CA1136039A - Gaseous antimicrobial treatment of storage grains - Google Patents

Abstract

GASEOUS ANTIMICROBIAL TREATMENT OF
STORAGE GRAINS
ABSTRACT OF THE DISCLOSURE
Process for treating storage grains to prevent microbial spoilage by treating the grain with gaseous sulphur dioxide in combination with a gas such as ammonia, carbon dioxide, chlorine, or nitrogen, such that the total amount of gas is from 0.25 to 3.0 liters per kilogram of grain.

Description

This invention relates to an antimicrobial treatment of storage grain, and more particularly, it relates to a treat-ment in which the storage grain is subjected to a combination of gases, one of which is sulfur dioxide.
It iS well known that grains such as corn, wheat, sorghum, and the like must be stored at various times and loca-tions from the time they are harvested to their eventual con-version into a consumers product such as flour, molasses, etc.
These grains are always subject to the possibility of mold growth and growth of other microorganisms because they are moist and contain the organisms which will multiply under the natural conditions of storage. It is, of course, very import-ant to inhibit such growth in order to prevent unnecessary wastage of food. Normally the grain is treated with a dry dust or with a liquid spray of suitable antimicrobial activity or dried in order to accomplish this purpose. It has now been found that treatment with certain gases can accomplish this purpose more economically and efficiently.
It is an object of this invention to provide an im-proved process for treating storage grains with an antimicro-bial material. It is another object of this invention to provide an improved process for treating storage grains with gaseous antimicrobial material. Still other objects will appear from the more detailed description of this lnvention which follows.
In accordance with this invention there is provided a process for treating storage grains to inhibit the growth of microorganisms which comprises treating the grain with a com-bination of gases, one of which is sulfur dioxide, the total amount of gas being from 0.25 to 3.0 liters per kilogram of grain. In embodiments of this invention there is employed gaseous treatments in which sulfur dioxide is combined with -~,,.s ~

~13~i()39 ammonia, chlorine, nitrogen, or carbon dioxide. In still other embodiments of this invention the process of treatment involves alternately lntroducing sulfur dioxide and one or more of the other treatment gases mentioned above.
The pxocess of this invention relates to the treatment of any grain which is subjected to storage in bulk under moist conditions. Such grains include wheat, corn, sorghum, oats, rye, soybeans, etc. Normally such grains are not completely dry, and contain about 15-40% of moisture. When the grains contain moisture they are particularly suitable for the growth of microorganisms.
The process of this invention involves subjecting the grain to the action of gaseous sulfur dioxide in combination with other gases. Among those gases are ammonia, chlorine, nitrogen, and carbon dioxide. When sulfur dioxide and ammonia are combined to treat moist grain it is quite possible that there is formed in situ ammonium bisulfite.
The gas is introduced into the volume of storage grain in any convenient manner which will produce the most intimate contact between the grain and the gas. This may be accomplish-ed by introducing the gas into the stream of grain entering a storage bin, blanketing the entire atmosphere around a mass of grain with a gas, or any other convenient means which those skilled in the art will readily recognize. It has been found convenient and effective in certain embodiments of this inven-tion to introduce portions of each gas alternately ~ntil the entire amount of gas is used up in such alternate additions.
For example if 500 parts of each of sulfur dioxide and ammonia are to be employed it is advantageous in some instances to introduce 100 parts of sulfur dioxide followed by 100 parts of ammonia followed by 100 parts o~ sulfur dioxide followed by 100 parts of ammonia, and so on until all of each gas is used

- 2 -~13~039 up. Normally such alternate introductions of gas follow one upon the other without any intermediate delay, but in some embodiments it has been found advantageous to delay a few hours or a day or two between gas introductions. It is not under-stood why this may be advantageous but it is possible that by such delays the gas has a better opportunity to completely impregnate the entire mass of ~rain and thus to provide a more complete opportunity to function as an antimicrobial agent.
It has also been found to be advantageous in the above-described alternate treatments to use sulfur dioxide - first and ammonia second, rather than the reverse order.
Furthermore, when the volume proportion of sulfur dioxide to ammonia is increased above 1;1 to levels of 2 or 3:1 the anti-microbial activity is enhanced.
Regardless of whether the gas is introduced all at one time or in a series of portions or in a series of alternate additions with another gas, the total amount of gas employed should be from about 0.25 to about 3.0 liters of gas at stand-ard conditions of temperature and pressure per kilogram of grain. Preferably the amount of gas is 0.5-2.5 liters per kilogram of grain since this range appears to provide the optimum in effectiveness.
It has been found that the combination treatment employ-ing sulfur dioxide and ammonia provides advantages in color and flavor which were not evident when either o~ these gases was used alone. Ammonia treatment causes corn quickly to darken in color. Sulfur dioxide alone provides an undesirable flavor. When both gases are used the color appears to become even brighter than the original and the flavor is much superior to that resulting from treatment by the separate gases.
In the following examples there are illustrations of the operation of this invention in providing antimicrobial ~136039 protection for moist corn. These examples are merely illustra-tive of the broader scope of this invention and it is not intended that the claims of this invention should be limited in any fashion by these examples. Parts and percentages are by weight unless otherwise indicated.
EX~MPL S 1 - 15 Samples of wet corn (about 25% moisture) in the amount of 500g. were placed in one pound brown bottles fitted with a rubber stopper through which was inserted polyethylene tubing (1/8"I.D. X 1/4"0.D.) long enough to reach the bottom of the bottle and to ex~end about two inches above the stopper. The tubing inside the bottle was pierced with several holes. The tubing outside the bottle was fitted with a tubing clamp to permit the tubing to be open or tightly clamped shut. About 400 ml of air was removed from each bottle and the tube clamp-ed shut. Gases were then introduced into the tubing in the amounts and in the order shown in Table I. In most instances the gases were introduced one after the other with no delay, in other instances as indicated there was a delay between gas admissions into the bottle. The initial microbial load in each instance was 34 x 107 organisms per gram of corn. At the end of one week, 5 weeks and 12 weeks the microbial load was determined to show the fungicidal activity of the system test-ed. The moisture content of the treated corn did not change appreciably from the initial levels at the end of 12 weeks.
The results are shown in Table I.
An alternate procedure for the treatment of grain is to place it in a column, introduce first one gas from the bottom and after a certain time interval add a second gas.

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In these examples, 500 g of corn (approx. 25% moi~ture) were placed in a chromatographic glass column (24" X 2" dia.).
About 400 ml of air was removed from the column and the gases were introduced into the column as indicated in Table II. The gases were allowed to remain in the column for about 15 min-utes and then the chromatographic column was connected to an ambient air supply through a flow regulator and wash bottles containing water or saturated potassium sulfate solution to provide appropriate humidities. Air was continuously blown into the column for 4 weeks before the contents were analyzed for total microbial load and moisture. This has the advantage of avoiding any microbial attack on moist grain before its moisture has been reduced, thus bringing the grain to a safe degree of moisture to avoid microbial contamination. The results are shown in Table II.

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~ X ~1~ o ~13~039 ___ In these examples 200 g of corn (about 25% moisture) were placed in tin cans with provision for introducing gases from the bottom. The first gas as shown in Table III was injected into the can and the gas allowed to stay for 1 minute.
The gas was then flushed out by blowing in, 10 times the amount of air. Then the second gas was introduced into the can, allowed to remain for 1 minute and then it was flushed out as before. After these treatments the cans were connected to an ambient air supply of about 40~-50% relative humidity and room temperature. Ambient air drying was continued for 4 days and the corn analyzed for % moisture, and % mold. The results are shown in Table III, The order of addition of the gases is as important as in the previous examples. Sulfur dioxide first followed by ammonia yielqed superior antimicrobial activity than the reverse order. For the ambient air drying procedure, a ratio of about 1:1 sulfur dioxide to ammonia is sufficient and the levels of the gases range between 25-100 ml each for 200 g of corn. Also, the effectiveness of the combined gas treatment can be clearly seen from the results in Table III when com-pared with the untreated control sample or either of the two gases alone.
As mentioned further above, the combined gas treat-ment yields corn with better color and flavor, compared to the individual gas treatments alone. In addition, ~he combined gas treatment is much less corrosive to metals when compared with a treatment of sulfur dioxide alone.

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_ 113~039 Although the invention has been descri~ed in consider-able detail with reference to certain preferred embodiments thereof, it will be understood that variations and modifica-tions can be effected within:the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

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Claims (13)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for preventing microbial spoilage of grains which comprises treating the grain with gaseous combination of sulfur dioxide and at least one additional gas selected from the group consisting of ammonia, chlorine, nitrogen and carbon dioxide, the total amount of gas being from 0.25 to 3.0 liters per kilogram of grain.

2. The process of Claim 1 in which the additional gas is ammonia.

3. The process of Claim 2 in which the volume proportion of sulfur dioxide to ammonia is from 2:1 to 3:1.

4. The process of Claim 1 in which the grain is subjected alternately to ammonia gas and to sulfur dioxide gas.

5. The process of Claim 4 in which there are a series of alternate treatments with ammonia gas and sulfur dioxide gas.

6. The process of Claim 2 in which the first treatment is with sulfur dioxide.

7. The process of Claim 1 in which the total amount of gas is from 0.5 to 2.5 liters per kilogram of grain.

8. The process of Claim 1 wherein the grain is wheat or corn.

9. The process of Claim 1 in which the grain has a mois-ture content of 15-40%.

10. The process of Claim 1 in which the treated grain is stored without any intentional passage of air for the purpose of drying.

11. A process for preventing microbial spoilage of grain which comprises treating the grain with a gaseous combination of sulfur dioxide and ammonia, the total amount of gas being from 250 ml to 1 liter per kilogram of grain, and then subjecting the grain to ambient air drying.

12. The process of Claim 11 in which the ratio of sulfur dioxide and ammonia is about 1:1 and in which sulfur dioxide is added first.

13, The ambient air drying of Claim 11 is carried out with air of relative humidity of 30-99%.