Abstract:
Methods of selectively reducing constituents in tobacco as well as the tobacco obtained by such methods are disclosed. Subcritical fluids, e.g., liquid carbon dioxide, serve as the reduction media.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation application of U.S. Ser. No. 10/623,006, filed Jul. 18, 2003, which claims the benefit of U.S. Provisional Application No. 60/397,060, filed Jul. 18, 2002, both of which are hereby incorporated by reference in their entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates to tobacco ( Nicotiana  spp.) and preparations thereof that have reduced concentrations of certain constituents. 
         [0003]    Plants contain a myriad of compounds that have industrial, agricultural, and medical uses. Such compounds may often be obtained by extraction using a variety of methods. In addition, plant matter itself is often employed in a variety of industries, e.g., textiles, and the chemical content of the plant matter may be altered prior to use, for example, by extraction processes, chemical treatment, heat treatment, or biological treatment. 
         [0004]    Several processes have been employed to extract compounds from plant matter. 
         [0005]    For example, extractions have employed aqueous based and organic solvents, gases, and supercritical fluids. The process employed determines the compounds that are removed from the plant matter and the compounds that are retained in association with the plant matter. 
         [0006]    In addition, the various processes used for extraction may differ according to cost, equipment needs, hazardous nature of the chemicals, complexity of the extraction, and adverse affects on the plant matter. For example, supercritical extraction in the manufacture of a plant-based product may negatively impact the economic feasibility of commercialization because the process is complex and expensive and requires specialized equipment. Other extraction methods may have a lower cost and be less complex but lead to an unsatisfactory product, e.g., one that has a negatively impacted flavor, aroma, or quality. Other processes may also be difficult to employ on a scale suitable for mass production. 
         [0007]    Thus, there is a need for a simple, scaleable, environmentally sound, and commercially viable process to reduce unwanted constituents in plant matter, such as tobacco, without otherwise substantially altering the attributes of the product. 
       SUMMARY OF THE INVENTION 
       [0008]    The invention features methods of reducing the amount of constituents in tobacco, as well as the tobacco obtained by such methods. More specifically, such methods are performed on the tobacco itself rather than on aqueous tobacco extracts. These methods are capable of reducing constituents without significant reduction in tobacco attributes. For example, the methods of the invention may be used to reduce secondary alkaloids selectively compared to primary alkaloids. 
         [0009]    Accordingly, the invention features a method of reducing an amount of a constituent, e.g., a secondary alkaloid or polycyclic aromatic hydrocarbon (PAH), in tobacco by providing a vessel containing tobacco comprising the constituent; contacting the tobacco with a subcritical fluid; and removing the subcritical fluid from the vessel, e.g., by venting to the atmosphere or a second vessel. Preferably, the methods of the invention selectively reduce the amount of the constituent relative to a primary alkaloid. 
         [0010]    In another aspect, the invention features a method of reducing the amount of a constituent in tobacco by providing a plurality of valved vessels connected to form a system, wherein the plurality of vessels contains tobacco comprising the constituent; contacting tobacco in a first vessel with a subcritical fluid; removing the subcritical fluid from the first vessel; and directing subcritical fluid, e.g., that from the first vessel, to a second vessel, to additional vessels, or to a waste vessel (or vented to atmosphere) as desired. The method may further include the steps of isolating the first vessel (or any other) from the system; and removing the tobacco from the first vessel, wherein the tobacco has a reduced amount of the constituent. This further step may occur before, during, or after the subcritical fluid has been removed from the first vessel. 
         [0011]    In various embodiments of the above aspects of the invention, the method may include the step of separating a constituent from the subcritical fluid. This separation from the subcritical fluid may include the step of flowing the subcritical fluid containing the constituent into a second vessel that may or may not contain a substance capable of extracting a given constituent from the subcritical fluid. Exemplary substances include solid citric acid, an aqueous solution of citric acid, activated carbon, and solid magnesium silicate. Upon exiting a vessel or entering a second vessel (e.g., a separator vessel), the pressure or temperature of the subcritical fluid may be changed. In certain embodiments, a decrease in pressure causes a precipitation of the dissolved constituents. In other embodiments, the method further includes recirculating the subcritical fluid, after separation of the constituent, to a vessel containing tobacco. During recirculation, any flavor or aroma compounds removed from the tobacco with a constituent may be re-deposited in the tobacco. 
         [0012]    A variety of subcritical fluids, as disclosed herein, may be employed in the methods of the invention. The temperature and pressures employed for each subcritical fluid (or mixture thereof) may vary depending on the subcritical fluids employed. The subcritical fluid may be in liquid form, e.g., a compressed gas, or in gas form. 
         [0013]    In various embodiments, the methods reduce the amount of a constituent, e.g., secondary alkaloids or PAHs, in the tobacco by at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 75%, 85%, or 95%. 
         [0014]    In yet another embodiment, the methods selectively reduce the amount of a constituent, e.g., secondary alkaloids or PAHs, in the tobacco by at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 75%, 85%, or 95%. The methods preferably retain at least 30%, 40%, 50%, 75%, 85%, 95%, or 99% of a primary alkaloid or a particular attribute, such as flavor or aroma compounds. 
         [0015]    The tobacco employed typically has a moisture content of between 5-60%, e.g., at least 10%, 15%, 20%, 30%, 40%, or 50%. The pH of the tobacco is typically between 4 and 9, e.g., at least pH 5, 6, 7, or 8. 
         [0016]    The invention further features tobacco or a tobacco product treated by the above-described methods. 
         [0017]    By a “chlorofluorocarbon” is meant a compound including only carbon, fluorine, and chlorine atoms. 
         [0018]    By a “chlorofluorohydrocarbon” is meant a compound including only carbon, hydrogen, fluorine, and chlorine atoms. 
         [0019]    By “constituent” is meant secondary alkaloids and polycyclic aromatic hydrocarbons (PAH) found in tobacco. By “PAHs” is meant anthracene, anthanthrene, benzo(a)pyrene, coronene, fluoranthene, fluorene, naphthalene, phenanthrene, pyrene, and perylene. By “secondary alkaloid” is meant N-nitrosodimethylamine, N-nitrosodiethylamine, N-nitrosopyrrolidine, N-nitrosodiethanolamine, N-nitrosonornicotine (NNN), 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), N-nitrosoanatabine (NAT), or N-nitrosoanabasine (NAB). 
         [0020]    By “primary alkaloid” is meant any alkaloid other than a secondary alkaloid. 
         [0021]    By “tobacco attribute” is meant a flavor or aroma compound. 
         [0022]    By a “hydrocarbon” is meant a compound including only carbon and hydrogen atoms. 
         [0023]    By “reducing” is meant a lowering the detectable amount of a constituent in tobacco. 
         [0024]    By “subcritical fluid” is meant a compound, or mixture of compounds, that is a gas at ambient temperature and pressure. The term encompasses both the liquid and gaseous phases for such a compound. Exemplary subcritical fluids include, without limitation, carbon dioxide, chlorofluorocarbons, chlorofluorohydrocarbons (e.g., Freon 22), hydrocarbons (e.g., ethane, propane, and butane), nitrous oxide, and combinations thereof. 
         [0025]    By “tobacco” is meant any part of any member of the genus  Nicotiana , e.g., leaves and stems. The tobacco may be whole, shredded, cut, cured, fermented, or otherwise processed. Tobacco may also be in the form of finished products, including but not limited to smokeless tobacco, snuff (moist or dry), chewing tobacco, cigarettes, cigars, and pipe tobacco. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]      FIG. 1  is a schematic representation of a system suitable for an industrial setting, utilizing, e.g., liquid carbon dioxide under subcritical conditions to reduce the amount of a constituent in tobacco. 
           [0027]      FIG. 2  is a schematic representation of a laboratory-scale apparatus, e.g., utilizing liquid carbon dioxide under subcritical conditions to reduce the amount of a constituent in tobacco. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]    Laboratory scale and suitable industrial scale methods of selectively reducing the amount of certain constituents in tobacco are described along with test data detailing the effectiveness of such methods. Notably, these methods are performed on tobacco itself. In addition, the tobacco can be from any source, including dried, cured, or processed, and can further be in the form of finished products, e.g., cigarettes, snuff (moist or dry), and cigars. These methods can reduce the amount of one or more constituents without substantially removing tobacco attributes. 
         [0029]    As shown in  FIG. 1 , an industrial type system utilizing, e.g., liquid carbon dioxide under subcritical conditions, can be used to reduce the amount of one or more constituents in tobacco. Although only one vessel  6  is shown in  FIG. 1 , it is understood that a plurality of such vessels can be utilized, in series, in a large-scale system. 
         [0030]    As further shown in  FIG. 1 , tobacco  5  is charged to vessel  6 , which is then sealed so as to be able to operate under elevated pressure conditions, e.g., necessary to maintain a subcritical fluid as a liquid therein. Subcritical fluid  2 , e.g., carbon dioxide, initially stored as shown in supply vessel  1 , is directed through and is pumped to a desired pressure by inlet pump  3 . After pressurized subcritical fluid  2  passes through inlet pump  3 , the liquid proceeds, via circulation pump  4  into vessel  6  and through the charge of tobacco  5 . As the liquid subcritical fluid  2  flows through tobacco  5 , the amount of constituents in tobacco  5  is reduced. After exiting vessel  6 , a subcritical fluid stream, which at this point may be gaseous, flows into and through separator vessel  7 . The separator vessel may contain a substance  8 , which traps basic constituents and, thereby, depletes the subcritical fluid of any dissolved or suspended constituents. The substance  8  can be drained from separator vessel  7  via drain valve  9 , particularly after the solution accumulates a significant amount of constituents. A suitable substance  8  is an aqueous citric acid solution. Other possible substances effective for separating out constituents include, for example, solid magnesium silicate or any other such solution or solid capable of binding the desired constituents. 
         [0031]    The subcritical fluid, once depleted of any dissolved or suspended constituents may be recirculated to the vessel  6 , as shown, via line R. Circulation pump  4  may be designed such that subcritical fluid entering its inlet from line R may, once again, be pressurized so as to liquify before entering vessel  6 . Those having ordinary skill in the art will recognize that pump  4  may thus act to re-pressurize the subcritical fluid entering pump  4  from either supply vessel  1  or line R. Following completion of the reduction process, the system may be depressurized and constituent-reduced tobacco  5  removed. The process time may vary depending on a variety of processing parameters. One of ordinary skill in the art will readily be able to determine suitable process times. Ranges of appropriate process times are discussed below in connection with trial runs performed on a laboratory-scale system. 
         [0032]    The virtually continuous circulation of subcritical fluid and the inherent capability of reducing constituents from multiple charges of tobacco residing in a plurality of vessels are two clear advantages to be exploited. Elimination of costly down time brought about by emptying and recharging of a single vessel  6  is achievable with use of several (typically three or four) valved vessels  6  operating in series. Vessels may also be operated in parallel. As noted above, subcritical fluid is pumped in series through the several vessels  6 . When the charge of tobacco in one of the vessels has become constituent-reduced and is ready to be removed, the subcritical fluid can be diverted from that vessel to another vessel containing tobacco or a separation vessel. This subcritical fluid may still be effective for reducing constituents from other charges of tobacco in other vessels. The vessel from which tobacco is ready to be removed may be isolated from the system without interfering with on-going reductions in other vessels. New tobacco may then be placed into the vessel, and the process can continue without overall system interruption. 
         [0033]    Preferably, treated tobacco substantially retains the taste and aroma of untreated tobacco. Alternatively, any flavor or aroma compounds removed during treatment may be re-deposited in the tobacco, e.g., after removal of any constituents from the subcritical fluid. The flavor and aroma content of tobacco can be determined by taste and smell tests. 
         [0034]    The following examples illustrate various embodiments of the present invention and are not intended to be limiting in any way. 
       Example 1 
     Reduction of Constituents Using Subcritical Carbon Dioxide 
       [0035]      FIG. 2  shows a schematic representation of a laboratory-scale system that can be used to produce reduced constituent content in tobacco. The representative data of Table 1 were developed using such a system, which was operated in the following manner. A sample of tobacco  16  was placed in vessel  15 , and the vessel was sealed. Gaseous subcritical fluid  12  was supplied from cylinder  11  and admitted to the system. When pressure (as measured by gauges A and B) reached cylinder pressure, compressor pump  13  was energized to liquify the fluid  12 . Temperature was adjusted and controlled using preheater  14  and was measured with thermocouples C and D. Flow of subcritical fluid  12  was then started using adjustable flow control valve  17  that was set so as to operate at a selected flow rate measured by flow meter  19 . The range of flow rate may be between about 5 grams/min to 150 grams/min; for convenience 20-30 grams/min rate was chosen for the experimental runs. Pressure was reduced across valve  17 , resulting in the gaseous subcritical fluid passing into filter flask  18  into which constituent-rich extract could be collected. Alternatively, the subcritical fluid was vented to a waste vessel. The total flow of subcritical fluid  12  passed through the charge of tobacco  16  during the duration of a run was measured by dry test meter  20 . In this laboratory system, no separation vessel was used to facilitate recirculation of subcritical fluid  12 . Vessel  15  was a stainless steel tube having a length of 10 inches, an outside diameter of 1 inch, and a volume of about 60 ml. After treatment, the tobacco  16  was analyzed for its constituent content and the percent reduction of constituent content. The run time necessary to produce such tobacco may be anywhere between about 2 and 14 hours, preferably in the range of about 4-8 hours. 
         [0036]    The carbon dioxide utilized according to the present invention should be a subcritical fluid (critical point 31° C. and 1070 psi), e.g., a liquid. In practicing the process of the present invention, carbon dioxide temperature, pressure, or both can be adjusted to ensure that it is a subcritical fluid, for example, by an inlet heat exchanger (not shown). The run pressure was held essentially constant (in the range of between about 1000 and 2200 psi) for a given run. Runs were performed at essentially constant temperatures ranging between about 0° C. and 24° C. Although a range of mass of subcritical fluid: mass of tobacco ratios can be used, typically between 21 to 50 grams of carbon dioxide per gram of tobacco were used to reduce the maximum amount of constituent. 
         [0037]    Table 1 shows data on the reduction of constituents in tobacco employing the laboratory-scale system described above. As shown in Table 1, the process is selective for the reduction of secondary alkaloids relative to primary alkaloids. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Reduction of constituents in tobacco with carbon dioxide 
               
             
          
           
               
                   
                   
                   
                 Mass of 
                   
                 % 
                   
               
               
                   
                   
                   
                 CO 2 :Mass 
                 % 
                 Secondary 
                 % Primary 
               
               
                   
                 Conditions 
                   
                 of 
                 Moisture 
                 Alkaloids 
                 Alkaloids 
               
               
                 Sample 
                 (° C./psi) 
                 pH 
                 Tobacco 
                 Content 
                 Reduction 
                 Reduction 
               
               
                   
               
               
                 1 
                 17/1200 
                 6 
                 21 
                 15 
                 39 
                 4 
               
               
                 2 
                 17/1200 
                 6 
                 23 
                 30 
                 81 
                 0 
               
               
                 3 
                 14/1200 
                 6 
                 24 
                 52 
                 74 
                 0 
               
               
                 4 
                 19/1200 
                 8 
                 50 
                 58 
                 91 
                 2 
               
               
                   
               
             
          
         
       
     
       Example 2 
     Reduction of Constituents Using Subcritical Freon 22 
       [0038]    Additional experiments according to the method of Example 1 were carried out using Freon 22 (chlorodifluoromethane) (critical point 96° C., 716 psi) instead of carbon dioxide. The data are shown in Table 2. Exemplary conditions for use of Freon 22 include 0 to 50° C., 100 to 2000 psi, and a mass of Freon 22 to mass of tobacco ratio of 20 to 100. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Reduction of constituents in tobacco with Freon 22 
               
             
          
           
               
                   
                   
                   
                 Mass of 
                   
                   
                   
               
               
                   
                   
                   
                 Freon 
                   
                 % 
                   
               
               
                   
                   
                   
                 22:Mass 
                 % 
                 Secondary 
                 % Primary 
               
               
                   
                 Conditions 
                   
                 of 
                 Moisture 
                 Alkaloids 
                 Alkaloids 
               
               
                 Sample 
                 (° C./psi) 
                 pH 
                 Tobacco 
                 Content 
                 Reduction 
                 Reduction 
               
               
                   
               
               
                 1 
                 27/1200 
                 6 
                 53 
                 15 
                 65 
                 52 
               
               
                 2 
                   
                 6 
                   
                 55 
                 98 
                 77 
               
               
                 3 
                 34/1000 
                 8 
                 33 
                 55 
                 95 
                 44 
               
               
                   
               
             
          
         
       
     
       Example 3 
     Reduction of Secondary Alkaloids Using Subcritical Propane 
       [0039]    Additional experiments according to the method of Example 1 were carried out using propane (critical point 96.7° C., 617 psi) instead of carbon dioxide. The data are shown in Table 3. In general, the conditions for use of propane are 0 to 50° C., 100 to 2000 psi, and a mass of propane to a mass of tobacco ratio of 20 to 100. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Reduction of secondary alkaloids in tobacco with propane 
               
             
          
           
               
                   
                   
                   
                 Mass of 
                 % 
                 % 
                   
               
               
                   
                   
                   
                 Propane:Mass 
                 Mois- 
                 Secondary 
                 % Primary 
               
               
                 Sam- 
                 Conditions 
                   
                 of 
                 ture 
                 Alkaloids 
                 Alkaloids 
               
               
                 ple 
                 (° C./psi) 
                 pH 
                 Tobacco 
                 Content 
                 Reduction 
                 Reduction 
               
               
                   
               
               
                 1 
                 20/1200 
                 6 
                 22 
                 15 
                 13 
                 10 
               
               
                 2 
                 20/1200 
                 6 
                 22 
                 60 
                 58 
                  3 
               
               
                 3 
                 20/1200 
                 8 
                 25 
                 60 
                 51 
                 67 
               
               
                   
               
             
          
         
       
     
       Example 4 
     Reduction of PAHs Using Subcritical Propane 
       [0040]    Table 4 shows data from an experiment according to Example 1 on the reduction of PAHs in tobacco by treatment with subcritical propane. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 Reduction of PAHs in tobacco with propane 
               
             
          
           
               
                   
                   
                   
                 Mass of 
                 % 
                   
                   
               
               
                   
                   
                   
                 Propane:Mass 
                 Mois- 
                   
                 % Primary 
               
               
                 Sam- 
                 Conditions 
                   
                 of 
                 ture 
                 % PAHs 
                 Alkaloids 
               
               
                 ple 
                 (° C./psi) 
                 pH 
                 Tobacco 
                 Content 
                 Reduction 
                 Reduction 
               
               
                   
               
               
                 1 
                 30/1000 
                 6 
                 24 
                 16 
                 77 
                 14 
               
               
                   
               
             
          
         
       
     
       Example 5 
     Reduction of Constituents Using Other Subcritical Fluids 
       [0041]    The amount of constituents in tobacco may also be reduced using the methods of the invention by employing ethane (critical point 32.2° C., 708 psi) or nitrous oxide (critical point 36.5° C., 1046 psi). Exemplary conditions for use of ethane include 0 to 30° C., 500 to 2000 psi, and a mass of ethane to a mass of tobacco ratio of 20 to 100. 
         [0042]    Exemplary conditions for use of nitrous oxide include 0 to 35° C., 500 to 2000 psi, and a nitrous oxide to tobacco ratio of 20 to 100. 
       Other Embodiments 
       [0043]    The description of the specific embodiments of the methods and tobacco obtained therefrom is presented for the purposes of illustration. It is not intended to be exhaustive nor to limit the scope of the invention to the specific forms described herein. Although the invention has been described with reference to several embodiments, it will be understood by one of ordinary skill in the art that various modifications can be made without departing from the spirit and the scope of the invention, as set forth in the claims. 
         [0044]    Other embodiments are within the claims.