Fermented foods obtained by allowing microorganisms to act on foods have been eaten since old times. Yogurt, which is a typical fermented food, is obtained by allowing lactic bacteria, bifidobacteria or the like (hereinafter, unless otherwise indicated, they are collectively abbreviated as “lactic bacteria”) to act on milk. When yogurt is ingested, lactic bacteria are delivered to the intestines, act actively in the intestines and actively improve intestinal disorders. However, since most of lactic bacteria die in the stomach due to their strong acidity, only a few living lactic bacteria can reach the intestine.
In order to solve this problem, it has been attempted to include lactic bacteria in an enteric capsule to deliver the lactic bacteria to the intestines (for example, Japanese Laid-Open Patent Publication No. 8-242763). However, the lactic bacteria included in the capsule are freeze-dried and it takes a long time until the freeze-dried lactic bacteria absorb water and exhibit their activities again.
If living cells can be delivered to the intestines, the living cell can exhibit their activities immediately and sufficiently. Therefore, there is a demand for a technique for delivering living cells to the intestines.
On the other hand, the remarkable advance of biotechnology has affected various fields such as development of pharmaceuticals or improvement of plants. In the field of plants, there have been attempts to produce artificial seeds from redifferentiable plant cell tissues (hereinafter, referred to simply as “cell tissues”). In general, to produce artificial seeds, at first, cell tissues are dispersed or suspended in a solution of polysaccharides, low molecular weight of polymeric substance or crosslinkable polymer. Then this dispersion or suspension is gelled so that the cell tissues are enclosed in gels, followed by being molded into a form of a bead, a plate, a bar or a fiber.
However, the artificial seeds in which cell tissues are enclosed in gels as described above have no tolerance with respect to dryness when left at a room temperature. Therefore, such artificial seeds have to be sown within four days after they are prepared. In addition, these artificial seeds cannot be stored even for one month, unless they are not stored in a refrigerator or a liquid in order to prevent them from being dried. Thus it is difficult to store them in a dry place, such as a barn of a farmer or a storehouse, without a special refrigerating facility.
In order to improve this dryness problem, it has been attempted to cover the surface of the gels with paraffin, wax or the like. It is possible to improve the storage stability by covering the surface of the gels. However, since paraffin or wax is stable and is hardly degraded, the artificial seeds covered with paraffin or wax cannot germinate when they are sown in soil. Therefore, it is necessary to make an opening for each artificial seed when sowing, which is inconvenient. Thus such artificial seeds cannot be used practically.
As described above, there is a demand for a technique to enclose living cells and grow the living cells. Such technique can be applied not only in a field of food chemistry, but also to a wide range of fields, for example, pharmaceutical or agricultural field. In particular, in the field of the artificial seeds, there is a demand for artificial seeds that can be stored for at least three months in a dry place without a special refrigerating facility, and can germinate in a few days when being sown in soil. If such artificial seeds can be obtained, this technique can actually be applied to a wide range of fields, for example, agriculture, forestry, horticulture and floriculture, in combination with a technique for cultivating plant cell tissues, a cloning technique or a virus-free technique.