivery did not decrease appreciably as the total alkaloids were decreased. On an average, the decrease was about 4 mg of condensate / cigarette when compared with normal-alkaloid types but the condensate : nicotine ratio increased greatly. The ratio of condensate : nicotine was lowered when lines high in nicotine were produced. In one test reported, the ratio of condensate : nicotine ranged from 5.3 (TI 717) to 75.0 for a low-nicotine line. N. rustica had higher nicotine than N. tabacum cultivars and a lower condensate : nicotine ratio. The gene(s) responsible for the production of nicotine in N. rustica were transferred into N. tabacum and some of the derived lines had a nicotine content about 1 % higher than SC 58, the highest-nicotine cultivar, or flue-cured tobacco available. The condensate delivery / g of tobacco smoked was lower for these lines when compared with SC 58. All of the lines tested gave a condensate : nicotine ratio lower than SC 58. The data showed that condensate deliveries from tobaccos vary with the environment, cultural practices and the weather conditions under which the tobacco is produced. To make progress in breeding for lower condensate delivery in tobacco, it is necessary to assay large numbers of samples and methods for doing this were discussed. To breed low-condensate delivery lines with good smoking flavour, it will be necessary, simultaneously, to select for certain flavour compounds. More research is needed on flavour chemicals of tobacco and their relationship to condensate.

Under conventional cultural practices for Burley tobacco, the pattern of soluble protein accumulation, namely Fraction I protein (F I protein) and Fraction II protein (F II protein), in bright (NC95) and Burley (Ky14) tobaccos were similar during the growing seasons of 1977 and 1978. Their quantities reached maximal levels around flowering, followed by a gradual decline. However, the loss of F I protein was much more rapid than that of F II protein during leaf maturation. The two-year results revealed that Ky14 contains significantly more F I protein, insoluble proteins, total proteins, free amino acids, total nitrogen, nitrate nitrogen and total alkaloids than NC95, if averaged over the growing season. The latter showed a greater amount of chlorophyll only. There was no difference in F II protein concentration between the two cultivars. On the basis of soluble protein concentration in leaf lamina and a double or quadruple plant population as plant size permits, the estimated yields of soluble proteins in Ky14 at the immature plant stage, about one week before topping, and by harvest time are 888, 470 and 281 kg/ha, respectively. When including both soluble and insoluble proteins, the immature plants of NC95 could yield 1387 kg/ha of protein, in comparison to 1308 kg/ha for Ky14. Multiple harvests of regrowth can further the protein yield per hectare. The present results strongly suggest that tobacco is a potential protein crop for the future.

Bright and Burley tobacco breeding lines carrying the chlorophyll-deficiency genes Py and yg were compared with the corresponding normal genotypes and dark fire-cured and Maryland tobacco types during the growing season for the quantity of proteins and chemical constituents affecting the quality of homogenized cured leaves. Varietal difference in soluble leaf protein content was not observed in the immature plant stage but became evident upon approach to leaf maturation. Fraction I protein (F I protein) accumulated to a maximum level of about 130 mg / g dry weight in all tobaccos analysed before topping. The greatest quantity of Fraction II protein (F II protein), ranging from 100 to 160 mg / g dry weight, occurred one to two weeks after maximum F I protein accumulation. F I protein concentration decreased at a faster rate than F II protein during leaf maturation and senescence. Among the chlorophyll genotypes, Ky14 and Burley 21-yg had the highest amounts of soluble leaf proteins and the lowest levels of plastid pigments and/or chlorogenic acid. These characteristics are desirable for the homogenized leaf curing (HLC) process, which yields smoking material as a main product and heat-denatured protein as a by-product. The present results also suggest that tobacco can be grown for the production of both water-soluble and insoluble proteins as main products and deproteinized fibers as a by-product. In this regard, protein production would be affected by the yield of leaf biomass since the concentrations of soluble and insoluble proteins were similar in plants of the different tobacco types and chlorophyll genotypes under comparison.