Field of the Invention
This invention relates to compositions used to inhibit sprouting of
tubers. More particularly, this invention relates to CIPC, benzothiazole and carvone
and to methods of applying same to tubers, especially to potatoes, to inhibit sprouting
Background of the Invention
Sprout control of harvested tubers, in particular of potatoes, is
an important part of potato storage which allows for subsequent distribution to
potato processors for French fry production, and to grocery stores and restaurants
of a satisfactory food product months beyond harvesting, skin formation and dormancy.
Potato sprout control is particularly important to maintain the desired texture
and sugar content of the harvested potatoes.
In potatoes, cell division and cell elongation of the tuber buds results
in formation and emanation of sprouts from the tuber buds after the potato has
entered a quiescent phase of dormancy that typically follows storage at or slightly
above 45°F. Although tuber sprout formation can be suppressed by storage of the
tubers at lower temperatures of from 38° to 39°F, the lower storage temperatures
cause increased reducing sugar levels in the stored potatoes. Potatoes with increased
levels of reducing sugars may turn brown when french fried, thereby producing an
unacceptable food product.
To inhibit sprout formation in potatoes, synthetically derived sprout
inhibitors, for example, tetrachloronitrobenzene, maleic hydrazide, and isopropyl-3-chlorophenylcarbamate
(CIPC) also commonly referred to as chlorpropham, have been applied. CIPC is typically
applied in one or two applications to the tubers to be stored using thermal fogging
techniques. Conventional thermal fogging involving the application of CIPC into
a stream of hot air or onto a hot surface of up to 1000°F, to produce a CIPC aerosol.
The CIPC aerosol is circulated through potatoes piled in a potato storage building
with the use of fans. Preferably the potatoes are firm rather than soft when treated
with the CIPC aerosol, since a pile of softened potatoes may be substantially compressed,
thereby impeding distribution of the aerosol. CIPC residue levels, will, however,
typically decrease over time due to biodegradation, venting and atmospheric loss.
To extend the effective sprout inhibiting capability of CIPC, further applications
may be needed.
However, it is becoming increasingly desirable worldwide to decrease
the application of synthetically derived substances to fruits and vegetables during
growth, storage and shipping. In particular, residue levels of CIPC are subject
to regulation. So, while CIPC has been utilized to inhibit sprout formation in
tubers for decades, its toxicology has been questioned and it is one of a number
of synthetically derived substances whose residue levels are of concern to the
U.S. Environmental Protection Agency.
In order to decrease use of synthetically derived substances such
as CIPC, naturally occurring biological control mechanisms and substances are
actively sought. Naturally occurring sprout inhibitors are known. For example,
U.S. Patent No. 5,436,226 for NATURAL SUPPRESSION OF SPROUTING IN STORED POTATOES
USING JASMONATES claims a method of inhibiting sprouting of tubers by exposure
to various forms of jasmonic acid, at some of which are naturally occurring compounds.
Also by way of example, Canadian Patent No. 1,203,394 teaches the
use of dimethylnaphthalene (DMN) and diisopropyinaphthalene (DIPN) as potato sprout
inhibitors. However, this patent teaches the need for application of DMN and DIPN
with an inert carrier which implies the utility of DMN and DIPN alone as the active
ingredient. However, long term effectiveness of DMN and DIPN as tuber sprout inhibitors
at tower residue levels under less than ideal circumstances has not been fully
By way of further example, carvone, an essential oil of caraway seeds,
has been promoted as a natural sprout suppressant for potatoes. However, sprout
inhibition by application of carvone does not appear to be as effective as with
WO-A-95 09536 describes a composition suitable for inhibiting potato
sprouting and inhibiting the growth of fungi and decay bacteria, comprising a
mixture of carvone and menthol.
Chemical Abstracts, volume 79, no. 7, 1973, abstract no. 40004 and
Phytochemistry (1973), 12(5), 987-93, 1973 disclose the production of growth-suppressing
volatile substances by stored potato tubers. Benzothiazole, 1,4-dimethylnaphthalene
and 1,6-dimethylnaphthalene were shown to be potent inhibitors of sprout growth
in the potato tuber.
Chemical Abstracts, volume 95, no. 17, 1973, abstract no. 145184
and Potato Research (1981), 24(1), 61-76, 1981 indicates that benzothiazole and
1,4-dimethylnaphthalene are effective in controlling sprouting in seed potatoes.
Chemical Abstracts, volume 83, no. 5, 1975, abstract no. 38688 and
Naturwissenschaften (1975), 62(4), 185-6, 1975 discloses that ethylene increases
respiration of both sprout-inhibited and untreated potatoes.
Journal of Applied Bacteriology, 1996, vol. 80, pp 535-539 describes
the inhibition of growth of tubers by S-(+)-carvone.
Ethylene in Plant Biology, 1973, Chapter 6, pp. 103-107 discusses
the growth and developmental effects of ethylene on buds, tubers, corms and bulbs.
It is against this background that the significant improvements and
advancements of the present invention have taken place.
Objects of the Invention
It is the principal object of the present invention to manage sprouting
of tubers during and after storage.
It is another object of the present invention to inhibit sprouting
of tubers during storage using decreased amounts of sprout inhibitors.
It is a further object of the present invention to inhibit sprouting
of tubers during storage using conventional equipment.
It is a still further object of the present invention to inhibit sprouting
of tubers in accordance with the aforementioned objects in such a manner that
four months after treatment, the quantity of marketable potatoes is maximized.
It is a yet further object of the present invention to stimulate the
sprouting of tuber previously treated with sprout inhibition compositions to accelerate
establishment and growth of tubers, and in particular, potato plants grown from
Summary of the Invention
In accordance with its major aspects, a composition specially adapted
for inhibiting sprout formation of tubers during storage includes CIPC and either
carvone or benzothiazole. In a preferred embodiment of the method of the present
invention, an effective amount of a composition comprising CIPC and carvone or
CIPC and benzothiazole is applied to the surface of potatoes, by, for example,
by thermal fogging, to form a residue on the outer surface of the potatoes. In
other preferred methods, the CIPC is applied by thermal fogging separately from
the carvone or the benzothiazole to form a residual mixture on the outer surface
of the potatoes. Thereafter, when planting of the treated potatoes is scheduled,
the potatoes are treated with ethylene, either at the facility where they have
been stored, in the truck or bin from which they will be distributed for planting,
or in the field at planting, prior to covering the ethylene-treated potatoes with
soil. The sprout inhibition effects of the CIPC and benzothiazole or CIPC and carvone
is thereby overcome, and sprout formation accelerated beyond those potatoes not
so treated with ethylene.
Employing the aforementioned method has resulted in substantial sprout
control of Russet Burbank potatoes stored for approximately four months upon which
an effective residue of CIPC and either carvone or benzothiazole of approximately
16.6 ppm each is applied. In addition, by subsequently overcoming the sprout inhibition
by application, at planting, with ethylene, subsequent plant growth of potato plants
grown from seed potatoes so treated is accelerated beyond plants grown from potatoes
not treated with ethylene, to produce an earlier or larger potato crop than otherwise
would be grown.
A more complete appreciation of the present invention and its scope
can be obtained from the following detailed description of presently preferred
embodiments of the invention, and the appended claims.
Detailed Description of the Invention
In accordance with the present application, it has been discovered
that under the particular conditions described below, benzothiazole and carvone,
when mixed with isopropyl-3-chlorophenyl-carbamate (CIPC) and applied to Russet
Burbank potatoes, appear to enhance the sprout inhibiting capability of reduced
amounts of CIPC through 125 days after application. In view of the marginal ability
of benzothiazole and carvone to inhibit sprouting of Russet Burbank potatoes under
the particular conditions described below for the same period of time, the effectiveness
of the combination was readily apparent. It understood that as used herein, the
term benzothiazole includes all isomers, derivatives and structurally similar compounds
having equivalent functionality. Similarly, the term carvone includes all isomers,
derivatives and structurally similar compounds having equivalent functionality.
It has also been discovered that ethylene, when applied to CIPC treated
potatoes, will controllably break the sprout inhibiting dormancy imposed by the
CIPC. By so treating CIPC-treated potatoes with ethylene, the establishment of
seed potatoes in the field may be accelerated, and the possibility of crop productivity
maximized. Ethylene is preferably applied to potatoes at planting, it being understood
that the term ethylene, as used herein, includes ethylene gas and compositions
that upon application to tubers, will directly or indirectly generate ethylene
To evaluate the sprout inhibiting effectiveness of CIPC and other
organic compounds, including carvone and benzothiazole, alone and with CIPC, fully
mature Russet Burbank potatoes were selected and treated. Russet Burbank potatoes
were chosen because of their standard dormancy and sprouting qualities. Prior to
treatment, the potatoes were stored in a dark, cool storage area to satisfy the
For each of the 21 treatments summarized in Table I, 36 mesh bags,
each containing ten Russet Burbank potatoes of from 4 to 10 ounces each, were
placed in a non-metallic drum having an approximate capacity of 35 gallons. The
total weight of 360 potatoes in each drum averaged 140.7 pounds.
The drums containing the mesh bags of potatoes were sealed and housed
in a building in which temperature was maintained throughout the testing period
at approximately 46°-47°F and approximately 96% relative humidity. Formed in each
drum was an inlet in which untreated air was introduced to the drum. Also formed
in each drum was an outlet at the top end of the drum in which untreated air was
exhausted from the drum and thence to the outside of the building.
For all drums except the control, the ethylene-treated tubers, and
the dihydroxybenzoic acid-treated tubers, CIPC, either alone or in combination
with another listed organic compound, was delivered to each drum through a stinger
inserted in the input port of the drum and extending the length of the drum. Treatment
levels were calculated based on 16 milligrams (mg) of each of the CIPC and the
other listed organic compound applied per kilogram (kg) of tubers treated, and
reported in parts per million (ppm). Conventional thermal fogging techniques were
used to generate the thermal fog delivered to the potatoes through the stinger.
Return flow obtained from the output port was returned to the thermal fogger and
recirculated through the stinger for five minutes. Each drum was then sealed for
24 hours after the application of the thermal fog. Then, for the next 125 days,
46°-47°F air having a relative humidity of 96% was circulated through the input
port of each drum and exhausted out the output port of each drum to the outside
of the building, at a rate of 0.5 cubic feet per minute on a three-hour on and
a three-hour off schedule.
Benzothiazole, an aromatic sulfonazole, was obtained from Sigma-Aldrich
in a 96% formulation, catalog No. 1-133-8. Carvone, a 6-carbon ring terpene with
ketone on the ring, in particular, (2-methyl-5-(1-methylethyenyl)-2-cylco-hexene-1-one,
was obtained from Sigma-Aldrich in a 98% formulation, catalog No. 12393-1. Cis-jasmone,
a terpene with the chemical name 3-methyl-2-(2-pentenyl)-2-cylco-penten-1-one,
was obtained from Sigma-Aldrich in a 90% formulation, catalog No. 27744-4. Limonene,
a terpene, was obtained in a 97% mixture of cis and trans forms of limonene oxide,
chemica name 1-methyl-4-(1-methylethenyl) cylcohexene, from Sigma-Aldrich, catalog
No. 21832-4. Cinieole, a terpene with the chemical name 1,3,3-trimethyl-2-oxabicyclo-(2.2.2)octane,
was obtained from Sigma-Aldrich in a 99% formulation, catalog No. C8060-1. Trans-cinnamaldehye,
an aromatic aldehyde with the chemical name 3-phyl-2-propenal was obtained from
Sigma-Aldrich in a 99+% formulation, catalog No. 23996-8.
For the tubers treated with CIPC and ethylene gas, the CIPC was first
applied using thermal fogging techniques as described above. However, because
of the potentially explosive nature of ethylene, ethylene gas was not applied using
thermal fogging techniques to the CIPC tubers or to the tubers to be tested only
with ethylene gas. To these tubers, ethylene gas was delivered through the vent
stem from a container with a measured volume of ethylene gas.
For the tubers treated with CIPC and dihydroxybenzoic acid, the CIPC
was applied using thermal fogging techniques as described above. However, because
dihydroxybenzoic acid thermally degrades under thermal fogging conditions, dihydroxybenzoic
acid was not applied using thermal fogging techniques. Instead, untreated tubers
were dipped in a solution of dihydroxybenzoic acid to obtain a residue concentration
of 16.6 ppm. For tubers to be tested with a combination of dihydroxybenzoic acid
and CIPC, the dihydroxybenzoic acid-dipped tubers where then fogged with CIPC.
Dihydroxybenzoic acid, an aromatic benzoic, was obtained from Sigma-Aldrich in
a 2,6-dihydroxyybenzoic acid 98% formulation, catalog No. D10960.
At 125 days after treatment, a sample of six of the 36 bags from each
drum were removed, and the sixty total tubers from the six bags examined. Each
eye on each tuber was evaluated for sprout development. No sprout development is
preferred, and tubers showing no sprout development are suitable for fresh pack.
As used herein, the term fresh pack indicates potatoes which meet conventional
standards set by groceries for the grade of potatoes sold as baking potatoes. Tubers
exhibiting sprout peeping wherein tissue swelling is detected and free tissue is
evident but no sprouts are measured, are suitable for fresh pack. Tubers having
sprouts, which, on average are greater than 1 mm are generally unacceptable for
fresh pack. Data obtained from evaluation of the potatoes at 125 days after treatment
is summarized in Table I.
125 DAYS AFTER TREATMENT
% suitable for fresh pack
% unsuitable for fresh pack
Benzothiazole + CIPC
Carvone + CIPC
Cineole + CIPC
Cinnamaldehyde + CIPC
Dihydroxybenzoic + CIPC
Ethylene + CIPC
Limonene + CIPC
Jasmone + CIPC
As is summarized in Table I above, at 125 days after treatment, on
average 44% (i.e., (52%+59%+21%)/3) of the tubers treated with CIPC alone at a
16.6 ppm residue level exhibited no sprout development beyond peeping, and thus
were suitable for fresh pack. Conversely, on average, 56% of tubers so treated
were unsuitable for fresh pack sale.
In contrast, as is also summarized in Table I, on average, only 2.5%
(i.e., (2%+3%)/2) of the untreated control tubers showed no sprout development
or peeping. Therefore, on average, 1.5% of the untreated control tubers were suitable
for fresh pack at 125 days after treatment, making 97.5% of untreated control tubers
unsuitable for fresh pack sale.
Only 5% of the tubers treated with benzothiazole showed no sprout
development or peeping. Accordingly, only 5% of the tubers treated with benzothiazole
were suitable for fresh pack at 125 days after treatment, making 95% of the tubers
treated with benzothiazole alone unsuitable for fresh pack sale.
In contrast, 72% of the tubers treated with benzothiazole and CIPC
showed no sprout development or peeping. Accordingly, 72% of the tubers treated
with benzothiazole and CIPC were suitable for fresh pack at 125 days after treatment,
and thus 28% of the tubers treated with benzothiazole and CIPC were unsuitable
for fresh pack sale.
None of the tubers treated with 16.6 ppm carvone showed no sprout
development or peeping. Accordingly, none of the tubers treated with this level
of carvone were suitable for fresh pack at 125 days after treatment, making 100%
of the tubers treated with 16.6 ppm carvone alone unsuitable for fresh pack sale.
Approximately 57% of the tubers treated with carvone and CIPC showed
no sprout development or peeping, and thus, 57% of the tubers treated with carvone
and CIPC were suitable for fresh pack at 125 days after treatment. Conversely,
43% of the tubers treated with carvone and CIPC were unsuitable for fresh pack
In contrast, in all tests where tubers were treated with cineole,
cinnamaldehyde, dihydroxybenzoic, ethylene, limonene or jasmone, alone or in combination
with CIPC, and in accordance with the method described herein, at 125 days 61%
to 100% of the tubers were unsuitable for fresh pack sale. It can be seen from
a review of Table I that at the residue levels tested, the sprout inhibition functionality
of CIPC was not universally enhanced when applied in conjunction with other compounds.
Moreover, in addition to utilizing thermal fogging techniques to
produce and apply the improved sprout inhibiting compositions of the present invention,
other conventional application methods may be employed. For example, potatoes may
be dipped into a solution or solutions comprising the improved sprout inhibiting
composition of the present invention. Also by way of example, the improved sprout
inhibiting compositions of the present invention may be applied in aerosol form
at temperatures less than the elevated temperatures utilized with thermal fogging,
for example at ambient temperatures. By way of further example, dusts of dried
sprout inhibiting compositions may be applied for some of the organic compounds
identified above, with or without the addition of dyes to improve product acceptability.
At the 125 days after treatment, average sprout length measurements
were determined for the untreated control tubers and for tubers treated CIPC,
ethylene, and CIPC plus ethylene. The data relating thereto is summarized in Table
AVERAGE SPROUT LENGTH 125 DAYS AFTER TREATMENT
Ethylene + CIPC
Clearly, the ethylene was able to overcome a portion of the sprout
inhibition functionality of the CIPC. Most importantly, the average thickness of
sprouts of potatoes treated with ethylene alone and ethylene and CIPC was 1.5 times
thicker than the thickness of sprouts from the untreated control tubers. The greater
average thickness is indicative of sprout vigor which is not evident from sprout
length measurements alone. Thus, application of ethylene to tubers, for example
to seed potatoes, shortly before or at planting, would be indicated for stimulating
sprout growth and thus subsequent establishment of potato plants grown therefrom.
Presently preferred embodiments of the present invention and many
of its improvements have been described with a degree of particularity. It should
be understood that this description has been made by way of preferred examples,
and that the invention is defined by the scope of the following claims.