Study on tobacco components involved in the pyrolytic generation of selected smoke constituents

Abstract

The aim of this study was to investigate the contribution of various tobacco components to the generation of smoke constituents using a tobacco pyrolysis model. We analyzed the amounts of primary tobacco components (sugars, protein, polyphenols, alkaloids, organic acids, inorganics etc.) in flue-cured and burley tobacco leaves. Each of the components was added to the tobacco leaves at the 0.5-fold and 1.0-fold amount naturally present in the leaves. The treated tobacco samples were pyrolyzed at 800 °C in a nitrogen atmosphere with an infrared image furnace, and the selected smoke constituents (benzo[a]pyrene, hydrogen cyanide, carbonyl compounds, aromatic amines, volatile organic compounds and phenolics) were quantitatively analyzed by several methods, including high performance liquid chromatography (HPLC) and gas chromatography/mass spectrometry (GC–MS). The contribution of each tobacco component to the generation of selected smoke constituents was estimated from a regression line determined by the three yields (no addition, 0.5-fold addition, and 1.0-fold addition). The results of this study can provide useful and comprehensive information on the relationship between tobacco components and selected smoke constituents during pyrolysis.

Introduction

Inside a burning cigarette, thousands of tobacco leaf components are exposed to various burning environments, and more than 4800 constituents have been identified in tobacco smoke (Green and Rodgman, 1996). Tobacco smoke includes “selected smoke constituents” which are thought to have toxic properties such as carcinogenicity and cytotoxicity (Hoffmann et al., 2001; Rodgman and Green, 2003), and epidemiological evidence suggests that smoking is a cause of human lung cancer (Vineis et al., 2004). However, the mechanism by which smoke constituent induces the cancer remains unestablished (Hecht, 1999; Rodgman and Green, 2003).

While some selected smoke constituents, such as tobacco-specific nitrosamines (TSNAs), originally exist in raw tobacco leaves and are assumed to directly transfer to tobacco smoke (Andres et al., 2003), many of the selected smoke constituents are formed by the pyrolysis or pyrosynthesis of the tobacco components. There is concentrated research at the worldwide level on technologies to reduce the level of selected smoke constituents (Shields, 2002; Hoffmann et al., 2001; Fisher, 2001). One effective way of developing additional technologies for the reduction of selected smoke constituents is to determine their generation pathways including precursors and mechanisms of chemical formation. Considerable research has been conducted over the past fifty years to understand these generation pathways. Some studies involved the analysis of pyrolysis products from a single component present in the tobacco leaf, the analysis of pyrolysis products from a solvent extracted fraction of the tobacco leaf, and the analysis of the distribution of radioactivity in tobacco smoke from cigarettes containing radioactive tobacco components (Baker, 1987; Chortyk and Schlotzhauer, 1973; Green, 1977; Schlotzhauer and Chortyk, 1987). Other studies investigated the correlations among smoke constituents and tobacco components (Tso et al., 1973; Norman et al., 1983), or analyzed the effects of additives on the generation of smoke constituents (Paschke et al., 2002). However, these studies do not necessarily provide sufficient information on the formation mechanisms of the various smoke constituents. For example, studies on single-component pyrolysis and pyrolysis of tobacco extracts have shown that each tobacco component has the potential to become a particular smoke constituent, but it remains unclear to what degree a given component plays the role of precursor in real tobacco pyrolysis. In addition, it is difficult to compare and discuss the results from the experiments carried out to date because they were conducted under different pyrolysis conditions (pyrolysis apparatus, temperature, carrier gas etc.). Therefore, a quantitatively and comprehensively designed experiment is needed in order to clarify the components involved in the generation of smoke constituents.

The present tobacco pyrolysis study was designed to reveal the relationship between tobacco components and smoke constituents. While there are over 60 known toxic constituents in cigarette smoke (Hoffmann et al., 2001; Rodgman and Green, 2003), we chose to examine 13 smoke constituents (Table 1) in order to obtain extensive information on the generation of smoke constituents. The 13 selected smoke constituents have a variety of chemical structure, and are generated by the pyrolysis or pyrosynthesis of tobacco components, not generated by the direct transfer from tobacco leaves such as TSNAs or toxic heavy metals. Tobacco components (sugars, protein, polyphenols, alkaloids, organic acids, inorganics, etc.) were each added to tobacco leaves (flue-cured and burley) at the 0.5-fold and 1.0-fold amount naturally present in the leaves. The treated tobacco samples were then pyrolyzed with an infrared image furnace, and the 13 selected smoke constituents were quantitatively determined by several methods, including high-performance liquid chromatography (HPLC) and gas chromatography (GC–MS).