Volumen 8 (1975): Heft 1 (January 1975)

With constant volumetric flow rate F at the end of the test specimen the pressure drop is dependent on the absolute pressure under which the volumetric flow rate is measured. The correlation between pressure drop Dp at the test specimen and volumetric flow rate F can be adequately described by

in which k is a constant for a certain object measured and p* designates the pressure under which the volumetric flow rate F is measured. p1 and p2 are the absolute pressures at the test specimen entrance and exit respectively. For the definition of draw resistance it results from this that the Coresta suggestion that p1 = 1 atm 760 Torr be determined as reference pressure is inexpedient for practical purposes. It would be more expedient to determine p* = p2 = 1 atm 760 Torr, i. e. that pressure is determined as reference pressure under which the volumetric flow rate F is measured at the end of the test specimen. The simple correction formulae resulting for this with fluctuating atmospheric pressure are quoted.

All the evidence obtained in our laboratories has shown that the total aldehyde yield in tobacco smoke is not related to either sugar content or the equilibrium moisture content of the tobaccos. There is, however, a relationship between particulate matter [PM(WNF)]⁺ and aldehyde delivery. This accounts for some 41 % of the total variation between different cigarettes. ⁺ PM(WMF) = Total particulate matter - (water + nicotine)

A series of cigarettes made from Burley tobacco containing different levels of added reducing sugar (10.5 to 17.8 %) have been examined. Compared to the control cigarette there was virtually no change in the deliveries of aldehydes and carbonyl constituents. However, an increase in the delivery of 2-furfural was observed, especially when fructose was the added sugar: even so, the conversion efficiency was only 1-2 %. A similar increase in the delivery of 2-furfural was also observed when glucose was added to flue-cured tobacco. An additional finding was that the addition of glucose and fructose reduced the delivery of nicotine. Radioactivity balance experiments on flue-cured cigarettes with added glucose indicated that this was probably due to an increase in the nicotine filtration efficiency of the cigarette rod. Filtration studies using air-cured cigarettes demonstrated that, on addition of glucose, there was a significant increase in the nicotine filtration efficiency of the tobacco rod and that less of the available nicotine was directed into the mainstream.

Flue-cured Virginia tobacco has been heated in nitrogen and nitrogen/oxygen mixtures under flow conditions, and the rate of formation of carbon monoxide and carbon dioxide has been determined as a function of temperature, heating rate, and proportion of oxygen in the gas. When the tobacco is heated in nitrogen at heating rates comparable to those in a smouldering cigarette, 27 % of the carbon content of the tobacco is converted to carbon oxides. Both carbon oxides show two distinct formation regions: a low-temperature region (about 100°-450°C), and a high-temperature region (about 550°-900°C). These temperature limits are almost identical to those predicted from studies on the combustion coal of a cigarette burning in air. When tobacco, or the carbonaceous residue remaining after the pyrolysis experiments, is heated in nitrogen / oxygen mixtures, the total amount of carbon converted to carbon monoxide and carbon dioxide is independent of heating rate, but the relative proportions of the two oxides are strongly dependent on heating rate. At the lower heating rate, proportionally less carbon monoxide, and more carbon dioxide, is produced. Under oxidation conditions, about 70 % of both carbon oxides formed in the low-temperature region (100°-450°C) are produced by tobacco decomposition reactions, whereas in the high-temperature region about 10-20 % of the carbon monoxide, and 2-9 % of the carbon dioxide, are produced by tobacco decomposition.

Cigarette smoke has been shown to contain free radicals in both the vapour and particulate phases. The present investigation was undertaken to find out whether these radicals could initiate or promote the formation of radical peroxides which might in turn lead to lipid peroxidation. To investigate this, a system involving the coupled oxidation of b-carotene and linoleic acid was utilized. In this coupled reaction, b-carotene is destroyed through oxidation by free peroxy radicals. The system can therefore be used as a convenient detector of auto-oxidative mechanisms in which peroxide radicals participate, as well as provide an assay for antioxidants, since in their presence oxidative destruction of b-carotene is blocked. Our results show that smoke did not contribute to the oxidative destruction of b-carotene but rather behaved as an antioxidant. Both smoke vapour and particulate matter were found to be highly antioxidant. A number of pure vapour phase components were tested and the bulk of antioxidant activity was found to be due to HCN. Smoke condensates from different tobacco types were compared and differentiated according to their relative efficiencies of antioxidant activities. For comparison, units of antioxidant activity were expressed as rate of change of optical density with time. The highest antioxidant activities were obtained with air-, flue-cured (cut) and perique tobaccos. Pipe tobacco had the least activity while cigar and flue-cured (granulated), stem and sheet tobaccos had intermediate values. Tests done on smoke fractions derived from the fractionation of total condensate revealed that antioxidant activity resided largely in the neutral and water-insoluble acid fractions with virtually no activity in the basic fractions. The mode of antioxidant action of tobacco smoke is discussed in terms of free-radical mechanisms.

ExperimentaI cigarettes from tobaccos varying in genotype, nitrogen nutrition, stalk position, suckering practice, and curing methods were used to examine the Ievels of N-dimethylnitrosamine (DMN) in smoke. Measurable amounts of DMN were found in all experimental samples, ranging from 1.7 to 115 ng per gram of tobacco burned. DMN content in smoke generally increased as rate of N fertilization increased. However, there were wide seasonal, cultural, and varietal effects. Burley-type tobacco produced a much higher level of DMN than the bright-type tobacco. DMN content in smoke was significantly and positively related to Ieaf total N, totaI alkaloids, nicotine, nornicotine, total volatile bases and nitrate N, but negatively related to reducing sugars. Reconstituted sheet tobaccos made with homogenized-leaf-curing samples produced much lower amounts of DMN than conventionally cured leaf. Additional information is needed to elucidate the primary leaf constituents that serve as precursors of DMN.

Average residue Ievels of DDT + TDE in flue-cured tobacco decreased from 6.1 ppm in 1970 to 0.85 ppm in 1972. DDT + TDE residues in Burley also dropped sharply from previous levels. In 1972 one sample from Kentucky contained 8.17 ppm; all other Burley samples were less than 0.25 ppm. DDT + TDE residues also declined in fire-cured and air-cured types; of these samples Tennessee dark air-cured tobacco contained the highest average residue (3.5 ppm of DDT + TDE). In 1972 over 90 % of the flue-cured samples were positive for toxaphene. Since each of our samples was a composite of tobacco from 10 farmers, we cannot conclude from this result that 90 % of the individual piles contained toxaphene. Significant amounts of toxaphene were found in other types also; for example, 50 % of the 1972 Burley samples had toxaphene concentrations greater than 0.5 ppm. Average endosulfan levels decreased between 1970 and 1972 in flue-cured and Burley tobaccos. However, in all of the dark air and dark fire-cured samples from Tennessee endosulfan residues exceeded 5 ppm. Average endrin residues were at or near the low detection limit in alI samples except fire-cured and dark air-cured tobacco from Tennessee; these averaged 0.26 and 0.17 ppm, respectively.

A new procedure (HLC) of curing tobacco leaf through homogenization, incubation, and dehydration is described. At the homogenate stage, chemicaI composition can be improved by controlled enzyme action, by extraction, or with chemical additives. PhysicaI properties can be improved by reconstitution. Preliminary results show HLC may provide smoke with quality comparable to that from conventionally cured material, but with relatively lower biologicaI response. There is a great potential in using the HLC procedure for labour saving as well as for improving leaf usability.