WO1995009535A2

WO1995009535A2 - Method for applying liquid potato sprout inhibitor

Info

Publication number: WO1995009535A2
Application number: PCT/US1994/011419
Authority: WO
Inventors: Darol Forsythe; John M. Forsythe
Original assignee: Darol Forsythe; Forsythe John M
Priority date: 1993-10-07
Filing date: 1994-10-07
Publication date: 1995-04-13
Also published as: WO1995009535A3

Abstract

Liquid sprout inhibitor for potatoes is introduced into a potato storage facility as a gas phase carried in an air stream. The liquid sprout inhibitor may be heated to a temperature at or near its boiling point prior to injection into a flowing air stream or a large surface area of the liquid sprout inhibitor may be exposed to the air stream to induce evaporation of the inhibitor into a gaseous phase. Sprout inhibitors such as dimethylnaphthalene (DMN) and trimethylnaphthalene are especially suitable for introduction to potato storage sheds by thermal fogging or evaporative fogging. This technique is especially useful for sprout inhibitors such as DMN which are found as natural ingredients in potatoes and are non-toxic to both the potato and humans.

Description

METHOD FOR APPLYING LIQUID POTATO SPROUT INHIBITOR

BACKGROUND OF THE INVENTION Field of the Invention: This invention relates to a method and apparatus for applying liquid sprout inhibitors to a potato storage facility.

State of the Art: A commercial sprout inhibitor has been chemically identified as Chloroisopropyl-N-carbonate (CIPC) which is a solid at room temperature. Various techniques and apparatus have been employed for distributing CIPC throughout a potato storage facility. Generally, CIPC is dissolved in a solvent, e.g., a polar solvent such as methanol, ethylene glycol, etc. and then atomized thermally or by other means and introduced, along with combustion products of the thermal fogging device, into an air stream which is generally the ventilation system for the potato storage facility in order to deposit a certain minor amount of CIPC evenly on all the potatoes in the storage shed.

The technique of distributing CIPC is frequently alluded to as "fogging," especially because the solvent/CIPC solution vapor emanating form a "fogger" forms either minute liquid droplets in the air stream or very fine solid crystals which precipitate from the solution droplets. These droplets or crystals are suspended in air and appear as a fog or cloud. Thus, there is a phase difference between the gas (air) in the ventilating system and the CIPC which is either a liquid or a solid, even though in minute particle form.

It is necessary for CIPC to be in contact with the potato in a storage facility in order for it to be effective. Thus, during a typical storage, usually beginning in about October, one or more treatments of the storage facility with a "dusting" of CIPC via thermal fogging is done.

Prior patents which disclose apparatus and discuss the techniques of distributing CIPCs throughout the potato storage facility are Morgan U.S. 5,009,152, Morgan U.S. 4,887,525, Luck U.S. 4,078,480, and Sheldon U.S. 4,226,179, and Plant U.S. 3,128,170. Sheldon discloses an ultrasound technique for fogging CIPC solutions.

The chemical CIPC has been the principal sprout inhibitor used commercially in agriculture for the past 20 years or more. Other sprout inhibitors have been considered and experimental work has been done with chemicals such as coumarin, fenilin, dimethylnaphthalene (DMN), the latter having three isomers, the 1,4, the 1,6, and the 2,3 and other chemicals. Effectiveness of some of these other potential sprout inhibitors has been reported in the following journals:

Potato Res. 24 (1981) 61-76 Beveridge et al. "T . Assessment of Some Volatile Organic Compounds as Sprout Suppressants for Ware and Seed Potatoes. " Potato Res. 24 (1981) 77-88 Beveridge et al. "Dimethylnephthalene as a

Sprout Suppressant for Seed and Ware Potatoes."

Potato Res. 27 (1984) 383-392 Filmer et al. "An assessment of 1, 4, 6 - Trimethylnapthalene as a Sprout Suppressant for Stored Potato Tubers."

Photochemistry v. 12 (1973) Mergh et al. "Growth-Inhibitory Volatile Isomatic Compound. Produced by Solanum Tuberosum Tubers. "

Although experimental work on such sprout inhibitors as DMN has shown promise, the commercial application of certain isomers DMN and other experimental sprout inhibitors has not been practiced.

In certain small scale experimental efforts, e.g., as described in Beveridge et al., the DMN was introduced into a small closed container by being absorbed on alumina and then allowed to evaporate, apparently to maintain a constant atmosphere of DMN in a closed environment. The alumina powder containing DMN was applied directly to the potatoes.

The potential usefulness of DMN as a potato sprout inhibitor has been disclosed in several publications, as indicated hereinabove.

Similarly, in British Patent Application 9117350, a technique was disclosed for measuring constantly the DMN concentration in the headspace of a potato storage facility. The DMN concentration measuring device interacted with a controller to cause more DMN to be introduced into the headspace when the concentration dropped below a certain minimum value (3 mg/m³) and to cease DMN introduction when it achieved a maximum value of about 6 mg/m³. This technique contemplated continuous introduction of DMN during an entire storage period.

Such a system requires a DMN applicator or injection unit for every storage shed. It also requires an expensive DMN concentration detection device for each storage shed. While such a system might be very appealing to the manufacturer of such an injection/monitor system, it would not be appealing to farmers who would have to buy such a system for each storage shed.

The profitability of storing potatoes for a period of time to await a more favorable potato price is such that it would not financially support the capital expenditure and regular maintenance and attention required of such a sophisticated injection and monitoring system.

The approach taken in B.P. Application 9117350, albeit an expensive one, is a direct application of the law of vapor pressure balancing. If the partial pressure of DMN in a potato storage facility equals the vapor pressure of DMN emanating from a potato, then the escape of DMN from the potato is prevented. Such an approach, straight forward scientifically, ignores a number of critical factors besides capital expenditure, maintenance, etc.

Potato storage facilities are rather large buildings with considerable headspace, voids (space between adjacent potatoes) and are not leak proof.

Furthermore, neutralizing DMN respiration would not foreclose respiration of other ingredients from the potatoes. Respiration involves the release of heat. It is therefore necessary to ventilate and cool the potato pile during storage. This is well known and potato storage facilities are equipped with ventilation, duct work and humidifiers. The air inside a potato storage facility is changed very frequently during warm weather; but even during the coldest days of winter in Idaho and Maine, some ventilation may be necessary.

A potato storage facility is not under constant supervision. Most air handling and humidifying systems require infrequent attention. The DMN treatment system proposed in B.P. Application 9117350 would require frequent attention. A constantly operating injector/monitor system is not appropriate for a farm situation. If the monitor malfunctioned, an entire crop of potatoes could be lost. The present method of treating storage facilities with sprout inhibitors is treatment of the facility by skilled applicators with specialized equipment three or four times a year with each treatment, including set up, requiring less than one day.

SUMMARY OF INVENTION The instant invention involves a method and apparatus for introducing controlled quantities of a liquid sprout inhibitor such as an isomer of dimethylnaphthalene (DMN). A liquid sprout inhibitor, for the purposes of this invention, is one which is liquid at room temperature and has a freezing point above about 0°C and a boiling point below about 300 °C into a large potato storage facility in a substantially uniform manner. Liquid sprout inhibitors, unlike solid sprout inhibitors such as CIPC, do not need to be dissolved in a solvent or diluted with some diluent. Although solvents or diluents could be utilized with liquid sprout inhibitors, it is generally preferred that an undiluted liquid sprout inhibitor be introduced as such as a vapor into an air stream which flows throughout the potato storage facility.

It is generally known that some chemicals within a potato begin to diminish at about the same time that sprouting occurs. One of these chemicals is dimethylnaphthalene. Thus, after a certain period of storage under certain conditions, potato chemicals, such as dimethylnaphthalene, begin to migrate through the potato skin, that is, respirate, so that the content of dimethylnaphthalene, for example, remaining in the potato is reduced. It is believed that this reduced quantity of DMN, as well as perhaps some other chemicals, in the potato is a condition that either promotes or permits sprouting.

Thus, the instant invention is directed to a method and means for introducing a certain atmosphere of liquid sprout inhibitor, for example, DMN in the potato storage facility such that the partial pressure of DMN in the atmosphere surrounding the potatoes approaches or, preferably, exceeds the partial pressure of DMN which would be naturally generated by respiring potatoes in the absence of an air stream through the potato storage facility. (Airstreams, especially humidified airstreams, are generally maintained in potato storage facilities to keep the storage temperature preferably between about 4° Celsius and 10° Celsius (40° and 50 °F) and at a relatively high humidity, for example, above 80% and preferably above about 90% with a relative humidity of 95 % being relatively common. Lower temperatures inhibit sprouting, but also cause starch conversion to sugars, degrading the quality of the potato for certain purposes.)

Several different techniques are desirable for injecting a vapor into the air space surrounding the stored potatoes. One especially effective method is to rapidly heat the liquid sprout inhibitor to evaporate it and to inject it into an airstream at a rate such that the vapor does not condense into droplets. Or, if there is condensation, it is so minimal that any droplets formed are revaporized because of the low content of the liquid sprout inhibitor in the airstream. The heating and/or evaporation of a liquid sprout inhibitor as preferably done in the absence of solvents, dilutents or combustion products. For example, in treating a potato storage facility with liquid sprout inhibitor such as an isomer of DMN, especially the 1,4 and 1,6 isomers of DMN, it is only necessary to have a very low concentration of DMN in the atmosphere inasmuch as the quantity of DMN in a potato is very low so that only very minor quantities of DMN respire or exit the potato. Thus, only a very low partial pressure for DMN is created in a static air space surrounding a potato by respiration. The purpose of DMN in the atmosphere surrounding potatoes is to stop or reduce the exiting of DMN from the potato. Once DMN exiting starts, it is believed that such departure initiates the process which leads to sprouting. It has been discovered that treatments with DMN on certain types of potatoes which have started to sprout does not reduce significantly the sprouting to any considerable extent unlike treatment with CIPC which generally retard potato sprouting even after sprouting has been initiated. Thus, in applying liquid sprout inhibitors which are found natively in potatoes it is generally preferred to initiate treatment prior to the onset of sprouting and preferably prior to any considerable exiting of DMN, for example, from the stored potato.

In certain of the prior experimental work stored potatoes, for example, were stored in a box with DMN saturated aluminum particles so that DMN was present during the entire time of storage. This is not practical with a large potato storage facility. For one thing, the quantity of DMN utilized would made it prohibitively expensive. Thus, the instant invention is directed to methods and apparatus for actively and economically treating a large potato storage facility with a liquid sprout inhibitor such as a DMN isomer.

DETAILED DESCRIPTION OF THE INVENTION The instant invention relates to methods and apparatus for applying a liquid sprout inhibitor to potatoes in a large potato storage facility in an effective and economic manner. Liquid sprout inhibitors for the purposes of this invention are those having a freezing point generally at about 0°C or lower and a boiling point of at least 100°C and higher. A particularly effective liquid sprout inhibitor, identified herein also as an "LSI", is selected from the class of dimethylnaphthalene isomers, especially the 1 ,4 and 1,6 isomers and diphenylamine. Other liquid sprout inhibitors which may be utilized in the instant invention are trimethylnaphthalene isomers, vanillin, coumarin and the like. The liquid sprout inhibitors of most interest in the instant invention are those which are found naturally in potatoes. These naturally occurring materials are volatile and are generally known to be released, that is respirated, from the potato upon a certain elapsed period of time after harvesting. Release of these volatile materials has been associated with the onset of the sprouting process.

A modern larger potato storage facility generally is one which will accommodate 907,000 kilograms to 9,070,000 kilograms (1000 tons to 10,000 tons) of potatoes. These facilities are generally equipped with ventilating systems by which the air flow and humidity within the storage facility is controlled. Frequently, the ventilation system involves a duct work grid beneath the potato stacks so that the full stack of potatoes may be controlled. Such as ventilation system is illustrated in certain patents such as noted hereinabove.

For large potato storage facilities, three principal methods of application are effective. First, a system which introduces the liquid sprout inhibitor (LSI) into the potato storage pile in a substantially uniform manner as a vapor. Frequent periodic applications are made sufficient to retard the loss of volatile agents from the potato and to prevent sprouting. The LSI may be vaporized by a thermal evaporator or by a large surface area evaporation technique exposed to a dynamic air flow. Second, the LSI may be applied in the form of a very fine mist so that minute droplets of LSI become deposited upon the potatoes and may be absorbed or remain upon the potatoes to maintain a high partial pressure of the LSI in the vicinity of the stored potatoes to minimize loss of volatiles and thereby inhibit sprouting. A third method of applying the LSI is to provide it in a solid form, that is wherein the LSI is either reacted with or mixed with another component so that the resulting form is a solid. Blocks of the solid could be placed in the storage shed prior to introduction of the potatoes with the block being designed to gradually evaporate to expose the LSI after a predetermined period of time so that the LSI would then be evaporating during the critical period beginning before sprouting is typically initiated in order to retard and inhibit sprouting. The details of these three methods will be set forth fully hereinafter.

The method of applying LSI to a potato storage shed preferably should be simple and reliable. A technique which permits a storage shed operator to easily and readily check the amount of LSI introduced during a particular period of time is very desirable. For example, with the addition of vapor LSI to a shed by means of a thermal generator, it is possible by adding a known quantity of LSI to the generator and then operating it for a certain period of time especially under closed circuit conditions, that is, where substantially no air is introduced from outside the shed, then the operator may be secure in the knowledge that such predetermined quantity of LSI has been introduced into the atmosphere surrounding the potatoes. Measuring devices generally are in place on storage sheds to determine temperature of the stored potatoes as well as the relative humidity of the circulating air. For example, it should be possible to add sufficient DMN to the air within a closed shed to raise partial pressure of the DMN to such a level that DMN is absorbed by the potatoes. Thus, the reverse of DMN respiration could be achieved.

It is recognized that a shed may be sealed only for a certain period of time before the storage temperature exceeds the upper storage temperature limit. Also, air within the shed may become too dry or contain too much carbon dioxide. However, if during the period that a shed is sealed, sufficient DMN is introduced as a vapor to elevate the DMN content in the skin of the potato then for a certain period of time there would need to be no further treatments of DMN and the usual cooling and humidifying of the shed could be resumed.

A similar method may be used with respect to an air evaporation system wherein a large surface area of LSI is exposed to an airstream. The evaporation surface generally need to be an extended surface inasmuch as most LSI materials such as DMN have very low vapor pressures at storage temperatures of 1.6° Celsius - 10° Celsius (35-50 °F). Generally storage temperatures are preferably between about 4.4° Celsius - 7.2° Celsius (40-45°F). Thus, to have any considerable vaporization, liquid DMN needs to be extended over a large surface. The technique for doing so, however, should be one which is readily directly measurable so that anyone applying the DMN will know from direct observation how much has been applied. For example, a elongated DMN reservoir with a fibrous mat or similar "wicking" material which extends, at least partially, into the airstream may be utilized whereby the LSI is wicked up from its reservoir into a porous fibrous structure through which air may pass and evaporate the LSI adhering to the fibers. If the LSI is too viscous to readily wick into the fibrous material then the reservoir may be heated to reduce the viscosity of the LSI. Also, a small pump may be used to pump an LSI material from its reservoir to a position wherein it may be allowed to cascade over a porous, extended surface to expose a large film area to an air stream.

The technique of the instant invention is to treat a potato storage facility periodically with DMN, or other liquid sprout inhibitor, at a relatively high concentration of LSI within the facility. Concentration of DMN may be maintained at levels significantly higher than 20mg/m³ and may approach vapor concentrations of 200 mg/m³ to 500 mg/m³. Such concentrations may be maintained for a short duration, e.g., several days, by significantly reducing the air exchanged within the facility, which may be done for a short duration without adversely affecting the stored potatoes. For example, DMN can be introduced into the facility over a period of a few hours to achieve a high concentration. The facility is then maintained in a sealed condition for several days to a week while the DMN containing air is circulated within the facility. During the coldest months of the winter it is feasible to maintain the facility in a substantially sealed condition for up to a week.

Although, as indicated in the Plant patent, CIPC is not applied until after subruzation (wound healing). DMN is preferably applied initially shortly after the potatoes have been put into the facility. Inventor's experience has been that DMN, unlike CIPC, does not retard sprouting once it has begun. Also, unlike CIPC, DMN is not a foreign material to a potato. Thus, absoφtion of DMN by a potato does not affect the edible nature of the potato.

In a storage facility containing 40,000 bushels (approximately 907,200 kilograms (2,000,000 lbs.)) such as described in the example of the Plant patent, approximately 1100 gms. (approximately 2^l lbs.) of DMN would be required per day to maintain a DMN vapor concentration of approximately 12.5 mg/m³ given 10% air exchange at an air rate of about 0.27 cubic meters/minute (9.5 cubic feet/minute) for the approximate 6,230 cubic meter (220,000 cubic feet) facility. Assuming a 2 % air exchange and a vapor concentration of 125 mg/m³, treatment over a two day period, about 4.5 kilograms (ten pounds) of DMN would be required. Assuming four treatments per storage season, a total of only about 18 kilograms (40 pounds) of DMN would be used while practice of the B.P. Application 9117350 technique would require about 227 kilograms (500 pounds) DMN. Practice according to Beveridge et al. at 100 mg/kg of potatoes (1 part per 10,000 parts) would require a DMN weight approximately 90 kilograms (200 lbs.) per treatment, or approximately 363 kilograms (800 lbs.) for a season (four treatments).

During the colder months of the storage season, a facility could be sealed, i.e., no fresh air introduced, treated with a high concentration of DMN as a vapor, e.g., 125 mg/m³ for a period of eight hours, then leave the facility sealed for a period of several days to a week.

Although an early treatment of stored potatoes is generally desirable, a quiescent period of about 30 to about 90 days typically exists in most temperature zones where potatoes are grown and stored before sprouting begins. A treatment with DMN during the latter stages of this quiescent period is required in order for the whole treatment regimen to be successful. Subsequent treatments should be sufficiently frequent to retard DMN respiration sufficiently to prevent the onset of sprouting.

Prior work with DMN appears to have been experimental in nature without addressing the challenges associated with treatment of commercial storage facilities. Commercial storage facilities are often located on remote farms. Storage sheds are large, frequently constructed of sheet metal and are not air tight.

Applying DMN on a carrier to such potatoes within such a facility would generally be impractical. A deep, long pile of potatoes would be difficult to treat with dig material; getting powdered material on potatoes at the bottom of the pile would not be easy. Ventilating of the facility would generally preclude effective filling of the void space with an effective concentration of DMN. At the temperature of storage, 4.4° Celsius to 10° Celsius (40-50°F), the vapor pressure of DMN is very low and would not create a sufficient concentration of DMN in the storage facility unless ventilation of the facility was ceased for a long period of time, e.g., for many weeks.

However, using the techniques of the instant invention, a high concentration of DMN can be obtained in a relatively short period. Liquid DMN has a boiling point of about 264°C (approximately 509°F) but can be readily evaporated by spraying a fine mist of DMN onto a hot surface, e.g., an electrically heated surface having a temperature of about 285°Celsius to 350°Celsius (550°F to 650°F). Vapors are then directed through an electrically heated duct into circulating air within a potato storage facility. The facility is sealed, i.e., no outside air is introduced. The introduction of DMN vapor is continued until a predetermined amount of DMN is introduced into the facility. Generally during treatment of a facility, DMN is maintained at a concentration of at least about 12 mg/m³, preferably about 20 mg/m³, and often as high as 30 mg/m³ or even higher.

The approach of the instant invention, unlike the B.P. Application approach, is to "shock" the potato with an substantial quantity of DMN, i.e., treat the facility intensely, to interrupt the normal biological cycle of the potato. Thus, the approach is to cause a potato's biological clock to reset and induce a new quiescent period after each treatment.

Claims

CLAIMS What is claimed is:

1. A method of applying a liquid sprout inhibitor to a potato storage facility comprising:

5 vaporizing said liquid sprout inhibitor (LSI); « introducing vapors of said liquid sprout inhibitor into said facility with said facility in a substantially sealed condition; and maintaining said facility in a substantially sealed condition for a limited duration of time; and 10 restarting conventional ventilating and humidifying procedures after said facility is unsealed.

2. The method of claim 1, wherein a known quantity of LSI is introduced into a storage facility of a certain known volume to achieve a certain

15 predetermined LSI concentration in said facility.

3. The method of claim 3, wherein said predetermined LSI concentration is above about 20 mg/m³.

20 4. The method of claim 3, wherein said predetermined LSI concentration is above about 50 mg/m³.

5. The method of claim 1, wherein said limited duration of time is at least 24 hours.

25

6. The method of claim 1, wherein said limited duration of time is at least 36 hours.

7. The method of claim 1 , wherein said limited period of time does not * 30 exceed about 72 hours.

8. The method of claim 1, wherein said vapors of LSI are introduced into a circulating air stream within storage facility.

9. The method of claim 1, wherein said LSI is an isomer of DMN.

10. The method of claim 1, wherein said isomer of DMN is 1,4 DMN or 1,6 DMN.

11. A method of applying a LSI to a potato storage facility comprising: introducing LSI into the humidifying unit of a potato storage facility; circulating air through said humidifying unit to vaporize said LSI and to circulate said LSI vapor containing air through said facility for a period of time sufficient to cause the vapor concentration of LSI in said facility to increase to a certain predetermined level; and maintaining said LSI concentration in said facility at a concentration of at least said predetermined concentration level for a short duration of time.

12. The method claim of 11, wherein said method is repeated at least once in said facility during a storage season.

13. The method of claim 11, wherein said method is repeated at intervals of not less than three months during storage of potatoes.

14. The method of claim 11, wherein said vapor concentrate of LSI is at least 20 mg/m³.

15. The method of claim 1, wherein said LSI is introduced into a potato storage facility prior to any significant sprouting of said potatoes.