US20140113350A1 - Method for killing microorganism - Google Patents

Method for killing microorganism Download PDF

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US20140113350A1
US20140113350A1 US14/119,071 US201214119071A US2014113350A1 US 20140113350 A1 US20140113350 A1 US 20140113350A1 US 201214119071 A US201214119071 A US 201214119071A US 2014113350 A1 US2014113350 A1 US 2014113350A1
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liquid
microbial cell
titer
heating treatment
carbohydrate
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Masakazu Ikeda
Tadashi Sato
Keiko Kasaha
Masahiko Ito
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Yakult Honsha Co Ltd
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Yakult Honsha Co Ltd
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Assigned to KABUSHIKI KAISHA YAKULT HONSHA reassignment KABUSHIKI KAISHA YAKULT HONSHA ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: IKEDA, MASAKAZU, ITO, MASAHIKO, KASAHA, KEIKO, SATO, TADASHI
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    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
    • C12N1/00—Microorganisms, e.g. protozoa; Compositions thereof; Processes of propagating, maintaining or preserving microorganisms or compositions thereof; Processes of preparing or isolating a composition containing a microorganism; Culture media therefor
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
    • C12N9/00—Enzymes; Proenzymes; Compositions thereof; Processes for preparing, activating, inhibiting, separating or purifying enzymes
    • C12N9/14—Hydrolases (3)
    • C12N9/24—Hydrolases (3) acting on glycosyl compounds (3.2)
    • C12N9/2402—Hydrolases (3) acting on glycosyl compounds (3.2) hydrolysing O- and S- glycosyl compounds (3.2.1)
    • C12N9/2468—Hydrolases (3) acting on glycosyl compounds (3.2) hydrolysing O- and S- glycosyl compounds (3.2.1) acting on beta-galactose-glycoside bonds, e.g. carrageenases (3.2.1.83; 3.2.1.157); beta-agarase (3.2.1.81)
    • C12N9/2471—Beta-galactosidase (3.2.1.23), i.e. exo-(1-->4)-beta-D-galactanase
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
    • C12N1/00—Microorganisms, e.g. protozoa; Compositions thereof; Processes of propagating, maintaining or preserving microorganisms or compositions thereof; Processes of preparing or isolating a composition containing a microorganism; Culture media therefor
    • C12N1/06—Lysis of microorganisms
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
    • C12N1/00—Microorganisms, e.g. protozoa; Compositions thereof; Processes of propagating, maintaining or preserving microorganisms or compositions thereof; Processes of preparing or isolating a composition containing a microorganism; Culture media therefor
    • C12N1/14—Fungi; Culture media therefor
    • C12N1/16—Yeasts; Culture media therefor
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12N—MICROORGANISMS OR ENZYMES; COMPOSITIONS THEREOF; PROPAGATING, PRESERVING, OR MAINTAINING MICROORGANISMS; MUTATION OR GENETIC ENGINEERING; CULTURE MEDIA
    • C12N9/00—Enzymes; Proenzymes; Compositions thereof; Processes for preparing, activating, inhibiting, separating or purifying enzymes
    • C12N9/14—Hydrolases (3)
    • C12N9/24—Hydrolases (3) acting on glycosyl compounds (3.2)
    • C12N9/2402—Hydrolases (3) acting on glycosyl compounds (3.2) hydrolysing O- and S- glycosyl compounds (3.2.1)
    • C12N9/2468—Hydrolases (3) acting on glycosyl compounds (3.2) hydrolysing O- and S- glycosyl compounds (3.2.1) acting on beta-galactose-glycoside bonds, e.g. carrageenases (3.2.1.83; 3.2.1.157); beta-agarase (3.2.1.81)
    • C—CHEMISTRY; METALLURGY
    • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
    • C12Y—ENZYMES
    • C12Y302/00—Hydrolases acting on glycosyl compounds, i.e. glycosylases (3.2)
    • C12Y302/01—Glycosidases, i.e. enzymes hydrolysing O- and S-glycosyl compounds (3.2.1)
    • C12Y302/01023—Beta-galactosidase (3.2.1.23), i.e. exo-(1-->4)-beta-D-galactanase

Definitions

  • the present invention relates to a method for killing a microorganism, more particularly relates to a method for killing a microorganism while maintaining the enzyme titer of a liquid of microbial cells having an enzymatic activity.
  • microorganisms that have a useful enzymatic activity, and such microorganisms are widely used in the production of functional food materials such as carbohydrates, amino acids, and phospholipids.
  • functional food materials such as carbohydrates, amino acids, and phospholipids.
  • microorganisms which can be used in the production of carbohydrate materials, particularly oligosaccharides, and for example, it has been reported that a galactooligosaccharide is produced by utilizing the ⁇ -galactosidase activity of yeast belonging to the genus Sporobolomyces singularis (PTL 1).
  • a microorganism is killed by a heating treatment and then stored etc, however, in the case where a microorganism having an enzymatic activity as described above is subjected to a heating treatment, whilst the microorganism is killed, the enzymatic activity is significantly decreased, which is practically useless.
  • a technique for killing a microorganism while maintaining the enzymatic activity there has been reported a technique for killing a microorganism while maintaining the enzymatic activity in which a transformed microorganism is treated with a chemical such as an alcohol at 25 to 35° C. (PTL 2).
  • PTL 2 a chemical such as an alcohol at 25 to 35° C.
  • this technique has a problem that the use thereof after killing the microorganism is limited because a genetically modified microorganism is used or the alcohol or the like used in the treatment for killing the microorganism remains.
  • an object of the invention is to provide a technique for enabling a liquid of microbial cells having an enzymatic activity to be easily stored and used.
  • the inventors of the present invention made intensive studies of the conditions for killing a microorganism by a heating treatment in order to solve the above problems, and as a result, they found that the microorganism can be killed while maintaining the enzyme titer by adjusting the pH before performing the heating treatment for killing the microorganism in a liquid of microbial cells having an enzymatic activity or by allowing a carbohydrate to be present when performing the heating treatment, and thus completed the invention. Further, they found that the microbial cell liquid in which the microorganism has been killed as described above maintains the enzyme titer of the microbial cell liquid before killing the microorganism, and thus completed the invention.
  • the invention is directed to a method for killing a microorganism while maintaining the enzyme titer of a microbial cell liquid, characterized by including adjusting the pH of a liquid of microbial cells having an enzymatic activity, and then performing a heating treatment of the liquid.
  • the invention is directed to a killed microbial cell liquid, characterized in that the enzyme titer of the microbial cell liquid before killing the microorganism is maintained.
  • the invention is directed to a method for killing a microorganism while maintaining the enzyme titer of a microbial cell liquid, characterized by including adding a carbohydrate to a liquid of microbial cells having an enzymatic activity, and then performing a heating treatment of the liquid.
  • the invention is directed to a killed microbial cell liquid, characterized in that a carbohydrate is contained, and the enzyme titer of the microbial cell liquid before killing the microorganism is maintained.
  • the microorganism can be killed while maintaining the enzyme titer of a liquid of microbial cells having an enzymatic activity.
  • the thermal stability of the enzyme can be increased, and the microorganism can be killed while maintaining the enzyme titer under wider temperature conditions. Therefore, the microbial cell liquid after killing the microorganism can be easily stored and used. That is, in the case where the microorganism is alive, some sort of metabolite is produced by the microorganism during storage to deteriorate the quality of the microbial cell liquid, and also the storage stability of the enzyme titer may be affected. Meanwhile, in the case where the microorganism has been killed, such a problem does not arise, and therefore, the killed microbial cell liquid has excellent storage stability with respect to the enzyme titer.
  • the killed microbial cell liquid of the invention is configured such that the microorganism has been killed in a state where the enzymatic activity is maintained, and therefore can be easily stored and used.
  • FIG. 1 is a view showing a residual titer ratio after performing a heating treatment by maintaining an Ss concentrate liquid having a lactose concentration of 2 mass/vol % at 45° C. or 50° C. for 5 hours in Example 9.
  • FIG. 2 is a view showing a residual titer ratio after performing a heating treatment by maintaining an Ss concentrate liquid having a lactose concentration of 2 mass/vol % at 45° C. or 50° C. for 18 hours in Example 9.
  • FIG. 3 is a view showing a residual titer ratio after performing a heating treatment by maintaining an Ss concentrate liquid having a lactose concentration of 5 mass/vol % at 45° C. or 50° C. for 5 hours in Example 9.
  • FIG. 4 is a view showing a residual titer ratio after performing a heating treatment by maintaining an Ss concentrate liquid having a lactose concentration of 5 mass/vol % at 45° C. or 50° C. for 18 hours in Example 9.
  • FIG. 5 is a view showing a residual titer ratio after adjusting the pH of an Ss culture solution using a sodium hydroxide solution, a potassium hydroxide solution, or a sodium carbonate solution at various concentrations in Example 11.
  • the method for killing a microorganism while maintaining the enzyme titer of a microbial cell liquid according to the invention can be performed by a method including adjusting the pH of a liquid of microbial cells having an enzymatic activity, and then, performing a heating treatment of the liquid (hereinafter referred to as “the present inventive method 1”) or a method including adding a carbohydrate to a liquid of microbial cells having an enzymatic activity, and then performing a heating treatment of the liquid (hereinafter referred to as “the present inventive method 2”).
  • the microorganism to be killed is not particularly limited as long as it is a microorganism such as a bacterium, yeast, or a fungus, and an enzyme is bound to cell walls or an enzyme is intracellularly and/or extracellularly produced, that is, it is a microorganism having an enzymatic activity.
  • microorganism having an enzymatic activity examples include bacteria belonging to the genus Streptococcus , the genus Lactobacillus , the genus Bacillus , the genus Bifidobacterium , etc.; and yeast belonging to the genus Sporobolomyces , the genus Bullera , the genus Kluyveromyces , the genus Lipomyces , the genus Candida , the genus Cryptococcus , the genus Sterigmatomyces , the genus Bensingtonia , the genus Ballistosporomyces , the genus Fellomyces , the genus Filobasidium , the genus Sirobasidium , the genus Tilletiopsis , the genus Itersonilia , the genus Tilletia , the genus Saccharomyces , the genus Schizosaccharomyces , the
  • examples of the enzyme include carbohydrate degrading enzymes such as amylase, sucrase, ⁇ -galactosidase, ⁇ -galactosidase, glucose isomerase, ⁇ -glucosidase, ⁇ -glucosidase, ⁇ -fructofuranosidase, ⁇ -mannosidase, ⁇ -mannosidase, and xylanase.
  • carbohydrate degrading enzymes such as amylase, sucrase, ⁇ -galactosidase, ⁇ -galactosidase, glucose isomerase, ⁇ -glucosidase, ⁇ -glucosidase, ⁇ -fructofuranosidase, ⁇ -mannosidase, ⁇ -mannosidase, and xylanase.
  • a microorganism having ⁇ -galactosidase activity is preferred.
  • examples of such a microorganism include yeast belonging to the genus Sporobolomyces , the genus Bullera , the genus Kluyveromyces , the genus Lipomyces , the genus Candida , the genus Cryptococcus , the genus Sterigmatomyces , the genus Bensingtonia , the genus Ballistosporomyces , the genus Fellomyces , the genus Filobasidium , the genus Sirobasidium , the genus Tilletiopsis , the genus Itersonilia , the genus Tilletia , the genus Saccharomyces , the genus Schizosaccharomyces , the genus Hansenula , the genus Rhodot
  • yeast or a bacterium is preferred, and in particular, yeast is more preferred.
  • yeast having ⁇ -galactosidase activity include particularly Sporobolomyces singularis, Sterigmatomyces elviae, Cryptococcus laurentii, Rhodotorula lactosa, Sirobasidium magnum , and Lipomyces lipofer .
  • bacterium having ⁇ -galactosidase activity include particularly Streptococcus thermophilus, Lactobacillus bulgaricus, Streptococcus lactis, Lactobacillus salivarius, Lactobacillus leichmannii, Lactobacillus helveticus, Bacillus brevis, Bacillus stearothermophilus, Bifidobacterium bifidum, Bifidobacterium breve, Bifidobacterium longum , and Bifidobacterium adolescentis.
  • Sporobolomyces singularis As the yeast having ⁇ -galactosidase activity which is particularly preferably used, Sporobolomyces singularis can be exemplified, and Sporobolomyces singularis JCM 5356 (ATCC 24193), which is one of the examples thereof, is available for a fee from RIKEN BioResource Center (2-1 Hirosawa, Wako-shi, Saitama-ken, 351-0198, Japan), ATCC (10801 University Boulevard Manassas, Va., 20110, USA), or the like.
  • yeast obtained as a ⁇ -galactosidase high-producing mutant microorganism by a production method described in JP-A-2003-325166 can be exemplified.
  • yeast obtained by the steps (a) to (c) in the above-described patent literature using the above-described Sporobolomyces singularis JCM 5356 as a parent strain Sporobolomyces singularis ISK-#4D4, ISK-#5A5, and ISK-##2B6 can be exemplified, and these strains were deposited on Apr.
  • a culture solution is obtained by culturing a microorganism having an enzymatic activity in a medium or the like according to a common procedure.
  • This culture solution may be used as the microbial cell liquid as it is, or a liquid obtained by appropriately performing washing or concentration using a centrifuge, a membrane concentration device, or the like may be used as the microbial cell liquid.
  • the solid content in this microbial cell liquid is not particularly limited, and specifically, a solid content of 0.5 to 10% can be exemplified.
  • the “solid content” in this specification refers to a solid content of the cells in the microbial cell liquid, and for example, in the case where medium components are contained in the microbial cell liquid, the solid content derived from the medium components is not included in the “solid content” in this specification.
  • the range of the pH is not particularly limited, however, from the viewpoint that the enzyme titer can be maintained higher in a wider temperature range, the range of the pH is preferably from 3.5 to 6.5, more preferably from 4.2 to 6.3, further more preferably from 4.5 to 5.7.
  • a substance to be used for adjusting the pH is not particularly limited, and any of an acid, a base, and a salt can be used.
  • hydrochloric acid, acetic acid, sulfuric acid, an aqueous solution of sodium hydroxide, potassium hydroxide, sodium carbonate, or the like, or any of a variety of buffers such as a sodium phosphate buffer can be used as needed, however, from the viewpoint that the titer after the pH adjustment is not decreased, it is preferred to use a carbonate, and it is more preferred to use one or more carbonates selected from the group consisting of sodium carbonate, potassium carbonate, ammonium carbonate, sodium hydrogen carbonate, potassium hydrogen carbonate, and ammonium hydrogen carbonate.
  • a carbohydrate is added to the microbial cell liquid before adjusting the pH and/or a carbohydrate is added to the microbial cell liquid after adjusting the pH and before performing the heating treatment.
  • the carbohydrate to be used here is not particularly limited, and any of a monosaccharide, a disaccharide, a tri- or higher oligosaccharide, and a polysaccharide can be used.
  • Examples of the monosaccharide include glucose, galactose, fructose, and mannose
  • examples of the disaccharide include lactose, lactose isomers, maltose, sucrose, and trehalose
  • examples of the tri- or higher oligosaccharide include various oligosaccharides such as galactooligosaccharides, maltooligosaccharides, and fructooligosaccharides
  • examples of the polysaccharide include dextrins and starch.
  • At least one carbohydrate selected from the group consisting of lactose, glucose, maltose, a galactooligosaccharide, and a dextrin is preferred, and in particular, it is preferred to use at least one carbohydrate selected from the group consisting of lactose, glucose, maltose, and a galactooligosaccharide.
  • the amount of the carbohydrate to be added to the microbial cell liquid is not particularly limited, however, the lower limit of the addition amount of the carbohydrate is, for example, preferably 0.2 mass/vol % (hereinafter simply expressed in “%”) or more, more preferably 0.5% or more, further more preferably 2% or more with respect to the amount of the microbial cell liquid.
  • the carbohydrate when or how the carbohydrate is added to the microbial cell liquid is not particularly limited, and for example, a method in which a separately prepared concentrated solution of the carbohydrate is added can be exemplified, however, when the amount of a carbohydrate solution to be added to the microbial cell liquid is too large, a problem may arise in some cases that the concentration of the microbial cells in the microbial cell liquid is decreased, and therefore, the enzyme titer per unit weight of the microbial cell liquid is decreased. Accordingly, the upper limit of the addition amount of the carbohydrate is preferably 30% or less, more preferably 15% or less, further more preferably 10% or less. In view of this, the amount of the carbohydrate to be added to the microbial cell liquid is preferably from 0.2 to 30%, more preferably from 0.5 to 15%, further more preferably from 0.5 to 10%, particularly preferably from 2 to 10%.
  • the carbohydrate to be added to the microbial cell liquid can be a substrate for the enzyme (for example, in the case where lactose is added to a liquid of microbial cells having ⁇ -galactosidase activity)
  • the carbohydrate to be added to the microbial cell liquid can be a substrate for the enzyme
  • the carbohydrate to be added to the microbial cell liquid can be a substrate for the enzyme
  • part or most of the carbohydrate is subjected to an enzymatic reaction during a period from when the carbohydrate is added to when the heating treatment is completed, however, the effect of the addition of the carbohydrate is exhibited regardless of the degree of reaction (the degree of degradation or the degree of polymerization), and therefore, there is no problem at all from the viewpoint of stabilization of the enzyme titer.
  • the carbohydrate is added, even if the microbial cell liquid is kept as it is, or is subjected to a cooling treatment or a heating treatment, there is no problem at all from the viewpoint of stabilization of the enzyme titer.
  • another carbohydrate produced by subjecting the added carbohydrate to the enzymatic reaction is contained in the microbial cell liquid in some cases, however, even if such a carbohydrate is present, there is no problem at all from the viewpoint of stabilization of the enzyme titer.
  • Examples of the carbohydrate to be produced by subjecting the carbohydrate added to the microbial cell liquid to the enzymatic reaction include monosaccharides, disaccharides, tri- or higher oligosaccharides, and polysaccharides, and examples of the monosaccharide include glucose, galactose, fructose, and mannose, examples of the disaccharide include lactose, lactose isomers, maltose, sucrose, and trehalose, examples of the tri- or higher oligosaccharide include various oligosaccharides such as galactooligosaccharides and fructooligosaccharides, and examples of the polysaccharide include dextrins and starch.
  • the carbohydrate to be added to the liquid of the microbial cells having a carbohydrate degrading enzyme (for example, ⁇ -galactosidase) activity is lactose
  • a carbohydrate degrading enzyme for example, ⁇ -galactosidase
  • glucose, galactose, lactose, a lactose isomer, and a galactooligosaccharide can be exemplified
  • the carbohydrate contained in the microbial cell liquid in the case where the carbohydrate to be added is maltose
  • glucose, maltose, and a maltooligosaccharide can be exemplified
  • the carbohydrate contained in the microbial cell liquid in the case where the carbohydrate to be added is a dextrin
  • glucose, maltose, a maltooligosaccharide, and a dextrin can be exemplified.
  • At least one carbohydrate selected from the group consisting of lactose, glucose, maltose, a galactooligosaccharide, and a dextrin is contained, specifically, at least one carbohydrate selected from the group consisting of lactose, glucose, galactose, a lactose isomer, a galactooligosaccharide, maltose, a maltooligosaccharide, and a dextrin is contained.
  • At least one carbohydrate selected from the group consisting of lactose, glucose, maltose, and a galactooligosaccharide as the carbohydrate to be added to the microbial cell liquid, it is more preferred that in the microbial cell liquid, at least one carbohydrate selected from the group consisting of lactose, glucose, galactose, a lactose isomer, a galactooligosaccharide, maltose, and a maltooligosaccharide is contained.
  • the heating treatment method is not particularly limited, and a method using a continuous plate heat exchanger, a method of heating a tank containing the microbial cell liquid by heating steam or hot water in a batchwise process, or the like can be applied, however, in order to control the temperature so as to prevent the inactivation of the enzyme as much as possible, a method of heating a tank containing the microbial cell liquid by heating steam or hot water in a batchwise process is preferred.
  • the heating treatment in a batchwise process is not particularly limited as long as the conditions for the heating treatment can kill the microorganism while maintaining the enzyme titer, however, it is performed at preferably 40 to 50° C., more preferably 40 to 48° C., further more preferably 40 to 46° C. Further, in the case where a carbohydrate is added to the microbial cell liquid before adjusting the pH and/or a carbohydrate is added to the microbial cell liquid after adjusting the pH and before performing the heating treatment in a batchwise process, the heating treatment is performed at preferably 40 to 60° C., more preferably 40 to 55° C., further more preferably 40 to 50° C.
  • the heating time is also not particularly limited, but is preferably 1 hour or more, more preferably 6 hours or more. However, if the heating time is too long, the enzyme titer is decreased in some cases, and therefore, the heating time is preferably 24 hours or less, more preferably 20 hours or less, further more preferably 18 hours or less. In view of this, the heating time is preferably from 1 to 24 hours, more preferably from 1 to 20 hours, further more preferably from 1 to 18 hours, still further more preferably from 6 to 24 hours, yet still further more preferably from 6 to 20 hours, particularly preferably from 6 to 18 hours.
  • the heating time is preferably from 1 to 24 hours, more preferably from 4 to 20 hours, further more preferably from 5 to 18 hours.
  • the phrase “killing a microorganism” in the present inventive method 1 refers to the reduction of the live microbial cells by the heating treatment to 1000 cfu/mL or less, and it is desirable to reduce the live microbial cells to preferably 100 cfu/mL or less, more preferably 10 cfu/mL or less.
  • the microorganism in the microbial cell liquid is killed while maintaining the enzyme titer of the microbial cell liquid.
  • the phrase “maintaining the enzyme titer” refers to that the enzyme titer after performing the heating treatment (after killing the microorganism) is 80% or more, preferably 90% or more, more preferably 95% or more of the enzyme titer before performing the heating treatment (before killing the microorganism).
  • the microbial cell liquid after the heating treatment (a killed microbial cell liquid) can be stored for a long time under low-temperature conditions of 25° C. or lower, preferably from 0 to 5° C. Then, the microbial cell liquid after the heating treatment can be used in various applications using the enzymatic activity.
  • the microbial cell liquid after the heating treatment can be further dried by a known drying method such as spray drying or lyophilization and formed into a killed microbial cell dry powder.
  • a drying method such as spray drying or lyophilization
  • the carbohydrate to be used is not particularly limited, and any of a monosaccharide, a disaccharide, a tri- or higher oligosaccharide, and a polysaccharide can be used.
  • Examples of the monosaccharide include glucose, galactose, fructose, and mannose
  • examples of the disaccharide include lactose, lactose isomers, maltose, sucrose, and trehalose
  • examples of the tri- or higher oligosaccharide include various oligosaccharides such as galactooligosaccharides, maltooligosaccharides, and fructooligosaccharides
  • examples of the polysaccharide include dextrins and starch.
  • the amount of the carbohydrate to be added is not particularly limited, and the lower limit of the addition amount of the carbohydrate is, for example, preferably 0.1% or more, more preferably 0.5% or more, further more preferably 1% or more with respect to the amount of the microbial cell liquid.
  • the upper limit of the addition amount of the carbohydrate is preferably 30% or less, more preferably 15% or less, further more preferably 10% or less, still further more preferably 5% or less, yet still furthermore preferably 3% or less.
  • the amount of the carbohydrate to be added to the microbial cell liquid is preferably from 0.1 to 30%, more preferably from 0.5 to 15%, further more preferably from 0.5 to 10%, still further more preferably from 1 to 10%, yet still further more preferably from 1 to 5%, particularly preferably from 1 to 3% with respect to the amount of the microbial cell liquid.
  • the method for adding the carbohydrate is not particularly limited, however, for example, a method in which a separately prepared concentrated solution of the carbohydrate is added can be exemplified.
  • the degree of drying is not particularly limited, however, for example, the drying is performed until the water content in the dry powder is reduced to about 10% or less.
  • the dry killed microbial cell powder can be used in various applications using the enzymatic activity.
  • the inlet and outlet temperatures of a drying chamber may be in a range in which the enzyme is not significantly inactivated, and further, the rotation speed of an atomizer, the feeding amount of a stock solution, etc. hardly affect the final enzyme titer, although a dry microbial cell powder having slightly different properties as a product is obtained depending on such conditions, and therefore, it is not necessary to pay much attention to such conditions.
  • the inlet temperature of a drying chamber can be, for example, from 70° C. to 200° C., preferably from 110° C. to 180° C.
  • the outlet temperature of a drying chamber can be, for example, from 50° C. to 120° C., preferably from 70° C.
  • the rotation speed of an atomizer can be, for example, from 10,000 to 30,000 rpm, and the feeding amount of a stock solution can be, for example, from 0.2 to 200 kg/hour.
  • the spray drying can also be performed using a spraying system such as a two-fluid nozzle other than an atomizer. Incidentally, from the viewpoint that continuous production can be performed industrially, it is preferred to use a spray drying method.
  • the thus obtained microbial cell liquid after the heating treatment and dry killed microbial cell powder can also be incorporated alone or in combination with each other to form an enzyme composition. It is also possible to add a diluent, an excipient, a surfactant, a preservative, or the like to this enzyme composition within a range that does not affect the enzymatic activity. Further, also this enzyme composition can be used in various applications using the enzymatic activity.
  • a method including adding a carbohydrate to a liquid of microbial cells having an enzymatic activity, and then performing a heating treatment of the liquid (the present inventive method 2) will be described.
  • a culture solution is obtained by culturing a microorganism having an enzymatic activity in a medium or the like according to a common procedure.
  • This culture solution may be used as the microbial cell liquid as it is, or a liquid obtained by appropriately performing washing or concentration using a centrifuge, a membrane concentration device, or the like may be used as the liquid of microbial cells having an enzymatic activity.
  • the solid content in this microbial cell liquid is not particularly limited, and specifically, a solid content of 0.5 to 10% can be exemplified.
  • the “solid content” in this specification refers to a solid content of the cells in the microbial cell liquid, and for example, in the case where medium components are contained in the microbial cell liquid, the solid content derived from the medium components is not included in the “solid content” in this specification.
  • a carbohydrate is added to this microbial cell liquid.
  • the carbohydrate to be used here is not particularly limited, and any of a monosaccharide, a disaccharide, a tri- or higher oligosaccharide, and a polysaccharide can be used.
  • Examples of the monosaccharide include glucose, galactose, fructose, and mannose
  • examples of the disaccharide include lactose, lactose isomers, maltose, sucrose, and trehalose
  • examples of the tri- or higher oligosaccharide include various oligosaccharides such as galactooligosaccharides, maltooligosaccharides, and fructooligosaccharides
  • examples of the polysaccharide include dextrins and starch.
  • At least one carbohydrate selected from the group consisting of lactose, glucose, maltose, a galactooligosaccharide, and a dextrin is preferred, and in particular, it is preferred to use at least one carbohydrate selected from the group consisting of lactose, glucose, maltose, and a galactooligosaccharide.
  • the amount of the carbohydrate to be added to the microbial cell liquid is not particularly limited, however, the lower limit of the addition amount of the carbohydrate is, for example, preferably 0.2% or more, more preferably 0.5% or more, further more preferably 2% or more with respect to the amount of the microbial cell liquid.
  • the carbohydrate when or how the carbohydrate is added to the microbial cell liquid is not particularly limited, and for example, a method in which a separately prepared concentrated solution of the carbohydrate is added can be exemplified, however, when the amount of a carbohydrate solution to be added to the microbial cell liquid is too large, a problem may arise in some cases that the concentration of the microbial cells in the microbial cell liquid is decreased, and therefore, the enzyme titer per unit weight of the microbial cell liquid is decreased. Accordingly, the upper limit of the addition amount of the carbohydrate is preferably 30% or less, more preferably 15% or less, further more preferably 10% or less. In view of this, the amount of the carbohydrate to be added to the microbial cell liquid is preferably from 0.2 to 30%, more preferably from 0.5 to 15%, further more preferably from 0.5 to 10%, particularly preferably from 2 to 10%.
  • the heating treatment method is not particularly limited, and a method using a continuous plate heat exchanger, a method of heating a tank containing the microbial cell liquid by heating steam or hot water in a batchwise process, or the like can be applied, however, in order to control the temperature so as to prevent the inactivation of the enzyme as much as possible, a method of heating a tank containing the microbial cell liquid by heating steam or hot water in a batchwise process is preferred.
  • the heating treatment in a batchwise process is not particularly limited as long as the conditions for the heating treatment can kill the microorganism while maintaining the enzyme titer, however, it is performed at preferably 40 to 60° C., more preferably 40 to 55° C., further more preferably 40 to 50° C.
  • the heating time is also not particularly limited, but is preferably 1 hour or longer, more preferably 4 hours or longer, further more preferably 5 hours or longer. However, if the heating time is too long, the enzyme titer may be decreased, and therefore, the heating time is preferably 24 hours or shorter, more preferably 20 hours or shorter, further more preferably 18 hours or shorter.
  • the heating time is preferably from 1 to 24 hours, more preferably from 4 to 20 hours, further more preferably from 5 to 18 hours.
  • the phrase “killing a microorganism” in the present inventive method 2 refers to the reduction of the live microbial cells by the heating treatment to 1000 cfu/mL or less, and it is desirable to reduce the live microbial cells to preferably 100 cfu/mL or less, more preferably 10 cfu/mL or less.
  • the microorganism in the microbial cell liquid is killed while maintaining the enzyme titer of the microbial cell liquid.
  • the phrase “maintaining the enzyme titer” refers to that the enzyme titer after performing the heating treatment (after killing the microorganism) is 80% or more, preferably 90% or more, more preferably 95% or more of the enzyme titer before performing the heating treatment (before killing the microorganism).
  • the carbohydrate to be added to the microbial cell liquid can be a substrate for the enzyme (for example, in the case where lactose is added to a liquid of microbial cells having ⁇ -galactosidase activity)
  • the carbohydrate to be added to the microbial cell liquid can be a substrate for the enzyme
  • the carbohydrate to be added to the microbial cell liquid can be a substrate for the enzyme
  • part or most of the carbohydrate is subjected to an enzymatic reaction during a period from when the carbohydrate is added to when the heating treatment is completed, however, the effect of the addition of the carbohydrate is exhibited regardless of the degree of reaction (the degree of degradation or the degree of polymerization), and therefore, there is no problem at all from the viewpoint of stabilization of the enzyme titer.
  • the carbohydrate is added, even if the microbial cell liquid is kept as it is, or is subjected to a cooling treatment or a heating treatment, there is no problem at all from the viewpoint of stabilization of the enzyme titer.
  • another carbohydrate produced by subjecting the added carbohydrate to the enzymatic reaction is contained in the microbial cell liquid, however, even if such a carbohydrate is present, there is no problem at all from the viewpoint of stabilization of the enzyme titer.
  • Examples of the carbohydrate to be contained in the microbial cell liquid include monosaccharides, disaccharides, tri- or higher oligosaccharides, and polysaccharides, and examples of the monosaccharide include glucose, galactose, fructose, and mannose, examples of the disaccharide include lactose, lactose isomers, maltose, sucrose, and trehalose, examples of the tri- or higher oligosaccharide include various oligosaccharides such as galactooligosaccharides and fructooligosaccharides, and examples of the polysaccharide include dextrins and starch.
  • the carbohydrate to be added to the liquid of the microbial cells having a carbohydrate degrading enzyme (for example, ⁇ -galactosidase) activity is lactose
  • a carbohydrate degrading enzyme for example, ⁇ -galactosidase
  • glucose, galactose, lactose, a lactose isomer, and a galactooligosaccharide can be exemplified
  • the carbohydrate contained in the microbial cell liquid in the case where the carbohydrate to be added is maltose
  • glucose, maltose, and a maltooligosaccharide can be exemplified
  • the carbohydrate contained in the microbial cell liquid in the case where the carbohydrate to be added is a dextrin
  • glucose, maltose, a maltooligosaccharide, and a dextrin can be exemplified.
  • At least one carbohydrate selected from the group consisting of lactose, glucose, maltose, a galactooligosaccharide, and a dextrin is contained, specifically, at least one carbohydrate selected from the group consisting of lactose, glucose, galactose, a lactose isomer, a galactooligosaccharide, maltose, a maltooligosaccharide, and a dextrin is contained.
  • At least one carbohydrate selected from the group consisting of lactose, glucose, maltose, and a galactooligosaccharide as the carbohydrate to be added to the microbial cell liquid, it is more preferred that in the microbial cell liquid, at least one carbohydrate selected from the group consisting of lactose, glucose, galactose, a lactose isomer, a galactooligosaccharide, maltose, and a maltooligosaccharide is contained.
  • the microbial cell liquid after the heating treatment (a killed microbial cell liquid) can be stored for a long time under low-temperature conditions of 25° C. or lower, preferably from 0 to 5° C. Then, the microbial cell liquid after the heating treatment can be used in various applications using the enzymatic activity.
  • the microbial cell liquid after the heating treatment can be further dried by a known drying method such as spray drying or lyophilization and formed into a dry killed microbial cell powder.
  • the degree of drying is not particularly limited, however, for example, the drying is performed until the water content in the dry powder is reduced to about 10% or less. By performing this drying, longer time storage as compared with the case of a liquid, for example, 1 year or more storage can be achieved while maintaining the enzyme titer at 80% or more of the enzyme titer immediately after drying.
  • the dry killed microbial cell powder can be used in various applications using the enzymatic activity.
  • the inlet and outlet temperatures of a drying chamber may be in a range in which the enzyme is not significantly inactivated, and further, the rotation speed of an atomizer, the feeding amount of a stock solution, etc. hardly affect the final enzyme titer, although a dry microbial cell powder having slightly different properties as a product is obtained depending on such conditions, and therefore, it is not necessary to pay much attention to such conditions.
  • the inlet temperature of a drying chamber can be, for example, from 70° C. to 200° C., preferably from 110° C. to 180° C.
  • the outlet temperature of a drying chamber can be, for example, from 50° C. to 120° C., preferably from 70° C.
  • the rotation speed of an atomizer can be, for example, from 10,000 to 30,000 rpm, and the feeding amount of a stock solution can be, for example, from 0.2 to 200 kg/hour.
  • the spray drying can also be performed using a spraying system such as a two-fluid nozzle other than an atomizer. Incidentally, from the viewpoint that continuous production can be performed industrially, it is preferred to use a spray drying method.
  • the thus obtained microbial cell liquid after the heating treatment and dry killed microbial cell powder can also be incorporated alone or in combination with each other to form an enzyme composition. It is also possible to add a diluent, an excipient, a surfactant, a preservative, or the like to this enzyme composition within a range that does not affect the enzymatic activity. Further, also this enzyme composition can be used in various applications using the enzymatic activity.
  • the invention will be more specifically described with reference to Examples, however, the invention is by no means limited to these Examples.
  • the ⁇ -galactosidase titer, the solid content, the residual water content in the dry microbial cell powder, a particle size distribution, the live cell count of Sporobolomyces singularis , and the sugar composition were measured or analyzed by the following methods.
  • a microbial cell liquid was accurately weighed in a 50-mL volumetric flask, and brought to a constant volume with a 50 mM sodium phosphate-citric acid buffer solution (pH 4.0) (hereinafter referred to as “buffer solution”), and then, sufficiently dissolved or suspended therein, whereby a test liquid was prepared. Further, in the case where the microbial cell liquid contained a carbohydrate (lactose), about 2.5 g of the microbial cell liquid was accurately weighed in a 50-mL centrifugal tube, and washing was performed by suspending the liquid in the buffer solution, followed by centrifugation (20,000 G, 15 mins), whereby the carbohydrate was removed.
  • buffer solution 50 mM sodium phosphate-citric acid buffer solution
  • test sample was a dry microbial cell powder (hereinafter referred to as “dry product”)
  • dry product a dry microbial cell powder
  • o-nitrophenyl- ⁇ -D-galactopyranoside (ONPG) was weighed, dissolved in the buffer solution and brought to a constant volume, whereby a 12.5 mM ONPG solution was prepared.
  • ONPG o-nitrophenyl- ⁇ -D-galactopyranoside
  • a test tube 0.8 mL of this ONPG solution was placed, and the test tube was maintained in a thermoregulated water bath at 30° C. for 5 minutes. Thereto, 0.2 mL of the test liquid was added and mixed well, and a reaction was allowed to proceed at 30° C. for 10 minutes. Then, 4 mL of a 0.25 M sodium carbonate solution was added to stop the reaction (a test system).
  • Activity ⁇ ⁇ value * A 1 - A 2 0.91 ⁇ 1 0.2 ⁇ 1 10 ⁇ B ⁇ ⁇ A 1 ⁇ : ⁇ ⁇ absorbance ⁇ ⁇ of ⁇ ⁇ test ⁇ ⁇ liquid ⁇ ⁇ A 2 ⁇ : ⁇ ⁇ absorbance ⁇ ⁇ of ⁇ ⁇ blank ⁇ ⁇ B ⁇ : ⁇ ⁇ dilution ⁇ ⁇ ratio ⁇ * : ⁇ ⁇ U ⁇ / ⁇ g [ Math . ⁇ 1 ]
  • the microbial cell liquid was a culture solution (when medium components were contained)
  • the microbial cell liquid was accurately weighed in a centrifugal tube, and washing was performed by centrifugation to remove the medium components, and then, the entire amount of the washed microbial cells were transferred onto an aluminum dish, and the microbial cells were dried in the same manner as described above, and then, the solid content was calculated.
  • the residual water content in the dry product obtained by spray drying was measured using an infrared aquameter manufactured by Kett Electric Laboratory under the conditions of 105° C. for 15 minutes.
  • the particle size distribution of the dry product was measured by a dry process using a laser diffraction particle size distribution analyzer (HELOS & RODOS system) manufactured by Sympatec, Inc.
  • HELOS & RODOS system laser diffraction particle size distribution analyzer
  • Lactose (2.5%), yeast extract (0.5%), monopotassium phosphate (0.1%), magnesium sulfate (0.05%), and agar (1.5%) were dissolved, and the pH of the resulting solution was adjusted to 5.0 with 2 N hydrochloric acid. Then, the solution was sterilized by autoclaving (121° C., 10 mins), and a flat plate ( ⁇ 90 mm) was prepared. On this plate, 100 ⁇ L of a sample dissolved and diluted with physiological saline was plated, and cultured at 25° C. for about 1 week. The resulting colonies were counted and the obtained value was determined as the live cell count of Sporobolomyces singularis.
  • the sugar composition was analyzed using HPLC under the following conditions.
  • Ss Sporobolomyces singularis YIT 10047 (ISK-##2B6, hereinafter referred to as “Ss”) was aerobically cultured at 27° C. for 4 days in a medium (pH 5) containing glucose (5%), yeast extract (1.0%), monopotassium phosphate (0.1%), and magnesium sulfate (0.05%).
  • This culture solution was centrifuged (10000 G, 30 mins) to obtain wet cells, and sterilized tap water was added thereto and the wet cells were well suspended therein.
  • the resulting suspension was centrifuged under the same conditions, and the obtained wet cells were suspended in a small amount of tap water such that the solid content was about 5%, and the thus obtained suspension was used as an Ss concentrate liquid.
  • the pH of the Ss concentrate liquid (solid content: 5.0%) obtained in the above (1) was adjusted stepwise from 3.5 to 6.3 with a 5 N sodium hydroxide solution.
  • the thus obtained liquids and the Ss concentrate liquid with an unadjusted pH of 3.1 were subjected to a heating treatment by maintaining the liquids at 35° C., 40° C., 45° C., 50° C., or 55° C. for 18 hours.
  • the results of the live cell count of Ss before and after the heating treatment and the ratio of the ⁇ -galactosidase titer after the heating treatment to the ⁇ -galactosidase titer before the heating treatment are shown in Table 1.
  • the Ss was killed at a heating temperature of 40 to 45° C., and the residual titer ratio was 80% or more at 45° C., and 90% or more at 40° C.
  • the pH was adjusted to 3.5
  • the Ss was killed and the residual titer ratio was 90% or more even at 35° C.
  • the heating treatment was performed after adjusting the pH to 4.2, 4.7, 5.0, 5.8, or 6.3
  • the Ss was killed and the residual titer ratio was 90% or more at a heating temperature of 40 to 45° C.
  • the Ss was killed at a heating temperature of 40° C., and the residual titer ratio at 40° C. was 90% or more, but the value thereof was 92.2%, and therefore, the residual titer ratio was lower as compared with the case where the pH adjustment was performed. Further, the residual titer ratio was lower than 80% when the heating temperature was 45° C., and therefore, it was presumed that the temperature conditions in which the microorganism can be killed and the enzyme titer can be maintained are narrower by 5° C. or more as compared with the other pH conditions.
  • the pH of an Ss concentrate liquid (solid content: 5.6%) obtained in the same manner as in the above (1) was adjusted to 4.0, 4.5, 4.9, 5.7, or 6.5 with a 5 N sodium hydroxide solution.
  • the thus obtained liquids were subjected to a heating treatment by maintaining the liquids at 44° C., 46° C., 48° C., 50° C., or 52° C. for 5 hours or 18 hours.
  • the results of the live cell count of Ss before and after the heating treatment and the residual titer ratio are shown in Table 2 (5-hour heating treatment) and Table 3 (18-hour heating treatment).
  • the Ss was killed at a heating temperature of 44 to 48° C., and the residual titer ratio was 80% or more at 48° C., and 90% or more at 44 to 46° C.
  • the heating treatment was performed after adjusting the pH to 4.5
  • the Ss was killed at a heating temperature of 46 to 50° C.
  • the residual titer ratio was 80% or more at 50° C., and 90% or more at 46 to 48° C.
  • the heating treatment was performed after adjusting the pH to 4.9 or 5.7, the Ss was killed and the residual titer ratio was 90% or more at a heating temperature of 44 to 50° C.
  • the live cell count of Ss was 10 cfu/mL or less.
  • the Ss was killed at a heating temperature of 44 to 48° C., and the residual titer ratio was 80% or more at 48° C., and 90% or more at 44 to 46° C.
  • the live cell count of Ss was 10 cfu/mL.
  • the Ss was killed at a heating temperature of 44 to 46° C., and the residual titer ratio was 80% or more at 46° C., and 90% or more at 44° C.
  • the heating treatment was performed after adjusting the pH to 4.5, 4.9, or 5.7
  • the Ss was killed at a heating temperature of 44 to 48° C.
  • the residual titer ratio was 80% or more at 48° C., and 90% or more at 44 to 46° C.
  • the heating treatment was performed after adjusting the pH to 6.5
  • the Ss was killed and the residual titer ratio was 90% or more at a heating temperature of 44 to 46° C.
  • the live cell count of Ss was decreased over time at either of the heating temperatures of 40° C. and 45° C., and in the case where the heating treatment was performed at 40° C., the live cell count was decreased to 1000 cfu/mL or less when performing the heating treatment for 6 hours, and decreased to 10 cfu/mL or less when performing the heating treatment for 9 hours. Further, in the case where the heating treatment was performed at 45° C., the live cell count was decreased to 1000 cfu/mL or less when performing the heating treatment for 1 hour, and decreased to 10 cfu/mL or less when performing the heating treatment for 2 hours.
  • the pH of an Ss concentrate liquid (solid content: 5.3%) obtained in the same manner as in Example 1 was adjusted to 4.5 with a 5 N sodium hydroxide solution.
  • the thus obtained liquid was subjected to a heating treatment by maintaining the liquid at 40° C. for 18 hours.
  • 2.6 L of this killed Ss concentrate liquid 2.6 L of a 8, 20, or 40% lactose solution was added, followed by mixing well, whereby stock solutions to be dried were prepared such that the solid content of Ss was about 4%, and the lactose content was 2, 5, or 10%.
  • the concentration of lactose in the stock solutions to be dried was from 0 to 10%
  • dry products in which the residual titer ratio after drying was 90% or more could be obtained.
  • the live cell count of Ss in any of these dry products was 10 cfu/mL or less
  • the residual titer ratio before and after the heating treatment was 90% or more in all the cases.
  • each of Product 1 and Product 2 in an amount corresponding to 45 U was weighed, and 10 mL of ion exchanged water was added thereto to suspend the dry product.
  • the Ss concentrate liquid obtained in the above (1) and a lactose solution were mixed at 3:1, whereby Ss concentrate liquids containing lactose at 0.2 to 15% were prepared.
  • the thus obtained liquids and the Ss concentrate liquid to which lactose was not added were subjected to a heating treatment by maintaining the liquids at 35° C., 40° C., 45° C., 50° C., or 55° C. for 18 hours.
  • the results of the measurement of the live cell count of Ss before and after the heating treatment and the ratio of the ⁇ -galactosidase titer after the heating treatment to the ⁇ -galactosidase titer before the heating treatment are shown in Table 8.
  • the Ss was killed at a heating temperature of 40 to 45° C., and the residual titer ratio was 80% or more at 45° C., and 90% or more at 40° C.
  • the heating treatment was performed after adding lactose at 0.5 to 1%
  • the Ss was killed at 40 to 45° C.
  • the residual titer ratio was 90% or more.
  • the heating treatment was performed after adding lactose at 2 to 5%
  • the Ss was killed and the residual titer ratio was 90% or more at a heating temperature of 40 to 50° C.
  • the Ss was killed and the residual titer ratio was 90% or more at a heating temperature of 40 to 55° C.
  • the Ss was killed at a heating temperature of 40° C., and the residual titer ratio at 40° C. was 90% or more, but the residual titer ratio was lower than 80% at 45° C., and therefore, it was presumed that the temperature conditions in which the microorganism can be killed and the enzyme titer can be maintained are narrower by 5° C. or more as compared with the case where lactose is added.
  • An effect of stabilizing the enzymatic activity when a microorganism was killed was compared among a dextrin (NSD #300, San-ei Sucrochemical Co., Ltd.), a tri- or higher oligosaccharide fraction of a galactooligosaccharide, lactose, maltose, and glucose.
  • An Ss concentrate liquid (solid content: 5.6%) obtained in the same manner as in the above (1) and a 8 or 20% carbohydrate solution were mixed at 3:1, whereby Ss concentrate liquids containing a carbohydrate at 2% or 5% were prepared.
  • the thus obtained liquids were subjected to a heating treatment by maintaining the liquids at 45° C. or 50° C. for 18 hours.
  • the results of the ratio of the ⁇ -galactosidase titer after the heating treatment to the ⁇ -galactosidase titer before the heating treatment are shown in Table 9.
  • the live cell count of Ss before the heating treatment was 10 8 cfu/mL, however, after the heating treatment, the live cell count of Ss was decreased to 10 cfu/mL or less, and therefore, the Ss was killed in the case of any carbohydrate at any concentration.
  • the residual titer ratio was 72.7% at a heating temperature of 45° C., and 29.5% at a heating temperature of 50° C.
  • the residual titer ratio was higher, and except the case where the dextrin was allowed to coexist at a heating temperature of 50° C., the residual titer ratio was improved to 80% or more.
  • the live cell count of Ss was decreased over time at either of the heating temperatures of 40° C. and 45° C., and in the case where the heating treatment was performed at 40° C., the live cell count was decreased to 1000 cfu/mL or less when performing the heating treatment for 4 hours, and decreased to 10 cfu/mL or less when performing the heating treatment for 5 hours. Further, in the case where the heating treatment was performed at 45° C., the live cell count was decreased to 10 cfu/mL or less when performing the heating treatment for 1 hour.
  • the thus obtained liquids were subjected to a heating treatment by maintaining the liquids at 40° C. for 18 hours.
  • the sugar composition after the heating treatment was analyzed under the above HPLC conditions. The results are shown in Table 11. Further, the results obtained by measuring the titer before the heating treatment and calculating a residual titer are also shown in Table 11.
  • the live cell count of Ss before the heating treatment was 10 8 cfu/mL, however, after the heating treatment, the live cell count of Ss was decreased to 10 cfu/mL or less, and therefore, the Ss was killed in all the cases.
  • An Ss concentrate liquid (solid content: 5.3%) obtained in the same manner as in Example 1 and a 8, 20, or 40% lactose solution were mixed at 3:1, whereby stock solutions to be dried were prepared such that the solid content of Ss was about 4%, and the lactose content was 2, 5, or 10%.
  • the thus obtained liquids were subjected to a heating treatment by maintaining the liquids at 40° C. for 18 hours.
  • the concentration of lactose in the stock solutions to be dried was from 2 to 10%
  • dry microbial cell products in which the residual titer ratio after drying was 90% or more could be obtained.
  • the live cell count of Ss in any of these dry products was 10 cfu/mL or less
  • the residual titer ratio before and after the heating treatment was 90% or more in all the cases.
  • each of Product 5 and Product 6 in an amount corresponding to 45 U was weighed, and 10 mL of ion exchanged water was added thereto to suspend the dry product.
  • the Ss concentrate liquid obtained in the above (1) and a lactose solution were mixed at 3:1, whereby Ss concentrate liquids containing lactose at 2 to 5% were prepared.
  • the thus obtained liquids and the Ss concentrate liquid to which lactose was not added were subjected to a heating treatment by maintaining the liquids at 50° C. for 18 hours.
  • the results of the ratio of the ⁇ -galactosidase titer after the heating treatment to the ⁇ -galactosidase titer before the heating treatment are shown in Table 14. Incidentally, the live cell count of Ss after the heating treatment was 10 cfu/mL or less in all the cases.
  • the residual titer ratio was higher than 80% in the case where the concentration of lactose was from 2 to 5%. Further, it was found that in the case where the concentration of lactose was 3% or more, the residual titer ratio was higher than 90%.
  • the Ss concentrate liquid obtained in the above (1) three types of samples were prepared as follows: a sample in which the pH of the Ss concentrate liquid was adjusted to 4.5, 5.0, or 5.5 with a 2 N sodium hydroxide solution; a sample in which lactose was added at 2% to the Ss concentrate liquid (the pH adjustment was not performed); and a sample in which lactose was added at 2% to the Ss concentrate liquid, and then, the pH thereof was adjusted to 4.5, 5.0, or 5.5.
  • the thus obtained samples were subjected to a heating treatment by maintaining the samples at 50° C. for 5 hours or 18 hours.
  • the residual titer ratio of each of the Ss suspensions is shown in Table 16. Incidentally, the live cell count of Ss after the heating treatment was 10 cfu/mL or less in all the cases.
  • the residual titer ratio in the case where the pH adjustment and the addition of lactose were combined was higher than that in the case where a single treatment of either of the pH adjustment and the addition of lactose was performed. Further, in the case where the heating maintaining time was 18 hours, by adjusting the pH to 4.5 to 5.5, the residual titer ratio was 90% or more even when the concentration of lactose was 2%.
  • Ss was aerobically cultured at 27° C. for 4 days in a medium (pH 5) containing glucose (2%), yeast extract (0.4%), monopotassium phosphate (0.05%), and magnesium sulfate (0.025%).
  • This culture solution was centrifuged (10000 G, 30 min) to obtain wet cells, and sterilized tap water was added thereto and the wet cells were well suspended therein.
  • the resulting suspension was centrifuged under the same conditions, and to the obtained wet cells, a lactose solution and sterilized water were added, whereby Ss concentrate liquids containing lactose at 2% or 5% and having a cell density of 2.5%, 4.5%, or 6.5% (w/v) were prepared.
  • the Ss concentrate liquids obtained in the above (1) were subjected to a heating treatment by maintaining the liquids at 45° C. or 50° C. for 5 hours or 18 hours.
  • the measurement of the live cell count of Ss before and after the heating treatment and the ratio of the ⁇ -galactosidase titer after the heating treatment to the ⁇ -galactosidase titer before the heating treatment are shown in FIGS. 1 to 4 .
  • the residual titer ratio after killing the microorganism was 80% or more, and a difference in residual titer ratio was not observed.
  • the concentration of lactose was 5%
  • the residual titer ratio after killing the microorganism was 90% or more at any cell density.
  • Ss was aerobically cultured at 27° C. for 4 days in a medium (pH 5) containing glucose (4%), yeast extract (0.8%), monopotassium phosphate (0.1%), and magnesium sulfate (0.05%), whereby an Ss culture solution (solid content: 2.5%) was obtained.
  • the pH of the Ss culture solution obtained in the above (1) was adjusted stepwise from 3.5 to 5.0 with a 2 N sodium hydroxide solution.
  • the thus obtained solutions and the Ss culture solution in which the pH adjustment was not performed were subjected to a heating treatment by maintaining the solutions at 40° C. or 45° C. for 5 hours or 18 hours.
  • the results of the live cell count of Ss after the heating treatment and the ratio of the ⁇ -galactosidase titer after the heating treatment to the ⁇ -galactosidase titer before the heating treatment are shown in Table 17.
  • any of the culture solutions as the pH during the treatment of killing the microorganism was higher, the residual titer ratio was improved. Further, in any of the culture solutions, the conditions that met the requirements of 80% or more of the residual titer ratio and 10 cfu/mL or less of the live cell count of Ss were such that the pH was adjusted to 4.0 or higher and the heating treatment was performed at 45° C. for 5 hours. Further, also in the case where the pH was adjusted to 5.0 and the heating treatment was performed at 45° C. for 18 hours, the above-described requirement of the residual titer ratio was met.
  • Ss was aerobically cultured at 27° C. for 4 days in a medium (pH 5) containing glucose (4%), yeast extract (0.8%), monopotassium phosphate (0.1%), and magnesium sulfate (0.05%), whereby an Ss culture solution (solid content: 2.8%) was obtained.
  • the titer was decreased by 7 to 8% immediately after the pH adjustment. On the other hand, in the case where sodium carbonate was used as the pH adjusting agent, the titer was hardly decreased.
  • Ss was aerobically cultured at 27° C. for 4 days in a medium (pH 5) containing glucose (5%), yeast extract (1%), monopotassium phosphate (0.1%), and magnesium sulfate (0.05%), whereby an Ss culture solution (solid content: 2.5%) was obtained.
  • the pH of the Ss culture solution obtained in the above (1) was adjusted stepwise from 4.0 to 5.0 with a 2 N sodium hydroxide solution or a 20% sodium carbonate solution.
  • the thus obtained solutions were subjected to a heating treatment by maintaining the solutions at 40° C. or 45° C. for 5 hours or 18 hours.
  • the live cell count of Ss after the heating treatment and the ratio of the ⁇ -galactosidase titer after the heating treatment to the ⁇ -galactosidase titer before the heating treatment are shown in Table 18.
  • Ss was aerobically cultured at 27° C. for 4 days in a medium (pH 5) containing glucose (4%), yeast extract (0.8%), monopotassium phosphate (0.1%), and magnesium sulfate (0.05%).
  • This culture solution was centrifuged (10000 G, 30 mins), and a cell concentrate liquid was collected. Then, the cells were washed by adding sterilized tap water to the cell concentrate liquid and well suspending the cells. The resulting suspension was centrifuged under the same conditions, and adjustment was performed such that the solid content was about 5%, and the thus obtained material was used as an Ss concentrate liquid (solid content: 5.1%).
  • Ss was aerobically cultured at 27° C. for 4 days in a medium (pH 5) containing glucose (4%), yeast extract (0.8%), monopotassium phosphate (0.1%), and magnesium sulfate (0.05%), whereby an Ss culture solution was obtained.
  • the pH of the Ss concentrate liquid obtained in the above (1) was adjusted to 4.8 ⁇ 0.2 with a 20% sodium carbonate solution.
  • the thus obtained Ss concentrate liquid was subjected to a heating treatment by maintaining the liquid at 45° C. for 7 hours.
  • the results of the live cell count of Ss after the heating treatment and the ratio of the ⁇ -galactosidase titer after the heating treatment to the ⁇ -galactosidase titer before the heating treatment are shown in Table 19. Further, immediately before drying, the Ss concentrate liquid after killing the microorganism and a 24% lactose solution were mixed at 5:1, whereby a stock solution to be dried containing lactose at 4% was prepared.
  • the Ss concentrate liquid obtained in the above (1) and a 24% lactose solution were mixed at 5:1, whereby an Ss concentrate liquid containing lactose at 4% was prepared.
  • the thus prepared Ss concentrate liquid was subjected to a heating treatment by maintaining the liquid at 50° C. for 7 hours.
  • the results of the live cell count of Ss after the heating treatment and the ratio of the ⁇ -galactosidase titer after the heating treatment to the ⁇ -galactosidase titer before the heating treatment are shown in Table 19.
  • the Ss concentrate liquid after killing the microorganism was directly used as a stock solution to be dried.
  • the Ss concentrate liquid obtained in the above (1) and a 24% lactose solution were mixed at 10:1, whereby an Ss concentrate liquid containing lactose at 2.2% was prepared. Further, the pH of the thus prepared Ss concentrate liquid was adjusted to 4.8 ⁇ 0.2 with a 20% sodium carbonate solution.
  • the thus obtained Ss concentrate liquid was subjected to a heating treatment by maintaining the liquid at 50° C. for 7 hours.
  • the results of the live cell count of Ss after the heating treatment and the ratio of the ⁇ -galactosidase titer after the heating treatment to the ⁇ -galactosidase titer before the heating treatment are shown in Table 19. Further, immediately before drying, the Ss concentrate liquid after killing the microorganism and a 24% lactose solution were mixed at 11:1, whereby a stock solution to be dried containing lactose at 4% was prepared.
  • the pH of the Ss culture solution obtained in the above (2) was adjusted to 4.8 ⁇ 0.2 with a 20% sodium carbonate solution.
  • the thus obtained Ss culture solution was subjected to a heating treatment by maintaining the solution at 45° C. for 7 hours.
  • the results of the live cell count of Ss after the heating treatment and the ratio of the ⁇ -galactosidase titer after the heating treatment to the ⁇ -galactosidase titer before the heating treatment (residual titer ratio) are shown in Table 19. Further, the Ss culture solution after killing the microorganism was centrifuged (16000 G), and wet cells were collected.
  • the stock solutions to be dried obtained in the above (3) to (6) were dried using a pilot apparatus for spray drying (PRODUCTION MINOR, GEA Process Engineering, Inc.) under conditions that the inlet temperature was 120° C., the outlet temperature was 80° C., the rotation speed of the atomizer was 15000 rpm, and the processing amount of the stock solution was about 4.5 kg/hr, whereby favorable dry products were obtained.
  • the residual titer ratio, the average particle size, and the residual water content of each of these dry products were measured. The results are shown in Table 19.
  • Example 5 The dry products (Products 1 to 3) prepared in Example 2 and the dry products (Products 5 to 7) prepared in Example 5 were stored at 5° C. or 25° C. for 360 days.
  • Example 2 (pH adjustment)
  • Example 5 (addition of lactose) Product 1 Product 2 Product 3 Product 5
  • Product 6 Product 7 (lactose 2%) (lactose 5%) (lactose 10%) (lactose 2%) (lactose 5%) (lactose 10%)
  • a microorganism was killed in the same manner as in Example 1 except that Sporobolomyces singularis JCM 5356 (ATCC 24193) was used in place of Ss, and as a result, substantially the same results were obtained with respect to the residual titer ratio and the like.
  • the residual titer ratio when the heating treatment was performed at pH 5.0 and 45° C. was 80% or more.
  • a microorganism was killed in the same manner as in Example 4 except that Sporobolomyces singularis JCM 5356 (ATCC 24193) was used in place of Ss, and as a result, substantially the same results were obtained with respect to the residual titer ratio and the like.
  • the residual titer ratio when the heating treatment was performed at a lactose concentration of 5% and 45° C. was 80% or more.
  • a microorganism can be killed while maintaining the enzyme titer of a liquid of microbial cells having an enzymatic activity. Due to this, the microbial cell liquid treated by the present inventive method is easy to handle and also can be stored, and therefore can be advantageously used in the industry using the enzymatic activity.

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