JP7496198B2 - Yeast and foods made with it - Google Patents

Description

NPMD NITE P-03028

The present invention relates to yeast, and more specifically to yeast with high freeze-thaw resistance and foods using the same.

Commercially available baker's yeast products derived from wild yeast and whose strain origins are known include, for example, "Shirakami Kodama Yeast" (Patent Document 1, Non-Patent Document 1) and "Tokachino Yeast" (Patent Document 2). "Shirakami Kodama Yeast" is a yeast isolated from leaf mold in temperate deciduous forests, while "Tokachino Yeast" is a yeast isolated from cherries of the Siberian cherry tree that grows wild in the Tokachi region of Hokkaido.

JP 2001-178449 A JP 2010-068739 A

J. Appl. Glycosci., Vol. 56, Suppl., 2009

Yeast used for food is generally stored or distributed refrigerated. In Japan, the only yeast for baking and other uses that is stored and distributed frozen is Shirakami Kodama Yeast (registered trademark). However, when Shirakami Kodama Yeast is frozen and thawed multiple times, the survival rate of the yeast decreases, making it difficult to use in fermented foods and the like. For this reason, once frozen yeast has been thawed, it is not advisable to store it frozen again, and it must be used within about a week.

In view of the above circumstances, the present invention aims to provide yeast that has a high survival rate even after repeated freezing and thawing, and food products that use the yeast.

The inventors conducted screening using various indicators, and as a result of their intensive research, they discovered a yeast that can solve the above problems, and thus completed the present invention.

[1] Saccharomyces cerevisiae having a survival rate of 70% or more after two repeated freeze-thaw treatments.
[2] The Saccharomyces cerevisiae according to [1] above, which has a survival rate of 55% or more after three repeated freeze-thaw treatments.
[3] The Saccharomyces cerevisiae according to any one of [1] and [2] above, wherein the trehalose content in the cells recovered after culturing for 2 days in a YPD medium containing glucose as a carbon source is 19% by weight or more based on the dry cell weight of the cells.
[4] The Saccharomyces cerevisiae according to any one of [1] to [3] above, which has salt tolerance and can grow in a YPD medium containing 10% (w/v) salt.
[5] The Saccharomyces cerevisiae according to any one of [1] to [4] above, further having the ability to assimilate each of glucose, sucrose, and maltose as a carbon source.
[6] A Saccharomyces cerevisiae strain selected from the following strains (A) and (B):
(A) Saccharomyces cerevisiae KAY 723 strain, or (B) a strain having an identity of 90% or more to the entire genome sequence of the strain (A) and having a survival rate of 70% or more after two repeated freeze-thaw treatments.
[7] Saccharomyces cerevisiae KAY 723 strain.
[8] A frozen yeast composition, which is a frozen product containing the Saccharomyces cerevisiae cells according to any one of [1] to [7] above.
[9] A frozen bread dough comprising the Saccharomyces cerevisiae cells according to any one of [1] to [7] above.
[10] A dried baker's yeast which is a dried product of cells of the Saccharomyces cerevisiae strain according to any one of [1] to [7] above.
[11] A method for producing a fermented food, comprising fermenting using the Saccharomyces cerevisiae cells according to any one of [1] to [7] above.
[12] A method for producing bread, comprising baking dough containing the Saccharomyces cerevisiae cells according to any one of [1] to [7] above.
[13] A method for preserving Saccharomyces cerevisiae, comprising freezing the cells of the Saccharomyces cerevisiae according to any one of [1] to [7] above at -10 to -30°C.

The present invention provides yeast with high freeze-thaw resistance. The yeast of the present invention has a high survival rate even after repeated freezing and thawing, and is highly convenient for storage and distribution as a food additive or a food containing the same.

The following describes an embodiment of the present invention. The numerical values used to specify the present invention can be determined by the method described in the examples below.

1. Yeast of the Present Invention The present invention provides a yeast having high freeze-thaw resistance.
One embodiment of the present invention may be Saccharomyces cerevisiae having a viability of 70% or more after two repeated freeze-thaw cycles, more preferably 75%, and even more preferably 76, 77, 78, 79, or 80%.

In another embodiment of the present invention, the Saccharomyces cerevisiae has a survival rate of 55% or more after three repeated freeze-thaw cycles. The survival rate is more preferably 58%, and even more preferably 59 or 60%.

In another embodiment of the present invention, the survival rate after one freeze-thaw cycle may be 80% or more, more preferably 82% or more, and even more preferably 83, 84, or 85% or more.

In yet another embodiment, the yeast of the present invention may be Saccharomyces cerevisiae that highly accumulates trehalose. The degree of trehalose accumulation may be, for example, such that the trehalose content in the cells harvested after two days of culture in a YPD medium containing glucose as a carbon source is 19% by weight or more, preferably 20% by weight, more preferably 23% by weight, and even more preferably 25, 26, or 27% by weight, based on the dry cell weight of the cells.

Another embodiment of the present invention may be a highly salt-tolerant Saccharomyces cerevisiae. The presence or degree of salt tolerance can be determined, for example, by applying the bacteria to a YPD medium containing a predetermined concentration of salt and confirming whether or not the bacteria grows. More specifically, for example, the ability to grow in a YPD medium containing 10% (w/v) salt can be evaluated.

In yet another embodiment, the yeast of the present invention may be Saccharomyces cerevisiae that has the ability to assimilate glucose, sucrose, and maltose as carbon sources. Yeast that has the ability to assimilate various carbohydrates in this way can be used to make a variety of breads, and therefore can be said to have excellent suitability for bread making.

A preferred embodiment of the present invention is, for example, Saccharomyces cerevisiae KAY 723 strain. As described in detail in the Examples section below, KAY 723 strain is a strain isolated from leaf mold collected with permission from the competent authorities from the buffer zone of the World Natural Heritage site "Shirakami-Sanchi" in Hachimori, Hachimine-cho, Yamamoto-gun, Akita Prefecture (within the Tomeyama area). KAY 723 strain has been deposited as follows.
(1) (Accession number: NITE P-03028)
(2) (Accepted date: September 26, 2019)
(3) Deposit location: National Institute of Technology and Evaluation, Biotechnology Center, Patent Microorganisms Depositary (NPMD), 2-5-8 Kazusa Kamatari, Kisarazu, Chiba, Japan

The KAY 723 strain exhibits the following mycological characteristics. (+: positive, -: negative)
Freeze-thaw resistance: +
Trehalose accumulation ability: +
Glucose utilization: +
Sucrose utilization: +
Maltose assimilation ability: +
Fermentation ability in unsweetened bread dough: +
Fermentation ability in low sucrose dough: +
Fermentation ability in high sucrose dough: +
Grows well in the presence of 46% (w/v) glucose, can grow even in the presence of 50% (w/v) Grows well in the presence of 6% (w/v) salt, can grow even in the presence of 10% (w/v) Oval shape with nucleus and vacuoles Grows by budding Forms dull milky white colonies with a diameter of 2 to 8 mm on YPD plate medium

The yeast of the present invention may be a mutant strain having high freeze-thaw resistance equivalent to that of the above-mentioned KAY 723 strain. For example, the mutant strain may have an identity of about 90% or more to the entire genome sequence of the Saccharomyces cerevisiae KAY 723 strain, and a survival rate of 70% or more after two repeated freeze-thaw treatments. In another embodiment, the mutant strain may have an identity of about 90% or more to the entire genome sequence of the Saccharomyces cerevisiae KAY 723 strain, and a survival rate of 55% or more after two repeated freeze-thaw treatments.

The sequence identity can be determined by using known software such as BLAST (Basic Local Alignment Search Tool). In the yeast of the present invention, the identity to the entire genome sequence of the KAY 723 strain is preferably about 93% or more, more preferably about 95% or more, and even more preferably about 96, about 97, about 98, or about 99% or more. According to the entire genome sequences of Saccharomyces cerevisiae published so far, the genome size is generally about 12 Mb to 12.5 Mb. Known sequences of Saccharomyces cerevisiae can be searched, for example, through NCBI (National Center for Biotechnology Information), DDBJ (DNA Data Bank Of Japan), etc.

2. Use of the yeast of the present invention The yeast of the present invention may be in various forms. One embodiment of the present invention may be a frozen yeast composition obtained by freezing the above-mentioned Saccharomyces cerevisiae cells. As described above, the Saccharomyces cerevisiae of the present invention has excellent resistance to freezing and thawing, and is suitable for storage and distribution as a frozen product.

The frozen yeast composition can be, for example, frozen bread dough, frozen pizza dough, etc. In one embodiment, the Saccharomyces cerevisiae of the present invention has excellent bread-making suitability and is suitable as frozen bread dough. In one embodiment, the Saccharomyces cerevisiae of the present invention has excellent salt tolerance and can be used suitably in foods containing salt.

The yeast of the present invention can be added to food ingredients in the same way as regular yeast and used to produce fermented foods. The yeast of the present invention can be suitably used in the method of producing bread.

Furthermore, if the yeast added to the dough is not viable, fermentation will not proceed, and the dough and bread will not rise sufficiently. In one embodiment, the yeast of the present invention has a higher survival rate than conventional yeast even when repeatedly frozen and thawed in a freezer at around -18°C, which is commonly used in household refrigerators, making it suitable for use in bread dough for home bakeries.

In one embodiment, the yeast of the present invention has the ability to assimilate glucose, sucrose, and maltose, and also has the ability to ferment sugar-free, low-sugar, and high-sugar bread dough, making it highly suitable for bread making. Therefore, the yeast of the present invention can be suitably used in the production of bread by adding it to bread dough and baking it.

The yeast of the present invention may also be dried to give a dried cell form. In the case of dried cells, they may be stored at room temperature or in a refrigerator at a temperature of -10°C or higher and lower than 0°C.

One embodiment of the present invention may be a method for preserving Saccharomyces cerevisiae, in which the above-mentioned Saccharomyces cerevisiae cells are frozen at -10 to -30°C. The freezing temperature does not have to be constant, and for example, the cells may be flash-frozen at about -20°C to -30°C, and then frozen or refrigerated at about -19°C to -10°C. As described above, the yeast of the present invention has a higher survival rate than conventional yeast even when repeatedly frozen and thawed in a freezer at about -18°C, which is commonly used in household refrigerators. Therefore, preferred embodiments of the method for preserving the yeast of the present invention may be, for example, frozen storage at -10°C to -20°C, -15°C to -19°C, or around -18°C.

The present invention will be described in detail below with reference to examples, but the technical scope of the present invention is not limited to the following examples.

In the examples below, the dough amounts are expressed in baker's percentage. Baker's percentage is the weight percentage of the flour used in the dough, and is abbreviated as BP. To give an example, if you use 70 baker's percentage of water, you would use 70g of water for 100g of flour. Similarly, you would use 175g of water for 250g of flour.

YPD liquid medium was prepared as follows. 1 g of Yeast Extract (Difco), 2 g of Polypeptone (Difco), and 2 g of Dextrose (Kanto Chemical) were accurately weighed, dissolved in distilled water, and made up to 100 ml. This YPD liquid medium was sterilized in an autoclave at 121°C for 15 minutes, cooled to room temperature, and used. YPD agar medium was prepared by adding agar to the above YPD liquid medium components to make a concentration of 1.5% (w/v), and sterilizing before use.

The live yeast was prepared as follows. The live yeast was prepared by pre-culturing the stock strain, followed by main culture, and washing the resulting cells. The stock strains were stored at -80°C as 20% (w/w) glycerol suspension.
The cells were washed twice with sterile physiological saline and used as live yeast.

The KAY 723 strain, which is an example of the yeast of the present invention, was isolated by the method described below.
1. Isolation of Microorganisms 1.1. Isolation of Bacterial Strains 0.1 g of leaf mold collected with permission from the competent authorities from the buffer zone of the World Natural Heritage site "Shirakami-Sanchi" in Hachimori, Hachimine-cho, Yamamoto-gun, Akita Prefecture (within the area of Tome-sanchi) was placed in a medium containing 200 ppm chloramphenicol, 0.3 g glucose, 0.1 g peptone, 0.05 g yeast extract, and 10 ml of tap water, and cultured at 25-26°C with a shaking amplitude of 5 cm for 5-7 days to allow yeast to multiply. After that, the yeast was cultured at 27°C for 3 days on a koji juice agar medium containing 50 g powdered koji extract, 15 g agar, 1,000 ml of tap water, and a pH of 5.0, to isolate the pure strain.

1.2. Selection of Trehalose-producing Bacteria The strain isolated purely by the above method was placed in 5 ml of YPD medium consisting of 1 g yeast extract, 2 g peptone, 2 g glucose, and 100 ml distilled water, and cultured at 30°C, 5 cm amplitude, and 250 rpm for 2 days as a preculture. For main culture, 1/100 of the preculture liquid was inoculated into the YPD medium, and cultured at 30°C, 120 revolutions per minute, and 2 days as a shake culture. The cells obtained in the main culture were centrifuged at 4,000 rpm and 4°C for 10 minutes using a centrifuge, the supernatant was discarded, and the cells were collected.

0.5 g of the cells were extracted with 2.5% trichloroacetic acid, and the trehalose in the extract was measured by high performance liquid chromatography (Hitachi High-Tech Science Corporation). Eleven strains (high trehalose accumulation strains) that showed a trehalose content of 19% or more based on the dry cell weight were selected.

2. Selection of Saccharomyces cerevisiae Some yeasts are pathogenic. Among them, Saccharomyces cerevisiae is a yeast that is widely used in foods such as bread and sake. In order to obtain yeast that can be used in food processing such as bread making, it is necessary to select Saccharomyces cerevisiae from the trehalose-accumulating strains obtained above. Therefore, we attempted to identify and select Saccharomyces cerevisiae that can be widely used in foods from the 11 trehalose-accumulating strains obtained above.

Saccharomyces cerevisiae was identified by comparing the homology of the ribosomal RNA (rRNA) base sequences contained in the fungus. It has been shown that the homology of the base sequences of the ITS region of rRNA base sequences is 99% or more between strains of the same species, and this figure is generally used as a guideline for identification. Therefore, identification was attempted by comparing the homology of the base sequences of the D1/D2 regions of the 26/28S rRNA genes in addition to the ITS region of the rRNA base sequences. The homology comparison of the base sequences was performed using BLAST.

As a result, four strains of Saccharomyces cerevisiae were obtained. Of the four strains, three showed 100% homology in both the ITS region and the D1/D2 region. One strain had 99% homology in the ITS region, but the D1/D2 region of this strain showed 100% homology, and was therefore identified as Saccharomyces cerevisiae. From the above, four strains of yeast Saccharomyces cerevisiae that can be used as food were obtained from the 11 strains. These four strains are Saccharomyces cerevisiae that accumulate high amounts of trehalose.

3. Carbohydrate assimilation test for Saccharomyces cerevisiae Types of sugar-free bread include French bread and baguette. Wheat flour contains a lot of maltose as well as glucose as a carbohydrate. Therefore, we tried to select a strain that can grow using glucose, sucrose, or maltose as a carbon source.

The four trehalose-accumulating Saccharomyces cerevisiae strains obtained above were then cultured in 5 ml of YPD medium at 30°C with a shaking amplitude of 5 cm for 2 days at 250 rpm to obtain a preculture solution.

Three types of YPD medium with different carbohydrates were prepared, each consisting of 1 g yeast extract, 2 g peptone, 2 g carbohydrate, and 100 ml distilled water, with the carbohydrate being either 2 g glucose, 2 g sucrose, or 2 g maltose. 1/100 volume of preculture solution was added to 5 ml of each YPD medium and thoroughly suspended, after which 200 μl of each was transferred to a round-bottom 96-well microplate (manufactured by Iwaki Glass Co., Ltd.). The microplate was measured for absorbance at 600 nm every hour at 30°C using an incubation reader HiTS (manufactured by Synix Co., Ltd.), and the growth of the microorganisms was measured from the increase in the value.

As a result, one of the four strains showed very poor growth in the presence of maltose, suggesting that it had virtually no ability to utilize maltose. As a result, three strains were selected that showed good growth even in a medium containing maltose as the sole carbon source. These three strains are Saccharomyces cerevisiae that accumulate high amounts of trehalose and grow well in a medium containing maltose as the sole carbon source.

4. Measurement of the amount of carbon dioxide gas generated in low-sugar or sugar-free bread dough The amount of carbon dioxide gas generated in each low-sugar or sugar-free bread dough was measured for the three strains of Saccharomyces cerevisiae obtained through the above "3. Carbohydrate assimilation test of Saccharomyces cerevisiae".

The amount of carbon dioxide gas generated was observed based on the baker's yeast test method of the Japan Yeast Industry Association. As Comparative Example 1, a commercially available baker's yeast (Super Camellia Dry Yeast (Nissin Flour Milling Group)) was used. The commercially available baker's yeast used was live yeast obtained by culturing in YPD medium.

100g of wheat flour was accurately weighed out and mixed with water to BP = 70% and salt to BP = 1.5% to obtain the base dough. For the no-sugar dough, no sucrose was added to the base dough. For the low-sugar dough, sucrose was added to the base dough to BP = 6%. Live yeast or dry yeast was added as the test yeast.

The amount of carbon dioxide generated was measured at 30°C using a Fermograph (registered trademark, manufactured by ATTO). A Fermograph is a device that measures the amount of gas generated in a system over time, and the unit is ml. The amount of gas generated per unit time was measured as "each gas," and the cumulative total amount of gas generated was measured as "total gas." The amount of gas generated (ml) obtained was converted to 3 g of live yeast.

In the low sugar bread dough, the amount of carbon dioxide gas generated was measured over time for 900 minutes (15 hours). As a result of the measurement, the initial carbon dioxide gas generation pattern of each strain in the low sugar bread dough was similar. However, it was found that only one of the three strains of Saccharomyces cerevisiae obtained through the above-mentioned "3. Carbohydrate assimilation test of Saccharomyces cerevisiae" (No. 723 strain) and the commercially available baker's yeast of Comparative Example 1 continued to generate carbon dioxide gas slowly even after 6 hours. On the other hand, the other two strains obtained through the above-mentioned carbohydrate assimilation test showed a large decrease in carbon dioxide gas generation after 6 hours, and the degree of increase in the cumulative total amount of carbon dioxide gas generated became very slow.
From this result, it was judged that, although all strains are suitable for bread making in low sugar dough, No. 723 strain and the commercially available baker's yeast of Comparative Example 1 are particularly excellent.

Similarly, measurements using sugar-free bread dough showed good carbon dioxide gas generation patterns for strain No. 723 and the commercially available baker's yeast of Comparative Example 1. The other two strains obtained through the carbohydrate assimilation test above showed very similar carbon dioxide gas generation patterns, and it was found that the amount of carbon dioxide gas generated in sugar-free bread dough between 0 and 10 hours was significantly lower than that of No. 723 and Comparative Example 1.

From the above results, it was determined that, among the three strains of Saccharomyces cerevisiae obtained through the above "3. Carbohydrate assimilation test of Saccharomyces cerevisiae", strain No. 723 was the strain with the highest suitability for bread making in sugar-free dough.

Based on the results obtained so far, one strain, No. 723, was selected as Saccharomyces cerevisiae with excellent fermentation properties and high trehalose accumulation, and the selection test was completed. This No. 723 strain was named KAY 723.

5. Measurement of carbon dioxide gas generation in high sugar dough Selected by the test up to "4. Measurement of carbon dioxide gas generation in low sugar or sugar-free dough" above, has excellent bread making suitability and accumulates trehalose highly, KAY 723 strain is examined bread making suitability in high sugar dough, and compares the difference of fermentation characteristics with the commercially available baker's yeast of comparative example 1.

The high sugar dough was prepared by adding sucrose (BP = 30%) to the above base dough. All other points regarding the measurement method were the same as those for the low sugar or sugar-free bread dough.

The results of the measurements showed that the amount of gas generated by the KAY 723 strain over time was almost always greater than the amount of carbon dioxide generated by the commercially available baker's yeast of Comparative Example 1, and the cumulative amount of gas generated was always greater than the amount of gas generated by the commercially available baker's yeast of Comparative Example 1. In other words, it was determined that the KAY 723 strain has superior fermentation ability to the commercially available baker's yeast of Comparative Example 1.

These results suggest that KAY 723 can be used to produce sugar-free, low-sugar, and high-sugar bread, making it possible to improve the time efficiency of bread-making.

6. Survival rate after repeated freezing and thawing <Significance>
To determine the resistance to freezing and thawing, the survival rate against repeated freezing and thawing was calculated as follows. Generally, when freezing and storing microorganisms, a temperature of -80°C is used because the survival rate is high. In contrast, the temperature of a household freezer, -18°C, is a temperature at which the survival rate of microorganisms is very low, that is, a temperature at which microorganisms are likely to die.

Therefore, yeast that has a high survival rate at -18°C, the temperature of a domestic freezer, is highly useful for enabling repeated freezing and thawing of frozen blocks of live yeast used in the baking industry.

<Measurement of survival rate>
The test bacteria used were: Example 1: KAY 723 strain, Comparative Example 1: commercially available baker's yeast (Super Camellia Dry Yeast (Nisshin Flour Milling Group)), Comparative Example 2: Shirakami Kodama yeast, and Comparative Example 3: Kyokai No. 7 yeast, which is widely used as Saccharomyces cerevisiae. Live bacteria were used for each test bacteria.

YPD medium (1% (w/v) yeast extract, 2% (w/v) peptone, 2% (w/v) glucose) was prepared as the medium. A Sakaguchi flask containing 150 mL of YPD medium was prepared, the test bacteria was added, and cultured for 96 hours before the first freezing. 10 mL of the resulting culture was harvested in a 15 mL centrifuge tube (3000 rpm, 10 minutes) and washed once with sterile water. After washing, it was immediately cooled in a -20°C freezer. It was thawed every 2 or 3 days, and a portion was sampled, diluted with sterile water, and spread on YPD agar medium (agar 2% (w/v)).

The number of colonies formed on the YPD agar medium was counted, and the average colony count was calculated. The survival rate (%) was calculated from the average colony count after each thawing and the average initial bacterial count. The results are shown in Table 1.

As shown in Table 1, Example 1 (KAY 723 strain) maintained a viability rate of 80% or more even after the first and second freeze-thaw cycles, and even after three freeze-thaw cycles, the viability rate was still as high as 60%.

In contrast, the viability of the commercially available baker's yeast in Comparative Example 1 dropped to approximately 56% after one freeze-thaw cycle, and fell below 20% after three freeze-thaw cycles. Comparative Example 2 (Shirakami Kodama yeast) maintained a viability of approximately 80% after the first freeze-thaw cycle, but fell below 50% after three freeze-thaw cycles.

7. Measurement of Trehalose Content The trehalose content was measured using Kyokai No. 7 yeast, which is widely used as Saccharomyces cerevisiae, in the above-mentioned Example 1, Comparative Examples 1 and 2, and Comparative Example 3, and the results are shown in Table 2. The trehalose content was measured in the same manner as in the above "1.2. Selection of trehalose-producing bacteria".

The yeast of Example 1 was found to be a yeast that accumulates high amounts of trehalose.

8. Growth Ability in the Presence of High Salt Concentrations The YPD medium used in "1.2. Selection of Trehalose-Producing Bacteria" above was used as the default base medium, and the growth ability of yeast was evaluated under predetermined salt concentration conditions in 1% increments in the range of salt concentrations from 0 to 11%. The yeasts used were those of Example 1 and Comparative Examples 1 and 2. The growth of the yeast was measured over time using an incubation reader (manufactured by Synix Co., Ltd.) in the same manner as in "3. Carbohydrate assimilation test of Saccharomyces cerevisiae" above. Measurements were performed from 0 hours to 168 hours.

The growth rate of Example 1 (KAY 723 strain) tended to decrease as the salt concentration increased compared to Comparative Example 2 (Shirakami Kodama yeast). However, the maximum salt concentration at which the yeast of Comparative Example 2 could grow was 9%, whereas Example 1 began to grow after about 100 hours even under conditions of a salt concentration of 10%, and was shown to be capable of growing up to a maximum salt concentration of 10%. The maximum salt concentration at which the commercially available yeast of Comparative Example 1 could grow was 9%. Of these three types of yeast, the yeast of Example 1 was shown to be capable of growing even under conditions of the highest salt concentration, and to have excellent salt tolerance.

9. Growth in the Presence of High Concentration Glucose The YPD medium used in "1.2. Selection of Trehalose-Producing Bacteria" above was used as the default base medium, and YPD medium containing different concentrations of glucose was prepared, and the growth of yeast was evaluated under predetermined glucose concentration conditions in the range of glucose concentrations from 2 to 50% (w/v). The yeasts used were those of Example 1, Comparative Examples 1 and 2. The growth of yeast was measured over time using an incubation reader (manufactured by Synix Co., Ltd.) in the same manner as in "3. Carbohydrate assimilation test of Saccharomyces cerevisiae" above. Measurements were performed from 0 hours to 168 hours.

Example 1 (KAY 723 strain) showed good growth even at a glucose concentration of 46% (w/v), and could grow even at a glucose concentration of 50% (w/v). On the other hand, the commercial yeast of Comparative Example 1 showed significantly poor growth at glucose concentrations above 42% (w/v). Comparative Example 2 (Shirakami Kodama yeast) also showed a tendency for growth to be inferior to that of Example 1 at a glucose concentration of 50% (w/v). Among Example 1, Comparative Examples 1 and 2, the yeast of Example 1 was found to have the best sugar tolerance.

Claims (7)

Saccharomyces cerevisiae KAY 723 strain, which has the accession number NITE P-03028 . A frozen yeast composition, which is a frozen product containing the Saccharomyces cerevisiae cells according to claim 1. Frozen bread dough containing the Saccharomyces cerevisiae cells according to claim 1. Dried baker's yeast, which is a dried product of the Saccharomyces cerevisiae cells according to claim 1. A method for producing a fermented food, comprising fermenting the Saccharomyces cerevisiae cells according to claim 1. A method for producing bread, comprising baking dough containing the Saccharomyces cerevisiae cells according to claim 1. A method for preserving Saccharomyces cerevisiae, comprising freezing the cells of Saccharomyces cerevisiae according to claim 1 at -10 to -30°C.