Note: Descriptions are shown in the official language in which they were submitted.
l ~
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TOBACCO CURING BARN
FIELD OF THE INVENTION
The present invention relates to an improved method of treating tobacco to
reduce
the content of, or to prevent the formation of, harmful nitrosamines, which
are normally
found in tobacco. The present invention also relates to tobacco products
having low
nitrosamine content.
BACKGROUND OF THE INVENTION
Prior attempts to reduce tar and harmful carcinogenic nitrosamines primarily
have
1 p included the use of filters in smoking tobacco. In addition, attempts have
been made to use
additives to block the effects of harmful carcinogens in tobacco. These
efforts have failed
to reduce the oncologic morbidity associated with tobacco use. It is known
that fresh-cut,
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green tobacco has virtually no nitrosamine carcinogens. See, e.g., Wiernik et
al, "Effect of
Air-Curing on the Chemical Composition of Tobacco," Recent Advances in Tobacco
Science, Vol. 21, pp. 39 et seq., Symposium Proceedings 49th Meeting Tobacco
Chemists'
Research Conference, Sept. 24-27, 1995, Lexington, Kentucky (hereinafter
"Wiernik et
al."). On the other hand, cured tobacco products obtained according to
conventional
methods are known to contain a number of nitrosamines, including the harmful
carcinogens
N'-nitrosonornicotine (NNN) and 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-
butanone
(NNK). It is widely accepted that such nitrosamines are formed post-harvest,
during the
conventional curing process, as described further herein. Unfortunately, fresh-
cut green
tobacco is unsuitable for smoking or other consumption.
It is believed that tobacco-specific nitrosamines {TSNAs) are formed primarily
during the curing process. While not wishing to be bound by theory, it is
believed that the
amount of tobacco-specific nitrosamine (TSNA) in cured tobacco leaf is
dependent on the
accumulation of nitrites, which accumulate during the death of the plant cell
and are formed
during curing by the reduction of nitrates under conditions approaching an
anaerobic
(oxygen deficient) environment. It is believed that the reduction of nitrates
to nitrites occur
by the action of the micro flora on the surface of the leaf under anaerobic
conditions, and it
is also believed that this reduction is particularly pronounced under certain
conditions (e.g.,
humid conditions). Furthermore, during the curing process, the tobacco leaf
emits carbon
dioxide, which can further dilute oxygen levels in the environment.
Once the nitrites are formed, these compounds are believed to combine with
various
tobacco alkaloids, including pyridine-containing compounds, to form
carcinogenic
nitrosamines.
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In 1993 and 1994, Burton et al at the University of Kentucky carried out
certain
experiments regarding TSI\fA, as reported in the Abstract, "Reduction of
Nitrite-Nitrogen
and Tobacco N'-Specific Nitrosamines In Air-Cured Tobacco By Elevating Drying
Temperatures," Agronomy & Phytopathology Joint Meeting, CORESTA, Oxford 1995.
Burton et al reported that drying harvested tobacco leaves for 24 hours at 71
°C, at various
stages of air curing, including end of yellowing (EOY), EOY+3, EOY+5, etc.
resulted in
some reduction of nitrosamine levels. Reference is also made to freeze drying
and
microwaving of certain samples, without detail or results. It has been
confirmed that in the
actual work underlying this Abstract, carned out by Burton et al at the
University of
Kentucky, the microwave work was considered unsuccessful. Certain aspects of
Burton et
al's 1993-94 study are reported in Wiernik et al, supra, at pages 54-57, under
the heading
"Modified Air-Curing." The Wiernik et al article postulates that subjecting
tobacco leaf
samples, taken at various stages of air-curing, to quick-drying at 70°C
for 24 hours, would
remove excess water and reduce the growth of microorganisms; hence, nitrite
and tobacco-
specific nitrosamine (TSNA) accumulation would be avoided. In Table II at page
56,
Wiernik et al includes somE; of Burton et al's summary data on lamina and
midrib nitrite and
TSNA contents in the KY1~50 and KY171 samples. Data from the freeze-drying and
the
quick-drying tests are included. The article contains the following
conclusion:
It can be concluded from this study that it may be possible to reduce nitrite
levels and accumulation of TSNA in lamina and midrib by applying heat
(70°C) to dark tobacco after loss of cell integrity in the leaf. Drying
the
tobacco leaf quickly at this stage of curing reduces the microbial activity
that
occurs during slow curing at ambient temperature. It must be added,
however, that such a treatment lowers the Quality of the tobacco leaf.
25
Id. at page 56. The Wiernik et al article also discusses traditional curing of
Skroniowski
tobacco in Poland as an example of a 2-step curing procedure. The article
states that the
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tobacco is first air-cured arid, when the lamina is yellow or brownish, the
tobacco is heated
to 65°C for two days in order to cure the stem. An analysis of tobacco
produced in this
manner showed that both the tobacco-specific nitrosamine (TSNA) and the
nitrite contents
were low, i.e., in the range of 0.6-2.1 micrograms per gram and less than 10
micrograms per
5 gram, respectively. Wiemik et al theorized that these results were
explainable due to the
rapid heating which does not allow further bacterial growth. Wiernik et al
also noted that
tobacco-specific nitrosamine (TSNA) and nitrite contents of 0.2 microgram per
gram and
less than 15 micrograms pcr gram, respectively, were obtained for tobacco
subjected to air-
curing in Poland.
In practice, tobacco leaves are generally cured according to one of three
methods.
First, in some countries, sL~ch as China, a variation of the flue curing
process (described
below) is still being used on a commercial scale to cure tobacco leaves.
Specifically, this
variation of the flue curing; process features the use of a heat exchanger and
involves the
burning of fuel and the passing of heated air through flue pipes in a curing
bam.
Accordingly, in this older version of the curing process, primarily radiant
heat emanating
from the flue pipes is used to cure the tobacco leaves. While a relatively low
flow of air
does pass through the curing barn, this process utilizes primarily radiant
heat emanating
from the flue pipes to cure. the tobacco leaves within the barn. In addition,
this process does
not appreciate, and does not provide for, controlling the conditions within
the barn to
20 achieve prevention or reduction of TSNAs. This technique has been largely
replaced in the
United States by a different flue-curing process.
For more than twenty years, the heat exchanger method described above has been
supplanted in the U.S. wit:h a more economical version which features the use
of a propane
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burner. This second method is the so-called "flue curing" method. This process
involves
placing the tobacco leaves in a barn and subjecting the leaves to curing with
the application
of convective heat using a hot gaseous stream that includes combustion exhaust
gases.
When convective heat is used to dry the tobacco leaves, the combustion exhaust
gases
5 (including carbon monoxide, carbon dioxide, and water) are passed directly
through the
tobacco. In processes where convective heat is used for curing, no attempt is
made to
separate the heat from the combustion exhaust gases (i.e., to prevent an
anaerobic condition)
or to control the ambient conditions to reduce or suppress the formation of
TSNAs.
The third method is known as "air curing." This process involves placing the
tobacco leaves in a barn and subjecting the leaves to air curing without
controlling the
ambient conditions (e.g., air flow through the barn, temperature, humidity,
and the like) and
without the application of any heat.
U.S. Patent No. 2,758,603 to Heljo discloses a process for treating tobacco
with
relatively low moisture levels (i.e., already cured tobacco) with radio
frequency energy to
accelerate the aging process. Although the patent states that the tobacco
being treated is
"green" tobacco, it is clear that the patent is using the term "green" in a
non-conventional
sense because the tobacco being treated therein is already cured (i.e., the
tobacco is already
dried). This is clearly evident from the disclosed moisture levels for the
tobacco being
treated in the Heljo patent. In fact, Heljo rehydrates the fully cured tobacco
prior to the
20 radio frequency treatment. By contrast, in the present invention, the term
"green tobacco"
refers to freshly harvested tobacco, which contains relatively high levels of
moisture.
Additionally, the use of microwave energy to dry agricultural products has
been
proposed. For example, use of microwave energy to cure tobacco is disclosed in
U.S.
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Patent No, 4,430,806 to I3opkins. Further, U.S. Patent No. 4,898,189 to
Wochnowski
teaches the use of microwaves to treat green tobacco in order to control
moisture content in
preparation for storage or shipping. In U.S. Patent No. 3,699,976, microwave
energy is
described to kill insect infestation of tobacco. Still further, techniques
using impregnation
of tobacco with inert organic liquids (U.S. Patent No. 4,821,747) for the
puzposes of
extracting expanded organic materials by a sluicing means have been disclosed
wherein the
mixture was exposed to microwave energy. In another embodiment, microwave
energy is
disclosed as the drying mechanism of extruded tobacco-containing material
(L1.S. Patent
No. 4,874,000). In U.S. Patent No. 3,773,055, Sturgis discloses the use of
microwave to dry
l 0 and expand cigarettes made with wet tobacco.
Using a novel breakthrough curing technology, U.S. Patent No. 5,803,081 to
Williama discloses a method of reducing the nitrosarnine levels or preventing
the formation
of nitrosamines in a harvested tobacco plant using microwave energy.
In U.S. Patent RE 38,123, a process
_ -for reducing the amount of or preventing the formation of nitrosamines in
harvested tobacco
plant is disclosed, wherein the process comprises subjecting at least a
portion of the plant to
microwave radiation, while the portion is uncured and in a state susceptible
to having the
amount of nitrosamines reduced or formation of z>itrosamines arrested, for a
time sufficient
to reduce the amount of, or substantially prevent formation of, at least one
nitrosanvne.
Further, U.S. Patent 6,311,695 discloses that microwave and other types of
radiation are useful for treating tobacco
to reduce the amount of, or prevent the formation of, nitrosamines in tobacco.
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BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 illustrates a tobacco-curing apparatus according to the present
invention.
Figure 2 illustrates the air-handling device/heat exchanger system of the
tobacco-
curing apparatus according; to the present invention.
SUMMARY OF THE INVENTION
It has now been discovered that by controlling the conditions to which tobacco
leaves are subjected to within the curing barn during the curing process, the
formation of
TSNAs in the tobacco product can be prevented or reduced. The parameters that
can be
varied to control the conditions within the curing barn (or curing apparatus)
during the
curing process include humidity, rate of temperature change, temperature, the
time of
treatment of the tobacco, the airflow (through the curing apparatus or barn),
CO level, COZ
level, Oz level, and the arrmgement of the tobacco leaves.
By controlling the conditions during the curing process within certain
parameters, it
is believed that it is now possible to prevent or reduce the formation of
microbes capable of
causing the formation of TSNAs in the tobacco. Thus, under the conditions
contemplated
for the present invention, it is believed that there would be little or no
nitrites available for
the formation of TSNAs b;y reaction of the nitrites with various tobacco
alkaloids. For
example, it is postulated that if the conditions are made aerobic, the
microbes will consume
the oxygen in the atmosphere for their energy source, and therefore no
nitrites will form.
Further, it is believed that the microbes are "obligate" anaerobes, and thus
when they are
subjected to certain conditions, they will be suppressed and cannot
participate in the
formation of nitrites.
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Accordingly, one object of the present invention is to substantially eliminate
or
reduce the content of nitrosamines in tobacco intended for smoking or
consumption by
other means.
Another object of the present invention is to reduce the carcinogenic
potential of
tobacco products, includin;~ cigarettes, cigars, chewing tobacco, snuff and
tobacco-
containing gum and lozenges.
Still another object of the present invention is to substantially eliminate or
significantly reduce the arr~ount of tobacco-specific nitrosamines, including
N'-
nitrosonornicotine (NNN), 4-(N-nitrosomethylamino)-1-(3-pyridyl}-1-butanone
(NNK), N'-
nitrosoanatabine (NAT) anal N'-nitrosoanabasine (NAB), in such tobacco
products.
Another object of the present invention is to treat uncured tobacco at an
appropriate
time post-harvest so as to wrest the curing process without adversely
affecting the tobacco's
suitability for human consumption.
Another object of the present invention is to reduce the content of tobacco-
specific
1 S nitrosamines by treating uncured tobacco in a controlled environment.
Yet another object of the present invention is to reduce the content of
tobacco-
specific nitrosamines, particularly NNN and NNK, and metabolites thereof in
humans who
smoke, consume or otherwise ingest tobacco in some form, by providing a
tobacco product
suitable for human consumption, which product contains a substantially reduced
quantity of
tobacco-specific nitrosamines, thereby lowering the carcinogenic potential of
such product.
The tobacco product may be a cigarette, cigar, chewing tobacco or a tobacco-
containing
gum or lozenge.
Yet another object is to provide a novel curing barn (or curing apparatus)
which is
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capable of providing tobacco suitable for human consumption, wherein the
tobacco contains
relatively low levels to zero tobacco-specific nitrosamines.
In one embodiment, the above and other objects and advantages in accordance
with
the present invention can be obtained by a process for reducing the amount of
or preventing
the formation of nitrosami.nes in a harvested tobacco plant, comprising
subjecting at least a portion of the plant, while said portion is uncured and
in a state
susceptible to having the amount of nitrosamines reduced or formation of
nitrosamines
arrested, to a controlled environment capable of providing a reduction in the
amount of
nitrosamines or prevention of the formation of nitrosamines, for a time
sufficient to reduce
the amount of or substantially prevent the formation of at least one
nitrosamine, wherein
said controlled environment is provided by controlling at least one of
humidity, rate of
temperature change, temperature, airflow, CO level, COZ level, OZ level, and
the
arrangement of the tobacco leaves.
In a preferred embodiment of the invention, the step of subj ecting tobacco
leaf to the
controlled environment is carried out on a tobacco leaf or portion thereof
after onset of
yellowing in the leaf and prior to substantial accumulation of tobacco-
specific nitrosamines
in the leaf. It is also preferred that in the process of the invention, the
step of subjecting the
tobacco leaf to the controlled environment is carried out prior to substantial
loss of the leaf s
cellular integrity.
It is also preferred in accordance with the present invention that the tobacco
leaf or a
portion thereof is subjected to the controlled environment for a time
sufficient to effectively
dry the leaf, without any charnng when heat is applied, so that it is suitable
for human
consumption.
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The present invention also seeks to subject
tobacco leaves to the controlled environment to prevent
normal accumulation of at least one tobacco-specific
nitrosamine, such as N'-nitrosonornicotine, 4-(N-
nitrosomethylamino)-1-(3-pyridyl)-1-butanone, N'-
nitrosonanatabine and N'-nitrosoanabasine.
In another embodiment, the process of the
invention further comprises treating the tobacco leaves,
while in a state susceptible to having the content of at
least one TSNA prevented or reduced, to microwave energy or
other forms of high energy treatment.
The present invention in its broadest forms also
encompasses a tobacco product comprising non-green tobacco
suitable for human consumption and having a lower content of
at least one tobacco-specific nitrosamine than
conventionally cured tobacco.
In another embodiment, the present invention
relates to a novel curing barn which is capable of providing
a controlled environment in which the formation of tobacco-
specific nitrosamines can be prevented or reduced.
According to one aspect of the present invention,
there is provided a tobacco curing barn comprising a
generally enclosed container for curing tobacco, the tobacco
curing barn further comprising: an air handling device
capable of providing an air flow of at least about
25,000 CFM, wherein said air flow is at least partially and
at least temporarily in communication with the interior of
said container; and a heat exchanger capable of providing at
least about 1,000,000 BTU/hour; wherein the heat exchanger
provides at least about 40 BTU/hour per CFM at maximum air
flow.
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According to another aspect of the present
invention, there is provided a tobacco curing barn
comprising a generally enclosed container for curing
tobacco, the tobacco curing barn further comprising: an air
handling device capable of providing a flow of air which is
at least partially and at least temporarily in communication
with the interior of said container; and a heat exchanger
comprising a heating system for producing heat by burning a
combustible fuel, wherein the heating system is arranged to
prevent combustion exhaust gases from entering the interior
of said container, and wherein the heat exchanger provides
at least about 40 BTU/hour per CFM of airflow a maximum air
flow.
DETAILED DESCRIPTION OF THE INVENTION
For purposes of the invention, the phrase
"controlling the conditions" means determining and selecting
an appropriate humidity, rate of temperature change,
temperature, time of treatment of the tobacco, airflow,
CO level, C02 level, 02 level, and arrangement of the tobacco
leaves to prevent or reduce the formation of at least one
TSNA. For a given set of ambient conditions, it may be
necessary to adjust, within the curing apparatus or barn,
one or more of these parameters. For example, it is
possible to prevent or reduce the formation of TSNAs by
simply setting a high airflow through the curing apparatus
or barn. In other situations, it is possible to produce the
tobacco products of the present invention
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with low airflow, providc;d that other parameters such as humidity,
temperature, etc. are
appropriately selected.
In this disclosure., tobacco that has been "conventionally cured" is tobacco
that has
been air-cured or flue-cured, without the controlled conditions described
herein, according
S to conventional methods commonly and commercially used in the U.S.
Further, the term "green tobacco" means tobacco that is substantially uncured
and is
particularly inclusive of freshly harvested tobacco.
In flue curing processes that utilize a heat exchanger capable of providing
relatively
low airflow through the curing barn, I have discovered that it is possible to
somewhat
10 reduce the TSNA levels by not venting combustive exhaust gases into the
curing apparatus
or barn. The preferred aspects of the present invention are premised on the
discovery that
other parameters, as identified above (e.g., airflow), can be adjusted to
ensure the
prevention or reduction of at least one TSNA regardless of the ambient
conditions. Thus,
even under the most extreme conditions (i.e., conditions that enhance the
formation of
15 TSNAs), it is possible to achieve the prevention or reduction of at least
one TSNA.
It has been said that the practice of tobacco curing is more of an art than a
science,
because curing conditions during any given cure must be adjusted to take into
account such
factors as varietal differences, differences in leaves harvested from various
stalk positions,
differences among curing barns in terms of where they are used, and
environmental
20 variations during a single. season or over multiple seasons, especially in
terms of weather
fluctuations during air-curing. For example, the practice of flue curing is
empirical to a
certain degree, and is optimally carned out by individuals who have
accumulated
experience in this art over a significant period of time. See, e.g., Peele et
al, "Chemical and
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Biochemical Changes During The Flue Curing OfTobacco," Recent Advances In
Tobacco
Science, Vol. 21, pp. 81 et seq., Symposium Proceedings 49th Meeting Chemists'
Research
Conference, September 24-27, 1995, Lexington, Kentucky (hereinafter "Peele et
al"). Thus,
one of ordinary skill in the art of tobacco curing would understand that the
outer parameters
5 of the present invention, i.n its broadest forms, are variable to a certain
extent depending on
the precise confluence of the above factors for any given harvest.
In one embodiment, the present invention is founded on the discovery that a
window exists during the tobacco curing cycle, in which the tobacco can be
treated in a
manner that will essentially prevent the formation of TSNA. Of course,1he
precise window
10 during which TSNA formation can be effectively eliminated or substantially
reduced
depends on the type of tobacco and a number of other variables, including
those mentioned
above. In accordance with this embodiment of the present invention, the window
corresponds to the time fivame post-harvest when the leaf is beyond the fresh-
cut or "green"
stage, and prior to the time at which TSNAs and/or nitrites substantially
accumulate in the
15 leaf. This time frame typically corresponds to the period in which the leaf
is undergoing the
yellowing process or is in the yellow phase, before the leaf turns brown, and
prior to the
substantial loss of cellular integrity. (Unless otherwise clear from the
context, the terms
"substantial" and "significant" as used herein generally refer to predominant
or majority on
a relative scale, give or take.) During this time frame, the leaves are
susceptible to having
20 the formation of TSNAs substantially prevented, or the content of any
already formed
TSNA reduced, by subjecting the tobacco to a controlled environment capable of
providing
a reduction in the amount of nitrosamines or prevention of the formation of
nitrosamines,
for a time sufficient to reduce the amount of or substantially prevent the
formation of at
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least one nitrosamine, wherein said controlled environment is provided by
controlling at
least one of humidity, rate: of temperature change, temperature, airflow, CO
level, COZ
level, OZ level, and arrangement of the tobacco leaves. This treatment of the
tobacco
essentially arrests the natural formation of TSNAs, and provides a dried,
golden yellow leaf
5 suitable for human consumption. if TSNAs have already begun to substantially
accumulate, typically toward the end of the yellowing phase, the treatment
according to the
present invention effectively arrests the natural TSNA formation cycle, thus
preventing any
further substantial formation of TSNA. When yellow or yellowing tobacco is
treated in this
fashion at the most optimal time in the curing cycle, the resulting tobacco
product has
10 TSNA levels essentially approximating those of freshly harvested green
tobacco, while
maintaining its flavor and taste. In addition, the nicotine content of the
tobacco product
according to the present invention remains unchanged, or is substantially
unchanged, by the
treatment according to the present invention. Accordingly, the tobacco product
of the
present invention has relatively low contents of TSNAs, and yet the user of
the tobacco
15 product can experience the same sensations that are obtainable from using
conventional
tobacco products.
As discussed above, it is believed that tobacco-specific TSNAs are formed
primarily
during the curing process. Specifically, it is believed that the amount of
TSNAs in cured
tobacco leaf is dependent on the accumulation of nitrites, which are formed
during the
20 curing process by reduction of nitrates to nitrites under conditions
approaching an anaerobic
(i.e., oxygen deficient) environment. The nitrites accumulate during the death
of the plant
cell. Experimental evidence suggests that the nitrites are formed by the micro
flora on the
surface of the leaf under conditions approaching an anaerobic environment. If,
for example,
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conditions are made aerobic, the microbes will consume the oxygen in the
atmosphere for
their energy source, and thus, no nitrites will form. Once nitrites are
formed, however, they
can then combine with various tobacco alkaloids, including pyridine-containing
compounds, to form carcinogenic substances such as nitrosamines.
S In one conventional curing technique, the combustion exhaust gases pass
through
the tobacco, thereby creating a condition approaching an anaerobic
environment. This
conventional curing technique utilizes air that is normally recirculated
within the curing
barn and is often air having high humidity. Conventional curing has been
developed over
time without any appreciation for subjecting tobacco to a controlled
environment for the
10 purpose of eliminating or reducing TSNAs. Accordingly, such conventional
curing
techniques do not provide suitable conditions (e.g., adequate oxygen flow) and
fail to
prevent an anaerobic condition in the vicinity of the tobacco leaves.
Additionally, during
such conventional curing processes, the tobacco leaves will emit carbon
dioxide, which will
further dilute the oxygen present in the curing environment. Under such
anaerobic
15 conditions, it is believed that the micro flora reduce nitrates to
nitrites. Consequently,
TSNA are formed and become part of the tobacco product that is ultimately
consumed by
the tobacco user.
The present invention is applicable to the treatment of harvested tobacco,
which is
intended for human consumption. Much research has been performed on tobacco,
with
20 particular reference to tobacco-specific nitrosamines (i.e., TSNAs).
Freshly harvested
tobacco leaves are called "been tobacco" and contain no known carcinogens, but
green
tobacco is not suitable for human consumption. The process of curing green
tobacco
depends on the type of tobacco harvested. For example, Virginia flue (bright)
tobacco is
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typically flue-cured, whereas Burley and certain dark stxains are usually air-
cured. The
flue-curing of tobacco t;ypicaIly takes place over a period of five to seven
days compared to
about one to two or more months for air-curing. According to Peele et al, flue-
curing has
generally been divided into three stages: yellowing (35-40°C) for about
36-72 hours
S (although others report that yellowing begins sooner than 36 hours, e.g., at
about 24 hours
for certain Virginia flue strains), leaf drying (40-57°C) for 48 hours,
and midrib (stem)
drying (57-75°C) for 48 hours. Many major chemical and biochemical
changes begin
during the yellowing stage and continue through the early phases of leaf
drying.
In a typical flue-curing process, the yellowing stage is carried out in a
barn. During
10 this phase the green leaves gradually lose color due to chlorophyll
degradation, with the
corresponding appearance of the yellow carotenoid pigments. According to the
review by
Peele et al, the yellowing stage of flue-curing tobacco is accomplished by
closing external
air vents in the barn, ancf holding the temperature at approximately
35°-37°C. The
yellowing stage typically lasts about 3 to 5 days. After the yellowing stage,
the air vents are
15 opened, and the heat is gradually and incrementally raised. Over a period
of about 5 to 7
days from the end of yellowing, the tobacco product is dried. Thus, this
process utilizes a
somewhat controlled environment, but the controlled environment is
insufficient to ensure
the prevention or reduction of nitrosamines as in the present invention.
Specifically, the
process during the yellowing maintains the relative humidity in the barn at
approximately
20 85%, limits moisture lo., from the leaves, and allows the leaf to continue
the metabolic
processes that has begun in the field. The goal of the flue-curing process is
merely to obtain
a dry product that has a lemon or golden orange color. In the flue-curing
process, there is
no appreciation for subjecting the tobacco leaves to a set of controlled
conditions in order to
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ensure the prevention or reduction of TSNAs.
With one particular variety of Virginia tlue tobacco on which testing has been
carried out as described herein, freshly harvested green tobacco is placed in
a barn for about
24-48 hours at about 100--110°F until the leaves turn more or less
completely yellow. The
5 yellow tobacco has a reduced moisture content, i.e., from about 90 weight %
when green,
versus about 70-40 weight % when yellow. At this stage, the yellow tobacco
contains
essentially no known carcinogens, and the TSNA content is essentially the same
as in the
fresh-cut green tobacco. 'this Virginia flue tobacco typically remains in the
yellow stage
for about 6-7 days. At thc; end of curing, Virginia flue tobacco typically has
a moisture
10 content of about 11 to about 15 weight percent. The conversion of the
tobacco during the
curing process results in formation and substantial accumulation of
nitrosamines, and an
increased microbial content. The exact mechanism by which tobacco-specific
nitrosamines
are formed is not clear, but is believed to be enhanced by microbial activity,
involving
microbial nitrate reductases in the generation of nitrite during the curing
process.
1 S As previously mentioned, tobacco-specific nitrosamines are believed to be
formed
upon reaction of amines with nitrite-derived nitrosating species, such as NOz,
N20, and
Nz04 under acidic or anaerobic conditions. Wiernik et al discuss the
postulated formation
of TSNAs at pp. 43-45, the discussion being incorporated herein by reference;
a brief
synopsis is set forth below.
20 Tobacco leaves contain an abundance of amines in the form of amino acids,
proteins, and alkaloids. The tertiary amine nicotine (referenced as ( 1 ) in
the diagram below)
is the major alkaloid in tobacco, while other nicotine-type alkaloids are the
secondary
amines nornicotine (2), anatabine (3) and anabasine (4). Tobacco also
generally contains up
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to 5% of nitrate and traces of nitrite.
Nitrosation of nomicotine (2), anatabine (3), and anabasine (4) gives the
corresponding nitrosamines: N'-nitrosonornicotine (NNN, 5), N'-
nitrosoanatabine (NAT,
6), and N'-nitrosoanabasine (NAB, 7). Nitrosation of nicotine (1 ) in aqueous
solution
affords a mixture of 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone
(IV~NI~., 8) (NNN,
5) and 4-(N-nitrosomethylamino)-4-(3-pyridyl)-1-butanal (NNA, 9). Less
commonly
encountered TSNAs include NNAL (4-N-nitrosomethylamino)-I-(3-pyridyl)-1-
butanol,
10), iso-NNAL (4-N-nitrosomethylamino)-4-(3-pyridyl)-1-butanol, 11 ) and iso-
NNAC (4-
(I~r-nitrosomethylamino)-4-(3-pyridyl)-butanoie acid, 12). The formation of
these TSNAs
from the corresponding tobacco alkaloids is shown schematically below, using
the
designations 1-12 above (reproduced from Wiernik et al, supra, p. supra, p.
44):
Dcmcthylation N N
CHa ~~ 'H. ~~ 'H ~~ 'H
1 = Nicotine 2 = Nornicotine 3 = Anatabine 4 = Anaba_sine
............... Nitrosation.......___.....
__....... Nitrosation -___._._.
r
O
N J
s = NNN ~ n'
~H O
N-NO NO N
Oxidation CHO N-CH 6 = NAT N
3
O 9 = NNA O 8 =_ NNK ~ NO
N-NO N ._....... '1 = NA13
~\=~COOH --- Reduction------------
~H,
N 12 = iso-NNAC N-NO H NO
.~ ~ ~ N-CHI
~~~CHZOH O H
NJ N
11 ~ Lso-NNAL 10 = NNAL
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It is now generally agreed that green, freshly harvested tobacco contains
virtually no
nitrite or TSNA, and that these compounds are generated during curing and
storage of
tobacco. Studies have been made during the past decade to try to determine the
events
related to the formation of TSNA during curing of tobacco, and several factors
of
5 importance have been identified. These include plant genotype, plant
maturity at harvest,
curing conditions and microbial activity.
Studies have shown that nitrite and TSNA accumulate on air-curing at the time
intervals starting after the end of yellowing and ending when the leaf turns
completely
brown, e.g., 2-3 weeks after harvest for certain air-cured strains, and
approximately a week
10 or so after harvest in flue-cured varieties. This is the time during which
loss of cellular
integrity occurs, due to moisture loss and leakage of the content of cells
into the
intercellular spaces. Therefore, there is a short window in time during air-
curing when the
cells have disintegrated, making the nutrition available for microorganisms.
Wiernik et al
have suggested that nitrite may then substantially accumulate as a result of
dissimilatory
15 nitrate reduction, thus rendering formation of TSNA possible.
There are a few published reports on the effects of microbial flora on the
tobacco
leaf during growth and curing and on cured tobacco, as cited in Wiernik et al.
However, the
involvement of microbial nitrite reductases in the generation of nitrate
during curing is
presumed. When cell structure is broken down after the yellow phase, and
nutrients are
20 made accessible to invading microorganisms, these may produce nitrite under
favorable
conditions, i.e., high humidity, optimal temperature and anoxia. There is
normally a rather
short "window" in time when the water activity is still sufficiently high, and
the cell
structure has disintegrated..
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In accordance with one embodiment of the present invention, the formation of
nitrosamines in a harvested tobacco plant is substantially prevented or
arrested by a process,
comprising
subjecting at least a portion of the plant, while said portion is uncured and
in a state
susceptible to having the ~unount of nitrosamines reduced or formation of
nitrosamines
arrested, to a controlled environment capable of providing a reduction in the
amount of
nitrosamines or prevention of the formation of nitrosamines, for a time
sufficient to reduce
the amount of or substantially prevent the formation of at least one
nitrosamine, wherein
said controlled environment is provided by controlling at least one of
humidity, rate of
temperature change, temperature, airflow, CO level, COZ level, O, level, and
arrangement of
the tobacco leaves.
In accordance with preferred embodiments of the present invention, non-green
and/or yellow tobacco products can be obtained which are suitable for human
consumption,
and which have a lower content of at least one tobacco-specific nitrosamine
than
conventionally cured tobacco. Green or fresh-cut tobacco is generally
unsuitable for human
consumption as noted above; "non-green" as used herein means the tobacco has
at least lost
the majority of chlorophyll, and includes without limitation partially yellow
leaves, full
yellow leaves, and leaves which have begun to turn brown in places.
The present invention is applicable to all strains of tobacco, including flue
or bright
varieties, Burley varieties, dark varieties, oriental/'Turkish varieties, etc.
Within the
guidelines set forth herein, one of ordinary skill in the art could determine
the most efficient
time in the cure cycle for carrying out the treatment step to achieve the
objects and
advantages of the present invention.
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Although the airflow through the barn may vary on a case-by-case basis and may
be
dependent on the arrangement of the tobacco leaves to be treated (i.e., the
degree of tobacco
leaf surface exposure) and the size of the curing apparatus or barn, the
minimum flow of air
is preferably about ten percent higher than the flow of flue gas commonly used
in the prior
art. As discussed above, however, it is within the scope of the present
invention to provide
relatively low airflow, provided that other parameters (e.g., humidity,
temperature, etc.) are
selected so that the prevention or reduction of at least one TSNA is achieved.
Preferably, the minimum flow of air may be about 70 CFM at 1" static pressure
per
cubic feet of curing apparatus or barn volume, more preferably 80 CFM at I"
static pressure
per cubic feet of curing apparatus or barn volume. The specific minimum flow
of air
needed for a given set of conditions may be determined on a routine basis
given the
disclosure of the present invention.
To maximize the effects of the present invention, the humidity of the heated
or
unheated air is desirably controlled using a commercially-available
dehumidifier or
humidifier. Preferably, thc; heated or unheated air flow comprises dehumidifed
air with a
humidity level of less than about 85%, more preferably less than about 60%,
most
preferably less than about 50%.
In one aspect, the air is fresh outside air, while the heated air is
substantially free
from combustion exhaust gases including water vapor, carbon monoxide, and
carbon
dioxide.
In addition, the air may be recirculated as long as an anaerobic condition is
avoided.
The temperature within the curing barn of the present invention may range from
ambient (i.e., outside) temperature to as high as about 250°F or more,
without charnng the
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tobacco product. If heated air (i.e., convective heat) is used to accelerate
the drying of the
tobacco product, suitable temperatures may range anywhere from about
100°F to about
250°F, more preferably from about 160 °F to about 170°F.
However, the optimum
temperature within the curing barn can be determined for each case, depending
on the
overall conditions of the envirorunent and the tobacco product being treated.
The determination of the time for treating the tobacco according to the
process of
the present invention can be determined by trial and error. Typically, the
treatment time
may be from about 48 hours up to about 2 weeks.
The arrangement of the tobacco leaves is not critical, but it is advantageous
to
provide the highest exposed surface area for the tobacco leaves.
While it is not essential, it may be desirable to expose the tobacco product
to UV
light, either simultaneously with, or separately from, the treatment described
above. It is
believed that this LJV light exposure can further reduce the amount of TSNA
accumulation.
TM
For example, the UV light can be supplied using "Germicidal Sterilamp" tubes
obtained
from Philips Lighting , wherein the light has wavelengths of between 100 and
280 nm.
Although the curing process as described above is preferable over microwave
curing
techniques because microwaving requires moist tobacco whereas the inventive
curing
process does not, it is within the scope of the present invention to further
treat the tobacco
product with microwave or other high energy treatment, as described in
U.S. ('atent Nos. RE 38,123 and 6,311,695.
This additional microwave or other high energy treatment is conveniently
performed within the window of time in which it is possible to further prevent
or reduce the formation of at least one TSNA.
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The preferred aspects of the microwaving or other high energy treatment are
described
below.
The process of this invention may further comprise a microwaving process for
reducing the amount of or preventing formation of nitrosamines in a harvested
tobacco
plant, which microwaving process comprises
subjecting at least a portion of the plant to microurave radiation, while said
portion
is uncured and in a state susceptible to having the amount of nitrosamines
reduced or
formation of nitrosamincs arrested, for a sufficient time to reduce the amount
of or
substantially prevent formation of at least one nitrosamine.
It is preferred that in this aspect of the process of the invention, the step
of
subjecting to microwave radiation is carried out on a tobacco leaf or portion
thereof after
onset of yellowing in the leaf and prior to substantial accumulation of
tobacco-specific
nitrosamines in the leaf. It is also preferred that in this aspect of the
process of the
invention, the step of subjecting to microwave radiation is carried out prior
to substantial
1 S loss of the leaf s cellular integrity. Using microwave energy eliminates
the potential for
activation of the microbes that cause TSNAs in tobacco, particularly in
tobacco that has
been rehydrated.
The term "microwave radiation" as used herein refers to electromagnetic energy
in
the form of microwaves having a frequency and wavelength typically
characterized as
falling within the microwave domain, The term "microwave" generally refers to
that
portion of the electromagnetic spectrum which lies between the far-infrared
region and the
conventional radiofrequency spectrum. The range of microwaves extends from a
wavelength of approximately 1 millimeter and frequency of about 300,000 MHz to
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wavelength of 30 centimeters and frequency of slightly less than about 1,000
MHz. The
present invention preferably utilizes high power applications of microwaves,
typically at the
lower end of this frequency range. Within this preferred frequency range,
there is a
fundamental difference between a heating process by microwaves and by a
classical way,
such as by infrared (for ex~unple, in cooking): due to a greater penetration,
microwaves
generally heat quickly to a depth several centimeters while heating by
infrared is much
more superficial. In the United States, commercial microwave apparatuses, such
as kitchen
microwave ovens, are available at standard frequencies of approximately 91 S
MHz and
2450 MHz, respectively. T hese frequencies are standard industrial bands. In
Europe,
microwave frequencies of :?450 and 896 MHz are commonly employed. Under
properly
balanced conditions, however, microwaves of other frequencies and wavelengths
would be
useful to achieve the objects and advantages of the present invention.
Microwave energy can be generated at a variety of power levels, depending on
the
desired application. Microwaves are typically produced by magnatrons, at power
levels of
600-1000 watts for conventional kitchen-level microwave apparatuses (commonly
at about
800 watts), but commercial units are capable of generating power up to several
hundred
kilowatts, generally by addition of modular sources of about 1 kilowatt. A
magnatron can
generate either pulsed or continuous waves of suitably high frequency.
The applicator (or oven) is a necessary link between the microwave power
generator
and the material to be heated. For purposes of the present invention, any
desired applicator
can be used, so long as it is adapted to permit the tobacco plant parts to be
effectively
subjected to the radiation. The applicator should be matched to the microwave
generator to
optimize power transmission, and should avoid leakage of energy towards the
outside.
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Multimode cavities (microwave ovens), the dimensions of which can be larger
than several
wavelengths if necessary for large samples, are useful. To ensure uniform
heating in the
leaves, the applicator can be equipped with a mode stirrer (a metallic moving
device which
modifies the field distribution continuously), and with a moving table
surface, such as a
5 conveyor belt. The best results are attained by single leaf thickness
exposure to microwave
radiation, as opposed to stacks or piles of leaves.
In preferred embodiments of the invention, the microwave conditions comprise
microwave frequencies of about 900 MHz to about 2500 MHz, more preferably
about 915
MHz and about 2450 MHz, power levels of from about 600 watts up to 300
kilowatts, more
10 preferably from about 600 to about 1000 watts for kitchen-type applicators
and from about
2 to about 75 kilowatts, more preferably from about 5 to about 50 kilowatts,
for commercial
multimode applicators. The heating time generally ranges from at least about 1
second, and
more generally from about 10 seconds up to about 5 minutes. At power levels of
about
800-1000 watts the heating time is preferably from about 1 minute to about 2%Z
minutes
15 when treating single leaves as opposed to piles or stacks. For commercial-
scale applicators
using higher power levels 'in the range of, e.g., 2-75 kilowatts, heating
times would be
lower, ranging from about 5 seconds up to about 60 seconds, and generally in
the 10-30
second range at, say, 50 kilowatts, again for single leaves as opposed to
piles or stacks. Of
course, one of ordinary skill in the art would understand that an optimal
microwave field
20 density could be determined for any given applicator based on the volume of
the cavity, the
power level employed, and the amount of moisture in the leaves. Generally
speaking, use
of higher power levels will require less time during which the leaf is
subjected to the
microwave radiation.
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However, the above-described conditions are not absolute, and given the
teachings
of the present invention, one of ordinary skill in the art would be able to
determine
appropriate microwave parameters. The microwave radiation is preferably
applied to the
leaf or portion thereof for a time sufficient to effectively dry the leaf,
without charnng, so
that it is suitable for human consumption. It is also preferred to apply the
microwave
radiation to the leaf or portion thereof for a time and at a power level
sufficient to reduce the
moisture content to below about 20 % by weight, more preferably about 10% by
weight.
It is also preferred in accordance with the present invention that the
microwave
radiation is applied to the leaf or portion thereof for a time sufficient to
effectively dry the
leaf, without charnng, so that it is suitable for human consumption.
It is also possible to use forms of electromagnetic radiation having higher
frequencies and shorter wavelengths than the microwave domain discussed above
and in
more detail below, can be used to achieve the basic objects of the present
invention -
reduction or substantial elimination of TSNAs in tobacco products, by treating
the tobacco
with such energy forms in the same time frame post-harvest as discussed above
with regard
to the microwave embodiment. Thus, the present invention further comprises a
method for
reducing the amount of or preventing formation of nitrosamines in a harvested
tobacco
plant, comprising
subjecting at least a portion of the plant to radiation having a frequency
higher than
the microwave domain, while said portion is uncured and in a state susceptible
to having the
amount of nitrosamines reduced or formation of nitrosamines arrested, for a
sufficient time
to reduce the amount of or substantially prevent formation of at least one
nitrosamine.
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As with the microwave embodiments, it is preferred that in the process of the
invention, the step of subjecting to radiation having a frequency higher than
the microwave
domain is carried out on a tobacco leaf or portion thereof after onset of
yellowing in the leaf
and prior to substantial accumulation of tobacco-specific nitrosamines in the
leaf. It is also
5 preferred that in the process of the invention, the step of subjecting to
such radiation is
carried out prior to substantial loss of the leafs cellular integrity.
Preferred energy sources
capable of producing such radiation are described further below, and include
far-infrared
and infrared radiation, UV (ultraviolet radiation), soft x-rays or lasers,
accelerated particle
beams such as electron beams, x-rays and gamma radiation.
On a scale within the electromagnetic spectrum where microwaves are generally
defined as inclusive of those forms of electromagnetic radiation having a
frequency of 10"
Hz and a wavelength of 3 x. 10-3 meters, such energy sources include, without
limitation,
far-infrared and infrared radiation having frequencies of about 10'2 to 10" Hz
and
wavelengths of 3 x 10~ to ?'~ x 10-6 meters, ultraviolet radiation having
frequencies of about
15 10'6 to 10'8 Hz and wavelengths of 3 x 108 to 3 x 10-'° meters, soft
x-rays or lasers, cathode
rays (a stream of negatively charged electrons issuing from the cathode of a
vacuum tube
perpendicular to the surface;), x-rays and gamma radiation typically
characterized as having
frequencies of 102' Hz and higher at corresponding wavelengths.
As would be apparent to one of ordinary skill in the art, the greater the dose
of
radiation delivered by the energy source, the less time the leaves need to be
subjected
thereto to achieve the desired results. Typically, radiation application times
of less than one
minute, preferably less than 30 seconds and even more preferably less than
about ten
seconds are needed when using such higher frequency radiation sources. Defined
another
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way, radiation application times of at least about one second are preferred.
However, the
exposure rate can be controlled to deliver the radiation dosage over time, if
desired. For
example, 1 megarad of radiation can be delivered instantaneously, or at a
predetermined
exposure rate. When using high frequency radiation sources, it is preferred to
use an
S amount of radiation which achieves at least a SO% reduction in TSNAs, in
comparison to
untreated samples. While the particular radiation dosages and exposure rate
will depend on
the particular equipment ~~nd type of radiation source being applied, as would
be apparent to
one of ordinary skill in the art, it is generally preferred to subject the
tobacco samples to
radiation of from about .1 to about 10 megarads, more preferably from about .5
to about 5
10 megarads, and more preferably from about .7S to about 1.5 megarads.
It is preferred that the microwaving or other high energy treatment, as
described
above, is conducted after subjecting the tobacco to the controlled environment
of the present
invention. However, it is also possible to conduct the optional microwaving or
high energy
treatment prior to subjecting the tobacco to the controlled environment of the
present
15 invention.
The treatment according to the present invention, with or without microwaving
or
other high energy treatment, may be performed in conventional barns as well as
large-scale
processing centers capable of treating tens of acres of tobacco. It is also
possible to perform
the process of the present invention in any size, including miniature curing
apparatuses or
20 barns.
On a bench scale, the treatment of the tobacco product according to the
present
invention, using airflow and temperature control, would be similar to treating
tobacco
product using a convective heating air oven or treating the tobacco product
using a clothes
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dryer. Thus, it is within the present invention to operate the process of the
present invention
in a convective heating air oven or a clothes dryer, although these
apparatuses are not within
the scope of the curing apparatus or barns as defined in the appended claims.
In another embodiment, the present invention relates to a tobacco product
comprising cured non-green or yellow tobacco suitable for human consumption
and having
a content of at least one tobacco-specific nitrosamine selected from N'-
nitrosonornicotine
(NNN), 4-(N-nitrosomethylamino)-1-(3-pyridyl)-1-butanone (NNK), N'-
nitrosoanatabine
(NAT) and N'-nitrosoanabasine (NAB) which is less than about 50% by weight of
the
content of said at least one tobacco-specific nitrosamine in conventionally
cured tobacco,
more preferably less than about 75% by weight, most preferably less than about
95% by
weight, without the use of organic solvent extraction.
Thus, it is possible to reduce the TSNA content by about 97% or more by
practicing
the present invention, even down to "food safe" TSNA levels.
For example, the NNN level of the tobacco product according to the present
invention is typically less than about 0.05 ug/g, the combined NAT and NAB
level is
typically less than about 0.10 pg/g, and the NNK level is typically less than
about 0.05
pg/g. Further, the combined TSNA level is typically less than about 0.16
p,g/g, even as low
as less than about 0.009 p,g/g.
Thus, in yet another aspect of the present invention, the tobacco product
according
to the present invention comprises cured non-green or yellow tobacco having a
NNN
content less than about 0.05 p,g/g.
In a further aspect, the tobacco product of the present invention comprises
cured
non-green or yellow tobacco having a combined NAT and NAB content of less than
about
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0.10 p,g/g.
Still further, the tobacco product of the present invention comprises cured
non-green
or yellow tobacco having a NNK content of less than about 0.05 ~g/g.
Additionally, the present invention also contemplates tobacco product
comprising
cured non-green or yellow tobacco having a total TSNA content of less than
about 0.16
pg/g.
In a preferred embodiment, the tobacco product of the present invention has a
NNN
level of less than about 0.05 pg/g, a combined NAT and NAB level of less than
about 0.10
pg/g, and a NNK level less than about 0.05 p,g/g.
The tobacco product according to the present invention can be converted to
various
final tobacco products, including, but not limited to, cigarettes, cigars,
chewing tobacco,
snuff and tobacco-containing gum and lozenges.
In yet another embodiment, the present invention is directed to an apparatus
for
curing tobacco products comprising:
an enclosed or substantially enclosed container comprising a base frame,
optionally
at least one wall, optionally a roof, and optionally a door;
an air handling device capable of providing an air flow of at least about 70
CFM at
1" static pressure per cubic feet of apparatus volume, wherein said air flow
is at least
partially and at least temporarily in communication with the interior of said
container; and
a heat exchanger capable of providing at least about 1,100 BTU/hour per cubic
feet
of apparatus volume.
If desired, the container may be in the form of a mobile unit with transport
means.
The container may be constructed to any suitable size typical of tobacco
curing barns. For
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example, the container may have a width of about 120 inches, a depth of 60
inches, and a~
height of 82 inches. It is possible to provide a container that is
significantly smaller or
larger than this exemplified container size. In addition, the container may be
insulated.
The container may comprise means that are capable of receiving the tobacco
products to be cured. Preferably, these means are arranged so that the tobacco
product is
exposed for optimal curing.
Preferably, the air circulation within the container may be of a vertical or
horizontal
draft design, with the flow of air being in any suitable direction, with
manually or
automatically controlled frf;sh air dampers and weighted exhaust dampers. The
blower for
the air handling device can have a blower rating of, e.g., about 100 CFM at
0.4 inch WC
static pressure per cubic feet of apparatus volume.
The heat exchanger is preferably constructed of stainless steel. The heat
exchanger
system is preferably supplied with a flame detector, ignitor wire, sensor
cable, dual valve
gas train and/or air proving switch. The burner setting can be variable. As
mentioned
previously, however, it is possible to carry out the process of the present
invention without
the use of any heat. That is, the process can be conducted using simply a
sufficient flow of
air.
In the present invention, the apparatus for curing the tobacco products uses
air that
is free from combustion exhaust gases, such as carbon monoxide and carbon
dioxide.
However, it should be noted that with sufficient airflow, the effects of the
present invention
can be realized even with a:ir containing combustion exhaust gases.
Reference is now made to the drawings. Figure 1 shows a container (1) and an
air
handling device/heat exhanger system (2). Fugure 2 shows the air handling
device/heat
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exhange system (2) in greater detail. It can be seen from Figure 2 that the
exhausts (3) of
the heat exchanger system is far removed from the air intakes (4) to minimize
the possibility
of combustion exhaust gases being introduced into the curing apparatus.
Further, unlike
conventional curing barns., the curing apparatus of the present invention
features an
externalized air handling device/heat exchanger system.
The following examples illustrate the advantages of the present invention.
EXAMPLES
In each of the examples described below, five grams of ground tobacco were
placed
in a 300-ml Erlenmayer flask and suspended in 150-ml water to which S ml of
20%
ammonium sulfamate in 3.6 N HZS04 was added to prevent the artificial
formation of
TSNA during extraction. Prior to shaking on the wrist-action shaker overnight,
the flask
was capped using parafilm and wrapped up in aluminum foil to prevent
degradation of
TSNA by light. The TSNA were extracted.
The final TSNA e~saract (pH 9 fraction) was transfer ed quantitative using a
Pasteur
pipette into a 1 ml volumetric flask and adjusted for full volume. Samples
were stored in
GC vials until GC-TEA analysis.
For the TSNA analysis, an aliquot of 0.1 ml was dried in a GC vial with a
gentle
stream of nitrogen and the GC standard (N-nitrosoguvacoline; 3.2 ppm) in
acetonitrile was
added prior to analysis. The GC-TEA was calibrated with a standard TSNA
mixture on a
daily basis, before and after analyses of tobacco extracts.
GC Hewlett Packard Model 5890 and TEAS Model 543 Analyzer were used.
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FXAMPT.F 1
This experiment shows the advantages of the present invention on a reduced
scale.
Yellow tobacco leaf was finely diced with scissors and subjected to curing for
45
minutes at 167°F using connective heat in the form of a hot air stream
substantially free
5 from combustion exhaust gases. (A hot convection air oven was used for this
purpose.)
The sample was rather moist, and therefore, a wet weight was taken and
calculations were
made to correct the TSNA. content to dry weight basis. 75% of the leaf was
moisture, and
thus the wet weight was rrmltiplied by 0.25 to obtain the dry weight. The
results are
tabulated in Table 1 below.
10 Although the treatment was made only for 45 minutes, longer or shorter
treatment
times are envisioned depending on the conditions and the results desired.
COMPARATIVE EXAMPLE 1
Instead of the connective heat treatment described in Example 1 above, yellow
15 tobacco leaf was microwaved. The results are set forth in Table 1 below.
EXAMPLE 2
Instead of the connective heat treatment described in Example 1 above, yellow
tobacco leaf (Virginia) was subjected to a modified flue-curing technique that
eliminates the
20 flow of combustion exhaust gases into the curing barn. This was
accomplished by using a
heat exchanger. The treated tobacco was tested, and the results are given in
Table 1.
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Table 1
EXAMPLE p,g/g pg/g pg/g p,g/g
NO. NNN NAT + NAB NNK TSNA
Ex.l 0.0310 0.0843 <0.0004 0.1157
Comp. Ex. <0.0004 <0.0006 <0.0005 <0.0014
I
Ex.2 0.0451 0.1253 0.0356 0.2061
As can be seen from Tabie 1, the process of the present invention provides
tobacco
having substantially reduced amounts of TSNA.
Example 3
TM
Yellow tobacco leaf was treated with a flow of air using a MAYTAG clothes
dryer
under "fluff dry" at 85°F in Example 3. The results are shown in Table
2.
Example 4
This experiment shows the efficacy of the present invention featuring drying
without the use of heat. In this example, yellow tobacco Ieaf was treated with
a flow of
unheated air using a MAYTAGTclothes dryer for six hours. The results are shown
in Table
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Comparative Example 2
Tobacco leaf was flue cured according to a predominant version of the
conventional
flue curing process in a curing barn. As is the common practice for such
conventional flue-
curing, the combustion exhaust gases were vented through the curing barn in
this process.
In this conventional flue curing process, tobacco was placed in a barn with
relatively low
flow of air and closed external air vents. The temperature was incrementally
increased
(about 0.5 to 1.5°F per hour) to about 130°F over a period of
about 3 days. At this point
(i.e., end of yellowing), the external air vents were opened, and the
temperature was
maintained at 130°F for about 24-36 hours. The external air vents were
then closed and the
temperature was raised to .about 160°F to initiate the "killing out
phase" (i.e., the phase in
which the stem is dried) with relatively low air flow. It is important to note
that in the
conventional flue curing process, the air flow (any fresh air plus any
recirculating air) is
significantly lower than what is typically used in the present invention. The
results are
shown in Table 2.
Comparative Example 3
Yellow tobacco leaf was microwaved for 60 seconds in a commercial tobacco
microwaving plant. The results are shown in Table 2.
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Comparative Example 4
Yellow tobacco leaf was again microwaved for 60 seconds in a commercial
tobacco
microwaving plant. The results are shown in Table 2
5 Table 2
EXAMPLE ~g/g pg/g pg/g ~g/g
i
NO. NNN NAT + NAB NNK TSNA
Ex.3 0.0:37 0.046 <0.001 0.084
Ex.4 0.042 0.054 <0.001 0.097
Comp. Ex. 0.7'7 0.89 1.37 3.03
2
Comp. Ex. 0.04 0.054 <0.001 0.095
3
I
I Comp. <0.001 0.042 <0.001 0.044
Ex. 4
i
Examples 3 and 4 provided very low levels of TSNA, especially NNN and NNK,
even when microwaving was not used.
10 Example 5
Yellow tobacco leaf in the outer portion of a curing bam was subjected to a
flow of
air for 7 days according to the present invention. The results are tabulated
in Table 3.
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Example 6
Yellow tobacco leaf in the inner portion of a curing barn was subjected to a
flow of
air for 7 days according to the present invention. The results are tabulated
in Table 3.
Comparative Example 5
Yellow tobacco leaf cured in a curing barn according to a conventional curing
process was tested for TSNA levels. The results are shown in Table 3.
Table 3
EXAMPLE p,P,lg wP~g pP~g N.g~g
NO. NNN NAT + NAB NNK TSNA
Ex.S 0.03:f.02 0.06 0.05 0.14.02
Ex.6 0.04f.01 0.081.02 0.04 0.15.01
Comp. Ex. 0.41a.04 1.161.13 1.56.21 3.141.36
5
As is apparent from Table 3, the curing process according to the present
invention
provided unexpectedly lower levels of TSNA as compared to a conventional
curing process.
Example 7
15 This example illustrates the advantageous effects obtainable by practicing
the
present invention even under the most severe environmental conditions.
Throughout all
phases of the curing, combustion exhaust gases were not allowed to flow into
the barn.
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Green tobacco was left in a curing barn according to the present invention for
about
72 hours with the external air vent closed, but with recirculating air of
about 25,000 CFM,
and with heating of about 300,000 BTUs to provide a temperature of about
105° F. After
this period of about 72 hours (end of yellowing), the external air vents were
opened and the
air handling device was adjusted to provide virtually all fresh air flow of
approximately
25,000 CFM (with only a minor amount of recirculating air), and the heat was
increased to
about 1,000,000 BTUs to provide a rapid temperature increase to about
140° F. This
treatment was continued for about 72 hours. At this point, the "killing out"
phase (i.e.,
drying of the stems) was initiated by closing the external air vents and
increasing the
temperature to about 160 °F. Treatment continued for about 1-2 days.
The resulting tobacco product was tested for TSNAs according to the analytical
technique described above;. The levels for each individual nitrosamine were so
low that
they could not be detected.
20
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