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Desiccant Patent
 

Desiccant, method for producing the same and method for using the same

Abstrict

A desiccant comprising crystalline, anhydrated nystose, which contains 70% or more of nystose and 2% or less of moisture and is in the form of a crystalline powder, is capable of maintaining water activity of a food at an extremely low level without heat drying the food or drying the food with silica gel or the like and can safely prevent deteriorations of foods and maintain the qualities at a low cost. The desiccant can be produced by anhydrating crystalline nystose hydrate under reduced pressure or in the presence of a dehydrating agent. The desiccant is used for lowering water activity of a food and maintaining the same, by directly contacting the desiccant with the food or mixing the same with the food.

Claims

What is claimed is:

1. A method for lowering the water activity of a food and maintaining the same, which comprises directly contacting a desiccant comprising crystalline, anhydrated nystose which contains 70% or more of nystose and 2% or less of moisture and is in the form of a crystalline powder, with the food or mixing the same with the food.

Description

FIELD OF THE INVENTION

This invention relates to a desiccant comprising crystalline, anhydrated nystose, a method for producing the same and a method for applying the same to foods. The desiccant of the present invention, which comprises crystalline, anhydrated nystose, is an edible one and has strong moisture absorption characteristics. Thus it is useful as a desiccant which can be directly contacted with or added to a food to thereby control the moisture content thereof.

BACKGROUND OF THE INVENTION

In general, the moisture in a food is an important factor affecting its physicochemical properties, storage life, texture and flavor. For example, physical deteriorations in shape and hardness due to the evaporation or absorption of water, microbial deteriorations due to fungi and bacteria and chemical deteriorations such as color change, fading out and oxidation of fats are serious problems in the preservation of foods. In order to cope with these problems, it is essential to control the moisture content and water activity of foods.

Namely, a food contained in a closed space has a certain vapor pressure. The ratio of this vapor pressure to the saturated vapor pressure is referred to as the water activity. In order to prevent the above-mentioned deteriorations, there have been known methods for effectively storing foods by using desiccants to thereby lower the water activity or maintain it at a constant level. A number of desiccants have been applied to foods. These desiccants are generally used by introducing into a closed container separately from a food. On the other hand, it has been required to develop edible desiccants which can be directly contacted with or added to foods and there have been proposed some materials for producing such desiccants. For example, silica gel can be directly added to foods, though the acceptable content and taste thereof restrict its addition.

On the other hand, anhydrous maltose described in JP-A-62-125854 and anhydrous raffinose described in JP-A-62-152537 are usable as edible desiccants (the term "JP-A" as used herein means an "unexamined published Japanese patent application"). However these substances are still unsatisfactory in properties relating to water activity. It is, therefore, urgently required to develop an edible desiccant of improved characteristics. Furthermore, anhydrous raffinose becomes deliquescent when absorbing water, which makes its food processing properties poor.

Regarding nystose, there have been reported crystalline nystose trihydrate obtained by recrystallizing from water/methanol [m.p.: 129.degree.-131.degree. C.; H., Tsuchida et al., Agric. Biol. Chem., 30 429-433 (1966)], crystalline nystose monohydrate obtained by recrystallizing from ethanol/methanol [m.p.: <134.degree. C.; J. P. Kamerling et al., Carbohydr. Res., 25 293-297 (1972)] and amorphous nystose anhydride obtained by heating the crystalline nystose trihydrate at a high temperature under reduced pressure [no m.p. is given; H. Tsuchida et al., Agric. Biol. Chem., 30 429-433 (1966)]. However it is reported that none except the amorphous nystose anhydride shows water absorption characteristics.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a desiccant which is edible and has excellent moisture absorption characteristics.

The present inventors have conducted extensive studies in order to solve the problems observed in conventional desiccants and drying methods. As a result, they have successfully found that crystalline, anhydrated nystose has excellent moisture absorption characteristics as a desiccant. More specifically, it has been found that a desiccant comprising crystalline, anhydrated nystose obtained by dehydrating a crystalline nystose hydrate can maintain the water activity at an extremely low level while keeping its crystallinity without causing any phase transition and that it is therefore usable as a desiccant capable of controlling the moisture content of foods.

The present invention relates to a desiccant comprising crystalline, anhydrated nystose which contains 70% or more of nystose and 2% or less of moisture and being a crystalline powder, a method for producing a desiccant comprising said crystalline, anhydrated nystose which comprises anhydrating a crystalline nystose hydrate under reduced pressure, a method for producing a desiccant comprising said crystalline, anhydrated nystose which comprises anhydrating a crystalline nystose hydrate in the presence of a dehydrating agent and a method for lowering and maintaining the water activity of a food which comprises directly contacting a desiccant comprising said crystalline, anhydrated nystose with the food or mixing the same with the food.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing the relation between the absorbed moisture content and water activity of desiccants comprising crystalline, anhydrated nystose (sometimes hereinafter referred to as anhydrated nystose) (-.DELTA.-), anhydrous raffinose (-.box-solid.-) or anhydrous maltose (-.circle-solid.-).

FIG. 2 is a graph showing the water absorption curves of desiccants comprising crystalline, anhydrated nystose (-.circle-solid.-) or anhydrous maltose (-.DELTA.-) at a relative humidity of 31%.

FIG. 3 is a graph showing the water absorption curves of desiccants comprising crystalline, anhydrated nystose (-.circle-solid.-) or anhydrous maltose (-.DELTA.-) at a relative humidity of 51%.

FIG. 4 is a graph showing the water absorption curves of desiccants comprising crystalline, anhydrated nystose (-.circle-solid.-) or anhydrous maltose (-.DELTA.-) at a relative humidity of 81%.

FIG. 5 is a graph showing the water activity and the survival ratio of bifidus bacteria in a powder for tablet candy containing bifidus bacteria blended with desiccants comprising crystalline, anhydrated nystose having water activity of 0.20 (-.DELTA.-), anhydrous raffinose having water activity of 0.23 (-.box-solid.-) or a control (sucrose) having water activity of 0.28 (-.circle-solid.-) at 25.degree. C. and at a relative humidity of 65%.

FIG. 6 is a graph showing changes in the texture (hardness) of a tablet candy obtained by blending a powder for tablet candy containing bifidus bacteria with desiccants comprising crystalline, anhydrated nystose (-.DELTA.-), anhydrous raffinose (-.box-solid.-) or a control (sucrose) (-.circle-solid.-) followed by molding, which was stored at 25.degree. C. and at a relative humidity of 81%.

FIG. 7 is a graph showing the pigment-fading suppression effects of desiccants comprising crystalline, anhydrated nystose (-.diamond-solid.-) or a control (-.quadrature.-) on a colored white chocolate dough.

DETAILED DESCRIPTION OF THE INVENTION

The desiccant of the present invention comprises crystalline, anhydrated nystose which is a crystalline powder containing 70% or more of nystose and 2% or less of moisture. It has a powerful ability to absorb moisture while keeping its crystallinity and, furthermore, maintaining the water activity at an extremely low level, thus showing excellent moisture absorption characteristics. This crystalline powder may be solidified and used in the form of, for example, tablets if needed.

The desiccant comprising crystalline, anhydrated nystose can be produced by anhydrating a crystalline nystose hydrate to be used as a starting material under reduced pressure or in the presence of a dehydrating agent. Any crystalline nystose hydrate may be used as the starting crystalline nystose hydrate so long as it contains at least 70% of nystose. A preferable example thereof is a crystalline nystose hydrate of a nystose purity of about 84% or above, which is crystals in the form of columns, shows polarization when observed by polarizing microscope and has melting point of 118.degree. to 126.degree. C. Such a crystalline nystose hydrate can be obtained by (i) fractionating a fructooligosaccharide mixture by liquid chromatography to obtain a fraction rich in nystose and crystallizing nystose out of the fraction by cooling, (ii) fractionating a fructooligosaccharide mixture, which is obtained by enzymatically treating sucrose, by liquid chromatography to obtain a nystose-rich fraction, concentrating the fraction and crystallyzing nystose out of the concentrate by cooling, or (iii) subjecting nystose hydrate obtained in the above (i) or (ii) to recrystallization repeatedly from water.

The anhydration under reduced pressure can be performed under a pressure of 100 mmHg or below within a temperature range of from room temperature to 110.degree. C. for 4 to 96 hours. It is preferable to perform this treatment under a pressure of 10 mmHg or below at a temperature of from 60.degree. to 90.degree. C. for 4 to 72 hours. The anhydration in the presence of a dehydrating agent can be performed by introducing the starting material into a closed container together with a marketed inorganic dehydrating agent. As a preferable example of the dehydrating agent, phosphorus pentaoxide may be cited in an amount of 0.5 part by weight per part by weight of the starting material. The dehydration reaction can be carried out at room temperature for about 240 hours.

The desiccant comprising crystalline, anhydrated nystose is obtained as a white powder containing 2% or less of moisture. The crystals of the anhydrated nystose is in the form of columns and show polarization when observed by polarizing microscope. It is highly advantageous in being usable as an edible desiccant, since nystose per se is a sweetener harmless to man.

As the moisture absorption characteristics of this substance, the excellent ability to maintain water activity and the powerful ability to absorb water may be cited. It exerts immediate water absorption effects over a wide range of relative humidity, which makes it highly useful as a desiccant.

A method for using the desiccant of the present invention comprising crystalline, anhydrated nystose is described in detail below.

It is a serious problem in the storage of foods to suppress deteriorations in functions, texture and form due to the evaporation or absorption of water. For example, moisture content, in particular, water activity closely relate to the survival ratio of bacteria contained in tablet candies having viable bacteria, the texture (including hardness) of tablet candies, biscuits and Senbei (rice-cake), and fading out of edible pigments contained in foods. It is known that these deteriorations can be suppressed by lowering the water activity and maintaining the same at a low level.

That is to say, the commercial value of tablet candies containing bifidus bacteria depends on the survival ratio of the bifidus bacteria contained in the product. It is considered that the optimum water activity (Aw) of bifidus bacteria is about 0.1 [Toshio Tatematsu et al., Toketsu oyobi Kanso Kenkyukai-shi (Journal of Society of Freezing and Drying), 28 40-45 (1982)]. It is, therefore highly important how to maintain the water activity at the optimum level. In the prior art, it is considered necessary to strictly dry starting materials in order to elevate the survival ratio of bifidus bacteria contained in tablet candies having bifidus bacteria.

In contrast, the present invention makes it possible to achieve a lower water activity and to remarkably elevate the survival ratio of bifidus bacteria by adding an edible desiccant to the materials for producing such tablet candies. As described in Example 4 below, the water activity of a tablet candy containing a desiccant of the present invention comprising crystalline, anhydrated nystose was lowered to 0.20 while the control one showed a water activity of 0.28. After 10 weeks, the survival ratio of bifidus bacteria in the product of the invention was thrice as high as that of the control. Accordingly, the desiccant of the present invention can remarkably improve the commercial value of a product and is highly applicable to foods.

Furthermore, the texture (hardness), the form and the fading out of foods are deteriorated due to water absorption. It is therefore needed to maintain the initial qualities of the foods. When the decrease in the water activity of a food is suppressed by adding the desiccant of the present invention comprising crystalline, anhydrated nystose, the hardness of tablet candies can be maintained and the fading out of pigments contained in foods can be effectively prevented. Thus the desiccant of the present invention is widely usable.

The desiccant of the present invention, which is an edible one having powerful moisture absorption characteristics, can be directly contacted or mixed with foods under dry conditions. Accordingly, it is widely applicable to, for example, confectioneries such as tablet candies, chocolates and biscuits, powedered foods such as powdered juice, soup and seasonings, powdered milk products such as powdered cream for coffee and processed powdered milk and freeze-dried foods such as freeze-dried vegetables, fish paste and the like. The desiccant of the present invention can absorb up to 8% of moisture based on the weight thereof. The amount of the dessicant of the present invention to be added to foods can be adjusted depending on moisture content of the foods. The desiccant of the present invention may be used with other additives which do not inactivate moisture absorbent ability of the dessicant. Examples of the additives include dry starch, powdered sugar and the like.


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