BACTERICIDE AND METHOD OF RETAINING FRESHNESS OF FOOD

Abstract: A bactericide prepared by firing oyster shells at 600 to 1,200 °C. When applied to food to which harmful microbes adhere, it can inhibit the growth of the microbes or kill them, thus protecting the food from the microbes.

Description: The present invention relates to an antimicrobial agent and to its use in a method for sustaining the degree of freshness of food. Fungi may appear in various kinds of food and industrial products such as paints, paste, and so on. Once the fungi appear in the food and the industrial products, the commercial value of the goods is damaged to a great extent and they have to be thrown away in many cases. Even if the fungi does not appear, the growth or the propagation of hazardous microorganisms may damage the commercial value of the goods to a remarkable extent and cause the goods to be thrown away in some cases. Further, the growth or the propagation of such microorganisms in food may cause food poisoning. Heretofore, as antimicrobial agents superior in safety with respect to the human body and applicable to food, ethanol, an hypochlorite, and an allylisothiocyanate are mainly employed. However, ethanol is an inflammable liquid so that the requirement for caution in handling is a weak point. The hypochlorite has the defect that it generates an unpleasant odor derived from chlorine. The allylisothiocyanate presents the defects that it is decomposed in water generating a malodorous smell and it is strongly irritating as well. It therefore would be desirable to provide an antimicrobial agent which is highly safe with respect to the human body, which is easy to handle, and which does not generate any unpleasant odor. It is known that calcium oxide obtained by calcining shells, such as oyster shells, can be used to preserve foodstuff of various kinds. See: Database WPI, Week 7394, 1979, Abstract No. 79-62113B; Pat. Abst. Jap. Vol. 443, No. 14, (C-762), 1990; Chem. Abstr. Vol. 114, No. 22, 1991, Abstr. No. 209942; Pat. Abstr. Jap., Vol. 184, No. 8, 1984, Abstract No. 840823; and Chem. Abstr. Vol. 95, No. 20, 1981, Abstr. No. 175778y. It is also known that the shelf-life of vegetables can be prolonged by treatment with an aqueous solution of calcium hydroxide formed by hydrating calcium oxide obtained by calcining shells. See Pat. Abstr. Jap., Vol. No. 159, No. 11, 1987, Abstract No. 870522. In accordance with the present invention there is provided an antimicrobial agent comprising a mixture of (a) a calcined product of a calcium oxide type, prepared by calcining shells of an oyster, and (b) a hydrated product of a calcium hydroxide type prepared by calcining shells of an oyster and then hydrating the calcined product, wherein the weight ratio of (a) to (b) is from 3 to 7 to 7 to 3. The present invention also provides a process for the preparation of an antimicrobial agent, comprising the step of mixing (a) a calcined product of a calcium oxide type prepared by calcining shells of an oyster, with (b) a hydrated product of a calcium hydroxide type prepared by calcining shells of an oyster and then hydrating the calcined product, in a weight ratio of (a) to (b) of from 3 to 7 to 7 to 3. Further, the present invention provides a method for sustaining the freshness of food, comprising treating the food with an antimicrobial agent as defined above. It is to be noted herein that the term "antimicrobial action" and its related terms are intended to encompass both a germicidal action and a germistatic action. Further, the term "germ" and its related terms are intended to encompass bacteria, fungi, spores thereof, algae and other hazardous microorganisms. The first essential component of the antimicrobial agent according to the present invention is a calcined product of the shells of an oyster or Ostracea. More specifically, the oyster may include, for example, Ostrea, Crassostrea, Sexostrea, and so on. The calcined product may be prepared by calcining the shells of the oyster at high temperatures of approximately 600° C or higher, preferably in the range of from 900° C to 1,200° C. As the atmosphere in which the shells of the oyster are calcined, air is usually employed; however, an inert gas such as nitrogen or argon may be employed. The time of calcination may range usually from 15 minutes to 60 minutes, preferably from 20 minutes to 45 minutes. The calcination may be carried out preferably by generating heat (Joule's heat) upon application of electric current to the shells of the oyster employed as resistor and then calcining the shells of the oyster with the heat generated. The calcination of the shells of the oyster in the manner as described hereinabove causes organic materials of the shells of the oyster to be thermally decomposed and then removed, thereby giving a product of white or grayish white color. The calcined product is then divided into fine powders having a desired range of grain sizes. The calcined product contains calcium oxide as a major ingredient in the range of from 60% to 80% by weight, preferably from 65% to 75% by weight, when translated into Ca, and, as minor ingredients, magnesium in the range of from 3,000 to 6,000 wtppm, preferably from 3,500 to 5,500 wtppm; iron in the range of from 350 to 650 wtppm, preferably from 400 to 600 wtppm; phosphorus in the range of from 100 to 300 wtppm, preferably from 150 to 250 wtppm; potassium in the range of from 40 to 150 wtppm, preferably from 50 to 100 wtppm; sodium in the range of from 0.5 to 10 wtppm, preferably from 1 to 5 wtppm; and heavy metals in the range of from 0.5 to 5 wtppm, preferably from 1 to 3 wtppm. The pH of a saturated aqueous solution of the calcined product may be in the range of from approximately 12 to 13. The calcined product of calcium oxide type used according to the present invention preferably consists of powder having an average particle size of 74 µm (200 mesh) or smaller, more preferably 43 µm (325 mesh) or smaller. If the calcined product of calcium oxide type is treated by having water absorbed in at least a portion thereof, the resulting hydrate contains calcium hydroxide as a major ingredient. Such a hydrated product of calcium hydroxide type constitutes the second essential component of the antimicrobial mixture of the present invention. Thus, in accordance with the present invention, it is found that as the calcined product of the calcium oxide type alone is so high in alkalinity and highly hygroscopic, it is poor to handle. However, this problem can be solved by admixing the calcined product of the calcium oxide type with the calcined product of the calcium hydroxide type. The ratio of the weight of the calcined product of the calcium oxide type to the weight of the calcined product of the calcium hydroxide type ranges from 3 to 7 to 7 to 3, preferably from 4 to 6 to 6 to 4. It is also advantageous to use a calcined product prepared by calcination at lower temperatures in the range of from 600° to 900°C, preferably from approximately 750° to 850°C in combination with a calcined product prepared by calcination at higher temperatures in the range of from 900° to 1200°C, preferably from 1000° to 1150°C. It can be noted herein that the calcined products calcined at the lower temperatures and the calcined products calcined at the higher temperatures are different in properties to a considerable extent from each other. For instance, the calcined products calcined at the lower temperatures are lower in alkalinity than the calcined products calcined at the higher temperatures and superior in handling to the latter. Hence, the mixture of the former with the latter can provide products superior in handling. The ratio of the weight of the calcined product calcined at the lower temperatures to the calcined product calcined at the higher temperatures may be in the range of from 3 to 7 to 7 to 3, preferably from 4 to 6 to 6 to 4. The antimicrobial agent according to the present invention may additionally contain, as a filler, an additive harmless to food and the human body. The additive may include, for example, powders of inorganic compounds, such as silica, alumina, magnesia, calcium oxide, a hydrate thereof, magnesium carbonate, calcium carbonate, and so on. Further, it is possible to add finely divided oyster shells of the calcium carbonate type prepared by pulverizing the dry shells of the oyster. The rate of the additive may range from approximately 10 parts to 400 parts by weight, preferably from approximately 50 parts to 200 parts by weight with respect to 100 parts by weight of the antimicrobial agent according to the present invention. The antimicrobial agent according to the present invention demonstrates an excellent antimicrobial action. Until now the reasons for this high antimicrobial action are not yet clarified, although it is considered that some minute metallic ingredients contained in the shells of the oyster may exert some influence upon imparting the antimicrobial action. The antimicrobial agent according to the present invention may be employed in the form of powders, an aqueous solution or an aqueous dispersion. Further, the antimicrobial agent according to the present invention may be employed advantageously as an antimicrobial agent for food, for industrial uses, and for medicinal uses. In particular, the antimicrobial agent according to the present invention may be used advantageously as an agent for sustaining the degree of freshness of food. To this end, the antimicrobial agent may be admixed with and dispersed in the food or brought into contact with the food in the form of an aqueous solution or an aqueous dispersion. The aqueous solution and the aqueous dispersion may contain, as needed or as requested, an appropriate quantity of an alcohol, such as ethanol, isopropyl alcohol, glycerin, polyethylene glycol, propylene glycol, sugar alcohol, and so on. When the antimicrobial agent according to the present invention is employed in the form of an aqueous solution or aqueous dispersion, each being prepared by adding water to the antimicrobial agent mixture, the concentration of the antimicrobial agent in the aqueous solution or the aqueous dispersion is usually 0.01% by weight or more, preferably 0.1% by weight or more. The upper limit of the concentration of the antimicrobial agent is not restricted; however, generally, the concentration thereof may be up to approximately 30% by weight or lower. It is preferred to use the antimicrobial agent mixture in the aqueous solution or the aqueous dispersion in the amount ranging usually from 0.05% to 10% by weight, preferably from 0.1% to 5% by weight. The antimicrobial agent according to the present invention may be applied to various kinds of food. The term "food" referred to herein is intended to mean any food, including processed food in a liquid or solid state, raw meat of livestock, fish, raw fish meat, raw shellfish, vegetables, edible roots, fruits, and so on. When the antimicrobial agent according to the present invention is applied to processed food in the liquid state and in the solid state, the antimicrobial agent may be admixed with and dispersed in the food in the amount ranging usually from approximately 0.05% to 10% by weight, preferably from 0.1% to 5% by weight. The antimicrobial agent in the aqueous solution or aqueous dispersion may be sprayed on the surface of the food, thereby sterilizing the hazardous microorganisms and sustaining the food at a high degree of freshness. Further, when the calcined product according to the present invention is applied to fresh food such as the meat of the livestock, fish, raw fish meat, raw shellfish, vegetables, edible roots, fruits, and so on, the antimicrobial agent may be brought into contact with the fresh food, in the form of the aqueous solution or the aqueous dispersion which may contain the antimicrobial agent in an amount in the range of from 0.05% to 10% by weight, preferably from 0.1% to 5% by weight. As the procedures for contacting the food with the antimicrobial agent, there may be included, for example, a method for immersing the fresh food in an aqueous solution or dispersion of the antimicrobial agent, or a method for spraying the food with the aqueous solution thereof or the aqueous dispersion thereof. In addition, when the antimicrobial agent according to the present invention is applied to the food immersed in an aqueous solution, for example, raw shellfish, immersed in salty water or fish egg immersed in seasonings, the antimicrobial agent may be added to the aqueous solution in an amount ranging usually from 50 wtppm to 1% by weight, preferably 100 ppm to 0.5% by weight. The antimicrobial agent according to the present invention may be employed as an antimicrobial agent for food, industrial purposes and medical use on the basis of its superior antimicrobial action. Further, the antimicrobial agent may advantageously be used for sustaining the degree of freshness of food. By applying the antimicrobial agent to the food as agent for sustaining the degree of freshness of the food, the antimicrobial agent can suppress the growth or the propagation of the hazardous microorganisms adhering to the surface of the food or sterilize them, thereby preventing the food from decaying and sustaining the food at a high degree of freshness. Experiment 1 The shells of natural Japanese oyster ( Crassosterea gigas) were calcined with Joule's heat at approximately 1100°C, and the resulting calcined product was pulverized into fine particles (350 mesh; 90% by weight or more). The fine particles were found to contain calcium oxide as a major ingredient. The result of the elemental analysis is as follows: Ca: 68% by weight; Fe: 47 mg/100 grams; Heavy metals: 2.1 wtppm; Na: 2 mg/100 grams Mg: 489 mg/100 grams; P: 10 mg/100 grams; K: 7 mg/100 grams; The pH of a saturated aqueous solution of the calcined product used in this experiment was 12.4. The following experiments illustrate the antimicrobial action of the calcined product of a calcium oxide type, and of the hydrated product of a calcium hydroxide type which are used in the antimicrobial agent of the present invention. Experiment 2 The calcined product A, prepared in Experiment 1, and agar culture media were autoclaved separately while applying heat. The composition of the agar culture medium was as follows: (Agar culture medium) Beef meat extract: 3 parts by weight Peptone: 5 parts by weight Agar: 15 parts by weight Then, the agar culture medium was mixed with and dispersed homogeneously in the calcined product A at the temperature as high as 40° to 50° C in the concentration of 0.5% by weight. The dispersion was poured into Petri dishes in the amount of approximately 20 ml per each Petri dish and allowed to solidify. The surface of the agar culture medium in the Petri dish was then coated uniformly with physiological saline containing an inoculant of germs as will be described hereinafter. The inoculating germs were as follows: (Inoculating germs) Germ I: Salmonella enteritidis Germ II: Escherichia coli Then, the Petri dish was allowed to stand at 37° C for given periods of time and the number of germs grown on the agar culture medium was counted. The results are shown in Table 1 below. ADDITIVE GERM I NO. OF GERMS (GERMS PER GRAM) INITIAL DAY 3 DAY 7 CALCINED PRODUCT A 2.5 x 10 4 0.1 12 NONE 2.5 x 10 4 >10 5 - ADDITIVE GERM II NO. OF GERMS (GERMS PER GRAM) INITIAL DAY 3 DAY 7 CALCINED PRODUCT A 4.0 x 10 4 0.1 14 NONE 4.0 x 10 4 >10 8 - Experiment 3 Tests were carried out with inoculants of germs as will be described in Table 2 below in substantially the same manner as in Experiment 2 by varying the amount of the calcined product A as well as the incubation temperatures and periods of time. In Test (i), the culture medium was incubated at 10° C for 2 weeks; and, in Test (ii), the culture medium was incubated at 37° C for 48 hours. After the completion of the tests, the number of living germs grown on the culture medium was counted. Further, the minimum inhibitory concentrations (MICs) of the calcined product A against the germs as will be described in Table 2 below were computed on the basis of the number of the living germs counted. The results are also shown in Table 2 below. INOCULATING GERMS MIC (% BY WEIGHT) TEST (i) TEST (ii) Salmonella typhimurium 0.25 0.1 Salmonella enteritides 0.25 0.1 Escherichia coli 0.25 0.1 Staphylococcus aureus 0.15 0.1 Bacillus subtilis 0.15 0.1 Experiment 4 The powders of the calcined product A (0.5 gram or 0.5 gram), prepared in Experiment 1, were added to shucked oyster immersed in water (wet weight of the shucked oyster: 700 grams; water: 300 grams), thereby giving a dispersion which in turn was packed in a vinyl chloride package bag. As a comparison, the shucked oyster immersed in water containing no calcined product was packed in a vinyl chloride package bag in the same manner as described hereinabove. The package bags were held at the temperature of 10° C or lower for given periods of time. The standard plate counts were measured at day 0, week 1, and week 2 in accordance with standard procedures for testing food. The results are shown in Table 3 below. AMOUNT OF CALCINED PRODUCT A (grams per kg) STANDARD PLATE COUNT (COUNTS PER GRAM) DAY 0 WEEK 1 WEEK 2 NOT ADDED 1.9 x 10 4 4.9 x 10 4 1.5 x 10 9 0.2 3.1 x 10 3 2.2 x 10 3 9.0 x 10 3 0.5 1.3 x 10 3 2.0 x 10 3 6.0 x 10 3 Experiment 5 The procedures were followed in substantially the same manner as in Experiment 4, except for the use of 1,000 grams of noodle containing sea weeds in place of the dispersion of the shucked oyster in water. The results are shown in Table 5 below. AMOUNT OF CALCINED PRODUCT A (grams per kg) STANDARD PLATE COUNT (COUNTS PER GRAM) DAY 0 WEEK 1 WEEK 2 NOT ADDED 1.3 x 10 6 1.9 x 10 7 1.1 x 10 8 0.2 2.2 x 10 3 6.0 x 10 3 1.5 x 10 4 0.5 1.6 x 10 3 4.2 x 10 3 6.7 x 10 3 Experiment 6 Japanese-style noodles, buckwheat vermicelli noodles, and Chinese-style noodles were prepared by using 10 kg of wheat flour with 30 grams of the calcined product A added thereto. These products were then tested for measuring the degree of freshness. As a control, the products were used which were prepared in the same manner as described hereinabove, except for the addition of no calcined product. For the tests, the test samples were packed in vinyl chloride package bags and allowed to stand at 10° C or lower for given periods of time as will be described hereinafter. The results are shown in Table 6 below. In the Table 6, noodle A stands for Japanese-style noodles not boiled; noodle B for Japanese-style noodles boiled; soba A for buckwheat vermicelli noodles not boiled; soba B for buckwheat vermicelli noodles boiled; and Chinese noodles for Chinese-style noodles not boiled. SAMPLE AMOUNT OF CALCINED PRODUCT A (grams per 10 kg) STANDARD PLATE COUNT (COUNTS PER GRAM) DAY 1 DAY 3 DAY 6 NOODLE A NONE 6.7 x 10 5 5.4 x 10 6 1.5 x 10 8 NOODLE B NONE 1.2 x 10 5 8.6 x 10 6 4.9 x 10 8 NOODLE A 30 1.5 x 10 4 2.8 x 10 4 4.3 x 10 4 NOODLE B 30 1.6 x 10 3 7.6 x 10 5 1.8 x 10 7 SOBA A NONE 3.4 x 10 6 9.3 x 10 6 1.3 x 10 8 SOBA B NONE 1.3 x 10 5 1.9 x 10 5 9.0 x 10 8 SOBA A 30 2.3 x 10 4 4.3 x 10 5 3.5 x 10 6 SOBA B 30 4.2 x 10 3 -- 1.1 x 10 5 CHINESE NOODLES NONE 5.4 x 10 4 6.8 x 10 4 3.6 x 10 5 CHINESE NOODLES 30 6.0 x 10 2 4.2 x 10 3 5.7 x 10 4 Experiment 7 To vanilla ice creams was added the calcined product A at the rate of 0.1% by weight, and the ice creams were allowed to stand at 0° C or below for 10 days. After the storage for 10 days, the standard plate count indicated 300 germs per gram or lower. For comparative purposes, vanilla ice creams with no calcined product added thereto were stored under the same conditions as described hereinabove. The standard plate count indicated 830 germs per gram. Experiment 8 A cucumber was washed with water without cutting and immersed for 2 hours at room temperature in an aqueous solution containing the calcined product A at the rate of 0.5% by weight. The cucumber was then tested for the standard plate count. The number of the germs was 2.7 x 10 3 germs per gram. For comparative purposes, a cucumber was washed with water without cutting and immersed for 2 hours at room temperature in an aqueous solution containing no calcined product. The cucumber was then tested for the standard plate count. The number of the germs was 1.6 x 10 6 germs per gram. Experiment 9 A cut cabbage was washed with water and immersed for 2 hours at room temperature in an aqueous solution containing the calcined product A at the rate of 0.5% by weight. The cucumber was then tested for the standard plate count. The number of the germs was 9.8 x 10 3 germs per gram. For comparative purposes, a cut cabbage was washed with water without cutting and immersed for 2 hours at room temperature in an aqueous solution containing no calcined product. The cucumber was then tested for the standard plate count. The number of the germs was 1.1 x 10 6 germs per gram. Experiment 10 To a raw egg was added the calcined product A at the rate of 0.2% by weight, and the egg was scrambled. The scrambled eggs were then allowed to stand at 5° C for 7 days and tested for the standard plate count. As a result, it was found that they contained the germs at the rate of 100 counts per gram or lower. It is thus confirmed that the addition of the calcined product A allows the scrambled eggs to be stored at a high degree of freshness. Experiment 11 A cuttlefish was stored at 5° C for 7 days in an aqueous solution containing the calcined product A at the rate of 0.2% by weight and then tested for the standard plate count. As a result, it was found that it contained the germs at the rate of 30 counts per gram or lower. On the other hand, for comparative purposes, a cuttlefish was stored at 5° C for 7 days in water containing no calcined product A. As a result, it was found that it contained the germs at the rate of 1.2 x 10 8 counts per gram or lower. Experiment 12 An edible jellyfish with germs at the rate of 100 counts per gram or lower was immersed in an aqueous solution containing the calcined product A at the rate of 0.2% by weight and stored at 5° C for 7 days. As a result, it was found that it contained the germs at the rate of 100 counts per gram or lower, when measured for the standard plate count. It is thus confirmed that the fresh jellyfish was stored at a high degree of freshness.

Claims: An antimicrobial agent comprising a mixture of (a) a calcined product of a calcium oxide type prepared by calcining shells of an oyster, and (b) a hydrated product of a calcium hydroxide type prepared by calcining shells of an oyster and then hydrating the calcined product, wherein the weight ratio of (a) to (b) is from 3 to 7 to 7 to 3. An antimicrobial agent as claimed in Claim 1, wherein the weight ratio of (a) to (b) is from 4 to 6 to 6 to 4. An antimicrobial agent as claimed in Claim 1 or Claim 2, wherein said calcined product (a) is a mixture of shells of oyster calcined at from 600° to 900°C and of shells of oyster calcined at 900° to 1200°C. An antimicrobial agent as claimed in any preceding claim, wherein both said calcined product (a) and said hydrated product (b) has an average particle size of 74 µm or smaller. A process for the preparation of an antimicrobial agent, comprising the step of mixing (a) a calcined product of a calcium oxide type prepared by calcining shells of an oyster, with (b) a hydrated product of a calcium hydroxide type prepared by calcining shells of an oyster and then hydrating the calcined product, in a weight ratio of (a) to (b) of from 3 to 7 to 7 to 3. A process as claimed in Claim 5, wherein both said calcined product (a) and said hydrated product (b) has an average particle size of 74 µm or smaller. A method for sustaining the freshness of food, comprising treating the food with an antimicrobial agent according to any preceding claim. A method as claimed in Claim 7, wherein said antimicrobial agent is admixed with the food. A method as claimed in Claim 7, wherein the food is brought into contact with an aqueous solution or dispersion of said antimicrobial agent.

Inventors: ISHIJIMA ICHIRO, ISHIJIMA, ICHIRO, ISHIJIMA, ICHIRO 32-29, EBISUNISHI 1-CHOME
Applicants: KAIHO CO LTD, KAIHO CO., LTD.
Application year: 1992
Main classification: A01N61
IPC codes: A23B7, A23L3, A01N63