GB2275195A - Controlling bacteria in sugar processing plants - Google Patents

Abstract

Glutaraldehyde when combined with biocidally active dithiocarbamates is effective in controlling the growth of bacteria of the genus Leuconostoc present in sugar processing plants.

Description

CONTROLLING BACTERIA IN SUGAR PROCESSING PLANTS This invention deals with the use of biocidally active chemicals which control the growth of Leuconostoc bacteria in the production of sugar.

Sucrose, which constitutes up to 2% of the weight of the cane or beet, is readily degraded by bacterial action. The first step in the degradation is the production of invert sugars, fructose and glucose.

The second step is the production of lactic acid under the conditions prevailing in beet sugar manufacture, or dextran, under the conditions common in the cane sugar mills. Since this degradation is primarily caused by bacteria, it is important to maintain control of microbial organisms throughout the mill to avoid loss of production of sucrose. Microbial activity also causes processing difficulties, such as filter blinding, slime formation, and odors. The primary cause of these bacteria generated problems is bacteria of the genus, Leuconostoc.

As the crops arrive at the mill they contain soil and trash accumulated during the harvesting operation. In the case of cane sugar harvested by pushers, similar to bulldozers, the refuse may constitute as much as 1 to 25X of the weight of the material delivered to the mill. This is not merely inert material; it represents a major source of bacterial inoculation since soil organisms are present with appreciable fecal matter from birds, rodents, and other small animals that live on the crop lands.

Because of this, washing is a critical operation to the preparation of raw materials going to further extraction processes. On the other hand, washing should not be excessive, as this leads to loss of sucrose in the wash water.

After washing, sucrose is extracted from the raw material. In cane sugar mills, this is usually done by crushing and milling the washed, cut cane stalks, producing juice containing approximately 12 to 15% sucrose. In the beet sugar industry, the beets are sliced into long, narrow pieces (cossettes), and the sucrose extracted by washing with water in diffusers at about 168 degrees Fahrenheit (7 degrees Centigrade). There is growing interest in the use of diffusers in place of crushers and mills in cane processing to reduce maintenance costs and improve yield. These impure sucrose solutions are raw sugar.

The cane stalks are pressed after initial crushing and milling to reclaim as much sugar as possible, and the remaining solids (called bagasse) are usually burned in boilers to generate steam.

Bagasse may also be used as a raw material for such products as insulation board or acoustical tile. In the beet sugar industry, the beet pulp residue is quite high in protein, and it may be mixed with some of the plant production of molasses for cattle feed.

As with most other natural products, there area variety of chemicals other than sucrose in the cane and beets. These must be removed from the raw sugar solutions to maximize the yield of sugar, minimize the production of molasses, and reduce taste-, color-, and odor-producing impurities. This is done in a purification or clarification step. Lime is used to precipitate these impurities, and the lime mud is removed by conventional solidslliquid separation devices. The mud is washed to reclaim as much sugar as possible, and it may then be (a) reburned to produce fresh lime, (b) returned to the fields for its fertilizer value (it often contains significant phosphate), or (c) sent to landfill.

The purified juice must be concentrated to produce a thick syrup, the form of sugar often used by the beverage industry, or to produce a crystalline product. The juice is concentrated by evaporation. Since it contains calcium from the lime treatment, a common problem in the industry is the formation of scale in the pans (simple steam-jacketed evaporators) or in the multiple effect evaporators.

THE DRAWINGS Fig.l shows the effectiveness of dithiocarbamates in controlling Leuconostoc species bacteria in sugar mill process environments.

Fig.2 shows the effectiveness of glutaraldehyde in controlling Leuconostoc species bacteria in sugar mill process environments.

Fig.3 shows that when a dithiocarbamate blend is combined with glutaraldehyde that improved control of Leuconostoc species bacteria in sugar mills is achieved at low dosages.

THE INVENTION The invention comprises a method for controlling bacteria of the genus, Leuconostoc in sugar processing plants. Specifically the method comprises treating the raw sugar prior to its clarification with a biocidally active amount of a composition comprising: a) a biocidally active dithiocarbamate and mixtures thereof; and.

b) Glutaraldehyde, with the weight ratio of a:b being within the range of 1:1 to 1:17.

THE BIOCIDAL ACTIVE DITHIOCARBAHATES The biocidal active dithiocarbamates are partially illustrated by the following compounds: a) Sodium dimethyldithiocarbamate b) Potassium dimethyldithiocarbamate c) Potassium-N-hydroxymethyl-N-methyl dithiocarbamate d) Potassium dimethyldithiocarbamate e) Disodium ethylene bis dithiocarbamate f) Sodium dimethyl dithiocarbamate g) Disodium cyanodithiocarbonate h) Sodium N-methyl dithiocarbamate The dithiocarbamates may be used as blends. A particularly effective blend is referred to hereafter as NABAM.This is an industry recognized abbreviation for the following composition: Disodium ethylenebisdithiocarbamate 15% by weight Sodium dimethyl dithiocarbamate 15% by weight Water Balance DOSAGE AND RATIO OF NABAn TO GLUTARALDEHYDE In treating the sugar mills to prevent the growth of Leuconostoc species bacteria, it is necessary that the compositions used in the practice of the invention be added to the raw sugar prior to the clarification step. Typically, the compositions of the invention would be added to the extraction process in the initial processing of the sugar cane or the beets. A general dosage range of the compositions, based on active ingredients, is within the range of 5-188 ppm by weight.

Satisfactory results are frequently achieved using dosages within the range of 10-50 ppm with good results in most cases being achieved when the dosage is within the range of ler-30 ppm by weight.

In order to produce the synergistic effects of the invention the microbiocidally active carbamate, and, in particular, the NABAM, is combined in a weight ratio, based on active ingredients, to glutaraldehyde in a general ratio from 1:1 to 1:17. A preferred ratio of the NABAM to the glutaraldehyde is 1:3 to 1:8, with the most preferred range being 1:3 to 1:5.

One of the major advantages of the invention is that the blend of the biocidally active carbamates and the glutaraldehyde work very quickly to reduce the numbers of Leuconostoc bacteria in these sugar mill systems. When added prior to the clarification step, they provide a good biocidal prevention against Leuconostoc bacteria proliferation within the entire plant system.

EVALUATION OF THE INVENTION Inoculum: A bacterium isolated from sugar beet raw juice and belonging to the genus, Leuconostoc. was used as the test microorganism. The Leuconostoc bacterium was cultured at 3 degrees C. in 5 mL of a broth medium (lg sucrose, 25g Nail. lg tryptone, 5g. yeast extract, and .2g NaN3 per liter). The cells were washed once with sterile saline solution (0.85X NaCl) and resuspended in 12.5mL sterile saline.

Test Protocol: A 1:5 mixture of filter sterilized sugar beet raw juice and sugar beet pulp press water was inoculated with the resuspended Leuconostoc bacteria to a cell density of 16 colony forming units (CFU) per mL. 25mL volumes of the inoculated raw juice/pulp press water mixture was dispensed to vials containing the appropriate quantities of the carbamate and glutaraldehyde to achieve the following test matrix:: Carbamate Glutaraldehyde Glut./Carbamate only only combination No Biocide No Biocide No Biocide Sppm Sppm Sppml6ppm 18ppm lppm lppm\6ppm 2ppm 2ppm 20ppm/6ppm 5ppm 5ppm 5ppm\6ppm All biocide concentrations are shown as active ingredient (a. i.).

Each test vial was sampled at 1 hour, 3 hours1 and 24 hours. Surviving Leuconostoc bacteria were enumerated by standard microbiological techniques using sucrose/gelatin/azide agar incubated 48 to 72 hours at 30degrees C.

The Drawings show the results achieved using the above test procedure by comparing (CFU) v. Time of Exposure. Fig. 1 shows that NABAM gives only mediocre results even at high dosages.

Increasing the dosage did not substantially improve performance.

Fig. 2 illustrates that to be effective glutaraldehyde must be fed to the raw sugar at dosages of about 5 ppm or more. Fig. 3 demonstrates that as little as 6ppm of NABAM allows a much smaller amount of glutaraldehyde to give good results.

Claims (7)

1. A method for controlling bacteria of the genus Leuconostoc in sugar processing plants which comprises treating the raw sugar prior to its clarification with a composition comprising: (a) a biocidally active dithiocarbamate and mixtures thereof; and, (b) Glutaraldehyde, with the weight ratio of a:b being in the range 1:1 to 1 :17.

2. A method according to claim 1 where the ingredient (a) is a mixture containing disodium ethylenebisdithiocarbamate and sodium dimethyldithiocarbamate.

3. A method according to claim 2 where the said dithiocarbamates are in equal amounts in the mixture.

4. A method according to claim 1, claim 2 or claim 3 where the ratio of a:b is in the range of 1:3 to 1:8.

5. A method according to claim 4 where the ratio of a:b is in the range of 1:3 to 1:5.

6. Methods for controlling bacteria in sugar processing plants substantially as herein described and exemplified.

7. A mixture of (a) dithiocarbamate(s) and (b) glutaraldehyde for use in bacteria control in sugar processing, the weight ratio of a:b being in the range 1:1 to 1:17.