The effect of tobacco ingredients on smoke chemistry. Part I: Flavourings and additives

Abstract

The effects of 450 tobacco ingredients added to tobacco on the forty-four “Hoffmann analytes” in mainstream cigarette smoke have been determined. These analytes are believed by regulatory authorities in the USA and Canada to be relevant to smoking-related diseases. They are based on lists published by D. Hoffmann and co-workers of the American Health Foundation in New York. The ingredients comprised 431 flavours, 1 flavour/solvent, 1 solvent, 7 preservatives, 5 binders, 2 humectants, 2 process aids and 1 filler. The cigarettes containing mixtures of the ingredients were smoked using the standard ISO smoking machine conditions. The levels of the “Hoffmann analytes” in the smoke from the test cigarettes containing the ingredient mixture were compared to those from control cigarettes without the ingredients. In practice, flavouring ingredients are typically added to tobacco that also contains casing ingredients and reconstituted tobacco materials. In order to keep the tobacco mixtures as authentic as possible, three comparisons have been made in this study. These are: (a) control cigarette containing a typical US blended, cased tobacco incorporating reconstituted tobacco versus test cigarettes that had flavouring ingredients added to this tobacco; (b) control cigarette containing tobacco only versus test cigarettes with the tobacco cased and incorporating flavourings; (c) control cigarette containing tobacco only versus test cigarette incorporating additives made in an experimental sheet material. The significances of differences between the test and control cigarettes were determined using both the variability of the data on the specific occasion of the measurement, and also taking into account the long-term variability of the analytical measurements over the one-year period in which analyses were determined in the present study. This long-term variability was determined by measuring the levels of the 44 “Hoffmann analytes” in a reference cigarette on many occasions over the one-year period of this study. The ingredients were added to the experimental cigarettes at or above the maximum levels used commercially by British American Tobacco. The effect of the ingredient mixtures on total particulate matter and carbon monoxide levels in smoke was not significantly different to the control in most cases, and was never more than 10% with any ingredient mixture. It was found that, in most cases, the mixtures of flavouring ingredients (generally added in parts per million levels) had no statistically significant effect on the analyte smoke yields relative to the control cigarette. Occasionally with some of the mixtures, both increases and decreases were observed for some smoke analyte levels relative to the control cigarette. These differences were generally up to about 15% with the mixtures containing flavouring ingredients. The significance of many of the differences was not present when the long-term variability of the analytical methodology was taken into account. For the test cigarettes with ingredient mixtures containing casing ingredients, there were again no significant changes in smoke analyte levels in most cases. Those changes that were observed are as follows. Decreases in smoke levels were observed with some ingredient mixtures for most of the tobacco specific nitrosamines (up to 24%), NO_x, most of the phenols (up to 34%), benzo[a]pyrene, and some of the aromatic amines and miscellaneous organic compounds on the “Hoffmann list”. Increases were observed for some test cigarettes in smoke ammonia, HCN, formaldehyde and lead levels (up to 24%). The significance of the ammonia and lead increases was not present when the long-term variability of the analytical methodology was taken into account. The yields of some carbonyl compounds in smoke were increased in one comparison with an additives mixture containing cellulosic components; in particular, formaldehyde was increased by 68%. This was the largest single change seen in any smoke analyte level in this study. These carbonyls are produced from the pyrolysis of cellulosic and other polysaccharide materials, present in the additives mixture. With this test cigarette, all tobacco specific nitrosamines, phenols, semi-volatile bases, NO_x and some aromatic amines and miscellaneous organic compounds on the “Hoffmann list” were decreased, by up to 22%. The significance of many of these differences remained even when the long-term variability of the analytical methodology was taken into account. The levels of all other “Hoffmann analytes” in the smoke were not significantly different to those of the control cigarette. With the exception of the determinations of “tar”, nicotine and carbon monoxide, there are currently no internationally recognised standard methods for measurement of the other “Hoffmann analytes”. Each laboratory uses its own methods and there are large laboratory-to-laboratory variations, as well as variations over time in a given laboratory. Therefore, it is important that in any comparison of smoke analytes amongst different cigarettes, all the analytes should be measured in the same laboratory and at the same time. This was the case in the present study and all the methods have been validated internally.

Introduction

In some parts of the world tobacco companies add ingredients to tobacco, either to increase the subjective characteristics of the smoke or, for example, to increase the moisture-holding capacity of tobacco. Justification for the use of tobacco ingredients cannot be based solely on their approved use in food since, potentially, they could decompose into other substances during tobacco combustion in the smoking process. An assessment should include consideration of possible thermal decomposition of the ingredients, their effects on smoke chemistry and potential impact on smoke toxicity. The present study is part of a wider assessment of ingredients used on tobacco products, and other aspects are being published in separate papers (Baker, and Bishop, 2003, Baker et al., 2003a, Baker et al., 2003b). The objective of this study was to assess the effects of addition of a range of ingredients to tobacco on the chemistry of cigarette mainstream smoke.

The complexity of tobacco and the cigarette combustion processes makes this a difficult task. Tobacco consists of at least 3800 chemical constituents (Dube and Green, 1982). In a burning cigarette these are subjected to temperatures up to 950 °C in the presence of various levels of oxygen. Many types of chemical reaction take place, yielding at least 4800 chemical constituents in smoke (Baker, 1999). Unambiguously assessing the effect of individual tobacco ingredients on overall smoke chemistry is difficult. Consequently, in the present study the effect of the ingredients has been determined on a sub-set of 44 substances in smoke. These analytes are believed by some regulatory authorities to be relevant to smoking-related diseases. They were selected by the Commonwealth of Massachusetts (Massachusetts Tobacco Control Program, 2001), which are identical to those used by the Canadian Federal Authorities [Department of Health (Canada), 2000] with the exception that eugenol is not included. These substances are sometimes colloquially called “Hoffmann analytes” since similar lists of toxicological substances have been proposed by Dietrich Hoffmann and co-workers of the American Health Foundation in New York since the mid 1980s (e.g. Hoffmann, and Hoffmann, 1998, Hoffmann, and Hoffmann, 2001, Hoffmann et al., 2001). Some other common smoke and tobacco measurements have also been included in the present study since they are often quoted in the scientific literature. These include alkaloids and nitrosamines in tobacco, tobacco and smoke “pH”, and filter filtration efficiencies.

There has been a considerable amount of research done on examining the effects of tobacco ingredients on smoke properties over the last fifty years. Three major reviews were published in 2002 (Paschke et al., 2002, Rodgman, 2002a, Rodgman, 2002b). Paschke et al. gave an overview of 189 published papers that covered the effects of well over 300 ingredients, not all of which are used commercially. They summarised the results from studies that reported the effects of 150 ingredients on different aspects of smoke chemistry, investigated the pyrolysis products from 104 ingredients, and examined the biological effects of smoke generated from cigarettes with 322 ingredients. Paschke et al. concluded that the results from most of the studies clearly indicate that ingredients do not increase the biological activity of cigarette smoke (carcinogenicity, mutagenicity and cytotoxicity). However, they found many gaps in the chemical effects of the ingredients and emphasised the need for standard methods for the chemical assessment of ingredients on cigarette smoke.

In addition to reviewing published studies, Rodgman (Rodgman, 2002a, Rodgman, 2002b) also included details of the extensive research undertaken in the R.J. Reynolds Tobacco Company from the 1950s onwards that was previously unpublished or available only as abstracts of papers presented at scientific meetings. He divided his review into the effects of flavourant ingredients and casing materials. In particular, Rodgman covered in detail the effects of ingredients on the levels of polynuclear aromatic hydrocarbons in smoke. His conclusions were similar to those of Paschke et al., namely that neither flavouring nor casing ingredients added to tobacco during commercial cigarette manufacture in the USA increase the toxicity of cigarette smoke.

Rustemeier et al. (Rustemeier et al., 2002) have recently published specific results on the effect of 333 ingredients used in Philip Morris products on levels of potentially toxicological substances in smoke. This was part of a comprehensive study on the evaluation of the tobacco ingredients, which included smoke chemistry, in vitro genotoxicity and cytotoxicity, and animal sub-chronic inhalation toxicity (Carmines, 2002, Roemer et al., 2002, Vanscheeuwijck et al., 2002). The ingredients were added to tobacco representative of a commercial US blended cigarette in three mixtures and two levels. The levels were approximately those used in a commercial cigarette and at 1.5–3 times higher than normal use. They found that addition of the ingredients to tobacco increased the yield of total particulate matter (TPM) by 13–28%. They believed this was due to the high transfer rate of the added ingredient to smoke. They reported that the yields of many individual constituents relative to TPM decreased compared to the control cigarette, while it increased for a few. Overall, taking into account all the smoke chemistry and biological data, they concluded that the addition of the ingredients to tobacco did not increase the toxicity of the smoke.

Throughout this paper, the term “tobacco constituent” is defined as a substance naturally present in tobacco. The term “tobacco ingredient” is defined as a substance (except water) that is added to tobacco during the manufacturing process and having a specific function on the final tobacco product. Tobacco ingredients are classified as flavours and additives.

Flavours impart a specific taste, flavour or aroma to a product. They may be used as casing ingredients or flavourings (sometimes referred to as top flavours). Casing ingredients are substances used to enhance the tobacco product sensory quality by balancing sensory attributes and developing certain required taste and flavour characteristics. Casing ingredients are often recognised foodstuffs and are applied early in the manufacturing process to the pre-cut tobacco. Flavourings (or top flavours) are substances used to impart a specific taste and flavour in a tobacco product. They are applied to the cut and processed tobacco prior to cigarette manufacture, usually in parts per million (ppm) quantities in a complex mixture in solution. Flavourings give the tobacco brand its unique sensory characteristics.

Additives are substances used for a specific technological purpose in the manufacture of tobacco products. Typical tobacco ingredient additives include: Humectants–substances which increase the moisture-holding capacity of the tobacco. Preservatives–substances that protect the product from deterioration caused by micro-organisms. Solvents – substances used to dissolve or dilute ingredients, without altering their function, in order to facilitate their handling and application. Binders and strengtheners – substances that make it possible to maintain the physical state of the product. Fillers – substances that contribute to the volume of the product without contributing significantly to odour, taste or flavour.

In addition, there are some additives that are used as process aids.

The present paper is Part I of the study and deals mainly with the effects of flavourings and additives; Part II of the study will consider casing ingredients in more detail (Baker et al., 2003a).