Volume 12 (1984): Issue 3 (February 1984)

The discovery of the first diterpenoids of the cembrane type in tobacco dates back to the early 1960's. Since then some forty tobacco cembranoids have been encountered. Most of these have a hydroxyl substituent at C-4 and are commonly divided into two series: those having a 4R- and those having a 4S-configuration. Additional oxygenation is found at C-6, C-7, C-8, C-11 or C-12. These compounds, which are present in the gummy exudate of the tobacco leaf and flower, are susceptible to biodegradation thus accounting for the presence of the large number of odoriferous norcembranoids in tobacco. They are also reported to include representatives having growth inhibiting and insect resistance properties. A considerable insight into the biological transformations of the tobacco cembranoids has been obtained by isolation and determination of the stereostructures of new compounds and by biomimetic experiments. The latter have involved singlet oxygen reactions, epoxidations and acid- and base-induced rearrangements. The results obtained support the importance of the (1S,2 E,4R,6R,7E,11 E)- and (1 S,2 E,4 S,6R,7 E,11 E)-2,7,11-cembratriene-4,6-diols, the major tobacco cembranoids, as key metabolites in the biogenesis of the other cembranic compounds. An account of these biogenetic reactions will be given and the isolation of a few new cembranoids will be reported.

A method for the determination of the neutral sugar content of tobacco cell wall fractions has been developed. The seven neutral sugars - rhamnose, fucose, arabinose, xylose, mannose, glucose and galactose - determined in the analysis represent the usual glycosyl residues found in plant cell wall polysaccharides. In this procedure, the structural polysaccharides are acid hydrolysed into their constituent monosaccharides. The monosaccharides are then reduced with sodium borohydride to the corresponding alditols. The alditols are converted to the acetates with acetic anhydride. The alditol acetates are quantitatively measured by capillary gas chromatography with flame ionization detection. Both 72 % H₂SO₄ and 2 N trifluoroacetic acid have been used for acid hydrolysis of polysaccharides. Using model compounds, it was found that more complete recovery of the neutral sugars was obtained when the polysaccharide was hydrolysed with 72 % H₂SO₄. When the bright tobacco insoluble fraction was hydrolysed under these conditions, an H₂SO₄-insoluble residue remained. The neutral sugar method was applied to fractions isolated from bright tobacco. The results of the analysis provided a measure of the homogeneity of the cell wall fractions and thus helped indicate whether different types of structural polysaccharides were effectively separated from each other.

It has been well established that nornicotine is formed in Nicotiana species by the demethylation of nicotine. However, the reverse reaction has not been unequivocally substantiated. This problem has been examined by feeding (RS)-[2'-¹⁴C]nornicotine to Nicotiana tabacum plants. Most of the administered nornicotine was recovered unchanged, but a small amount of activity was detected in the nicotine. Activity was also found in myosmine. The nicotine was degraded and found to have essentially all its radioactivity located at the C-2' position, indicative of a direct synthesis from nornicotine. It has thus been established that the methylation of nornicotine to nicotine does occur in the tobacco plant, but it is not considered to be a major pathway for the biosynthesis of nicotine.

A microprocessor-controlled device for the spiking of cigarettes with variable amounts of radiolabelled material is described. Cigarettes can be spiked at rates in excess of 100/min, compared with the very slow manual methods in existence. The deposition of the radiolabelled material ([16,17-¹⁴C]dotriacontane) is very reproducible with a coefficient of variation of around 3 %. The device is capable of injecting cigarettes of various physical configurations, and of producing variable distributions of the radiolabelled material along the tobacco rod.

A computer model was developed which makes it possible to predict the effects of several cigarette properties on the different degrees of ventilation (total degree of ventilation, degree of ventilation of the tobacco rod, degree of ventilation of the filter) and on the pressure drop. A special advantage of this model is its ability to predict the degree of ventilation from the properties of the materials (e.g. of filter, paper, tobacco) instead of from the properties of the manufactured cigarette. Thus it is no longer necessary to manufacture an experimental cigarette each time. Another advantage results from the fact that the fluctuations of the degree of ventilation can be attributed directly to the factors responsible. Each contribution of the individual factors responsible can be determined separately, which is normally not possible by means of experiments. Thus this model is not only a component of a computer-aided product design, but is also a useful tool for quality control. Some examples are presented which are typical of the effects of various properties of the materials on the ventilation. It becomes obvious that a low level of fluctuations of the filter ventilation does not only imply constant properties of the applied materials (such as tipping paper) but also a uniform primary process.

Small samples of tobacco powder, prepared by grinding the dried tobacco leaves, were heated in a micro-thermo-balance in different atmospheres and at different heating rates. The size distribution and the mass concentration of the smoke particles produced were measured simultaneously with a laser particle counter and a piezo balance mass monitor. In addition, the change of weight loss with time was also measured during each experiment. It was found that a larger amount of smoke particles was produced when tobacco was heated in the atmosphere of inert gas and/or at higher heating rates. Furthermore, comparison of measured and calculated size distributions showed that the particle size distribution was governed mainly by coagulation.

A three-year field study with Oriental Kabakulak (Nicotiana tabacum L. cv. Kabakulak-S2) was conducted on a sandy clay loam soil at Drama, Greece, to determine nutrient concentration patterns in tobacco plants. All cultural practices were those in use for commercial production of Oriental neutral type tobacco. Whole tobacco plants were sampled at weekly intervals from transplanting to the end of the harvesting season and separated into leaves, stalks and roots. The samples were washed, dried, weighed, ground, and analysed for nitrogen, phosphorus, potassium, calcium and magnesium. Nitrogen and potassium concentrations in leaves, stalks and roots tended to decrease during the 1st week after transplanting, then increased up to the 3rd or 4th week and declined thereafter. Phosphorus concentration in all plant parts decreased with time after transplanting. This decrease was greater during the first two weeks than later on. Calcium concentration in leaves and stalks increased from the first to the 2nd or 3rd week, then declined slowly up to the 8th week and remained constant thereafter. In roots, calcium decreased from the 1st to the 8th week and then remained constant. Magnesium concentration in leaves increased from the 1st to the 4th week and then remained constant. In stalks, magnesium increased from transplanting to the 2nd week and then declined slightly, whereas in roots magnesium decreased after the 1st week. Concentrations of nitrogen, potassium and calcium in leaves were similar and much higher than those of magnesium and phosphorus.

This paper comprises a review of the published literature (1936-1979) dealing with the relationship between the chemical constituents of tobacco and smoke and tobacco and smoke quality. Various components thought to be influential in determining quality are identified; conclusions of researchers regarding the effects of these components are recorded and discussed. A summary table is presented which details the nature of the relationship between these constituents and tobacco quality.