Vegetable seeds sterilizing method

Abstract: Sprouted vegetable seeds before rearing are sterilized so as to grow without being putrefied and to be harvested without sticking of food poisoning germs. Sprouted vegetable seeds are first pre-soaked (1) in water of 5 to 25°C for 30 to 60 minutes, then pre-heated (2) at 40 to 80°C for 10 to 30 seconds, exposed (3) to 70 to 90°C for 10 to 120 seconds for sterilization and cooled (4) at 15 to 25°C.

Description: The present invention relates generally to a sprouted vegetable seeds sterilizing method and more particularly to a sterilizing method for destroying bacteria existing on raw material seeds in the process of cultivating sprouted vegetables, for example various kinds of sprouts such as black mung bean sprouts, mung bean sprouts, soybean sprouts or alfalfa sprouts, and KAIWARE radish or the like, said bacteria including not only microorganisms breeding during the cultivation of the sprouted vegetables to damage their growth or to putrefy them but also germs, such as food poisoning germs to cause food poisoning when the sprouted vegetables after harvested are eaten, or the like. It is to be noted flat the term "sprouted vegetable seeds as used in the present description has the meaning of vegetable seeds to be sprouted. In cultivating the sprouted vegetables wherein seeds of various kinds of sprouts are sprouted to grow slightly to be good for eating, it is important to promote their rearing while restraining breeding of harmful bacteria. Also, as these sprouted vegetables are often eaten fresh or half-cooked, it is needed to make lessened various kinds of microorganisms or germs, such as food poisoning germs, sticking to the sprouted vegetables as harvested. Especially, while the sprouted vegetables are cultivated at a temperature and humidity suitable for their sprouting and growth, such rearing environment is also an environment suitable for breeding of various kinds of microorganisms or germs. Hence, in rearing the sprouted vegetables, it is important to ensure such condition that the microorganisms, even in a small quantity, sticking to the seeds of the sprouted vegetables are removed sufficiently. In terms of poisoning from eating of alfalfa sprouts or the like, it is known that microorganisms or germs coming from their raw material seeds relate thereto. These microorganisms or germs are considered to come from contamination by excrement of wild animals at farms where the seeds are harvested or by small animals, such as rats, while the seeds are stored. There are often seen accidents of poisoning from eating of alfalfa sprouts in countries of America and Europe and countermeasures therefor are being seeked variously. As seeds of the alfalfa sprouts are harvested by machinery and their shells are weak comparatively to be broken easily, even in a case of contamination by disease germs from outside, it is considered that interiors of the seeds are contaminated and in this case, there is a possibility that the contamination has come up to inside of the shells or embryos of the seeds. Conventionally, sterilization of the seeds has been done in such way that chemicals of hypochloric acid or the like are used or the seeds are dipped in a hot water of about 60 to 70°C for a few minutes. However, there have been some cases where the effect of the sterilization is not obtained sufficiently even by use of a high concentration hypochloric acid and this is considered because the contamination has spread to the interiors of the seeds, as mentioned above. It is difficult to destroy microorganisms or germs without damaging life activities of the seeds to sprout and grow as a living thing and in addition, it is not permitted to use strong chemicals because sprouted vegetables are foods which are often eaten fresh or half-cooked. Under the mentioned circumstances, the present applicant has heretofore disclosed a new method in the Japanese laid-open patent application No. Hei 6-261634 to perform a sterilization effectively of microorganisms or germs existing on outer surfaces or inner surfaces of outer shells of the sprouted vegetable seeds by bringing all the seeds into contact uniformly for a controlled time with a high temperature adjusted to such a temperature condition as not to damage living powers of the seeds. However, in the case of the seeds having damages on their shells (damaged seeds) as mentioned above, there is found a problem that a sterilization cannot be done sufficiently even if they are treated by a sufficient thermal treatment condition. US-A-5 615 518 discloses a sterilizing method, wherein seeds are exposed to temperatures of 70 to 90 °C for about 10 to 90 seconds. There is no description of any pre-soaking step before the high temperature sterilizing treatment. Though there is a description about the soaking comprising dipping vegetables in warm (30° - 40°C) water, this soaking step is not a step for a sterilization process but a step for a cultivating process of vegetable seeds. GB-A-2 320 883 discloses a soaking process which is to reduce oligosaccharide contents, noxious base metals and substances causing discoloration. This soaking step is employed as one step in a canning operation for preserving soya beans. The soaking is done by using a specific liquor containing chloride, carbonates or bicarbonate and optional cheating agents. The soaking time is 70 - 110 minutes at 70 - 80°C or 6 - 8 hours at 4 -12°C. DE 21 54 528 A discloses a heat treatment which is for the elimination of bacteria from sprouted grain. The heat treatment, i.e. the sterilization, is done by heating up to 85°C for an hour. The object to be sterilized is sprouted grain and not grain to be sprouted. There is a description about a soaking step for germinating the grain. In view of the problem in the prior art, it is the object of the present invention to provide a vegetable seeds sterilizing method by which the above-mentioned vegetable seeds sterilization disclosed by the present applicant can be done effectively and also especially food poisoning germs can be destroyed. This object is solved by a vegetable seeds sterilizing method according to claim 1. Based on the fact that even if an accurate thermal sterilization has been done for the sprouted vegetable seeds, food poisoning germs have not been destroyed completely, the inventors here have pursued the cause therefor and found that according to a lot of raw material seeds, the shells are largely damaged so that the food poisoning germs encroach up to interiors of the seeds and this is the reason why the thermal sterilization has been insufficient. Thus, in order to destroy the food poisoning germs which have encroached up to insides of the shells, the present invention provides a sprouted vegetable seeds sterilizing method comprising steps of; pre-soaking the sprouted vegetable seeds in water; then pre-heating them; then exposing them to a high temperature of 70 to 90°C for 9 to 120 seconds for sterilization; and cooling them. In the sprouted vegetable seeds sterilizing method of the present invention, the pre-soaking which is to be done before the thermal sterilizing treatment is needed to be carried out at a temperature which is as low as possible in order not to damage embryos in the subsequent thermal sterilizing treatment and also to be carried out in an accurate and suitable temperature and time in order to make the sterilization in the high temperature sterilizing treatment effective. In terms of the temperature and time of the pre-soaking, there are optimum values thereof according to the kinds of the sprouted vegetable seeds and the place and year of harvest thereof and while being needed to be selected suitable, the pre-soaking is generally in the range of 30 to 60 minutes at a temperature of 5 to 25°C. The accurate pre-soaking can be judged by measuring a water absorption of the seeds after soaking them in water. Also, in the sprouted vegetable seeds sterilizing method of the present invention, while the temperature and time of the pre-heating are needed to be selected according to the sprouted vegetable seeds, the pre-heating is generally in the range of 9 to 30 seconds at a temperature of 40 to 80°C. The temperature and time of the high temperature sterilizing treatment are also needed to be selected suitably according to the sprouted vegetable seeds but the high temperature sterilizing treatment is generally in the range of 9 to 120 seconds at a temperature of 70 to 90°C. Also, as to the temperature and time of the cooling, they are needed to be selected according to the sprouted vegetable seeds and it is effective to do the cooling immediately after the high temperature sterilizing treatment at temperature of 15 to 25°C generally. In the pre-soaking of the present invention, it is possible to add a low concentration sterilizing agent of hypochloric acid, chlorine, ethanol or the like or to use an ozone water. Also, in the cooling treatment after the high temperature sterilization, it is effective to enhance the sterilizing effect further by using a hypochloric acid water solution or ozone water. In the thermal sterilizing treatment method according to the present invention, as mentioned above, the sprouted vegetable seeds are pre-soaked in water so that the shells are swollen to improve the heat transfer to the shell interiors and also to remove bubbles existing between the shells and the embryos, thereby the heat of the subsequent high temperature treatment encroaches from damaged portions of the shells and the food poisoning germs existing inside of the shells can be destroyed efficiently by the heat. Also, the low temperature water is used in the pre-soaking, thereby a damage which the embryos may receive in the subsequent high temperature treatment can be mitigated and lowering of a sprouting rate due to the high temperature treatment can be suppressed. In the thermal sterilizing treatment method according to the present invention as mentioned above, as the sprouted vegetable seeds are treated by the pre-soaking and then by the thermal sterilization, the sprouted vegetable seeds which have been swollen by the pre-soaking become in the state where the outside heat is easy to transfer therein and the thermal sterilizing treatment to be then carried out can be perfected uniformly to the entire interiors of the sprouted vegetable seeds as well as the damage which the embryos may receive in the subsequent high temperature treatment can be mitigated. Thus, according to the sterilizing method of the present invention, the thermal sterilizing treatment before rearing the seeds is perfected so that the seeds are reared in an almost completely sterilized state, hence there occurs no case of the microorganisms breeding to obstruct a normal rearing of the sprouted vegetables or to putrefy them and also there is no case of the food poisoning germs sticking to the sprouted vegetables as harvested, thereby the sprouted vegetables can be served safely for eating. BRIEF DESCRIPTION OF THE DRAWING: Fig. 1 is a block diagram showing an embodiment of a sprouted vegetable seeds sterilizing method according to the present invention. Herebelow, an embodiment of a sprouted vegetable seeds sterilizing method according to the present invention will be described concretely with reference to Fig. 1. In Fig. 1, numeral 1 designates a pre-soaking step, in which sprouted vegetable seeds, for example alfalfa seeds, are soaked in water of a temperature of 5 to 25°C for 30 to 60 minutes. Numeral 2 designates a pre-heating step, in which the sprouted vegetable seeds after the pre-soaking step 1 are dipped in a warm water, which is kept in a temperature of 40 to 80°C for example, for 9 to 30 seconds. Numeral 3 designates a high temperature sterilizing step, in which the sprouted vegetable seeds after the pre-heating step 2 are brought into contact with a high temperature water, which is kept in a temperature of 70 to 90°C, for 9 to 120 seconds. Numeral 4 designates a cooling step, in which the sprouted vegetable seeds after the high temperature sterilizing step 3 are dipped in water which is kept in a temperature of 15°C for example. Functions of the mentioned steps of the sterilizing method will be described. The seeds to be treated, which are dry, are first soaked in water to be swollen at the pre-soaking step 1. By the seeds to be treated being so swollen, the seeds become in the state where heat from outside is easy to transfer into interiors of the seeds uniformly as well as a thermal damage given on embryos in the next high temperature sterilizing treatment step is mitigated. The seeds to be treated after swollen at the pre-soaking step 1 are sent to the pre-heating step 2, in which the seeds are moved in the warm water or 40°C, for example, so that every piece of particles of the seeds is pre-heated uniformly. By being so pre-heated, the seeds are kept in a predetermined temperature without being influenced by the surrounding temperature, which results in enhancing an accuracy in which the seeds are kept in a predetermined temperature needed at the next high temperature sterilizing step 3. The seeds to be treated are then sent to the high temperature sterilizing step 3, where the seeds are moved in the high temperature water of a predetermined accurate temperature, which is limited narrowly, 80°C for example, so that all the particles of the seeds are kept uniformly in the predetermined accurate sterilizing temperature for a predetermined time, thereby microorganisms existing inside or outside of shells of the seeds are destroyed while the seeds remain with their living power being not damaged. Upon completion of the sterilization, the seeds to be treated are sent to the cooling step 4 to be brought into contact with a low temperature cooling water. In the cooling step 4, the seeds after sterilized by contact with the high temperature water are moved in the cooling water so that all the particles of the seeds are quenched uniformly to a temperature of 25°C or lower. The seeds so quenched are collected as sterilized seeds. It is to be noted that while in the present embodiment as illustrated, the sterilizing treatment in the high temperature sterilizing step 3 is done by use of the high temperature water, this high temperature sterilizing treatment may be done by a thermal sterilizing treatment using wet heat, other than the high temperature water, of a high temperature steam or the like or dry heat of a high temperature gas, a high temperature air or the like, as shown in the Japanese laid-open patent application No. Hei 6-261634. Also, the mentioned values of the temperature are only for examples and needless to mention, the exact temperature may be selected suitably within the scope of the present invention according to the kinds of the sprouted vegetable seeds to be treated. Actual examples of sterilization according to the present invention will be described below. (Example 1) Alfalfa seeds inoculated with food poisoning germs are heat-treated as follows. The seeds are treated in advance to be inoculated with colitis germs and are sterilized by the following hot water treatment and number of the colitis germs alive in the seeds immediately after sterilized and existence of the colitis germs in the seeds left in a peptone water for one night after sterilized are inspected. Pre-soaking: 30 minutes at 15°C, Pre-heating: 9 seconds at 70°C, High temperature treatment: 9 seconds at 85°C and Cooling: 9 seconds at 15°C. The results are shown in Table 1. While a considerable sterilizing effect is seen even only by the high temperature treatment, the colitis germs inoculated can be destroyed completely by applying the pre-soaking. Seeds treatment Number of colitis germs alive Sterilizing effect (%) Colitis germs inspection of next day Non-treatment 7800000 ..... Hot water treatment 270 99.997 ..... Hot water treatment with pre-soaking 0 100 Negative (Example 2) Lowering of sprouting rate of alfalfa seeds due to the thermal treatment is inspected. The same thermal treatment as in the Example 1 is applied to the seeds which are not inoculated with germs and the sprouting rate is as per shown in Table 2. It is observed that while both of the sprouting rate and the normal rearing rate are lowered by the thermal treatment as compared with the non-treatment case, such lowering can be mitigated by applying the pre-soaking treatment. Seeds treatment Sprouting rate (%) Normal rearing rate (%) Non-treatment 97.2 ± 1.4 91.3 ± 1.4 Hot water treatment 86.3 ± 7.4 70.7 ± 3.4 Hot water treatment with pre-soaking 89.7 ± 2.6 83.3 ± 1.7 (Example 3) Change in the sterilizing effect due to difference in the pre-soaking time is inspected. The same thermal treatment as in the Example 1 is applied, except changing the pre-soaking time, and degree of the sterilization by the high temperature treatment using the hot water is inspected and the results are shown in Table 3. As shown there, there is seen no complete effect of the soaking in the pre-soaking of 10 minutes but in the case of the pre-soaking of 30 minutes or more, a complete sterilization is realized. Pre-soaking time Number of colitis germs alive Sterilizing effect (%) Colitis germs inspection of next day 10 minutes 180 99.998 ..... 30 minutes 0 100 Negative 60 minutes 0 100 Negative (Example 4) Change in the sprouting rate according to the pre-soaking time and temperature is inspected. The same thermal treatment as in the Example 1 is applied and the sprouting rate and the normal rearing rate according to the pre-soaking time and temperature are inspected. The results are shown in Table 4. It is observed that as the pre-soaking temperature is higher and the time is more, the sprouting rate and the normal rearing rate are lower but in the pre-soaking up to 15°C and 30°C, favorable sprouting rate and normal rearing rate are realized. Pre-soaking treatment Sprouting rate (%) Normal rearing rate (%) 10 minutes at 15°C 90.7 ± 3.4 83.7 ± 3.7 30 minutes at 15°C 89.7 ± 2.6 83.3 ± 1.7 30 minutes at 25°C 80.7 ± 3.9 58.7 ± 1.4 60 minutes at 5°C 77.3 ± 8.7 68.3 ± 9.2 60 minutes at 15°C 73.3 ± 6.1 65 ± 8.6 60 minutes at 25°C 15.3 ± 3.4 7.7 ± 2.4 (Example 5) Alfalfa seeds are applied by the pre-soaking in various water temperature and time and water content of the seeds after the pre-soaking and sprouting rate after the subsequent thermal treatment are inspected, wherein the thermal treatment is done as follows; pre-heating: 9 seconds at 50°C, thermal treatment: 9 seconds at 85°C and cooling: 9 seconds at 15°C. The results are shown in Table 5. By the pre-soaking of 60 minutes at water temperature of 15°C and that of 30 minutes at 25°C, the water contents of the seeds after the pre-soaking are 122% and 117%, respectively, and the sprouting rates according to them are 75.7% and 73%, respectively. This means that even at the temperature of 25°C, a satisfactory sprouting rate in the same level as in the lower temperature of 15°C can be obtained with a shorter time. Pre-soaking treatment Seeds (%) Water temperature (°C) Time (minutes) Water content (%) Sprouting rate (%) 15 30 111 83.3 60 122 75.7 70 126 47.5 80 132 34 25 30 117 73 40 125 64.5 50 135 28.5

Claims: Vegetable seeds sterilizing method comprising the steps of: first pre-soaking said seeds in water; followed by pre-heating said seeds; followed by exposing said seeds to a high temperature for a short time for sterilization wherein said seeds are sterilized at a temperature of 70 to 90°C for 9 to 120 seconds; and followed by cooling said seeds. Vegetable seeds sterilizing method according to claim 1, characterized in effecting said pre-soaking in the water of 5 to 25°C for 30 to 60 minutes. Vegetable seeds sterilizing method according to claim 1 or 2, characterized in effecting said pre-heating from 40 to 80°C for 9 to 30 seconds by dipping said seeds in warm water. Vegetable seeds sterilizing method according to any of the preceding claims, wherein said seeds are cooled at a temperature of from 15 to 25°C.

Inventors: ENOMOTO KATSUYOSHI, KEMURIYAMA TAKAYUKI, REGLI GERMAN, ENOMOTO, KATSUYOSHI, KEMURIYAMA, TAKAYUKI, REGLI, GERMAN, Enomoto, Katsuyoshi, c/o Daisey Machinery Co., Ltd, Kemuriyama, Takayuki, c/o Daisey Machinery Co.,Ltd, Regli, German, c/o Daisey Machinery Co., Ltd.
Applicants: DAISEY MACHINERY CO LTD, DAISEY MACHINERY CO., LTD.
Application year: 2000
Main classification: A23B9
IPC codes: A23B9, A01C1