Method for preparing sweet potato sugar by using compound enzyme method

Abstract

The method has remarkable advantages, the prepared sweet potato syrup is high in total sugar yield and maltose yield and excellent in comprehensive aspect of sensory evaluation, and the core purpose of the method is that the sweet potato syrup is prepared by optimizing the use conditions of alpha-amylase and beta-amylase, so that the sweet potato syrup is prepared. The defects of the traditional process and the existing compound enzyme method are effectively overcome, and a new path is opened up for efficient and high-quality production of the sweet potato sugar.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of food processing, and particularly relates to a method for preparing sweet potato sugar by using a complex enzyme method. BACKGROUND

[0002] Sweet potato, as a widely planted and nutrient-rich crop, is a high-quality raw material for preparing sugar products. The traditional sweet potato sugar production process mainly relies on natural saccharification or simple enzymatic hydrolysis, and has problems such as low efficiency, incomplete saccharification, unstable product quality, etc. With the development of modern food industry, the complex enzyme technology is gradually applied to the preparation of sweet potato sugar, which can improve the saccharification efficiency and product quality, but the current complex enzyme method still has problems such as non-optimized process parameters and product quality to be improved. SUMMARY

[0003] The purpose of the present application is to provide a method for preparing sweet potato sugar by using a complex enzyme method, which can improve the yield and quality of sweet potato sugar by optimizing the use conditions of α-amylase and β-amylase and realizing the synergistic effect, and solve the problems existing in the traditional process and the current complex enzyme method.

[0004] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows:

[0005] A method for preparing sweet potato sugar by using a complex enzyme method, the method is as follows:

[0006] S1: raw material pretreatment: select fresh sweet potatoes of different varieties, wash and peel, and cut into uniform slices or small pieces; steam the cut sweet potatoes to make the sweet potato starch fully gelatinize;

[0007] S2: preparation of complex enzyme: prepare high-activity α-amylase and β-amylase, slowly dissolve them in an appropriate amount of water, and accurately adjust the pH value of the buffer solution to 6.2-6.5, and maintain the solution temperature at 48-52℃, so as to ensure that the activity of the enzyme is in the best state;

[0008] S3: enzymatic hydrolysis: mix the pretreated sweet potato material with the enzyme solution according to the mass ratio, first, control the temperature of the mixed system at 55-60℃, and use α-amylase for enzymatic hydrolysis to promote the initial hydrolysis of sweet potato starch into dextrin and oligosaccharide; then, accurately adjust the temperature to 43-47℃, and continue to use β-amylase for enzymatic hydrolysis to promote the further conversion of dextrin and oligosaccharide into maltose and glucose;

[0009] S4: filtration: finely filter the enzyme-inactivated reaction liquid to effectively remove the solid residues that are not completely hydrolyzed, so as to obtain clear and pure sugar liquid;

[0010] S5: boiling: the obtained sugar liquid is boiled, continuously heated and stirred until the dry matter content in the sugar liquid reaches 72%-75%, obtaining high-quality sweet potato sugar syrup.

[0011] Further, the cooking in S1 uses a cooking device with a power of 1300W, and the time is 30-40min.

[0012] Further, the method for determining the optimal conditions of α-amylase and β-amylase in the preparation of composite enzymes in S2 is as follows:

[0013] S21: single factor conditions are used for enzyme hydrolysis of sweet potatoes, and sweet potato sugar syrup under different enzyme hydrolysis conditions is obtained;

[0014] S22: the components are analyzed by HPLC, and the results of the single factor experiment are obtained;

[0015] S23: taking the α-amylase addition amount X1, the β-amylase addition amount X2, and the enzyme hydrolysis time X3 as independent variables, and taking the total sugar yield Y1 in sweet potatoes and the maltose yield Y2 in sweet potatoes as observation values, Box-Behnken design is used to carry out experiments, and the range, level and observation value data of the BBD independent variables are obtained;

[0016] S24: multiple regression analysis is performed on the data in S23, and the multiple regression equations of the two models of the total sugar yield Y1 in sweet potatoes and the maltose yield Y2 in sweet potatoes are obtained;

[0017] S25: the fitting degree is analyzed, and the optimal α-amylase and β-amylase addition amount and enzyme hydrolysis time are obtained.

[0018] Further, the optimal process conditions are determined as follows: the α-amylase addition amount is 1.0g, the enzyme hydrolysis time is 30min; the β-amylase addition amount is 0.75g, and the enzyme hydrolysis time is 10min.

[0019] The above technical solutions can achieve the following beneficial effects:

[0020] Improve the saccharification efficiency: by optimizing the use conditions of α-amylase and β-amylase, including the ratio of enzymes, reaction temperature and time, etc., the sweet potato starch can be more fully converted into sugars, and the saccharification efficiency is significantly improved.

[0021] Improve product quality: the sweet potato sugar prepared by this process has a more reasonable sugar composition, higher maltose and glucose content, sweeter taste and richer flavor. At the same time, the product has golden and transparent color, less impurities and high purity, and has stronger competitiveness in the market. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 is the influence diagram of the α-amylase addition amount on different sugar contents.

[0023] Figure 2 is the influence diagram of the α-amylase addition amount on the sensory evaluation of sweet potato sugar soup.

[0024] Figure 3 is the influence diagram of the α-amylase enzyme hydrolysis time on different sugar contents.

[0025] Figure 4 is the influence diagram of the α-amylase enzyme hydrolysis time on the sensory evaluation of sweet potato sugar soup.

[0026] Figure 5 is the influence diagram of the β-amylase addition amount on different sugar contents.

[0027] Figure 6 is the influence diagram of the β-amylase addition amount on the sensory evaluation of sweet potato sugar soup.

[0028] Figure 7 is the influence diagram of the β-amylase enzyme hydrolysis time on different sugar contents.

[0029] Figure 8 is the influence diagram of the β-amylase enzyme hydrolysis time on the sensory evaluation of sweet potato sugar soup.

[0030] Figure 9 is the contour plot and response surface.

[0031] Figure 10 is the contour plot and response surface. DETAILED DESCRIPTION

[0032] The application will be further described below in combination with the drawings:

[0033] A method for preparing sweet potato sugar by using a composite enzyme method, the method is as follows:

[0034] S1: raw material pretreatment: select fresh sweet potatoes of different varieties, wash and peel, cut into uniform thin slices or small pieces; steam the cut sweet potatoes for processing to fully gelatinize the sweet potato starch;

[0035] S2: composite enzyme preparation: prepare high-activity ɑ-amylase and β-amylase, slowly dissolve them in an appropriate amount of water, accurately adjust the pH value of the buffer solution to 6.2-6.5, and maintain the solution temperature at 48-52℃, so as to ensure that the activity of the enzyme is in the best state;

[0036] S3: Enzymatic reaction: the pretreated sweet potato material is mixed with the enzyme solution according to the mass ratio. First, the temperature of the mixed system is controlled at 55-60℃, and the enzyme reaction is carried out by using a-amylase to promote the preliminary hydrolysis of sweet potato starch into dextrin and oligosaccharide; then, the temperature is accurately adjusted to 43-47℃, and the enzyme reaction is continued by using β-amylase to promote the further conversion of dextrin and oligosaccharide into maltose and glucose;

[0037] S4: Filtration: the enzyme-inactivated reaction liquid is finely filtered to effectively remove the solid residues that are not completely enzymatically hydrolyzed, thereby obtaining a clear and pure sugar liquid;

[0038] S5: Boiling: the obtained sugar liquid is boiled, continuously heated and stirred until the dry matter content in the sugar liquid reaches 72%-75%, and high-quality sweet potato sirup is obtained.

[0039] In S1, the cooking is carried out by using a cooking device with a power of 1300W for 30-40min.

[0040] In S2, the optimal conditions of a-amylase and β-amylase in the preparation of composite enzymes are determined as follows:

[0041] S21: The single-factor conditions are used for the enzymatic hydrolysis of sweet potatoes to obtain sweet potato sirup under different enzymatic hydrolysis conditions.

[0042] S22: The components are analyzed by HPLC to obtain the results of the single-factor test.

[0043] S23: The a-amylase addition amount X1, the β-amylase addition amount X2, and the enzymatic hydrolysis time X3 are used as independent variables, and the total sugar yield Y1 in sweet potatoes and the maltose yield Y2 in sweet potatoes are used as observation values. The Box-Behnken design is used to carry out tests, and the range, level and observation value data of the BBD independent variables are obtained.

[0044] S24: The data in S23 are subjected to multiple regression analysis to obtain the multiple regression equations of the total sugar yield Y1 in sweet potatoes and the maltose yield Y2 in sweet potatoes.

[0045] S25: The fitting degree is analyzed to obtain the optimal a-amylase and β-amylase addition amount and enzymatic hydrolysis time.

[0046] The optimal process conditions are determined as follows: the a-amylase addition amount is 1.0g, the enzymatic hydrolysis time is 30min; the β-amylase addition amount is 0.75g, and the enzymatic hydrolysis time is 10min.

[0047] As Figures 1-10The application discloses a preparation method of sweet potato sugar, and relates to the technical field of food processing, in particular to an optimized method for preparing sweet potato sugar based on synergistic effect of α-amylase and β-amylase. The method comprises the following steps: providing sweet potatoes and water with neutral pH; performing cooking pretreatment on the sweet potatoes to obtain sweet potato pulp; mixing the sweet potato pulp with the water solvent, adding different amylases for enzymolysis for a certain time, filtering impurities, compressing to obtain sugar liquid, and performing boiling under certain power. The step of performing pretreatment on the sweet potatoes comprises the following steps: washing the sweet potatoes, slicing the sweet potatoes (1-2 cm), performing cooking under 1300W power for 30-40 min, and then performing grinding to obtain the sweet potato pulp. In the method, the pH of the neutral water is 6.5-7.5, the solid-liquid ratio is 40:1 g / mL, the enzymolysis temperature is 55 DEG C, and the enzymolysis time is 5-60 min.

[0048] Example 1

[0049] 1000g of sweet potatoes are weighed, washed, peeled and cut into 1-2cm small pieces, and cooked under 1300W power for 30min to make the sweet potatoes cooked. Then the cooked sweet potatoes are stirred into pulp by using a stirrer to ensure uniform texture. α-amylase is dissolved in 250ml water with pH value of 6.5, and after complete dissolution, the α-amylase is mixed with the sweet potato pulp to perform enzymolysis reaction under the condition of 55 DEG C. Through single factor experiment, the effects of α-amylase addition amount, β-amylase addition amount and enzymolysis time on preparation of sweet potato sugar are studied, and the factors and levels are shown in Table 1. After the enzymolysis is completed, the mixture is filtered, and the collected filtrate is the sugar liquid. The sugar liquid is boiled until the dry matter content reaches 70%-75%, so that the sweet potato sugar with thick texture is obtained.

[0050] Table 1Factor level of single factor test

[0051]

[0052] In the experiment, the components of sweet potato sugar under different conditions are analyzed by HPLC, and the effects of the addition amount of α-amylase and β-amylase and the enzymolysis time on the total sugar yield and maltose yield of the sweet potatoes are mainly investigated.

[0053] From Figure 1It can be seen that when the α-amylase addition amount is moderate (1.0 g), the enzyme activity is high, which can effectively decompose starch to generate maltose, so that the content of maltose reaches the highest. At this time, the decomposition of amylase on sucrose is weak, which leads to the increase of sucrose content. With the increase of enzyme addition amount, the decomposition of enzyme on sucrose is enhanced, and the content of sucrose gradually decreases. Too much enzyme addition (more than 1.0 g) may lead to the further decomposition of maltose into glucose and other smaller sugars, or the decrease of substrate concentration limits the generation of maltose, so that its content decreases. Amylase continuously generates glucose in the process of decomposing starch and maltose, so with the increase of enzyme addition amount, the content of glucose gradually increases. The generation of fructose may have little to do with the action of amylase, and its content is less affected by other factors, so it changes little in the whole process.

[0054] From Figure 2 It can be seen that the α-amylase addition amount and the sensory score show a first increase and then decrease relationship. When the addition amount increases from 0.5 g to 1 g, the sensory score significantly increases and reaches the highest value; when it continues to increase to 1.5 g and 2 g, the score decreases but still remains at a high level; when it increases to 3 g, the score further decreases and approaches the level of 0.5 g. In summary, the α-amylase addition amount has a significant effect on the sensory score, and 1 g is the best addition amount, and too high or too low addition amount will reduce the sensory score, which is mainly related to the changes in taste and flavor caused by insufficient or excessive starch decomposition.

[0055] From Figure 3 It can be seen that in the initial stage of α-amylase enzymolysis (0-30 minutes), the enzyme mainly decomposes starch to generate other sugars, resulting in the decrease of sucrose content, and the content of fructose is stable because it does not depend on the action of amylase; with the progress of enzymolysis, part of the sugars may be converted back to sucrose or their decomposition slows down, so that the content of sucrose rises. During the whole enzymolysis process, amylase continuously decomposes starch into glucose, so that the content of glucose continuously increases. In the initial stage of enzymolysis (0-20 minutes), amylase efficiently decomposes starch to generate maltose, resulting in the rapid increase of its content; after 20 minutes, maltose may be further decomposed into glucose and other small sugars, or the decomposition of starch slows down, resulting in the decrease of its content. Overall, the content changes of different sugars reflect the action mechanism and reaction stage difference of α-amylase in the enzymolysis process, and in the initial stage, the enzyme activity is high and maltose and other sugars are preferentially generated, and in the subsequent stage, the balance between the generation and decomposition of each sugar changes due to the influence of substrate concentration and reaction environment changes.

[0056] From Figure 4It can be seen that the enzymatic hydrolysis time of α-amylase has a significant effect on sensory score, and the optimal sensory score is achieved at 30 minutes. Too short or too long enzymatic hydrolysis time will reduce the sensory score. From 5 minutes to 30 minutes, the sensory score gradually increases with the increase of enzymatic hydrolysis time, and reaches the highest value (about 95 points) at 30 minutes. After 30 minutes to 60 minutes, the sensory score shows a downward trend with the continuous increase of enzymatic hydrolysis time.

[0057] From Figure 5 It can be seen that when the β-amylase addition amount is moderate (0.8 g), its activity is high, which can effectively decompose starch to generate maltose, so that the maltose content reaches the highest value. At this time, β-amylase mainly acts on starch, and has weak decomposition effect on sucrose, so the sucrose content is relatively stable. With the increase of enzyme addition amount, part of the enzyme may decompose sucrose, resulting in the decrease of sucrose content. In the process of decomposing starch and maltose, β-amylase will gradually generate glucose, so with the increase of enzyme addition amount, the glucose content increases, especially when the enzyme addition amount exceeds 0.8 g, the glucose generation amount increases significantly, which may be because more starch is decomposed or the generation efficiency of the enzyme to glucose is improved. The generation of fructose may not be directly related to the action of β-amylase. When the enzyme addition amount is low, the content of fructose may decrease due to other factors, but when the enzyme addition amount increases to a certain extent, the content of fructose tends to be stable, indicating that the generation and decomposition reach a dynamic balance. In summary, the change of β-amylase addition amount has a significant effect on the content of different sugars, and the change trend of different sugars reflects the complex action mechanism of the enzyme in the process of decomposing starch and other sugars.

[0058] From Figure 6 It can be seen that with the increase of β-amylase addition amount from 0.25 g to 0.5 g, the sensory score significantly increases and reaches the highest value. When the addition amount is further increased to 0.75 g and 1.0 g, the sensory score decreases but still remains at a high level. When the addition amount is further increased to 1.5 g, the sensory score continues to decrease. This indicates that the addition amount of β-amylase has a significant effect on the sensory score, and about 0.5 g is the optimal addition amount, at which the degree of starch decomposition is appropriate, and the taste and flavor of the product are the best. Too low or too high addition amount will reduce the sensory score, which may be related to the changes in taste and flavor caused by insufficient or excessive starch decomposition.

[0059] From Figure 7It can be seen that β-amylase decomposes starch to produce maltose, and the maltose content reaches the highest at 40 minutes, indicating high enzymatic efficiency. After that, the enzyme may be saturated or part of the maltose is further decomposed, resulting in fluctuations in maltose content. In the early stage, the enzyme mainly acts on starch to produce maltose, and has weak decomposition effect on sucrose, causing the sucrose content to rise. After 20 minutes, with the increase of enzymatic time, part of the enzyme begins to decompose sucrose, causing the sucrose content to gradually decrease. At the same time, β-amylase gradually generates glucose and fructose in the process of decomposing starch and maltose, causing their contents to rise, especially at 40 minutes, which may be because starch is more deeply decomposed or the efficiency of the enzyme in generating glucose and fructose is improved. In summary, the β-amylase enzymatic time significantly affects the sugar content, and the change trend of different sugars reflects the mechanism of the enzyme in decomposing starch and other sugars.

[0060] From Figure 8 It can be seen that with the extension of β-amylase enzymatic time, the sensory score presents a trend of first decreasing, then rising and then decreasing. When the enzymatic time is short (10 minutes), the sensory score is relatively high; when the enzymatic time is extended to 20 minutes and 30 minutes, the sensory score decreases; at 40 minutes, the sensory score reaches the highest value; then at 50 minutes, the sensory score decreases again. This shows that the β-amylase enzymatic time has a significant impact on the sensory score, and 40 minutes may be the optimal enzymatic time, at which the degree of starch decomposition is appropriate, and the taste and flavor of the product are best. Too short or too long enzymatic time will reduce the sensory score, which may be related to the changes in taste and flavor caused by insufficient or excessive starch decomposition.

[0061] According to the experimental results, the optimal process conditions are determined as follows: α-amylase addition amount 1.0 g, enzymatic time 30 minutes; β-amylase addition amount 0.75 g, enzymatic time 10 minutes.

[0062] When the α-amylase addition amount is 1.0 g and the enzymatic time is 30 minutes, the enzyme activity is high, the maltose content reaches the highest, the sucrose content rises, the glucose content rises with the increase of the addition amount, and the sensory score is best at this time. During the enzymatic process, in the early stage (0-30 minutes), the enzyme mainly decomposes starch, causing the sucrose content to decrease, and the sucrose content rises after 30 minutes; the maltose content rapidly rises in the early stage of enzymolysis (0-20 minutes), and then decreases after 20 minutes, while the glucose content continuously rises throughout the enzymatic process.

[0063] When the β-amylase addition amount is 0.75 g, the enzyme activity is high, the maltose content reaches the highest, the sucrose content is relatively stable, and the fructose content tends to be stable with the increase of the addition amount. The sensory score reaches a relatively optimal level at an addition amount of about 0.5 g, and too high or too low addition amount will reduce the sensory score. The difference in β-amylase enzymatic time is not significant, but considering the production needs and time cost, the enzymatic time of 10 minutes is selected.

[0064] In general, the addition amount of α-amylase and β-amylase and the enzymolysis time have significant effects on the sugar content and sensory score. There are respective optimal addition amount and enzymolysis time, and too high or too low addition amount and too short or too long enzymolysis time will all reduce the sensory score, which is mainly related to the improper starch decomposition degree causing changes in taste and flavor.

[0065] Example 2

[0066] Table 2 Design factors and levels of response surface experiments

[0067]

[0068] Table 3 Box Behnken experimental design

[0069]

[0070] Table 4 Analysis of variance with whiteness as the response value

[0071]

[0072] Note: * indicates significant difference (P < 0.05); ** indicates very significant difference (P < 0.01); *** indicates extremely significant difference (P < 0.001).

[0073] Table 4 shows that the regression model with total sugar yield and maltose yield as the response value is highly significant (P < 0.0001), and the lack of fit is not significant (P > 0.05), and the equation fitting is good. The determination coefficients R 2 of the two models are 0.9978 and 0.9859 respectively, and the correlations are good. The discrete coefficients CV of the test are 4.3% and 2.37% respectively, and the results are reliable. The difference between Raj and Rpr is less than 0.2, and the predicted value is close to the experimental value. The accuracy (Adeq Precision) of the model is 21.319 and 49.058 respectively, both of which are greater than 4, and the values are reliable, which is suitable for regression analysis.

[0074] The corresponding multiple fitting regression equations obtained by Design-Expert 13 software are:

[0075] Y1=9.38+0.36A+0.32B+0.36C+0.82AB-0.29AC+0.28BC-1.93A 2 -0.78B 2 -2.06C 2

[0076] Y2=9.14+0.29A+0.52B+0.32C+0.28AB-0.11AC+0.26BC-2.52A 2 -1.55B 2 -2.26C 2

[0077] Based on the analysis of variance in Table 4, the analysis of variance table obtained using Design-Expert software shows that the F-value represents the F-statistic, which is used for hypothesis testing in analysis of variance. A larger F-value indicates a higher model fit. P represents the significance level; when P < 0.05, it indicates a significant correlation between the factor and the experimental results. Table 3 shows that A, B, C, AB, and A... 2 B 2 C 2 The corresponding P < 0.50 indicates that A, B, C, AB, A 2 B 2 C 2 The factors significantly affected the experimental results. Based on the comparison of F values, F(A) > F(C) > (BF), therefore, among the factors affecting the total sugar yield, the degree of influence on the total sugar yield of sweet potatoes is: α-amylase addition amount > enzymatic hydrolysis time > β-amylase addition amount. A, B, C, AB, BC, A 2 B 2 C 2 The corresponding P < 0.05, therefore A, B, C, AB, BC, A 2 B 2 C 2 The effects on the experimental results were significant. Based on the comparison of F values, F(B) > F(C) > F(A). Therefore, among the factors affecting maltose yield, the degree of influence on maltose yield in sweet potatoes was: β-amylase addition amount > enzymatic hydrolysis time > α-amylase addition amount.

[0078] Finding the extreme values ​​of the regression equation using Design-Expert 13 software (see attached) Figure 9 and 10), the quadratic multiple regression model is optimized, and two groups of optimal conditions are obtained through data fitting prediction: the first group of conditions is that the alpha amylase addition amount is 1.94g, the beta-amylase addition amount is 1.06g, and the enzymolysis time is 39.67min, and the corresponding maltose yield is 9.471; the second group of conditions is that the alpha amylase addition amount is 2.54g, the beta-amylase addition amount is 1.02g, and the enzymolysis time is 39.04min, and the corresponding maltose yield is 8.404. Overall, under the conditions that the alpha amylase addition amount is about 1.94-2.54g, the beta-amylase addition amount is about 1.02-1.06g, and the enzymolysis time is about 39-39.67min, the maltose yield can reach 8.404-9.471%.

[0079] The above are preferred embodiments of the present application, and modifications of various equivalent forms of the present application made by those skilled in the art without departing from the principles of the present application shall fall within the protection scope of the appended claims of the present application.

Claims

1. A method for preparing sweet potato sugar by using a complex enzyme method, characterized in that: The method is as follows: ​ S1: raw material pretreatment: select fresh, different varieties of sweet potatoes, wash and peel, cut into uniform thin slices or small pieces; the cut sweet potatoes are cooked to make the sweet potato starch fully gelatinized; S2: preparation of composite enzyme: prepare high-activity α-amylase and β-amylase, slowly dissolve them in an appropriate amount of water, accurately adjust the pH value of the buffer solution to 6.2-6.5, and maintain the solution temperature at 48-52℃ to ensure that the activity of the enzyme is in the best state; S3: enzymatic reaction: mix the pretreated sweet potato material with the enzyme solution according to the mass ratio, first, control the temperature of the mixed system at 55-60℃, use α-amylase for enzymatic reaction, and promote the preliminary hydrolysis of sweet potato starch into dextrin and oligosaccharide; then, accurately adjust the temperature to 43-47℃, continue to use β-amylase for enzymatic reaction, and promote the further conversion of dextrin and oligosaccharide into maltose and glucose; S4: filtration: finely filter the enzyme-inactivated reaction liquid to effectively remove the solid residues that are not completely hydrolyzed, thereby obtaining clear and pure sugar liquid; S5: boiling: boil the obtained sugar liquid, continuously heat and stir until the dry matter content in the sugar liquid reaches 72%-75%, and obtain high-quality sweet potato sirup.

2. The method for preparing sweet potato sugar by using complex enzyme method according to claim 1, characterized in that: In S1, the cooking uses a cooking equipment with a power of 1300W, and the time is 30-40min.

3. The method for preparing sweet potato sugar using a compound enzyme method according to claim 1, characterized in that: In S2, the method for determining the optimal α-amylase and β-amylase conditions in the preparation of composite enzymes is as follows: S21: single factor conditions are used for enzyme hydrolysis of sweet potatoes to obtain sweet potato sirup under different enzyme hydrolysis conditions; S22: analyze the components by HPLC to obtain the results of the single factor experiment; S23: α-amylase addition amount X 1. β-amylase addition amount X 2. Enzymatic hydrolysis time X 3. As an independent variable, the total sugar yield in sweet potato Y 1. Maltose yield in sweet potato Y 2. As an investigation value, the Box-Behnken design was used to conduct experiments, and the range, level and observation data of the BBD independent variables were obtained; S24: Multivariate regression analysis of the data in S23, the total sugar yield in sweet potato Y 1. Maltose yield in sweet potato Y 2. Multivariate regression equation of two models; S25: analyze the fitting degree to obtain the optimal α-amylase and β-amylase addition amount and enzyme hydrolysis time.

4. The method for preparing sweet potato sirup by using a composite enzyme method according to claim 1 or 3, characterized in that: The optimal process conditions are: α-amylase addition amount 1.0g, enzyme hydrolysis time 30min; β-amylase addition amount 0.75g, enzyme hydrolysis time 10min.

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