NL2028672B1 - Sweet potato probiotic drink and preparation method thereof - Google Patents

Abstract

Thepresent invention discloses a preparation method of a sweet potato probiotic drink. The method includes: preparing thick sweet potato liquid from sweet potatoes; and inoculating complex probiotics formed by mixing Lactobacillus acidophilus, Lactobacillus plantarum and Streptococcus thermophilus into the thick sweet potato liquid for fermentation. In the preparation method of the sweet potato probiotic drink, probiotic edible dairy products are prepared by taking the sweet potatoes as raw materials; nutritive materials in the sweet potatoes are fully reserved by a simple process; and dairy products that facilitate human absorption are produced by fermentation and may replace part of dairy products. The present invention further relates to a sweet potato probiotic drink prepared by the above preparation method.

Description

SWEET POTATO PROBIOTIC DRINK AND PREPARATION METHOD THEREOF Technical Field The present invention relates to the technical field of drinks, and particularly relates to a sweet potato probiotic drink and a preparation method thereof.

Background Sweet potatoes are recognized agricultural products having extremely high nutritive values, are enriched in proteins, starch, pectin, cellulose, amino acids, vitamins and multiple mineral substances, and have the reputation of “longevity food”. China is one of the countries with the richest sweet potato resources in the world, but processed products are relatively single in variety and low in added value. In addition, milk sources in China have obvious disadvantages. How to replace part of dairy products with the sweet potatoes and develop micro-ecological food with sweet potato health functions needs to be explored by those skilled in the art.

Summary One purpose of the present invention is to provide a sweet potato probiotic drink, for preparing probiotic edible dairy products by taking sweet potatoes as raw materials. The probiotic edible dairy products are enriched in nutritive materials, facilitate human absorption and may replace part of dairy products.

Another purpose of the present invention is to provide a preparation method of the sweet potato probiotic drink. Nutritive materials in the sweet potatoes are fully reserved by a simple process; and dairy products that facilitate absorption by people are produced by fermentation.

Technical solutions of the present invention adopted for solving technical problems are as follows: The preparation method of the sweet potato probiotic drink includes: preparing thick sweet potato liquid from sweet potatoes; and inoculating complex probiotics formed by mixing Lactobacillus acidophilus, Lactobacillus plantarum and Streptococcus thermophilus into the thick sweet potato liquid for fermentation.

Further, in a preferred embodiment of the present invention, a ratio of cell counts of Lactobacillus acidophilus, Lactobacillus plantarum and Streptococcus thermophilus in the complex probiotics is 1:(0.8-1.2):(0.8-1.2).

Further, in a preferred embodiment of the present invention, preparing thick sweet potato liquid from sweet potatoes includes: soaking the sweet potatoes in water; peeling the sweet potatoes; adding purified water for pulping; pasting the filtrate after filtering to obtain pasted liquid; sequentially adding amylase and glucoamylase into the pasted liquid for hydrolysing; and boiling for enzyme deactivation.

Further, in a preferred embodiment of the present invention, soaking the sweet potatoes in water includes: adding the sweet potatoes into water of which the mass is 4-6 times that of the sweet potatoes; and soaking the sweet potatoes at a temperature of 25-30°C for 22-30 hours.

Further, in a preferred embodiment of the present invention, pulping the peeled sweet potatoes includes: adding the peeled sweet potatoes into purified water of which the mass is 4-6 times that of the peeled sweet potatoes; and pulping the sweet potatoes for 4-7 min.

Further, in a preferred embodiment of the present invention, pasting the filtrate includes: heating the filtrate to 78-82°C; and stirring the heated filtrate for 5-8 min.

Further, in a preferred embodiment of the present invention, sequentially adding amylase and glucoamylase into the pasted liquid for hydrolysing includes: adding 0.8-1.2% of amylase by taking starch mass in the pasted liquid as a base; hydrolysing at a temperature of 78-82°C for 18- 22 min; adding 0.04-0.06% of glucoamylase by taking the starch mass in the pasted liquid as a base; and hydrolysing at a temperature of 50-60°C for 28-32 min.

Further, in a preferred embodiment of the present invention, inoculating complex probiotics into the thick sweet potato liquid for fermentation includes: after the complex probiotics are inoculated into the thick sweet potato liquid, incubating the thick sweet potato liquid at a constant temperature of 38-42°C for 5-8 hours; and preserving and after-ripening the thick sweet potato liquid at a temperature of 1-5°C.

Further, in a preferred embodiment of the present invention, an inoculated dose of the complex probiotics is 4-6 mg/100 ml.

A sweet potato probiotic drink is prepared by the above preparation method of the sweet potato probiotic drink.

The sweet potato probiotic drink and the preparation method of the sweet potato probiotic drink in the embodiments of the present invention have beneficial effects as follows: the thick sweet potato liquid is prepared from the sweet potatoes, and thus the sweet potatoes are conveniently fermented and prepared into the drink; and the complex probiotics formed by mixing Lactobacillus acidophilus, Lactobacillus plantarum and Streptococcus thermophilus are inoculated into the thick sweet potato liquid for fermentation.

By virtue of synergistic effects of the Lactobacillus acidophilus, Lactobacillus plantarum and Streptococcus thermophilus, a complex probiotic fermentation system is established.

By utilizing biological functions of the Lactobacillus acidophilus, Lactobacillus plantarum and Streptococcus thermophilus, respective advantages of the multiple probiotics in the product are achieved.

Moreover, the fermented emulsifiable liquid can be well absorbed by the human body; and rich nutritive materials in the sweet potatoes are reserved.

In the sweet potato probiotic drink and the preparation method thereof, the probiotic edible dairy products are prepared by fully utilizing the sweet potatoes as the raw materials.

On one hand, a problem of shortage of the milk sources is solved; and on the other hand, an application range of plants such as the sweet potatoes is effectively widened, thereby providing a good logistical support for sweet potato planting in China.

Detailed Description To make purposes, technical solutions and advantages of embodiments in the present invention clear, the technical solutions in the embodiments of the present invention will be clearly and fully described below. The embodiments in which specific conditions are not indicated are performed according to routine conditions or conditions suggested by manufacturers. Used reagents or instruments without indicated manufacturers are all commercially available conventional products.

A sweet potato probiotic drink and a preparation method thereof in the embodiments of the present invention are specifically described below.

The preparation method of the sweet potato probiotic drink includes: Step 1, thick sweet potato liquid was prepared from sweet potatoes.

Specifically, the sweet potatoes were dried in the sun first; the dried sweet potatoes were added into water of which the mass was 4-6 times that of the sweet potatoes; the sweet potatoes were soaked at a temperature of 25-30°C for 22-30 hours, so that sweet potato peels can be softened so as to be conveniently removed; and the soaked sweet potatoes were peeled. The sweet potato peels can be manually removed; or the sweet potatoes can be peeled in a sweet potato peeling machine. The water for soaking the sweet potatoes may be running water or purified water, preferably the purified water.

By peeling the sweet potatoes, the subsequently formed thick sweet potato liquid may be pure in colour, so that the product formed by fermentation has an excellent appearance effect and can well enter the market.

The sweet potato is also known as red potatoes, batatas, scammony root, sweet potato, yam (Hebei), pachyrhizus (north), ipomoea batatas, ipomoea batatas, Chinese sweet-potato, golden potato, dioscorea aculeate, ipomoea batatas, Chinese potato, pueraria lobata, taro, Hui taro Chinese potato, red-skinned sweet potato and cute sweet potato.

The sweet potato belongs to Tubiflorae, is an annual herb of Convolvulaceae, is more than 2 m long, and lays down on the ground obliquely. Each leaf of the sweet potato is generally broadly ovate, and is 4-13 cm long and 3-13 cm wide. The corolla is pink, white, light purple or purple, is bell-shaped or funnel-shaped, and is 3-4 cm long. The capsule is ovate or oblate and has a false dissepiments divided into 4 chambers. The sweet potato has underground tuberous roots. The tuberous roots are spindle-shaped. Peel of the sweet potato is earthy yellow or purplish red.

The sweet potato is enriched in proteins, starch, pectin, cellulose, amino acids, vitamins and multiple mineral substances, owns the reputation of “longevity foods”, has sugar content up to 15- 20%, and has effects of resisting cancers, protecting the heart, preventing pulmonary emphysema and diabetes and losing weight. Compendium of Materia Medica written by Shizhen Li in Ming Dynasty records that “the sweet potato has effects of tonifying deficiency, invigorating the spleen and whetting the appetite and strengthening kidney yin”, and indicates that people have longevity while eating the sweet potatoes. The sweet potato is regarded as a good medicine in traditional Chinese medicine. Secondly, the peeled sweet potatoes were added into purified water of which the mass was 4-6 times that of the peeled sweet potatoes; and the sweet potato liquid was pulped for 4-7 min. The pulping process was performed in a tissue masher. The sweet potatoes were mashed into meal in the tissue masher and forms thick liquid with the purified water, so that the nutritive materials in the sweet potatoes can be well mixed into water. Therefore, the sweet potatoes can be in full contact with complex probiotics in a subsequent fermentation process, thereby achieving an excellent fermentation effect and increasing content of absorbable nutritional ingredients of the finally formed dairy products.

Then, the preliminary thick sweet potato liquid formed by pulping was filtered; and the filtrate was heated to 78-82°C and then stirred for 5-8 min. The filtrate was preferably heated in a water bath. Through the water bath heating, the filtrate may be uniformly heated; the pasting process is gentle; and the nutritional ingredients were difficult to be damaged. After starch milk in the filtrate was heated, starch grains were damaged in a certain temperature range; a crystal structure disappeared; the volume was expanded; viscosity was suddenly increased; and the starch milk became sticky paste, thereby obtaining non-crystalline starch. According to the above pasting process, the starch can be fully combined with the water, thereby facilitating the fermentation process of the complex probiotics.

Then, 0.8-1.2% of amylase was added into the pasted liquid by taking starch mass in the pasted liquid as a base; hydrolysis was performed at a temperature of 78-82°C for 18-22 min; then 0.04-0.06% of glucoamylase was added into the pasted liquid by taking the starch mass in the pasted liquid as a base; hydrolysis was performed at a temperature of 50-60°C for 28-32 min; and then the hydrolysed pasted liquid was boiled to kill enzymes therein, thereby obtaining the thick sweet potato liquid that can be fermented.

By virtue of complex deep hydrolysis of the amylase and the glucoamylase, the starch in the pasted liquid was converted into glucose that facilitated full utilization of the complex probiotics. The glucose served as a carbon source for fermentation. Therefore, utilization efficiency of the raw materials is increased while lowering cost; and taste and product states can be improved.

The glucoamylase was added for further hydrolysis after the amylase was hydrolysed. On one hand, the obtained small-molecule glucose may promote growth of lactic acid bacteria and other stains in the complex probiotics; on the other hand, sweetness of the product can be increased; dosage of carbohydrates is decreased; the cost is saved; and viscosity of the paste may be lowered, thereby fully utilizing the raw materials.

Step 2, the complex probiotics formed by mixing Lactobacillus acidophilus, Lactobacilius plantarum and Streptococcus thermophilus were inoculated into the thick sweet potato liquid for fermentation.

Firstly, the Lactobacillus acidophilus, Lactobacillus plantarum and Streptococcus thermophilus are mixed according to a cell count ratio of 1:(0.8-1.2):(0.8-1.2) to form the complex probiotics.

Probiotics are a category of active microorganisms beneficial to a host, and are generic terms 5 of active beneficial microorganisms that colonize in the human intestinal tract and reproductive system and can achieve exact health effects so as to improve micro-ecological balance of the host and achieve beneficial effects. Beneficial bacteria or fungi in human bodies and animals mainly include Clostridium butyricum, lactic acid bacteria, bifidobacterium, Lactobacillus acidophilus, actinomycetes and saccharomycetes. The Lactobacillus acidophilus has high acid tolerance and bile salt tolerance, can be colonized in the intestinal tract, is an important microorganism in the human intestinal tract, is closely related to human health, and may regulate alteration of intestinal floras and inhibit reproduction of intestinal undesirable microorganisms. The Lactobacillus acidophilus can secrete biotins such as acidolin, acidophilin and lactein, and can achieve excellent antagonism on pathogenic enterobacteria. A sweet potato dairy product obtained by fermenting Lactobacillus acidophilus is long in fermentation time, excellent in curding effect and fine and smooth in tissue, but has severe whey separation; a fermented sweet potato dairy product of Lactobacillus plantarum is short in curding time and excellent in coagulation effect, basically has no whey separation, but is not smooth enough; and a fermented sweet potato dairy product of Streptococcus thermophilus is short in curding time and good in coagulation effect, basically has no whey separation, but is rough in tissue. By virtue of synergism of the three probiotics, the fermented sweet potato dairy products can be short in fermentation time, excellent in taste and high in nutritive value and facilitate human absorption.

Secondly, after the complex probiotics were inoculated into the thick sweet potato liquid, the thick sweet potato liquid was incubated at a constant temperature of 38-42°C for 5-8 hours; and the thick sweet potato liquid was preserved and after-ripened at a temperature of 1-5°C, thereby obtaining the sweet potato probiotic drink. An inoculated dose of the complex probiotics is 4-6 mg/100 ml, i.e., 4-6 mg of the complex probiotic is added into every 100 ml of thick sweet potato liquid.

Further, some fruits and vegetables may be added into the thick sweet potato liquid before fermentation of the thick sweet potato liquid, so as to improve taste of the prepared sweet potato probiotic drink.

The after-ripening means that, a cultured acid milk drink is placed in a low-temperature environment to terminate the fermentation process, and texture, taste, flavour and acidity of the acid milk drink are improved in the process. The after-ripening in the present invention has the same principle as a cold storage after-ripening process of yogurt.

The sweet potato probiotic drink is prepared by the above preparation method of the sweet potato complex probiotic drink.

Features and properties of the present invention will be further described below in combination with embodiments.

Embodiment 1 Firstly, sweet potatoes were dried in the sun first; the dried sweet potatoes were added into water of which the mass was 4 times that of the dried sweet potatoes; the sweet potatoes were soaked at a temperature of 25°C for 22 hours; and the soaked sweet potatoes were peeled in a sweet potato peeling machine.

Secondly, the peeled sweet potatoes were added into a tissue masher; then the sweet potatoes were added into purified water of which mass was 4 times that of the peeled sweet potatoes for pulping for 4 min; preliminary thick sweet potato liquid formed by pulping was filtered; the filtrate was heated to 78°C in a water bath and then stirred for 5 min; then 0.8% of amylase was added into the pasted liquid by taking starch mass in the pasted liquid as a base; hydrolysis was performed at a temperature of 78°C for 18 min; then 0.04% of glucoamylase was added into the pasted liquid by taking the starch mass in the pasted liquid as a base; hydrolysis was performed at a temperature of 50°C for 28 min; and then the hydrolysed pasted liquid was boiled to kill enzymes therein, thereby obtaining the thick sweet potato liquid that can be fermented.

Thirdly, Lactobacillus acidophilus, Lactobacillus plantarum and Streptococcus thermophilus were mixed according to a cell count ratio of 1:0.8:0.8 to form the complex probiotics; then after the complex probiotics were inoculated into the thick sweet potato liquid, the thick sweet potato liquid inoculated with the complex probiotics was incubated at a constant temperature of 38°C for 5 hours; and the thick sweet potato liquid was preserved and after-ripened at a temperature of 1°C, thereby obtaining the sweet potato probiotic drink.

An inoculated dose of the complex probiotics was 4 mg/100 ml.

Through detection of the sweet potato probiotic drink obtained in the present embodiment, protein content in the sweet potato probiotic drink is 1.5 g/100 g.

Embodiment 2 Firstly, sweet potatoes were dried in the sun first; the dried sweet potatoes were added into water of which the mass was 6 times that of the dried sweet potatoes, the sweet potatoes were soaked at a temperature of 30°C for 30 hours; and the soaked sweet potatoes were peeled in a sweet potato peeling machine.

Secondly, the peeled sweet potatoes were added into a tissue masher; then the sweet potatoes were added into purified water of which mass was 6 times that of the peeled sweet potatoes for pulping for 7 min; preliminary thick sweet potato liquid formed by pulping was filtered; the filtrate was heated to 82°C in a water bath and then stirred for 5 min; then 1.2% of amylase was added into the pasted liquid by taking starch mass in the pasted liquid as a base; hydrolysis was performed at a temperature of 82°C for 18 min; then 0.06% of glucoamylase was added into the pasted liquid by taking the starch mass in the pasted liquid as a base; hydrolysis was performed at a temperature of 60°C for 32 min; and then the hydrolysed pasted liquid was boiled to kill enzymes therein, thereby obtaining the thick sweet potato liquid that can be fermented.

Thirdly, Lactobacillus acidophilus, Lactobacillus plantarum and Streptococcus thermophilus were mixed according to a cell count ratio of 1:1.2:1.2 to form the complex probiotics; then after the complex probiotics were inoculated into the thick sweet potato liquid, the thick sweet potato liquid inoculated with the complex probiotics was incubated at a constant temperature of 42°C for 8 hours; and the thick sweet potato liquid was preserved and after-ripened at a temperature of 5°C, thereby obtaining the sweet potato probiotic drink.

An inoculated dose of the complex probiotics was 6 mg/100 ml.

Through detection of the sweet potato probiotic drink obtained in the present embodiment, protein content in the sweet potato probiotic drink is 1.3 g/100 g.

Embodiment 3 Firstly, sweet potatoes were dried in the sun first; the dried sweet potatoes were added into water of which the mass was 5 times that of the dried sweet potatoes; the sweet potatoes were soaked at a temperature of 28°C for 25 hours; and the soaked sweet potatoes were peeled in a sweet potato peeling machine.

Secondly, the peeled sweet potatoes were added into a tissue masher; then the sweet potatoes were added into purified water of which mass was 5 times that of the peeled sweet potatoes for pulping for 5 min; preliminary thick sweet potato liquid formed by pulping was filtered; the filtrate was heated to 80°C in a water bath and then stirred for 6 min; then 1.0% of amylase was added into the pasted liquid by taking starch mass in the pasted liquid as a base; hydrolysis was performed at a temperature of 80°C for 20 min; then 0.05% of glucoamylase was added into the pasted liquid by taking the starch mass in the pasted liquid as a base; hydrolysis was performed at a temperature of 55°C for 30 min; and then the hydrolysed pasted liquid was boiled so as to kill enzymes therein, thereby obtaining the thick sweet potato liquid that can be fermented.

Then, Lactobacillus acidophilus, Lactobacillus plantarum and Streptococcus thermophilus were mixed according to a cell count ratio of 1:1:1 to form the complex probiotics; then after the complex probiotics were inoculated into the thick sweet potato liquid, the thick sweet potato liquid inoculated with the complex probiotics was incubated at a constant temperature of 40°C for 7 hours; and the thick sweet potato liquid was preserved and after-ripened at a temperature of 3°C, thereby obtaining the sweet potato probiotic drink.

An inoculated dose of the complex probiotics was 5 mg/100 ml.

Through detection of the sweet potato probiotic drink obtained in the present embodiment, protein content in the sweet potato probiotic drink is 1.9 g/100 g.

Embodiment 4 Firstly, sweet potatoes were dried in the sun first; the dried sweet potatoes were added into water of which the mass was 5 times that of the dried sweet potatoes; the sweet potatoes were soaked at a temperature of 29°C for 24 hours; and the soaked sweet potatoes were peeled in a sweet potato peeling machine.

Secondly, the peeled sweet potatoes were added into a tissue masher; then the sweet potatoes were added into purified water of which mass was 6 times that of the peeled sweet potatoes for pulping for 7 min; preliminary thick sweet potato liquid formed by pulping was filtered; the filtrate was heated to 79°C in a water bath and then stirred for 7 min; then 0.8% of amylase was added into the pasted liquid by taking starch mass in the pasted liquid as a base; hydrolysis was performed at a temperature of 81°C for 21 min; then 0.05% of glucoamylase was added into the pasted liquid by taking the starch mass in the pasted liquid as a base; hydrolysis was performed at a temperature of 58°C for 31 min; and then the hydrolysed pasted liquid was boiled to kill enzymes therein, thereby obtaining the thick sweet potato liquid that can be fermented.

Then, Lactobacillus acidophilus, Lactobacillus plantarum and Streptococcus thermophilus were mixed according to a cell count ratio of 1:0.9:1.1 to form the complex probiotics; then after the complex probiotics were inoculated into the thick sweet potato liquid, the thick sweet potato liquid inoculated with the complex probiotics was incubated at a constant temperature of 41°C for 7 hours; and the thick sweet potato liquid was preserved and after-ripened at a temperature of 4°C, thereby obtaining the sweet potato probiotic drink. An inoculated dose of the complex probiotics was 5 mg/100 ml.

Through detection of the sweet potato probiotic drink obtained in the present embodiment, protein content in the sweet potato probiotic drink is 1.7 g/100 g.

Contrast test Various samples of the sweet potato probiotic drink prepared in the above embodiments and a lactic acid drink of a famous brand in the market were scored by 50 experienced assessors according to evaluation standards in Table 2; average values are solved; and results are shown as Table 2. Corresponding numbers are as follows: 1-embodiment 1; 2-embodiment 2; 3- embodiment 3; 4-embodiment 4; 5-commercially available sample.

Evaluation method

1. Colour: an appropriate amount of sample was added into a 50 ml transparent container; and the colour was observed under the light.

2. Taste and smell: the sample was smelled; and after the mouth was rinsed with warm water, the sample was tasted.

3. Tissue state: an appropriate amount of the sample was added into the 50 ml transparent container; and a tissue state of the sample was observed under the light.

Assessment requirements

1. Assessment items The items are assessed by a centesimal system, wherein scores of the various items are shown in Table 1. Table 1

2. Scoring standards The scoring standards of the various items are shown in Table 2. Table 2 Colour (10 Uniform milk white, slight yellow or intrinsic colour 10-8 yw Green and black spots or mould growing, 4-0 os Taste and smell | Excellent taste and smell, an appropriate ratio of 50-40 Tissue state (40 | Uniform and smooth emulsion, no layering 40-30 scores) phenomenon, no foreign impurities that can be mime Uniform and smooth emulsion, layering 30-20 phenomenon existing, no foreign impurities that can be seen with normal vision, having a small mmm Non-uniform, layering phenomenon existing, no 20-10 foreign impurities that can be seen with normal vision, having a small amount of precipitates at Tome Non-uniform, severely layered, having foreign 10-0 pS

3. Contrast results are shown as Table 3. Table 3 Colour 8 |e je fe [® | Taste and | 46 47 48 46 47 ma OO It can be seen from test results in Table 3 that, the colour, the taste and smell and the tissue state of the sweet potato probiotic drink prepared in each embodiment of the present invention can be up to, or even better than those of a fermented lactic acid drink that is sold in the market at present and has higher quality. The sweet potato probiotic drink has excellent market potential.

To sum up, the thick sweet potato liquid is prepared from the sweet potatoes, and thus the sweet potatoes are conveniently fermented and prepared into the drink; and the complex probiotics formed by mixing Lactobacillus acidophilus, Lactobacillus plantarum and Streptococcus thermophilus are inoculated into the thick sweet potato liquid for fermentation. By virtue of synergistic effects of the Lactobacillus acidophilus, Lactobacillus plantarum and Streptococcus thermophilus, a complex probiotic fermentation system is established. By utilizing biological functions of the Lactobacillus acidophilus, Lactobacillus plantarum and Streptococcus thermophilus, respective advantages of the multiple probiotics in the product are achieved. Moreover, the fermented emulsifiable liquid can be well absorbed by the human body; and rich nutritive materials in the sweet potatoes are reserved. Further, according to the sweet potato probiotic drink and the preparation method thereof, the probiotic edible dairy products are prepared by fully utilizing the sweet potatoes as the raw materials. On one hand, the problem of shortage of the milk sources is solved; and on the other hand, an application range of plants such as the sweet potatoes is effectively widened, thereby providing a good logistical support for sweet potato planting in China.

The above described embodiments are part of embodiments in the present invention, rather than all the embodiments. Detailed description of the embodiments in the present invention is not intended to limit the protection scope of the present invention, but to merely represent selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those ordinary skilled in the art without making creative labour shall belong to the protection scope of the present invention.

Claims (10)

CONCLUSIONS A method of preparing a sweet potato probiotic drink, the method comprising: preparing sweet potato thick liquid from sweet potatoes; and inoculating complex probiotics formed by mixing Lactobacillus acidophilus, Lactobacillus plantarum and Streptococcus thermophilus into the sweet potato thick liquor for fermentation. The method for preparing a probiotic drink of sweet potato according to claim 1, wherein the ratio of the cells number of Lactobacillus acidophilus, Lactobacillus plantarum and Streptococcus thermophilus in the complex probiotics is 1: (0.8 - 1.2): (0.8 - 1.2). The method of preparing a sweet potato probiotic drink according to claim 1, wherein preparing sweet potato thick liquid from sweet potatoes comprises: soaking the sweet potatoes in water; peeling the sweet potatoes; adding purified water for pulping; pasting the filtrate after filtering to obtain a pasty liquid; sequentially adding amylase and glucoamylase to the pasty liquid for hydrolysis; and boiling to deactivate the enzymes. The method of preparing a probiotic drink of sweet potato according to claim 3, wherein soaking the sweet potatoes in water comprises: adding the sweet potatoes to water whose mass is 4-6 times that of the sweet potatoes ; and soaking the sweet potatoes at a temperature of 25-30°C for 22-30 hours. The method for preparing a probiotic sweet potato drink according to claim 3, wherein the pulping of the peeled sweet potatoes comprises: adding the peeled sweet potatoes to purified water the mass of which is 4-6 times that of the peeled sweet potato. potatoes is; and pulping the sweet potatoes for 4 - 7 minutes. The method of preparing a sweet potato probiotic drink according to claim 3, wherein the pasting of the filtrate comprises: heating the filtrate to 78-82°C; and stirring the heated filtrate for 5-8 min. The method for preparing a probiotic sweet potato drink according to claim 3, wherein the successive addition of amylase and glucoamylase to the hydrolysis paste comprises: adding 0.8-1.2% amylase through the to take starch mass in the appropriate liquid as a base; hydrolyzing at a temperature of 78-82°C for 18-22 min; adding 0.04 - 0.06% glucoamylase by taking the starch mass in the appropriate liquid as a base; and hydrolyzing at a temperature of 50-60°C for 28-32 min. The method for preparing a probiotic sweet potato drink according to claim 1, wherein inoculating complex probiotics into the thick sweet potato liquor for fermentation comprises: after the complex probiotics are inoculated into the thick sweet potato liquor, incubating the thick sweet potato liquid at a constant temperature of 38-42°C for 5-8 hours; and preserving and post-ripening the thick sweet potato liquid at a temperature of 1-5°C. The method for preparing a probiotic sweet potato drink according to claim 1, wherein an inoculated dose of the complex probiotics is 4 - 6 mg/100 ml. A sweet potato probiotic drink prepared by the method for preparing a sweet potato probiotic drink according to any one of claims 1-9.