Homogenized tobacco material and method of production of homogenized tobacco material

Abstract

The invention relates to a method for the preparation of a homogenized tobacco material, said method comprising: —pulping and refining cellulose fibres to obtain fibres having a mean size per weight comprised between about 0.2 millimetres and about 4 millimetres; —grinding a blend of tobacco of one or more tobacco types to tobacco particles having a mean size per weight comprised between about 0.03 millimetres and about 0.12 millimetres; —Combining the cellulose fibres with the tobacco particles and with a binder to form a slurry; —homogenizing the slurry; —adding asparaginase to the slurry; and—forming the homogenized tobacco material from the slurry, wherein the homogenized tobacco material comprises from about 1 percent and about 5 percent in dry weight basis of the binder.

Claims

1. Method for the preparation of a homogenized tobacco material, said method comprising: pulping and refining cellulose fibres to obtain fibres having a mean size per weight comprised between about 0.2 millimetres and about 4 millimetres; grinding a blend of tobacco of one or more tobacco types to tobacco particles having a mean size per weight comprised between about 0.03 millimetres and about 0.12 millimetres; combining the cellulose fibres with the tobacco particles and with a binder to form a slurry; homogenizing the slurry; adding asparaginase to the slurry in an amount comprised between about 0.0012 percent and about 0.02 percent per weight on dry weight basis of said homogenized tobacco material; and forming the homogenized tobacco material from the slurry, wherein the homogenized tobacco material comprises from about 50 percent and about 93 percent in dry weight basis of the tobacco particles and wherein the homogenized tobacco material comprises between about 1 percent and about 5 percent per weight on dry weight basis of the binder.

2. Method according to claim 1, wherein the slurry has a temperature comprised between about 20 degrees Celsius and about 60 degrees Celsius while the asparaginase is added.

3. Method according to claim 2, wherein the slurry is maintained at a temperature comprised between about 20 degrees Celsius and about 60 degrees Celsius for a time interval comprised between about 2 minutes and about 60 minutes between the addition of the asparaginase and the formation of the homogenized tobacco material.

4. Method according to claim 1, wherein the slurry has a pH comprised between about 5 and about 7 while the asparaginase is added.

5. Method according to claim 1, wherein an aerosol-former is added to the slurry and wherein the homogenized tobacco material comprises between about 5 percent and about 30 percent in dry weight basis of an aerosol-former.

6. Method according to claim 1, wherein the step of forming a homogenized tobacco material from the slurry comprises the steps of: casting a web of the slurry; and drying said cast web.

7. Method according to claim 6, including the step of: cooling said slurry to a temperature below about 15 degree Celsius before casting said slurry.

8. Method according to claim 1, wherein said step of grinding tobacco of one or more tobacco types comprises grinding one or more of the following tobaccos: Bright tobacco; Dark tobacco; Aromatic tobacco; Filler tobacco.

9. Aerosol-generating article, comprising a component prepared from the method of claim 1.

10. A homogenized tobacco material comprising: between about 1 percent and about 7 percent per weight on a dry weight basis of cellulose fibres, the cellulose fibres having a mean length per weight comprised between 0.2 millimetres and about 4 millimetres; tobacco particles having a mean particle size per weight between about 0.03 millimetres and about 0.12 millimetres and in an amount comprised between about 50 percent and about 93 percent per weight on a dry weight basis; between about 1 percent and about 5 percent per weight on a dry weight basis of a binder; asparaginase an amount comprised between about 0.0012 percent and about 0.02 percent per weight on dry weight basis of said homogenized tobacco material; and water.

11. Homogenized tobacco material according to claim 10, comprising between about 5 percent and about 30 percent in dry weight basis of an aerosol-former.

12. Homogenized tobacco material according to claim 10, comprising aspartic acid.

13. Homogenized tobacco material according to claim 10, being solid and preferably in a form of a sheet.

14. Aerosol-generating article, comprising a component prepared from the homogenised tobacco material of claim 10.

Description

(1) The invention will be further described, by way of example only, with reference to the accompanying drawings in which:

(2) FIG. 1 shows a flow diagram of a method to produce an homogenized tobacco material according to the invention;

(3) FIG. 2 shows an enlarged view of one of the step of the method of FIG. 1;

(4) FIG. 3 shows a schematic view of an apparatus for performing a step of the method of FIG. 1;

(5) FIG. 4 shows a schematic view of an apparatus for performing another step of the method of FIG. 1;

(6) FIG. 5 shows a schematic view of an apparatus for performing a further step of the method of FIG. 1;

(7) FIG. 6 shows a schematic view of an apparatus for performing a further step of the method of FIG. 1;

(8) FIG. 7 shows a schematic view of an apparatus for performing a further step of the method of FIG. 1;

(9) FIG. 8 shows the amount of asparagine in dry weight basis present in the homogenized tobacco material in different samples realized according to the invention and in control samples;

(10) FIG. 9 shows the amount of ammonia in dry weight basis present in the homogenized tobacco material in different samples realized according to the invention and in control samples;

(11) FIG. 10 shows the amount of acrylamide in the aerosol generated by heating samples of aerosol-former devices obtained including a component prepared from the homogenized tobacco material of the invention and from samples obtained not according to the invention;

(12) FIG. 11 shows the amount of acetamide in the aerosol generated by heating samples of aerosol-former devices obtained including a component prepared from the homogenized tobacco material of the invention and from samples obtained not according to the invention;

(13) FIG. 12 shows the amount of pyridine in the aerosol generated by heating samples of aerosol-former devices obtained including a component prepared from the homogenized tobacco material of the invention and from samples obtained not according to the invention;

(14) FIG. 13 shows the amount of nicotine, triacetin, glycerine and CO in the aerosol generated by heating samples of aerosol-former devices obtained including a component prepared from the homogenized tobacco material of the invention and from samples obtained not according to the invention; and

(15) FIG. 14 shows the aspartic acid content of samples treated with asparaginase calculated vs. measured.

(16) With initial reference to FIG. 1, a method for the production of slurry according to the present invention is represented. The first step of the method of the invention is the selection 100 of the tobacco types and tobacco grades to be used in the tobacco blend for producing the homogenized tobacco material. Tobacco types and tobacco grades used in the present method are for example bright tobacco, dark tobacco, aromatic tobacco and filler tobacco.

(17) Only the selected tobacco types and tobacco grades intended to be production of the used for the homogenized tobacco material undergo the processing according to following steps of the method of the invention.

(18) The method includes a further step 101 in which the selected tobacco is laid down. This step may comprise checking the tobacco integrity, such as grade and quantity, which can be for example verified by a bar code reader for product tracking and traceability. After harvesting and curing, the leaf of tobacco is given a grade, which describes for example the stalk position, quality, and colour.

(19) Further, the lay down step 101 might also include, in case the tobacco is shipped to the manufacturing premises for the production of the homogenized tobacco material, de-boxing or case opening of the tobacco boxes. The de-boxed tobacco is then preferably fed to a weighing station in order to weight the same.

(20) Moreover, the tobacco lay down step 101 may include bale slicing, if needed, as the tobacco leaves are normally compressed into bales in shipping boxes for shipping.

(21) The following steps are performed for each tobacco type, as detailed below. These steps may be performed subsequently per grade such that only one production line is required. Alternatively, the different tobacco types may be processed in separate lines. This may be advantageous where the processing steps for some of the tobacco types are different. For example, in conventional primary tobacco processes bright tobaccos and dark tobaccos are processed at least partially in separate processes, as the dark tobacco often receives an additional casing. However, according to the present invention, preferably, no casing is added to the blended tobacco powder before formation of the homogenized tobacco web.

(22) Further, the method of the invention includes a step 102 of coarse grinding of the tobacco leaves.

(23) According to a variant of the method of the invention, after the tobacco lay down step 101 and before the tobacco coarse grinding step 102, a further shredding step 103 is performed, as depicted in FIG. 1. In the shredding step 103 the tobacco is shredded into strips having a mean size comprised between about 2 millimetres and about 100 millimetres.

(24) Preferably, after the shredding step 103, a step of removal of non-tobacco material from the strips is performed (not depicted in FIG. 1).

(25) Subsequently, the shredded tobacco is transported towards the coarse grinding step 102. The flow rate of tobacco into a mill to coarse grind the strips of tobacco leaf is preferably controlled and measured.

(26) In the coarse grinding step 102, the tobacco strips are reduced to a mean particle size of between about 0.25 millimetres and about 2 millimetres. At this stage, the tobacco particles are still with their cells substantially intact and the resulting particles do not pose relevant transport issues.

(27) Preferably, after the coarse grinding step 102, the tobacco particles are transported, for example by pneumatic transfer, to a blending step 104. Alternatively, the step of blending 104 could be performed before the step of coarse grinding 102, or where present, before the step of shredding 103, or, alternatively, between the step of shredding 103 and the step of coarse grinding 102.

(28) In the blending step 104, all the coarse grinded tobacco particles of the different tobacco types selected for the tobacco blend are blended. The blending step 104 therefore is a single step for all the selected tobacco types. This means that after the step of blending there is only need for a single process line for all of the different tobacco types.

(29) In the blending step 104, preferably mixing of the various tobacco types in particles is performed. Preferably a step of measuring and controlling one or more of the properties of the tobacco blend is performed. According to the invention, the flow of tobacco may be controlled such that the desired blend is obtained. For example, with reference to FIG. 2, it may be desirable that the blend includes bright tobacco 1 at least for about 30 percent in dry weight of the total tobacco in the blend, and that dark tobacco 2 and aromatic tobacco 3 are comprised each in a percentage between about 0 percent and about 40 percent in dry weight of the total tobacco in the blend, for example about 35 percent. More preferably, also filler tobacco 4 is introduced in a percentage between about 0 percent and about 20 percent in dry weight of the total tobacco in the blend. The flow rate of the different tobacco types is therefore controlled so that these ratios of the various tobacco types is obtained. Alternatively, where the coarse grinding step 102 is done subsequently for the different tobacco leafs used, the weighing step at the beginning of the step 102 determines the amount of tobacco used per tobacco type and grade instead of controlling its flow rate.

(30) In FIG. 2, the introduction of the various tobacco types during the blending step 104 is shown.

(31) It is to be understood that each tobacco type could be itself a sub-blend, in other words, the “bright tobacco type” could be for example a blend of Virginia tobacco and Brazil flue-cured tobacco of different grades.

(32) After the blending step 104, a fine grinding step 105, to a tobacco powder mean size of between about 0.03 millimetres and about 0.12 millimetres is performed. This fine grinding step 105 reduces the size of the tobacco down to a powder size suitable for the slurry preparation. After this fine grinding step 105, the cells of the tobacco are at least partially destroyed and the tobacco powder may become sticky.

(33) The so obtained tobacco powder can be immediately used to form the tobacco slurry. Alternatively, a further step of storage of the tobacco powder, for example in suitable containers may be inserted (not shown).

(34) The steps of tobacco blending 104 and grinding tobacco 102, 105 for the formation of a homogenized tobacco material according to FIG. 1 are performed using an apparatus for the grinding and blending of tobacco 200 depicted schematically in FIG. 3. The apparatus 200 includes a tobacco receiving station 201, where accumulating, de-stacking, weighing and inspecting the different tobacco types takes place. Optionally, in case the tobacco has been shipped into cartons, in the receiving station 201 removal of cartons containing the tobacco is performed. The tobacco receiving station 201 also optionally comprises a tobacco bale splitting unit.

(35) In FIG. 3 only a production line for one type of tobacco is shown, but the same equipment may be present for each tobacco type used in the homogenised tobacco material web according to the invention, depending on when the step of blending is performed. Further the tobacco is introduced in a shredder 202 for the shredding step 103. Shredder 202 can be for example a pin shredder. The shredder 202 is preferably adapted to handle all sizes of bales, to loosen tobacco strips and shred strips into smaller pieces. The shreds of tobacco in each production line are transported, for example by means of pneumatic transport 203, to a mill 204 for the coarse grinding step 102. Preferably, a control is made during the transport so as to reject foreign material in the tobacco shreds. For example, along the pneumatic transport of shredded tobacco, a string removal conveyor system, heavy particle separator and metal detector may be present, all indicated with 205 in the appended drawing.

(36) Mill 204 is adapted to coarse grind the tobacco strips up to a size of between about 0.25 millimetres and about 2 millimetres. The rotor speed of the mill can be controlled and changed on the basis of the tobacco shreds flow rate.

(37) Preferably, a buffer silo 206 for uniform mass flow control, is located after the coarse grinder mill 204. Furthermore, preferably mill 204 is equipped with spark detectors and safety shut down system 207 for safety reasons.

(38) From the mill 204, the tobacco particles are transported, for example by means of a pneumatic transport 208, to a blender 210. Blender 210 preferably includes a silo in which an appropriate valve control system is present. In the blender, all tobacco particles of all the different types of tobacco which have been selected for the predetermined blend are introduced. In the blender 210, the tobacco particles are mixed to a uniform blend. From the blender 210, the blend of tobacco particles is transported to a fine grinding station 211.

(39) Fine grinding station 211 is for example an impact classifying mill with suitable designed ancillary equipment to produce fine tobacco powder to the right specifications, that is, to a tobacco powder between about 0.03 millimetres and about 0.12 millimetres. After the fine grinding station 211, a pneumatic transfer line 212 is adapted to transporting the fine tobacco powder to a buffer powder silo 213 for continuous feed to a downstream slurry batch mixing tank where the slurry preparation process takes place.

(40) The method for the production of a homogenized tobacco material of FIG. 1 further includes a step of suspension preparation 106. The suspension preparation step 106 preferably comprises mixing an aerosol-former 5 and a binder 6 in order to form a suspension. Preferably, the aerosol—former 5 comprises glycerol and the binder 6 comprises guar.

(41) The step of forming a suspension 106 of binder in aerosol-former includes the steps of loading the aerosol-former 5 and the binder 6 in a container and mixing the two. Preferably, the resulting suspension is then stored before being introduced in the slurry. Preferably, the glycerol is added to the guar in two steps, a first amount of glycerol is mixed with guar and a second amount of glycerol is then injected in the transport pipes, so that glycerol is used to clean the processing line, avoiding hard-to-clean points within the line.

(42) A slurry preparation line 300 adapted to perform the suspension of binder in aerosol-former as per step 106 of the invention is depicted in FIG. 4.

(43) The slurry preparation line 300 includes an aerosol-former, such as glycerol, bulk tank 301 and a pipe transfer system 302 having a mass flow control system 303 adapted to transfer the aerosol-former 5 from the tank 301 and to control its flow rate. Further, the slurry preparation line 300 comprises a binder handling station 304 and a pneumatic transport and dosing system 305 to transport and weight the binder 6 received at the station 304.

(44) Aerosol-former 5 and binder 6 from tank 301 and handling station 304, respectively, are transported to a mixing tank, or more than a mixing tank, 306, part of the slurry preparation line 300, designed to mix binder 6 and aerosol-former 5 uniformly.

(45) The method to realize the homogenized tobacco material includes a step of preparing a cellulose pulp 107. The pulp preparation step 107 preferably comprises mixing cellulose fibres 7 and water 8 in a concentrated form, optionally storing the pulp so obtained and then diluting the concentrated pulp before forming the slurry. The cellulose fibres, for example in boards or bags, are loaded in a pulper and then liquefied with water. The resulting water—cellulose solution may be stored at different densities, however preferably the pulp which is the result of the step 107 is “concentrate”. Preferably, “concentrate” means that the total amount in the cellulose fibres in the pulp is between about 3 percent and 5 percent of the total pulp weight before dilution. Preferred cellulose fibres are soft wood fibres. Preferably, the total amount of cellulose fibres in the slurry in dry weight is between about 1 percent and about 7 percent, preferably, between about 1.2 percent and about 2.4 percent in dry weight of the slurry.

(46) Preferably, the step of mixing of water and cellulose fibres lasts between about 20 and about 60 minutes, advantageously at a temperature comprised between about 15 degrees Celsius and about 40 degrees Celsius.

(47) The storage time, if storage of the pulp is performed, may preferably vary between about 0.1 day and about 7 days.

(48) Advantageously, water dilution takes place after the step of storing of the concentrated pulp. Water is added to the concentrated pulp in such an amount that the cellulose fibres are less than about 1 percent of the total weight of the pulp. For example a dilution of a factor comprised between about 3 and about 20 can take place. Further, an additional step of mixing may take place, which comprises mixing the concentrated pulp and the added water. The additional mixing step preferably lasts between about 120 minutes and about 180 minutes at a temperature between about 15 degrees Celsius and about 40 degrees Celsius, more preferably at a temperature of between about 18 degrees Celsius and about 25 degrees Celsius.

(49) All tanks and transfer pipes for cellulose fiber, guar and glycerol are preferably designed to be as optimally short as possible to reduce transfer time, minimize waste, avoid cross contamination and facilitate ease of cleaning. Further, preferably, the transfer pipes for cellulose fiber, guar and glycerol are as straight as possible, to allow a swift and uninterrupted flow. In particular for the suspension of binder in the aerosol-former, turns in the transfer pipe could otherwise result in areas of low flow rate or even standstill, which in turn can be areas where gelling can occur and with that potentially blockages within the transfer pipes. As mentioned before, those blockages can lead to the need for cleaning and standstill of the entire manufacturing process.

(50) Preferably, after the step of pulp preparation 107, an optional step of fibres' fibrillation is performed (not depicted in FIG. 1).

(51) An apparatus 400 to perform the method step 107 of the pulp formation is depicted in FIG. 5. FIG. 5 schematically depicts a cellulose fibre feeding and preparation line 400 comprising a feeding system 401, preferably adapted to handle cellulose fibres 7 in bulk form, such as board/sheets or fluffed fibres, and a pulper 402. The feeding system 401 is adapted to direct the cellulose fibres to the pulper 402, which is in turn adapted to disperse the received fibres uniformly.

(52) The pulper 402 includes a temperature control unit 401a so that the temperature in the pulper is kept within a given temperature interval, and a rotational speed control unit 401b, so that the speed of an impeller (not shown) present in the pulper 402 is controlled and kept preferably comprised between about 5 rpm and about 35 rpm.

(53) The cellulose fibre feeding and preparation line 400 further comprises a water line 404 adapted to introduce water 8 in the pulper 402. A flow rate controller 405 to control the flow rate of water introduced in pulper 402 is preferably added in the water line 404.

(54) The cellulose fibre feeding and preparation line 400 may also further comprise a fibre refiner system 403 to treat and fibrillate fibres, so that long fibres and nested fibres are removed, and a uniform fibre distribution is obtained.

(55) Preferably, the mean size of the cellulose fibres at the end of the pulping and refining step is comprised between about 0.2 millimetres and about 4 millimetres, more preferably between about 1 millimetre and about 3 millimetres.

(56) Downstream the fibre refiner system 403, the cellulose fibre feeding and preparation line 400 may comprise a cellulose buffer tank 407 connected to the fibre refiner system 403 to store the high consistency fibre solution coming out of the system 403.

(57) At the end of cellulose fibre feeding and preparation line 400, a cellulose dilution tank 408 in which pulp is diluted is preferably present and connected to cellulose buffer tank 407. The cellulose dilution tank 408 is adapted to batch out cellulose fibres of right consistency for subsequent slurry mixing. Water for dilution is introduced in tank 408 via a second water line 410.

(58) The method to form a slurry according to the invention further comprises a step of slurry formation 108, where the suspension 9 of binder in aerosol-former obtained in step 106, the pulp 10 obtained in step 107 and the tobacco powder blend 11 obtained in step 104 are combined together (see FIG. 6).

(59) Further, in this step 108 an asparaginase mixture 12 containing asparaginase is introduced in the slurry. Optionally, a pH modifier 13 can be added as well before the step of asparaginase introduction.

(60) Preferably, the step of slurry formation 108 comprises first a step of introduction in a tank of the suspension 9 of binder in aerosol-former and of the cellulose pulp 10. Afterwards, the tobacco powder blend 11 is introduced as well. Preferably, the suspension 9, the pulp 10 and the tobacco powder blend 11 are suitably dosed in order to control the amount of each of them introduced in the tank. The slurry is prepared according to specific proportion among its ingredients. Optionally, also water 8 is added as well.

(61) Preferably, the step of slurry formation 108 also comprises a mixing step, where all the slurry ingredients are mixed together for a fixed amount of time. Preferably asparaginase mixture 12 and optionally pH modifier are added after a first mixing step and then mixing is continued in a second mixing step. More preferably, the pH modifier 13 is introduced in the water used to dilute the slurry and then added to the slurry itself.

(62) In a preferred embodiment, the step of slurry formation 108 also includes a step of heating the slurry to a predetermined temperature, preferably comprised between about 20 degrees Celsius and about 60 degrees Celsius, before the step of adding the asparaginase mixture 12. After the desired temperature has been reached, then the step of adding the asparaginase mixture 12 takes place. After the asparaginase mixture has been added, preferably the selected temperature comprised between about 20 degrees Celsius and 60 degrees Celsius is kept for about between about 2 minutes and about 60 minutes. Advantageously, during this step of keeping the desired temperature, the second mixing step takes place and the slurry is continuously mixed. In this step where the slurry is mixed and the temperature is at the desired value, the enzymatic activity of the asparaginase comprised in the asparaginase mixture takes place.

(63) In a preferred embodiment, the pH modifier 13 is also added before the asparaginase mixture 12 addition, so that the desired pH, for example a pH comprised between about 5 and about 7 is reached, so as to optimize enzymatic activity of the asparaginase included in the mixture 12. Preferably, the amount of asparaginase mixture added in the slurry is such that the amount of asparaginase per weight in dry weight basis of the slurry is comprised between about 0.0012 percent and about 0.02 percent.

(64) Further, the step of slurry formation 108 may also include a subsequent cooling step, so that the slurry is cooled after the desired enzymatic activity has taken place, in order to block or minimize the latter. Preferably, the temperature reached by the slurry after this cooling step is of about between about 9 degrees Celsius and about 11 degrees Celsius. The cooling step takes place in case the slurry is stored before casting, as described below.

(65) In a further step of the method according to the invention, the slurry is then transferred to a following casting step 109 and drying step 110.

(66) An apparatus 500 for the slurry formation adapted to realize step 108 of the method of the invention is schematically depicted in FIG. 6. Apparatus 500 includes a mixing tank 501 where cellulose pulp 10 and suspension 9 of binder in aerosol-former are introduced. Further, the tobacco powder blend 11 from the blending and grinding line is fine-ground and dosed into the mixing tank 501 in specified quantity to prepare the slurry.

(67) For example, the tobacco powder blend 11 may be contained in a tobacco fine powder buffer storage silo to ensure continuous upstream powder operation and meeting demand of slurry mixing process. Tobacco powder is transferred to the mixing tank 501 preferably by means of a pneumatic transfer system (not shown).

(68) The apparatus 500 further comprises preferably a powder dosing/weighing system (also not shown) to dose required amount of the slurry's ingredients. For example, the tobacco powder may be weighted by a scale (not shown) or weighting belt (not shown) for precise dosing. The mixing tank 501 is specially designed to mix the dry and liquid ingredients to form a homogenous slurry. The slurry mixing tank preferably comprises a cooler (not shown), such as water jacket wall to allow water cooled on the external walls of the mixing tank 501. Further, it may also include heating means (also not visible) to change the temperature of the slurry in the mixing tank. The slurry mixing tank 501 is further equipped with one or more sensors (not shown) such as a level sensor, a temperature probe and a sampling port for control and monitoring purpose. Mixing tank 501 has an impeller 502 adapted to ensure uniform mixing of the slurry, in particular adapted to transfer slurry form the external walls of the tank to the internal part of the tank or vice-versa. The speed of the impeller can be preferably controlled by means of a dedicated controlling unit. Mixing tank 501 also includes a water line for the introduction of water 8 at a controlled flow rate. Preferably, in the water line 8 the pH modifier 13 is added before being poured into the tank 501. Asparaginase mixture 12 is added into the mixing tank as well.

(69) Preferably, mixing tank 501 includes two separated tanks, one downstream to the other in the flow of slurry, one tank for preparing the slurry and the second tank with slurry for transfer to provide continuous slurry supply to a casting station.

(70) The method of the invention to produce a homogenized tobacco web includes further a casting step 109 in which the slurry prepared in step 108 is cast in a continuous tobacco web onto a support. The casting step 109 includes transferring the slurry from the mixing tank 501 to a casting box. Further, it preferably includes monitoring the level of slurry in the casting box and the moisture of the slurry. Then, the casting step 109 includes casting, preferably by means of a casting blade, the slurry onto a support, such as a steel conveyor. Further, in order to obtain a final homogenized tobacco web for the use in an aerosol-formed article, the method of the invention includes a drying step 110 in which the cast web of homogenized tobacco material is preferably dried. The drying step 110 includes drying the cast web, by means of steam and heated air. Preferably the drying with steam is performed on the side of the cast web in contact with the support, while the drying with heated air is performed on the free side of the cast web.

(71) An apparatus 600 for performing the steps of casting 109 and drying 110 is schematically depicted in FIG. 7. The casting and drying apparatus 600 includes a slurry transfer system 601, such as a pump, preferably having a flow control, and a casting box 602 to which the slurry is transferred by the pump. Preferably, casting box 602 is equipped with level control 603 and a casting blade 604 for the casting of the slurry into a continuous web of homogenized tobacco material. Casting box 602 may also comprise a density control device 605 to control the density of the cast web.

(72) A support, such as a stainless steel belt conveyor 606, receives the slurry cast by the casting blade 604.

(73) Casting and drying apparatus 600 also includes a drying station 608 to dry the cast web of slurry. Drying station 608 comprises a steam heating 609 and top air drying 610.

(74) Preferably, at the end of the casting step 109 and of the drying step 110, the homogenized tobacco web is removed from the support 606. Doctoring of the cast web after the drying station 608 at the right moisture content is preferably performed.

(75) The cast web goes preferably through a secondary drying process to remove further moisture content of the web to reach moisture target or specification.

(76) After the drying step 110, the cast web is preferably wound in one or more bobbins in a winding step 111, for example to form a single master bobbin. This master bobbin may be then used to perform the production of smaller bobbins by slitting and small bobbin forming process. The smaller bobbin may then be used for the production of an aerosol-generating article (not shown).

EXAMPLES

(77) In the following examples, the asparaginase used may be Acrylaway® L produced by Novozymes U.K. Ltd.

1. Reference Control Examples

(78) A reference aerosol—generating article is prepared using a cast and dried homogenized tobacco material realized according to the method above described of steps 101-111 but without the addition of the asparaginase mixture 12 into the slurry. This is used as reference control sample.

(79) The slurry is prepared according to steps 101-108 without the addition of asparaginase mixture 12 and with the composition according to TABLE 1:

(80) TABLE-US-00001 TABLE 1 % DWB Kg/100 kg batch Tobacco 75% 21 Binder Guar 3% 0.75 Fibers 2% 0.5 Aerosol Glycerin 20% 5 former Water 73 DWB = dry weight basis (referred to the total slurry)

(81) Always using the slurry having the composition of TABLE 1, four different types of control samples have been prepared: a) The pH of the slurry is maintained at about pH 5.2. The temperature of the slurry is maintained at about 28 degrees Celsius. The slurry is then cast according to steps 109-111 above described. b) The pH of the slurry is maintained at about pH 5.2. The temperature of the slurry is raised at about 55 degrees Celsius and this temperature is maintained for about 60 minutes. The slurry is then cast according to steps 109-111 of the method of the invention. c) The pH of the slurry is modified by means of a pH modifier (NaOH) and raised at about pH 6. The temperature of the slurry is maintained at about 55 degrees Celsius for about 60 minutes. The slurry is then cast according to steps 109-111 above described. d) The pH of the slurry is modified by means of a pH modifier and raised at about pH 6.5. The temperature of the slurry is maintained at about 55 degrees Celsius for about 60 minutes. The slurry is then cast according to steps 109-111 above described.

2. Process Control Examples

(82) The slurry preparation and composition is identical to the first control example, but to the slurry an inactive asparagine enzyme has been added. The enzyme is included in an asparaginase mixture which was inactivated by placing an amount of about 2-3 ml of asparaginase mixture in boiling water bath for five minutes. Two different samples have been prepared, which includes a slurry according to Table 1 with the addition of the inactive asparaginase mixture: a) The pH of the slurry is modified by means of a pH modifier (NaOH) and raised to about pH 6. The temperature of the slurry is maintained at about 55 degrees Celsius for about 60 minutes. The slurry is then cast according to steps 109-111 above described. b) The pH of the slurry is modified by means of a pH modifier (NaOH) and raised to about pH 6.5. The temperature of the slurry is maintained at about 55 degrees Celsius for about 60 minutes. The slurry is then cast according to steps 109-111 above described.

3. Homogenized Tobacco Material According to the Invention

(83) A slurry according to steps 101-108 is formed according to the ingredients of TABLE 2:

(84) TABLE-US-00002 TABLE 2 % DWB Kg/100 kg batch Tobacco 75% 21 Binder Guar  3% 0.75 Fibers  2% 0.5 Aerosol Glycerin 20% 5 former Water 73 Asparaginase 0.5%  0.125 mixture (4100 U/mL)

(85) In the slurry of the following examples of the invention, the asparaginase mixture comprises 4% of Asparaginase, which results in 0.0054 kg of Asparaginase.

(86) The enzyme used has a declared activity of 3500 ASNU/g and a density of 1.17 g/ml.

(87) Three different samples of homogenized tobacco materials have been prepared using the above asparaginase mixture: a) The slurry is not heated (temperature maintained at about 30° C.) and the pH is not changed (no addition of NaOH and pH at about 5.3). More in detail: about 800 grams of slurry is prepared according to steps 101-108. Slurry is maintained at about 30 degrees Celsius in a water bath. pH is not modified. About 850 μl of Asparaginase mixture is added while stirring in an amount of about 0.5 percent in dry weight basis. After asparaginase has been added, slurry is maintained at 30 degrees Celsius for about 60 minutes with stirring. Slurry is placed in ice bath to stop reaction. Slurry is casted according to steps 109-111. b) The asparaginase mixture in an amount of about 0.5 percent in dry weight basis is added to the slurry (total slurry 800 ml). Further a pH modifier is added as well, in this case an amount of about 10 percent of NaOH (12.4 g) to raise the pH of tobacco slurry from about 5.39 to about 6.00. The NaOH is added into the water used for slurry preparation. This also avoids tobacco coming into immediate contact with high concentration of NaOH before dispersion into slurry. Slurry is heated to about 55 degrees Celsius on water bath while stirring the slurry. The slurry is covered while heating to minimise water loss. The slurry is left for about 10 minutes to reach the temperature of about 55 degrees Celsius, then about 850 μl asparaginase mixture is added while stirring. After the addition of asparaginase mixture, the slurry is maintained at about 55 degrees Celsius for specified time (about 10 min) with stirring. Slurry is placed in ice bath to stop reaction. pH of slurry is measured. Slurry is casted according to steps 109-111. c) As in 3(b), but the slurry is maintained at about 55 degrees Celsius for 30 minutes after asparaginase addition. d) As in 3(b), but the slurry is maintained at about 55 degrees Celsius for 60 minutes after asparaginase addition. e) As in 3(d), but the amount of added NaOH is modified so that the pH of the slurry is changed to about 6.5.

(88) All samples, both reference and process samples and the samples according to the invention are summarized in the Table 3:

(89) TABLE-US-00003 TABLE 3 Time Temperature Description Name pH_Target (min) ° C. Reference 1a 5.3 — 28 example without 1b 5.3 60 55 Enzyme 1c 6 60 55 1d 6.5 60 55 Process example 2a 6 60 55 with Inactive 2d 6.5 60 55 Enzyme Examples with 3a 5.3 60 30 Active Enzyme 3b 6 10 55 3c 6 30 55 3d 6 60 55 3e 6.5 60 55

(90) The “Name” is the name of the sample: sample 1a refers to the sample realized according to the example 1a (control sample). “pH target” identifies the target pH for the slurry. “Temperature” refers to the temperature reached in degrees Celsius before the addition of asparaginase mixture and maintained for “time” in minutes after the addition of asparaginase mixture.

(91) The homogenized tobacco materials produced using the slurry realized according to the above examples in Table 3 have been analysed and the results in term of the amount of nicotine, glycerine, ammonia, reducing sugar (RS) and total alkaloids (TA) in dry weight basis (DWB) of the total weight of the homogenized tobacco material are listed in Table 4:

(92) TABLE-US-00004 TABLE 4 Glycerin Nicotine TA RS NH.sub.3 Time Temperature (DWB) (DWB) (DWB) (DWB) (DWB) Description Name pH_Target (min) ° C. % (w/w) % (w/w) % (w/w) % (w/w) % (w/w) Tobacco — — — 2.62 10.35 0.12 power blend NO 1a 5.3 — 28 20.1 1.9 2.62 11.00 0.10 Enzyme 1b 5.3 60 55 19.5 1.9 2.61 11.51 0.10 1c 6 60 55 20.0 1.9 2.53 11.42 0.09 1d 6.5 60 55 19.4 1.8 2.46 11.05 0.09 Inactive 2a 6 60 55 20.3 1.8 2.49 11.31 0.09 Enzyme 2b 6.5 60 55 19.9 1.8 2.44 10.91 0.09 Active 3a 5.3 60 30 20.1 1.9 2.54 11.20 0.16 Enzyme 3b 6 10 55 20.2 1.9 2.48 10.79 0.14 3c 6 30 55 19.9 1.8 2.38 10.88 0.12 3d 6 60 55 20.2 1.9 2.55 11.17 0.15 3e 6.5 60 55 20.2 1.8 2.51 11.05 0.14

(93) The above Table 4 shows that the amounts of Nicotine, Reducing Sugars and Total Alkaloids (in dry weight basis, DWB) in the homogenized tobacco materials are substantially the same (no substantial variations, or variations below 10 percent) in the control samples without enzyme or with inactive enzyme and with active enzyme, and they do not vary with the addition of asparaginase. On the other hand, ammonia increases when asparaginase in an active form is added in the slurry, as per the examples 3 (a, b, c, d, e) described above. The ammonia does not increase when asparaginase is introduced in the inactive form.

(94) The amount of ammonia increases due to the enzymatic transformation of L-asparagine+H.sub.2O.fwdarw.L-aspartate+NH.sub.3. Some ammonia is always present in tobacco regardless of the presence of asparaginase. The increase due to asparaginase addition is comprised between about 36 percent and about 51 percent.

(95) According to the reaction, it can be written that:
Asparagine (Mol.wt=132.1 g/mole)=Aspartic acid (Mol.wt=133.11 g/mole)+NH.sub.3 (17.03 g/mole)

(96) 1 mg Asparagine transformed=1.01 mg Aspartic acid+0.13 mg NH.sub.3

(97) The amount of Aspartic acid (mg) and Ammonia (mg) formed in all samples where active Asparaginase is used can be calculated as below.
Mass of aspartic acid formed (mg)=1.01*Mass_mg of (aparagine in Asparaginase treated tobacco plug-asparagine in process control)
Mass of Ammonia (NH.sub.3) formed (mg)=0.13*Mass_mg of (aparagine in Asparaginase treated tobacco plug-aparagine in process control)

(98) The results are summarized in FIG. 13 for the amount of Nicotine, Glycerine, CO and triacetine delivery for some reference/process and samples according to the invention. FIG. 13 shows the amount of Nicotine, Glycerin, CO and Triacetin present in the aerosol formed by aerosol-generating articles fabricated using a component fabricated using the homogenized tobacco material casted using the slurry of reference samples 1a, 1b, 1c, or the slurry of process samples 2a, and of the samples of the invention 3a and 3d. The amount shown is represented as milligrams per “cig”, that is milligrams per single article. As visible, there is no noticeable difference among the different samples.

(99) FIG. 9 shows the ammonia content in dry weight basis of the homogenized tobacco material of all examples 1a-c, 2a-b and 3a-e. It is clear that the samples of the invention 3a-3e including active asparaginase enzyme has a higher ammonia content.

(100) The main difference between the homogenized tobacco material with or without (active) asparaginase addition lies also in the amount of aspartic acid and asparagine present in the homogenized tobacco material. The results are summarized in Table 5.

(101) TABLE-US-00005 TABLE 5 mg Free AA/g tobacco powder (DWB) Corrected for Glycerin and Binder content Time Temperature Aminobutyric Aspartic Glutamic Enzyme pH_Target Name (min) ° C. Alanine acid Arginine Asparagine acid acid Glutamine Glycine Tobacco — — — 0.92 0.36 1.16 4.93 2.42 0.70 1.25 0.11 Powder NO 5.3 1a — 28 0.91 0.34 1.14 4.65 2.39 0.67 1.11 0.11 Enzyme 5.3 1b 60 55 0.95 0.35 1.20 4.63 2.44 0.71 1.08 0.11 6 1c 60 55 0.96 0.36 1.21 4.61 2.52 0.73 1.10 0.11 6.5 1d 60 55 0.89 0.33 1.11 4.39 2.42 0.70 0.92 0.10 Inactive 6 2a 60 55 0.91 0.34 1.15 4.41 2.48 0.71 1.00 0.11 Enzyme 6.5 2b 60 55 0.89 0.33 1.09 4.39 2.41 0.71 0.93 0.11 Active 5.3 3a 60 30 0.94 0.34 1.27 0.14 7.12 0.72 0.92 0.11 Enzyme 6 3b 10 55 0.95 0.35 1.26 0.12 7.11 0.72 1.00 0.11 6 3c 30 55 0.94 0.35 1.26 0.10 7.16 0.74 0.99 0.11 6 3d 60 55 0.99 0.37 1.33 0.06 7.34 0.79 0.97 0.11 6.5 3e 60 55 0.95 0.36 1.27 0.09 7.13 0.76 0.97 0.11

(102) The amount of asparagine decreases in all examples realized according to the invention 3a-3e. The decrease in asparagine is equal or above 97 percent the asparagine present in a sample without enzyme or with an inactive enzyme. The variation in asparagine is depicted in FIG. 8, where the amount of asparagine in milligrams per gram of homogenized tobacco material in dry weight basis is shown. Consequently to the decrease in asparagine, there is an increase in aspartic acid in those samples including active asparaginase.

(103) 6% reduction in the asparagine content of the homogenized tobacco material takes place during production of cast leaf. Process control with no added asparaginase enzyme also shows the same reduction, showing that change in temperature or pH of slurry to 6/6.5 does not induce any change in the asparagine utilization. Similar reduction is observed in the process control with inactive asparaginase.

(104) For all homogenized tobacco material preparations treated with active asparaginase, between about 97 percent and about 99 percent reduction is observed in the asparagine content of tobacco in cast leaf (FIG. 8). Enzymatic treatment for about 60 minutes at about pH 6 and slurry temperature of about 55 degrees Celsius shows the highest reduction.

(105) No change in the aspartic acid content of tobacco takes place during production of cast leaf, that is during casting and drying of the homogenized tobacco material produced with the slurry of the invention. No remarkable changes are observed in the process control cast leaf. About 200 percent increase in aspartic acid is observed in aspartic acid content of homogenized tobacco material samples treated with active asparaginase (FIG. 14). Enzymatic treatment for about 60 minutes at pH of about 6 and slurry temperature of about 55 degrees Celsius provides the highest transformation. The increase in aspartic acid content of cast leaf can be explained by the stoichiometric transformation of L-asparagine+H.sub.2O⇄L-aspartate+NH.sub.3. Indeed FIG. 14 compares the measured value of aspartic acid in the various samples 3a-3e according to the invention (right column for each sample) vs the calculated amount (left column) using the stoichiometric transformation above written.

(106) Prototypes of smoking articles using the homogenized tobacco sheet according to the invention have been prepared and tested as well.

(107) In these articles the following characteristics have been tested.

(108) Acrylamide content. No remarkable variation is observed between the acrylamide content of reference examples (no asparaginase) and process control examples (inactive asparaginase). About 71 percent reduction is observed in acrylamide content of aerosol from asparaginase treated prototypes compared to the reference samples (FIG. 10). The residual acrylamide in aerosol from the asparaginase treated products (depicted examples 3a and 3d) may be explained by formation of asparagine from peptides during the smoking run or by the presence of other precursors for acrylamide in the slurry.

(109) Nitrogen containing constituents, in particular acetamide and pyridine content. No remarkable variation was observed in Acetamide and Pyridine content of aerosol from process control/asparaginase treated prototypes compared to the reference and process ones (FIGS. 11 and 12). An increase of Aspartic acid or ammonia does not influence the concentration of these constituents.