Method for activating freeze-thaw tolerance of yeast in fermented flour product

Abstract

The invention discloses a method for activating freeze-thaw tolerance of yeast in a fermented flour product, and belongs to the technical field of fermented flour product processing. The method for activating the freeze-thaw tolerance of the yeast in the fermented flour product specifically comprises the following steps: mixing and pretreating the yeast with ethanol to obtain the freeze-thaw tolerant yeast, then processing the freeze-thaw tolerant yeast for frozen fermented dough, and preparing the frozen fermented dough through the processes of dough kneading, compression molding, pre-fermentation, freezing or cold storage and the like. According to the method, the yeast is pretreated by ethanol, and a protection mechanism of yeast cells is activated, so that the freeze-thaw tolerance of the yeast is improved by a convenient and feasible method, the activity of the yeast in the freeze-thaw process is maintained, and meanwhile, the problem of quality deterioration of frozen dough products after freeze-thaw is solved.

Description

Technical Field

[0001] The invention relates to a method for activating freeze-thaw tolerance of yeast in fermented flour products, and belongs to the technical field of fermented flour product processing. Background Art

[0002] The application of frozen dough is conducive to large-scale industrial production, product quality standardization, saving time, labor, materials, land, and ready-to-use. However, in the actual industrial application and enterprise production process, there will be inevitable temperature fluctuations, and the product quality will deteriorate to varying degrees. Among them, the weakening of yeast activity during the freeze-thaw cycle is an important factor affecting the quality of frozen dough, especially fermented dough and its products.

[0003] At present, the research on maintaining yeast activity mainly focuses on adding improvers and antifreeze agents to reduce the damage of freezing to yeast cells, or selecting more frost-resistant yeast strains and bioengineering yeast to improve frost resistance. However, there are problems such as the use of many additives, complex processes and high costs. Chinese invention patent CN 114982799B discloses a composite improver for frozen dough of whole wheat bread and its application, wherein the improver includes xanthan gum, lipase and xylanase. Chinese invention patent CN 115530209B discloses a frozen dough containing yeast and its preparation method, wherein the yeast is embedded with succinic acid monoglyceride, propylene glycol and modified starch in the improver before use. Frozen dough fermentation improvers have the problems of complex ingredients, complex production process and high cost, which greatly limits their practical application in the food industry.

[0004] Therefore, it is necessary to develop a simple, effective and economical method to improve the quality deterioration of frozen dough caused by temperature fluctuations in actual production. Summary of the invention

[0005] [Technical issues]

[0006] Frozen dough has the advantages of saving processing time and space in the food industry. However, due to the inevitable temperature fluctuations in the actual production and transportation process, yeast activity decreases, gas production capacity is insufficient, and product quality deteriorates. Therefore, solving the problem of yeast gas production and improving yeast's ability to resist freezing and thawing are technical issues that need to be urgently addressed in the promotion and development of frozen dough technology.

[0007] [Technical solution]

[0008] In order to overcome the problems and defects of the prior art, the present invention provides a method for activating the freeze-thaw tolerance of yeast by pre-treating yeast with ethanol, and at the same time improving the quality of frozen dough products. Compared with adding improvers, antifreeze agents, laboratory screening and yeast transformation, the present invention is a more convenient and easy method suitable for industrialization. Pre-treating yeast with ethanol activates the cell protection mechanism of yeast, protects cells from damage, so that yeast has a better ability to cope with freeze-thaw, maintain cell homeostasis, maintain the vitality of yeast during the freeze-thaw process of fermented dough, and improve the quality of products.

[0009] In order to achieve the above purpose, the technical solutions provided are as follows:

[0010] The present invention provides a method for activating freeze-thaw tolerance of yeast in a fermented flour product, the method comprising the following steps:

[0011] (1) Dispersing yeast in purified water to form yeast solution;

[0012] (2) preparing a food-grade ethanol aqueous solution with a volume fraction of 10% to 30%;

[0013] (3) Mixing the yeast solution of step (1) and the ethanol aqueous solution of step (2), stirring and mixing, standing, centrifuging, and removing the supernatant to obtain freeze-thaw tolerant yeast.

[0014] In one embodiment, the yeast in step (1) is commercial yeast.

[0015] In one embodiment, the concentration of the yeast solution in step (1) is 0.1-10 g / ml.

[0016] In one embodiment, the volume fraction of ethanol in the food-grade ethanol aqueous solution in step (2) is 10% to 20%.

[0017] In one embodiment, the volume ratio of the yeast solution and the ethanol aqueous solution in step (3) is 1:1.

[0018] In one embodiment, the standing temperature in step (3) is 0 to 25° C. and the standing time is 1 to 24 hours.

[0019] In one embodiment, the centrifugation condition in step (3) is 3000-5000×g, 3-5 min.

[0020] The present invention also provides a freeze-thaw tolerant yeast obtained by the above method.

[0021] The invention also provides a method for preparing frozen fermented dough, which comprises mixing flour, water and the freeze-thaw tolerant yeast, kneading the dough, pressing and shaping the dough, pre-proofing the dough, and freezing or refrigerating the dough to obtain the frozen fermented dough.

[0022] In one embodiment, the dough is kneaded in a dough mixer under the following conditions: mixing at a medium speed of 200 to 240 r / min for 3 to 6 minutes.

[0023] In one embodiment, the pre-proofing is performed at 35-40° C. and 65%-85% relative humidity for 10-30 minutes.

[0024] In one embodiment, the freezing or refrigeration is followed by storage at -10 to -40°C.

[0025] In one embodiment, the freezing or refrigeration further comprises: freezing in a -40°C refrigerator until the core temperature reaches -18°C, transferring to a -18°C refrigerator for frozen storage and multiple freeze-thaw cycles.

[0026] In one embodiment, the multiple freeze-thaw cycles are to pre-freeze the pre-proofed dough at -10 to -40°C for 30 to 60 minutes, then transfer the pre-frozen dough to -10 to -20°C for 1 to 10 days of frozen storage, and then thaw the frozen dough at a temperature of 10 to 30°C and a relative humidity of 30% to 70% for 20 to 60 minutes, which is one freeze-thaw cycle, and perform 1 to 3 freeze-thaw cycles respectively.

[0027] The invention also provides frozen fermented dough prepared by the method.

[0028] The invention also provides a frozen fermented dough product prepared by using the frozen fermented dough.

[0029] In one embodiment, the frozen fermented dough products include steamed buns, rolls, dumplings, sesame cakes, bread, and fried dough sticks.

[0030] Beneficial effects:

[0031] (1) The present invention pre-treats yeast with ethanol, which affects yeast cell growth and vitality, inhibits key enzyme activities, interferes with various cell metabolisms and reduces yeast fermentation performance. At this time, yeast will adjust the composition and structure of the cell membrane to cope with the effects of ethanol to enhance the stability of the cell membrane; secondly, yeast can also activate antioxidant stress systems, such as peroxidase system and glutathione system, to remove active oxygen free radicals and protect cells from damage. Since ethanol pre-treats yeast, the cell protection mechanism of yeast is activated, and the content of protective metabolites such as trehalose in yeast cells increases, the yeast pre-treated with ethanol has better freeze-thaw tolerance than the yeast that has not been activated.

[0032] (2) The present invention pre-treats yeast with ethanol to activate the protective mechanism of yeast cells, thereby improving the freeze-thaw tolerance of yeast in a convenient and easy way, maintaining the activity of yeast during the freeze-thaw process, and improving the quality deterioration problem of frozen dough products after freeze-thaw. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a graph showing the change in specific volume of the frozen fermented dough steamed bread of Example 1 during the freeze-thaw cycle;

[0034] Figure 2 is a graph showing the change in specific volume of the frozen fermented dough steamed bread of Example 2 during the freeze-thaw cycle;

[0035] Figure 3 is a graph showing the change in specific volume of the frozen fermented dough steamed bread of Example 3 during the freeze-thaw cycle;

[0036] Figure 4 is a graph showing the change in specific volume of the frozen fermented dough steamed bread of Comparative Example 1 during the freeze-thaw cycle;

[0037] Figure 5 The figure is a graph showing the changes in yeast survival rate in Examples 1 to 3 and the comparative example. DETAILED DESCRIPTION

[0038] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention. The following specific implementation methods further describe the present invention.

[0039] The present invention relates to a determination method:

[0040] Determination of specific volume: Cool the steamed frozen dough buns to room temperature, use a balance to measure their mass (g), accurate to 0.1g, and use the rapeseed displacement method to measure the volume (mL) of the buns, accurate to 1mL. Calculate the ratio of the volume (mL) of the buns to the mass (g), which is the specific volume. Repeat the test at least three times and take the average value.

[0041] Yeast survival rate determination method: Dilute the pretreated yeast with pure water, then mix the yeast with 0.05% methylene blue dye solution, drop the stained yeast on the cell counting plate, observe the yeast under an optical microscope and count the cells. The counting formula is as follows:

[0042]

[0043] NL is the number of live cells that were rejected for staining, and ND is the number of dead cells that were stained.

[0044] The reagents and raw materials used in the embodiments and comparative examples of the present invention can be purchased on the market, such as fresh yeast (Saccharomyces cerevisiae): Yanshan fresh yeast, Yantai Mauri Yeast Co., Ltd., Yantai City, Shandong Province; anhydrous ethanol (Ethanol): Tianjin Hengxing Chemical Reagent Manufacturing Co., Ltd., Tianjin City.

[0045] Example 1

[0046] A method for activating freeze-thaw tolerance of yeast in fermented flour products comprises the following steps:

[0047] (1) Disperse fresh yeast in purified water at room temperature to a concentration of 0.1 g / mL to obtain yeast solution;

[0048] (2) preparing an ethanol aqueous solution with a concentration of 10% (V / V) using food grade anhydrous ethanol;

[0049] (3) The yeast solution of step (1) and the ethanol solution of step (2) are mixed in a volume ratio of 1:1, stirred and mixed, and allowed to stand at 25° C. for 18 hours to obtain a yeast pretreatment mixture; the yeast pretreatment mixture is centrifuged at 3000×g for 3 minutes, and the supernatant is removed to obtain the pretreated yeast.

[0050] A method for preparing frozen fermented dough steamed buns comprises the following steps:

[0051] (1) Preparation of frozen fermented dough

[0052] 1) Frozen dough formula: 500g flour, 238g purified water, 10g pretreated yeast;

[0053] 2) After the above formula is mixed evenly, it is mixed in a dough mixer at a medium speed of 240 r / min for 3 minutes to obtain a dough, and then the dough is pressed 12 times by a dough press, and the pressed dough is cut into 50 g pieces, and kneaded 15-20 times into a cylindrical shape, and transferred to a proofing box, and pre-proofed for 20 minutes in an environment with a relative humidity of 65% and a temperature of 35° C.;

[0054] 3) Place the pre-proofed dough in a -40°C refrigerator and freeze until the center temperature reaches -18°C. Then transfer it to a -18°C refrigerator for 23 hours to obtain frozen fermented dough.

[0055] (2) freeze-thaw cycle process: the frozen fermented dough prepared in step (1) was thawed at a temperature of 30° C. and a relative humidity of 65% for 1 h, and then frozen at −18° C. for 23 h, which was one freeze-thaw cycle. The freeze-thaw cycles were performed 1, 2, and 3 times respectively;

[0056] (3) Preparation of frozen dough steamed bread

[0057] The fermented dough after the freeze-thaw cycle in step (2) is transferred to a proofing box at 38° C. and a relative humidity of 75% for fermentation for 1 hour, and the fermented dough is transferred to a multi-purpose steaming oven and steamed for 15 minutes at a steaming condition of 100° C. and a relative humidity of 100%, thereby obtaining frozen fermented dough steamed buns.

[0058] A method for preparing fresh steamed buns: the dough pre-proofed in step (1) is further proofed for 20 minutes, and then steamed in a multi-purpose steaming oven at a temperature of 100° C. and a humidity of 100% for 15 minutes to obtain fresh steamed buns.

[0059] Example 2

[0060] A method for activating freeze-thaw tolerance of yeast in fermented flour products comprises the following steps:

[0061] (1) Disperse fresh yeast in purified water at room temperature to a concentration of 0.1 g / mL to obtain yeast solution;

[0062] (2) preparing an ethanol aqueous solution with a concentration of 20% (V / V) using food grade anhydrous ethanol;

[0063] (3) The yeast solution of step (1) and the ethanol solution of step (2) are mixed in a volume ratio of 1:1, stirred and mixed, and allowed to stand at 25° C. for 18 hours to obtain a yeast pretreatment mixture; the yeast pretreatment mixture is centrifuged at 3000×g for 3 minutes, and the supernatant is removed to obtain the pretreated yeast.

[0064] A method for preparing frozen fermented dough steamed buns comprises the following steps:

[0065] (1) Preparation of frozen fermented dough

[0066] 1) Frozen dough formula: 500g flour, 238g purified water, 10g pretreated yeast;

[0067] 2) After the above formula is mixed evenly, it is mixed in a dough mixer at a medium speed of 240 r / min for 3 minutes to obtain a dough, and then the dough is pressed 12 times by a dough press, and the pressed dough is cut into 50 g pieces, and kneaded 15-20 times into a cylindrical shape, and transferred to a proofing box, and pre-proofed for 20 minutes in an environment with a relative humidity of 65% and a temperature of 35° C.;

[0068] 3) Place the pre-proofed dough in a -40°C refrigerator and freeze until the center temperature reaches -18°C. Then transfer it to a -18°C refrigerator for 23 hours to obtain frozen fermented dough.

[0069] (2) freeze-thaw cycle process: the frozen fermented dough prepared in step (1) was thawed at a temperature of 30° C. and a relative humidity of 65% for 1 h, and then frozen at −18° C. for 23 h, which was one freeze-thaw cycle. The freeze-thaw cycles were performed 1, 2, and 3 times respectively;

[0070] (3) Preparation of frozen dough steamed bread

[0071] The fermented dough after the freeze-thaw cycle in step (2) is transferred to a proofing box at 38° C. and a relative humidity of 75% for fermentation for 1 hour, and the fermented dough is transferred to a multi-purpose steaming oven and steamed for 15 minutes at a steaming condition of 100° C. and a relative humidity of 100%, thereby obtaining frozen fermented dough steamed buns.

[0072] A method for preparing fresh steamed buns: the dough pre-proofed in step (1) is further proofed for 20 minutes, and then steamed in a multi-purpose steaming oven at a temperature of 100° C. and a humidity of 100% for 15 minutes to obtain fresh steamed buns.

[0073] Example 3

[0074] A method for activating freeze-thaw tolerance of yeast in fermented flour products comprises the following steps:

[0075] (1) Disperse fresh yeast in purified water at room temperature to a concentration of 0.1 g / mL to obtain yeast solution;

[0076] (2) preparing an ethanol aqueous solution with a concentration of 30% (V / V) using food grade anhydrous ethanol;

[0077] (3) The yeast solution of step (1) and the ethanol solution of step (2) are mixed in a volume ratio of 1:1, stirred and mixed, and allowed to stand at 25° C. for 18 hours to obtain a yeast pretreatment mixture; the yeast pretreatment mixture is centrifuged at 3000×g for 3 minutes, and the supernatant is removed to obtain the pretreated yeast.

[0078] A method for preparing frozen fermented dough steamed buns comprises the following steps:

[0079] (1) Preparation of frozen fermented dough

[0080] 1) Frozen dough formula: 500g flour, 238g purified water, 10g pretreated yeast;

[0081] 2) After the above formula is mixed evenly, it is mixed in a dough mixer at a medium speed of 240 r / min for 3 minutes to obtain a dough, and then the dough is pressed 12 times by a dough press, and the pressed dough is cut into 50 g pieces, and kneaded 15-20 times into a cylindrical shape, and transferred to a proofing box, and pre-proofed for 20 minutes in an environment with a relative humidity of 65% and a temperature of 35° C.;

[0082] 3) Place the pre-proofed dough in a -40°C refrigerator and freeze until the center temperature reaches -18°C. Then transfer it to a -18°C refrigerator for 23 hours to obtain frozen fermented dough.

[0083] (2) freeze-thaw cycle process: the frozen fermented dough prepared in step (1) was thawed at a temperature of 30° C. and a relative humidity of 65% for 1 h, and then frozen at −18° C. for 23 h, which was one freeze-thaw cycle. The freeze-thaw cycles were performed 1, 2, and 3 times respectively;

[0084] (3) Preparation of frozen dough steamed bread

[0085] The fermented dough after the freeze-thaw cycle in step (2) is transferred to a proofing box at 38° C. and a relative humidity of 75% for fermentation for 1 hour, and the fermented dough is transferred to a multi-purpose steaming oven and steamed for 15 minutes at a steaming condition of 100° C. and a relative humidity of 100%, thereby obtaining frozen fermented dough steamed buns.

[0086] A method for preparing fresh steamed buns: the dough pre-proofed in step (1) is further proofed for 20 minutes, and then steamed in a multi-purpose steaming oven at a temperature of 100° C. and a humidity of 100% for 15 minutes to obtain fresh steamed buns.

[0087] Comparative Example 1

[0088] A method for preparing frozen fermented dough steamed buns comprises the following steps:

[0089] (1) Preparation of frozen fermented dough

[0090] 1) Frozen dough formula: 500g flour, 238g purified water, 10g untreated yeast;

[0091] 2) After the above formula is mixed evenly, it is mixed in a dough mixer at a medium speed of 240 r / min for 3 minutes to obtain a dough, and then the dough is pressed 12 times by a dough press, and the pressed dough is cut into 50 g pieces, and kneaded 15-20 times into a cylindrical shape, and transferred to a proofing box, and pre-proofed for 20 minutes in an environment with a relative humidity of 65% and a temperature of 35° C.;

[0092] 3) Place the pre-proofed dough in a -40°C refrigerator and freeze until the center temperature reaches -18°C. Then transfer it to a -18°C refrigerator for 23 hours to obtain frozen fermented dough.

[0093] (2) freeze-thaw cycle process: the frozen fermented dough prepared in step (1) was thawed at a temperature of 30° C. and a relative humidity of 65% for 1 h, and then frozen at −18° C. for 23 h, which was one freeze-thaw cycle. The freeze-thaw cycles were performed 1, 2, and 3 times respectively;

[0094] (3) Preparation of frozen dough steamed bread

[0095] The fermented dough after the freeze-thaw cycle in step (2) is transferred to a proofing box at 38° C. and a relative humidity of 75% for fermentation for 1 hour, and the fermented dough is transferred to a multi-purpose steaming oven and steamed for 15 minutes at a steaming condition of 100° C. and a relative humidity of 100%, thereby obtaining frozen fermented dough steamed buns.

[0096] A method for preparing fresh steamed buns: the dough pre-proofed in step (1) is further proofed for 20 minutes, and then steamed in a multi-purpose steaming oven at a temperature of 100° C. and a humidity of 100% for 15 minutes to obtain fresh steamed buns.

[0097] Results Analysis

[0098] 1. Specific volume (mL / g) of the steamed bread prepared in Examples 1 to 3 and Comparative Example 1 was measured

[0099] Table 1 Specific volume results of steamed bread obtained in Examples 1-3 and Comparative Example 1

[0100] Fresh steamed buns Freeze-thawed steamed buns Freeze-thaw steamed buns Freeze-thaw 3 times steamed buns Example 1 3.08 3.05 2.95 2.94 Example 2 3.10 3.05 2.90 2.90 Example 3 3.09 3.01 2.72 2.71 Comparative Example 1 3.05 2.78 2.76 2.35

[0101] From Table 1 and Figures 1 to 4 The results show that the specific volume of steamed bread will decrease with the progress of freeze-thaw cycles. This is because the activity of yeast decreases after freeze-thaw, which affects the quality of frozen dough steamed bread. The specific volumes of steamed bread in Examples 1, 2 and 3 increased by 25.11%, 23.40% and 15.32% respectively compared with Comparative Example 1 after three freeze-thaw cycles. This is because ethanol pretreatment of yeast effectively activates the protective mechanism of yeast cells, increases the content of protective metabolites such as trehalose in yeast cells, improves the freeze-thaw tolerance of yeast, and alleviates the decrease in the specific volume of steamed bread after freeze-thaw. The specific volume of frozen dough steamed bread in Examples 1 and 2 is significantly improved compared with that of Comparative Examples 1 and 3, because low concentrations of ethanol have little effect on yeast survival rate. It can be seen that low concentrations of ethanol treatment of yeast can not only not affect the yeast survival rate but also activate the yeast's protective mechanism to effectively alleviate the quality deterioration of frozen dough products after freeze-thaw.

[0102] 2. Analysis of the results of yeast survival rate determination in Examples 1 to 3 and Comparative Example 1

[0103] Table 2 Survival results of pretreated yeast in Examples 1-3 and Comparative Example 1

[0104] Example 1 Example 2 Example 3 Comparative Example 1 78.20％ 82.44％ 72.81％ 83.48％

[0105] From Table 2 and Figure 5Results: It can be seen from Examples 1 to 2 and Comparative Example 1 that the use of low-concentration ethanol to pretreat yeast does not have an adverse effect on yeast survival rate. It can be seen from Example 3 and Comparative Example 1 that high concentration (30%) ethanol can affect yeast cell viability. At this time, the activity of key enzymes in yeast cells is inhibited and cell metabolism is disturbed. Therefore, yeast will adjust the composition and structure of the cell membrane to cope with the effects of ethanol to enhance the stability of the cell membrane. Therefore, yeast pretreated with ethanol has better freeze-thaw tolerance than yeast that has not been activated, thereby maintaining the vitality of yeast during the freeze-thaw process of fermented dough and improving product quality.

[0106] The embodiments provided above are not intended to limit the scope of the present invention, and the steps described are not intended to limit the execution order thereof. Those skilled in the art may make obvious improvements to the present invention in combination with existing common knowledge, which also fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for activating freeze-thaw tolerance of yeast in fermented flour products, characterized in that: The method comprises the following steps: (1) Dispersing yeast in water to form yeast solution; (2) preparing a food-grade ethanol aqueous solution with a volume fraction of 10% to 30%; (3) Mixing the yeast solution of step (1) and the food-grade ethanol aqueous solution of step (2), stirring and mixing, standing, centrifuging, and removing the supernatant to obtain freeze-thaw tolerant yeast.

2. The method according to claim 1, characterized in that The concentration of the yeast solution in step (1) is 0.1-10 g / ml.

3. The method according to claim 1, characterized in that The volume fraction of ethanol in the food-grade ethanol aqueous solution in step (2) is 10% to 20%.

4. Freeze-thaw tolerant yeast obtained by the method according to any one of claims 1 to 3.

5. A method for preparing frozen fermented dough, characterized in that: The method comprises the steps of mixing flour, water and the freeze-thaw tolerant yeast according to claim 4, kneading the dough, pressing and shaping the dough, pre-proofing the dough, and freezing or refrigerating the dough to obtain the frozen fermented dough.

6. The method for preparing frozen fermented dough according to claim 5, characterized in that: After the freezing or refrigeration, the mixture is stored at -10 to -40°C.

7. The method for preparing frozen fermented dough according to claim 5, characterized in that: The freezing or refrigeration also includes freezing in a -40°C refrigerator until the core temperature reaches -18°C, transferring to a -18°C refrigerator for frozen storage and multiple freeze-thaw cycles.

8. Frozen fermented dough obtained by the method for preparing frozen fermented dough according to any one of claims 5 to 7.

9. A frozen fermented dough product prepared using the frozen fermented dough according to claim 8.

10. The frozen fermented dough product according to claim 9, characterized in that The frozen fermented dough products include steamed buns, rolls, dumplings, sesame seed cakes, bread and fried dough sticks.

Images