阅读说明：本技术 一种通过添加混合镁盐提高赤藓糖醇转化率的方法 (Method for improving erythritol conversion rate by adding mixed magnesium salt ) 是由 李克文 熊小兰 栾庆民 张莉 贾慧慧 张倩 李珍珍 任晓洁 李新华 尹郑 于 2019-11-18 设计创作，主要内容包括：本发明涉及一种通过添加混合镁盐提高赤藓糖醇转化率的方法。该方法先进行解脂假丝酵母菌种子液的培养,再对解脂假丝酵母菌种子液进行发酵培养,制得赤藓糖醇。其中,发酵培养基的组分为：葡萄糖0.3～0.35kg/L、有机氮源4～7g/L、无机盐5～6g/L。本方法通过对发酵培养基部分原料替代、由添加单一镁盐改为混合镁盐并调整混合镁盐的比例优化发酵培养基,使其菌种代谢途径更利于生成赤藓糖醇,从而有效地提高赤藓糖醇转化率。(The invention relates to a method for improving erythritol conversion rate by adding a mixed magnesium salt. The method comprises the steps of firstly culturing the candida lipolytica seed solution, and then fermenting and culturing the candida lipolytica seed solution to obtain the erythritol. Wherein, the components of the fermentation medium are as follows: 0.3-0.35 kg/L glucose, 4-7 g/L organic nitrogen source and 5-6 g/L inorganic salt. According to the method, partial raw materials of the fermentation medium are replaced, the single magnesium salt is added to be changed into the mixed magnesium salt, and the proportion of the mixed magnesium salt is adjusted to optimize the fermentation medium, so that the strain metabolic pathway is more favorable for generating erythritol, and the erythritol conversion rate is effectively improved.)

1. A method for increasing erythritol conversion rate by adding a magnesium salt mixture comprises the following steps:

(1) culturing the lipolytic candida seed solution: inoculating the lipolytic candida to a shake flask culture medium for shake flask culture, and then performing primary seed culture and secondary seed culture to obtain a lipolytic candida seed solution;

(2) fermentation culture: inoculating the prepared candida lipolytica seed liquid into a fermentation tank filled with a fermentation culture medium for fermentation culture, and finishing fermentation when the glucose content in the fermentation liquid is less than or equal to 0.2g/100mL to prepare erythritol;

wherein the fermentation medium comprises the following components: 0.3-0.35 kg/L glucose, 4-7 g/L organic nitrogen source and 5-6 g/L inorganic salt; the organic nitrogen source is a mixture of yeast powder and soybean protein powder; the inorganic salt is a combination of more than two of magnesium sulfate, magnesium carbonate, monopotassium phosphate and ammonium citrate.

2. The method for increasing erythritol conversion rate by adding the magnesium salt mixture according to claim 1, wherein the inoculation of candida lipolytica in step (1) is specifically: under the aseptic environment, 1-2 rings of candida lipolytica are hooked by an inoculating ring and transferred to a shake flask culture medium.

3. The method for increasing erythritol conversion rate by adding the mixed magnesium salt according to claim 1, wherein the shake flask culture medium in step (1) comprises the following components in percentage by weight: 20-25% of glucose, 1.5-2.5% of yeast extract and the balance of water.

4. The method for increasing erythritol conversion rate by adding the magnesium salt mixture according to claim 1, wherein the shake flask culture conditions in step (1) are: the rotating speed of the shaking table is 100-105 r/min, the temperature is 29-32 ℃, and the culture period is 20-24 hours.

5. The method of claim 1, wherein the step of culturing the primary seed and the step of culturing the secondary seed in step (1) comprises the steps of: inoculating a candida lipolytica shake flask culture solution into a first-level seed culture medium, and culturing for 14-20 hours at the temperature of 30-34 ℃ and under the condition of 180-200r/min, wherein the inoculation amount is 1-2% of the mass of the first-level seed culture medium; inoculating the primary seed solution into a secondary seed culture medium according to the inoculation amount of 9-10%, and culturing for 7-12 h at 30-34 ℃ under the condition of 180-200r/min to obtain a candida lipolytica seed solution;

wherein, the components of the first-stage seed culture medium and the second-stage seed culture medium are as follows, and the weight percentages are as follows: 20-25% of glucose, 1.0-2.0% of yeast powder, 0.04-0.06% of magnesium sulfate, 0.5-0.8% of ammonium citrate, 0.04-0.06% of monopotassium phosphate and the balance of water.

6. The method for increasing the conversion rate of erythritol by adding the magnesium salt mixture according to claim 1, wherein the inoculation amount of the candida lipolytica seed solution inoculated into the fermentation tank in the step (2) is 9-10%.

7. The method for increasing the conversion rate of erythritol by adding the mixed magnesium salt according to claim 1, wherein the inorganic salt in the step (2) is a combination of monopotassium phosphate, magnesium sulfate, magnesium carbonate and ammonium citrate in a weight ratio of 1 (0.5-0.8) to (0.2-0.5) to (8-9).

8. The method for improving the conversion rate of erythritol by adding the mixed magnesium salt according to claim 1, wherein glucose in the fermentation medium component in the step (2) is liquid glucose, and the concentration of glucose is 55-70%, and the DE value is ≧ 95%.

9. The method of claim 1, wherein the fermentation culture conditions in step (2) are: the stirring speed of the fermentation tank is 70-100 r/min, the pressure is 0.05-0.1 MPa, the amount of introduced compressed air is 0.5-0.8 cubic meter of air/cubic meter of fermentation liquor/min, the temperature is 30-34 ℃, and the fermentation time is 98-102 hours.

Technical Field

The invention belongs to the technical field of microbial fermentation production, and particularly relates to a method for improving erythritol conversion rate by adding a mixed magnesium salt.

Background

Erythritol is widely distributed in nature and is a natural sugar. Erythritol tastes sweet like sucrose, and is distinguished from sucrose. Erythritol is cool and refreshing in mouth and has good processing characteristics. It can be widely used in various foods and beverages such as candy, beverage, jelly type beverage, oral health product, etc. Like other sugar alcohols, erythritol does not cause dental caries. The reason for this is that there is no enzyme system which metabolizes erythrose alcohol in the human body, so that it is not metabolized after absorption into the blood in the small intestine, but is almost completely excreted with urine, and is suitable for use as a sweetener for diabetic patients. It also avoids the side effects of bloating, borborborygmus and diarrhea caused by excessive use of other sugar alcohols. In addition, the erythritol can partially replace glycerin to be used for cosmetics to delay the deterioration of the cosmetics; as an intermediate of organic synthesis, used as a raw material for manufacturing products such as paint, explosive, medicine and the like; polyether polyols are produced as components and additives for high molecular weight polymers. The erythrose alcohol is the only sugar alcohol produced by adopting a microbial fermentation method internationally at present.

The preparation of erythritol is completed by taking glucose as a main raw material and adding different inorganic salts through a pentose phosphate pathway by hypertonic yeast under an oxygen consumption condition. The fermentation period of the erythritol is generally different according to different specific fermentation processes and strains, the longer the fermentation time is, the higher the infection probability is, and the lower the conversion rate is. Therefore, the conversion rate is higher in a shorter time, which becomes a key factor of the erythritol production cost, and the yield of the post-extraction process is improved after the conversion rate of the erythritol is improved.

Chinese patent document CN103290068A discloses a method for producing erythritol by using high-exudation-resistant Aureobasidium pullulans, wherein the erythritol is produced by using a fermentation culture medium with xylose as a main carbon source, but the conversion rate is low and is only 25-42%.

Chinese patent document CN104894095A discloses a method for producing erythritol by using waste erythritol bacterial sludge. The method comprises the following steps: inoculating strains activated by a conventional inclined plane to a culture medium taking cane sugar and/or glucose and yeast powder as raw materials, performing primary seed culture, secondary seed culture and fermentation in a fermentation tank to prepare a mixture of erythritol sugar solution and bacterial sludge, collecting the bacterial sludge after separation, immobilizing the bacterial sludge by using an immobilized carrier to prepare immobilized particles, adding the immobilized particles into sterilized fermentation liquor containing glucose and a small amount of nitrogen sources for fermentation to obtain the erythritol sugar solution, decoloring the erythritol sugar solution, purifying the erythritol sugar solution by ion exchange, concentrating according to a conventional method, crystallizing, and performing centrifugal separation to prepare the erythritol crystals. However, the conversion rate of the method is also low and is only 30-40%.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a method for improving the conversion rate of erythritol by adding a mixed magnesium salt, and the method can effectively improve the conversion rate of erythritol by changing the addition type and proportion of inorganic salt.

The technical scheme of the invention is as follows:

a method for increasing erythritol conversion rate by adding a magnesium salt mixture comprises the following steps:

(1) culturing the lipolytic candida seed solution: inoculating the lipolytic candida to a shake flask culture medium for shake flask culture, and then performing primary seed culture and secondary seed culture to obtain a lipolytic candida seed solution;

(2) fermentation culture: inoculating the prepared candida lipolytica seed liquid into a fermentation tank filled with a fermentation culture medium for fermentation culture, and finishing fermentation when the glucose content in the fermentation liquid is less than or equal to 0.2g/100mL to prepare erythritol;

wherein the fermentation medium comprises the following components: 0.3-0.35 kg/L glucose, 4-7 g/L organic nitrogen source and 5-6 g/L inorganic salt; the organic nitrogen source is a mixture of yeast powder and soybean protein powder; the inorganic salt is a combination of more than two of magnesium sulfate, magnesium carbonate, monopotassium phosphate and ammonium citrate.

Preferably, the inoculation of candida lipolytica in step (1) is specifically as follows: under the aseptic environment, 1-2 rings of candida lipolytica are hooked by an inoculating ring and transferred to a shake flask culture medium.

Preferably, the shake flask culture medium in step (1) has the following components, all in weight percent: 20-25% of glucose, 1.5-2.5% of yeast extract and the balance of water.

Preferably according to the present invention, the shake flask culture conditions in step (1) are: the rotating speed of the shaking table is 100-105 r/min, the temperature is 29-32 ℃, and the culture period is 20-24 hours.

Preferably, the primary seed culture and the secondary seed culture in step (1) are: inoculating a candida lipolytica shake flask culture solution into a first-level seed culture medium, and culturing for 14-20 hours at the temperature of 30-34 ℃ and under the condition of 180-200r/min, wherein the inoculation amount is 1-2% of the mass of the first-level seed culture medium; inoculating the primary seed solution into a secondary seed culture medium according to the inoculation amount of 9-10%, and culturing for 7-12 h at 30-34 ℃ under the condition of 180-200r/min to obtain a candida lipolytica seed solution;

wherein, the first-stage seed culture medium and the second-stage seed culture medium comprise the following components in percentage by weight: 20-25% of glucose, 1.0-2.0% of yeast powder, 0.04-0.06% of magnesium sulfate, 0.5-0.8% of ammonium citrate, 0.04-0.06% of monopotassium phosphate and the balance of water.

According to the invention, the inoculation amount of the candida lipolytica seed solution inoculated into the fermentation tank in the step (2) is preferably 9-10%.

According to the invention, the inorganic salt in the step (2) is potassium dihydrogen phosphate, magnesium sulfate, magnesium carbonate and ammonium citrate, and the weight ratio of the inorganic salt to the inorganic salt is 1 (0.5-0.8) (0.2-0.5) (8-9).

According to the invention, the glucose in the fermentation medium component in the step (2) is liquid glucose, the concentration is 55-70%, and the DE value is ≧ 95%.

Preferably, according to the present invention, the conditions of the fermentation culture in step (2) are: the stirring speed of the fermentation tank is 70-100 r/min, the pressure is 0.05-0.1 MPa, the amount of introduced compressed air is 0.5-0.8 cubic meter of air/cubic meter of fermentation liquor/min, the temperature is 30-34 ℃, and the fermentation time is 98-102 hours.

The invention has the following beneficial effects:

(1) on the premise of not influencing the conversion rate, the invention partially replaces yeast powder with cheaper soybean protein powder, thereby reducing the cost of raw materials. Meanwhile, single magnesium salt fermentation is changed into mixed magnesium salt fermentation, the mixture ratio of the mixed magnesium salt is adjusted, the pH value in the later period of fermentation is adjusted to be increased to 3.5-4.0 from the original 2.5-3.3, and the metabolism of the candida lipolytica strain is in an environment most suitable for producing erythritol. Through the optimization of the fermentation medium, the synergistic effect of various enzymes is brought into play to the condition most beneficial to the production of erythritol, the conversion rate of erythritol can be maximized to 63%, the conversion rate is improved by more than 20% compared with the prior art, the content of erythritol in the fermentation liquid is obviously improved, and the method has good economic benefit.

(2) The preparation method provided by the invention has the advantages of few processes, low cost and simplicity in operation, and can maximize the metabolic efficiency of the lipolytic Candida, so that the fermentation period is shortened to 98-102 h, the preparation efficiency of erythritol is improved, and the product competitiveness is increased.

Detailed Description

The candida lipolytica is a self-owned strain BLB-24 of biological shares Limited of bowling, is preserved in the common microorganism center of China Committee for culture Collection of microorganisms in 11 months and 25 days in 2010, and has the preservation number of CGMCC No.4364 and the address: the institute of microbiology, national academy of sciences No. 3, Xilu No. 1, Beijing, Chaoyang, Beijing.

Other materials are commercially available.