JP2000342234A - Electron beam sterilization - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily sterilize a solid material consisting of protein or the like in an excellent sterilization efficiency while keeping desired functional properties by adjusting the solid material so that the water content becomes equal to or below the second critical point and subsequently irradiating the material with electric beams. SOLUTION: A solid material containing a protein or a sugar preferably selected from corn starch, gluten meal, potato starch and the like as the main component is adjusted so that the water content becomes equal to or below the second critical point, preferably equal to or below the water content of monomolecular absorption. Subsequently, the material is irradiated with electron beams, preferably by energizing the beams through an electron beam accelerator at an acceleration voltage of 50 keV to 10 MeV, and preferably at a dosage rate of 1.0×105 to 1.0×109 Gy/hr to sterilize it. Microorganisms to be sterilized are preferably spore-forming bacteria.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for sterilizing a solid material by electron beam irradiation, a solid material treated by the method, and a product obtained from the material.

[0002]

2. Description of the Related Art In general, materials containing proteins or carbohydrates as main components and used for foods and other industrial products include primary processes such as cultivation, growth, harvesting and sun drying, or subsequent processing. It is easily contaminated by microorganisms and the like in the secondary process, and it is difficult to maintain an aseptic condition. Such contamination is a daily problem in the fields of manufacturing foods, medicines, cosmetics, and the like that use the material, and various methods for preventing or sterilizing microorganisms have been proposed.

[0003] For example, a sterilization method using UV (Japanese Unexamined Patent Publication No. 61-18 / 1986)
7987) or a heat sterilization method using a large autoclave or the like (JP-A 08-242807, 09-19278, 0
9-163925 and 09-266781) and a method for controlling microbial contamination by changing the liquidity (pH) (Japanese Patent Laid-Open No. 03-290172).
No. 08-89563), a sterilization method using ethylene oxide (Japanese Patent Application Laid-Open No. 05-148114), a pressure sterilization method (Japanese Patent Application Laid-Open
No. 02-257864, No. 09-285526), sterilization method by chemical treatment (Japanese Patent Application Laid-Open No. 07-265398, No. 08-228735, No. 09-285526)
No. 154562) is known. In addition, techniques for applying radiation to food for sterilization, which has been conventionally used for preventing germination, adjusting maturity, and improving storage properties, have been studied, and a sterilization method using electromagnetic waves (Japanese Unexamined Patent Application Publication No. 05-76582, 09/09) has been studied. -313865
No.) has been proposed.

[0004]

However, sterilization by irradiation with gamma rays or X-rays has good penetration of these rays and is expected to have a sterilization effect. Due to its properties, the particles may collide with each other on the surface of the substance, or the secondary radicals generated by the irradiation of the electron beam may concentrate and act on each other, so that a sufficient sterilizing effect may not be obtained. .

Further, it is known that sterilization by electron beam irradiation is caused by an indirect action between water in a target substance and an electron beam. Therefore, in some cases, moisture is added from outside to improve the sterilization effect. Yes, rather, the increased water content of the substance may result in increased microbial growth and pest growth.

[0006] Further, the raw material is not only a raw material constituting a final product, but also a gel, a viscosity imparting, an emulsifying, a bubble / body feeling imparting, a solid content imparting, a kokumi flavoring, a taste improvement, a flavor or a storage stability. It is also used in expectation of improvement and enhancement of functional characteristics such as imparting, sweetening, enzymatic activity, and nutrition. However, when a starch material is simply irradiated with an electron beam, there is a high possibility that the electron beam cuts the polymer chain of the material, thereby deteriorating functional properties of the final product such as gel strength. Accordingly, there is a need for a method of sterilizing a material that can maintain desired functional characteristics and can be easily used in the manufacturing and processing steps of the material itself or a product obtained therefrom.

[0007]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, a material whose water content has been adjusted to a certain amount or less is irradiated with an electron beam. And a good bactericidal effect. Therefore, according to the present invention, a solid material comprising a protein or carbohydrate as a main component, the water content of which is adjusted to be equal to or less than the second inflection point, and then the material is irradiated with an electron beam. A sterilization method, a material treated by the method, and a product obtained from the material.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In the method of the present invention, a solid material containing protein or saccharide as a main component is used for foods, pharmaceuticals,
Any kind of material can be used as long as it can be used as a raw material or a raw material mixture for quasi-drugs, cosmetics, and other industrial products. Specific examples include corn starch, gluten meal, potato starch, potato protein, wheat starch, gluten, crude sugar, rice flour, wheat flour, buckwheat flour, soy flour, soy protein, wheat protein, milk powder, and the like. Corn starch, gluten meal , Potato starch, potato protein, wheat starch and gluten are particularly preferred. The material may consist of one or a mixture of these, and may contain other components such as ash and minerals.

The method of the present invention adjusts the water content of such a material so as to be equal to or lower than the second inflection point of the material, preferably equal to or less than the water content of a single molecule adsorbed, and then irradiating the material with an electron beam. Consisting of

That is, the solid substance is usually bonded to the water molecules by adsorbing the water molecules one by one on the interface. The term “single-molecule adsorption” refers to a state in which only one water molecule is adsorbed on the interface in such a phenomenon, and the water content necessary to cause this state is called a single-molecule-adsorbed water content. After this, the water molecules are gradually adsorbed to the substance in layers, but when the amount of water molecules that exceeds the amount required for the composition of the substance becomes adsorbed, free water that can move freely in the substance is generated I do. The second inflection point is a water content at a branch point where the free water is generated, and means an upper limit of the water content at which the solute is directly hydrated. For this reason, the monomolecule absorbed water content and the second inflection point play an important role in determining the properties of substances during storage or distribution, and a book published by Hayao Noguchi (Food and Water Science, 180 ~ 197 pages, Koshobo, 1992) can be obtained as a value unique to each material. According to the study of the present inventors, for example, the second inflection point and the monomolecular adsorption moisture content of corn starch are 13.0.
% And 7.6%, and the second inflection point and single molecule adsorbed water content of the potato protein are 9.4% and 5.2%.

Therefore, the material to which the method of the present invention is applied can be prepared by any method, for example, under high temperature conditions, spray drying, By subjecting it to drum drying, hot air drying, or the like, the water content can be adjusted to a value not higher than the second inflection point specific to the material, and preferably to a value not higher than the water content of single molecule adsorption.

The fact that the water content of the material is not more than the second inflection point or the water content of single molecule adsorption is confirmed by subjecting the material whose water content has been adjusted to, for example, the 13th Japanese Pharmacopoeia, a test for loss on drying. can do. In addition, in the material whose moisture content is adjusted, moisture may remain in an amount of about 1 to 13%.
Preferably, the amount is measurable, such as 8%, by methods known to those skilled in the art.

The raw material whose water content has been adjusted to the second inflection point or the water content of a single molecule adsorbed or less can have a bactericidal effect by being irradiated with an electron beam. The electron beam is usually generated from an electron beam generator, and for example, a linear electron accelerator, a Van de Graaf electron accelerator, an area beam type or a Cockcroft-Walton type electron beam generator can be used. .

The accelerating voltage for electron beam irradiation is 50 keV
It is in the range of 10 MeV, preferably in the range of 300 keV to 5 MeV. Acceleration voltages below 50 keV do not produce the expected effect, and acceleration voltages above 10 MeV are prohibited from being used in foods. In the present invention, the electron beam means that the dose rate is
1.0x10 ^{5 to} 1.0x10 ⁹ Gy / hr.

The electron beam can be irradiated directly or indirectly to the edible material in the presence of air in an open system or in the presence of air, oxygen gas or nitrogen gas in a closed system. Irradiation is preferably carried out under low oxygen and low humidity conditions in order to prevent the occurrence of water. For example, in the case of performing in an open system, the irradiation surface of the electron beam generator can be irradiated with an electron beam by making the irradiation surface inclined and sliding down the material. Alternatively, the material can be placed in a container having a thickness of 80 μm or less, such as a polyethylene bag, and the irradiation can be performed by spreading thinly so as to reduce the thickness. By doing this,
With a material having a specific gravity of 1, the electron beam can reach the inside of the polyethylene bag at a depth of about 2 mm from the film surface.
At the time of these treatments, the raw material is preferably in the form of a film, plate, granule or powder, and when irradiated in a container, the material may be in the form of granule or powder. More preferred.

[0016] Bacillus subtili
s), B. cereus, B. stearothermophilus, B. megaterium, B. thermoaceticum, Clostridium aceticum Spores such as Clostridium aceticum, C. thermoaceticum, C. botulinum, thermophiles Thermus aquaticus, and T. thermophilus Forming bacteria, hydrogen sulfide-producing bacteria, or spores or vegetative strains derived from these bacteria can be effectively killed by the method of the present invention.

The material treated by the method of the present invention can be used for various products as described above, in addition to food. For example, in the field of food, processed livestock products (ham, sausage, salami, sour pork, grilled pork, hormone grilled, meatballs, corn beef, liver paste, hamburger), processed fishery products (kamaboko, hampon, surimi, delicacy kamaboko, fried) Kamaboko, oden seeds, pickled in tuna oil, pickled sardine and mackerel miso, processed shellfish, boiled shrimp cream, processed agricultural products (side dishes, eight treasures, salad, lunch, sukiyaki, mabo tofu, sauce, sake, mirin, Stew, curry,
Meat sauce, soups, dairy products (milk for coffee, condensed milk, soy milk drinks, cheese, yogurt, various dairy products), egg products (mayonnaise, fried eggs, rolled egg), rice cakes, processed rice cakes, cooked rice (sushi) , Eel, pilaf, crabmeat, fried rice, etc.), desserts (pudding, jelly, flan, zenzai, etc.), frozen desserts (ice cream, shaved ice, sherbet, etc.) and frozen processed foods (frozen foods), pickles (Fukugami pickles, miso pickles,
Soy sauce pickles, mustard pickles, Nara pickles, fruit products (grape syrup pickles, orange juice, transparent apple juice, tomato juice, tomato ketchup, tomato sauce, apricot jam, jelly, preserves, kurikanroni, etc.), beverages (coffee, Coffee milk drinks, tea, carbonated drinks, carbonated drinks with cola, soft drinks, nectar, green tea), alcoholic drinks (sake, amazaki, fruit juice drinks, various cocktails, wine, beer, etc.), noodle products (cup noodles, udon, Ramen, soba, noodle soup, etc., flour products (cake, frozen cake, okonomiyaki powder, takoyaki powder, fried flour), soy products,
Examples include retort processing and aseptic filling process products. Products in other fields include pharmaceutical excipients, toothpastes, mouth care, mouth fresheners and the like.

[0018]

The present invention will be described below with reference to examples, but the present invention is not limited to these examples. Example 1 : Sterilization of corn starch and gluten meal Calculation of water content and second inflection point of single molecule From corn, corn starch (water content 14%) through delicate selection, immersion, coarse pulverization, germ separation, grinding, sieving, centrifugation, washing, filtration, drying process and Gluten meal (water content 13%) was obtained. The adsorption isotherm of these samples was measured under the following conditions using a moisture adsorption equilibrium measuring device (manufactured by Nippon Tobacco, EAM-01), and the single molecule adsorbed water content and the second inflection point of each sample were calculated. Solvent: distilled water Sample amount: about 1 g Set temperature: 25 ° C. Set relative vapor pressure: 10 to 90%, intervals of 10% The water adsorption phenomenon was analyzed using the BET theoretical equation shown below.

[0019]

(Equation 1)

V: Amount of water adsorbed at a vapor pressure of PmmHg (g / 100 g) Vm: Amount of water adsorbed necessary to form single molecule adsorption (g / 100 g)
100 g) P: Vapor pressure at measurement temperature (mmHg) Po: Saturation vapor pressure at measurement temperature (mmHg) C: Constant for heat of adsorption (kcal / mol) 13.0% and 7.6%, respectively, and the second inflection point of gluten meal and the moisture content
It was found to be 1.5% and 6.6%.

B. Adjustment of moisture content Corn starch and gluten meal were placed under a temperature condition of about 80 ° C for 30 minutes to several hours, and the moisture content was adjusted to the respective second inflection points or less. The moisture content of the sample below the second inflection point is determined by the 13th Japanese Pharmacopoeia as determined by the dry weight loss test method (1 g,
105 ° C., 5 hours).

C. Electron beam irradiation treatment The moisture-adjusted powder sample is placed in a polyethylene bag (made in Japan,
E-8, thickness 80 μm), and it was thinly stretched to a small thickness and irradiated with an electron beam in the presence of air. For irradiation,
Using a van de Graaff type electron accelerator (Nissin High Voltage), acceleration voltage 300keV (dose rate 3.6x10 ⁷ Gy / h
r), 1 kGy absorbed dose (electron flow: 2 mA, speed 50 m /
Min, irradiation width 20 cm).

D. Measurement of the number of bacteria in the sample 10 g of each of the sample irradiated with the electron beam and the control sample whose water content was not adjusted and not irradiated with the electron beam was sterilized in saline 9
After heating at 90 ° C for 30 minutes, the mixture was plated on a plate containing tryptosome agar medium (manufactured by Nissui), and the colonies formed after culturing at 35 ± 1 ° C for 24 hours were counted. The number of bacteria per gram was calculated. The results are shown in Table 1 (in the following table, nd means that sterilization cannot be detected).

[0024]

[Table 1]

Although Bacillus subtilis was confirmed as a control, none of the microorganisms was detected in the sample treated by the method of the present invention, even if the absorbed dose was as low as 1 kGy. In addition, when the change in the functional properties of the control and the sample treated by the method of the present invention were examined by a rheometer, the sample treated by the method of the present invention was more elastic than the control, and was superior in water retention. I knew it was there.

Example 2 : Sterilization of potato starch and potato protein Calculation of Single Molecule Adsorbed Water Content and Second Inflection Point Potato starch (water content: 18%) and potato protein (water content: 10%) were obtained from potato (water content: about 75%) through grinding, decanting, and drying steps. For these samples, Example 1
The adsorption isotherm was measured in the same manner as described above, and the second inflection point and the single molecule adsorbed water content of potato starch were 15.2 and 7.6, respectively.
It was calculated that the second inflection point and the single molecule adsorbed water content of the potato protein were 9.4 and 5.2.

B. Adjustment of moisture content In the same manner as in Example 1, the moisture content of each sample was adjusted to be equal to or lower than the second inflection point. C. Electron beam irradiation treatment The acceleration voltage was set to 300 keV (dose rate 3.6x10 ⁷ Gy / hr).
Performed in the same manner as in Example 1.

D. Measurement of Number of Bacteria in Sample The same procedure as in Example 1 was carried out except that the dispersion of each sample was heated at 100 ° C. for 10 minutes. The results shown in Table 2 were obtained.

[0029]

[Table 2]

As a control, Clostridium thermoseticam was confirmed, but no microorganism was detected from the sample treated by the method of the present invention. Also,
When the change in the functional characteristics was examined in the same manner as in Example 1,
The sample treated by the method of the present invention had better elasticity and water retention than the control.

Example 3 : Sterilization of wheat starch and gluten Calculation of Single Molecule Adsorbed Water Content and Second Inflection Point From wheat flour, wheat starch and gluten (12% each water) were obtained through steps such as kneading, washing, centrifugation, classification, and drying. The adsorption isotherms of these samples were measured in the same manner as in Example 1, and the wheat starch had the second inflection point and single-molecule adsorbed water content of 11.2 and 6.4, respectively. The adsorbed water content was calculated to be 11.3 and 6.6.

B. Adjustment of moisture content In the same manner as in Example 1, the moisture content of each sample was adjusted to be equal to or lower than the second inflection point. C. Electron beam irradiation treatment Accelerating voltage is 4.8MeV (dose rate 1.0x10 ⁷ Gy / hr),
Performed in the same manner as in Example 1.

D. Measurement of Number of Bacteria in Sample The same procedure as in Example 1 was carried out except that the dispersion of each sample was heated at 100 ° C. for 30 minutes. The results shown in Table 3 were obtained.

[0034]

[Table 3]

As a control, Bacillus cereus was confirmed, but no microorganism was detected in the sample treated by the method of the present invention. In other words, the sample in which the water content was adjusted to the second inflection point or less exhibited a bactericidal effect even with irradiation with a low absorbed dose. This indicates that a sample in which the water content is adjusted to be equal to or lower than the second inflection point, for example, equal to or lower than the water content of single molecule adsorbed, can obtain an excellent bactericidal effect at a lower dose.

Reference Example 1 : Influence of bactericidal effect by water content Water content 3.1%, second inflection point 25%, water content of single molecule adsorbed
6.59% potato starch powder (Matsuya Chemical) as a sample
The effect of the water content in the sample on the bactericidal effect was investigated. A. Bactericidal effect against Escherichia coli Escherichia coli uses E.coli IFO3972, DIFCO
The cells were cultured at 35 ± 1 ° C. for 24 hours in a Nutrient Broth liquid medium manufactured by the company. Three kinds of samples were prepared by adding 30 g of water to 1 kg of the powder sample, and further adding 70 g, 170 g, and 370 g of the above culture solution so that the water content was 10%, 20%, and 30%.
The desired moisture content of the sample was confirmed by the method described in Example 1. Next, each sample was irradiated with an electron beam in the same manner as in Example 1. The acceleration voltage is
2.5 MeV (dose rate 1.5 × 10 ⁶ Gy / hr), and the absorbed dose was divided into four levels of 1, 2, 3, and 4 kGy. 10 g of each of the sample not irradiated with the electron beam and the sample irradiated with the electron beam were sterilized phosphate buffered saline (10 mM phosphate buffer containing 0.85% NaCl,
A fixed amount of the undiluted solution added to 90 ml of pH 7.0) is plate-mixed on a plate containing a desoxycholate agar medium at 35 ± 1 ° C.
The colonies formed after the culture for 12 to 96 hours were counted, and the number of bacteria per 1 g of the sample was calculated.

The results shown in Table 4 were obtained.

[0038]

[Table 4]

Sterilization of Escherichia coli did not require doses above 5 kGy and could be killed by slightly increasing the dose as the water content increased. In other words, a sample with a high moisture content (30%) and a sample with a moisture content lower than the second inflection point (25%) must have high absorption to achieve the same bactericidal effect as would occur with a low dose of irradiation. It was recognized that irradiation treatment was necessary at the dose. In addition, as a result of seeking decimal attenuation dose D ₁₀ value for each sample, the moisture content
10% and 20% of the samples, whereas the 0.3 Both ₁₀ value D of 30% of the sample moisture content was 1.0.

B. Bactericidal effect on Bacillus cereus Bacillus cereus was isolated from a commercial salad and api5
It was identified using 0CHRB (manufactured by Nippon BioMerieux Biotech). Samples were prepared as in A above,
Electron beam irradiation was performed at six absorption dose levels of 2, 3, 4, 5, and 10 kGy. NGKG agar medium was used for the measurement of the number of bacteria.

The results shown in Table 5 were obtained.

[0042]

[Table 5]

The Bacillus cereus number in the sample decreased with decreasing water content at each absorbed dose, and at the same moisture content, tended to decrease with increasing absorbed dose. Water content 10%, 20%, D ₁₀ value of 30% of the sample,
They were 0.75, 1.5, and 12.0, respectively. Also, the water content
A 10% sample can be sterilized at 5 kGy, but a sample with a water content of 30% can hardly be sterilized even at a medium dose of 10 kGy, and above the second inflection point (25%), the free water increases. The effectiveness of the disinfection declined sharply.

C. Bactericidal effect on Bacillus subtilis Using Bacillus subtilis IFO3134, samples prepared in the same manner as in A above were used to prepare 1, 2, 3, 4, 5, and 10 kGy of 6
Electron beam irradiation was performed at the step absorption dose. For the measurement of the number of bacteria, tryptosome agar medium (manufactured by Nissui) was used.

The results shown in Table 6 were obtained.

[0046]

[Table 6]

Like Escherichia coli and Bacillus cereus, Bacillus subtilis tends to die with a decrease in water content or an increase in absorbed dose. At a water content of 10%, an absorption dose of 3 kGy is observed. A bactericidal effect was observed. Water content Each D ₁₀ value samples 10, 20 and 30%, 0.3, 0.7, was 2.4. These results demonstrate that the lower the water content, the more sterilized the sample can be with a lower absorbed dose, and that the second inflection point can be used as a basis for adjusting the water content.

[0048]

According to the method of the present invention, the microorganisms contaminating the material can be sterilized by adjusting the water content of the solid material to a certain amount or less and then irradiating the material with an electron beam. In particular, the moisture content of the material is below the second inflection point,
Preferably, by adjusting the water content to be equal to or less than the water content of single molecule adsorption, microorganisms such as spore-forming bacteria can be effectively killed at a low dose. In addition, there is no change in the functional characteristics of the material between the material sterilized in this way and the product containing the material. Since the electron beam can be used industrially at low cost and its irradiation technology has been established, a large amount of solid material can be sterilized by a simple operation according to the method of the present invention.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Setsuko Suzuki 4-10-1, Namiki, Tsukuba City, Ibaraki Prefecture 904 Building 301 301 (72) Inventor Mikio Tada 1-31-1, Tsushimanaka 102-1, Okayama City, Okayama Prefecture (72) Inventor Kazuyuki Sakagami 5-14-12 Higashi Tokiwadai, Toyono-cho, Toyono-gun, Osaka (72) Inventor Yoshihiko Tsuda 288-7 Mizonokuchi, Kakogawa-cho, Kakogawa-shi, Hyogo F-term (reference) 4B021 LA24 LA32 LA32 LP10 LW09

Claims (8)

[Claims] 1. A method for sterilizing a solid material comprising adjusting a water content of a solid material containing protein or carbohydrate as a main component to be equal to or lower than a second inflection point, and then irradiating the material with an electron beam. . 2. The method according to claim 1, wherein the water content of the raw material is adjusted to be equal to or lower than the water content of monomolecular adsorption. 3. The method according to claim 1, wherein the material is selected from the group consisting of corn starch, gluten meal, potato starch, potato protein, wheat starch and gluten. 4. The method according to claim 1, wherein the microorganism to be killed is a spore-forming bacterium. 5. An electron beam used through an electron beam accelerator with an acceleration voltage in the range of 50 keV to 10 MeV.
The method according to any one of Items 1 to 4, wherein 6. An electron beam having a dose rate of 1.0 × 10 ^{5 to} 1.0 × 10 ⁹ Gy /
The method according to any one of claims 1 to 5, wherein the irradiation is performed in the range of hr. 7. A solid material treated by the method according to claim 1. 8. A product obtained from the material according to claim 7.