Method for producing refined white granulated sugar through low-temperature enzymolysis of raw sugar

Abstract

The invention relates to a process for directly producing refined white granulated sugar at a low temperature of 50-60 DEG C by using raw sugar as a raw material through a composite enzymolysis technology (including a synergistic effect of alpha-amylase and saccharifying enzyme). Compared with traditional high-temperature refining, the process has the advantages that the energy consumption is reduced by 40%, more natural minerals are reserved, and the purity of the finished white granulated sugar reaches 99.9% or above. The key technology comprises enzymolysis pH value accurate control (6.0-6.5) and stepped low-temperature crystallization.

Description

Technical Field

[0001] This invention belongs to the field of sugar production technology, specifically relating to a method for producing refined white sugar by low-temperature enzymatic hydrolysis of raw sugar. Background Technology

[0002] White sugar is an important food ingredient, widely used in the food, beverage, and pharmaceutical industries. Currently, the traditional industrial process for refining white sugar mainly uses raw sugar as raw material, involving steps such as dissolving, clarifying, evaporating, crystallizing, separating, and drying. The clarification and evaporation stages typically require high-temperature conditions (100-120℃) to remove impurities and evaporate moisture. However, the traditional high-temperature refining process has several drawbacks: (1) High energy consumption: Evaporation, clarification and other processes under high temperature conditions require a large amount of steam and electricity, and energy consumption costs account for 40-50% of production costs, resulting in high product production costs.

[0003] (2) Product quality needs to be improved: High-temperature processing will cause some natural minerals (such as potassium, calcium, magnesium, etc.) in the raw sugar to be lost, and may produce a small amount of caramelization products, affecting the taste and nutritional value of white sugar; at the same time, high-temperature crystallization is prone to uneven crystal size and decreased purity, making it difficult to meet the demand of the high-end food industry for high-purity white sugar.

[0004] (3) High environmental pressure: Traditional processes generate a large amount of wastewater and waste residue, and high-temperature emissions will cause certain thermal pollution, which does not meet the requirements of green and environmentally friendly development.

[0005] (4) Low production efficiency: In high-temperature processes, the evaporation and crystallization steps take a long time, and the sugar recovery rate in the mother liquor is low, resulting in low production efficiency and large raw material loss.

[0006] Therefore, it is necessary to improve the traditional methods of refining white sugar. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of traditional high-temperature refining processes for white sugar, such as high energy consumption, low product quality, and significant environmental impact, and to provide a low-temperature enzymatic refining process for white sugar. This process employs a composite enzymatic hydrolysis technology to achieve efficient refining of raw sugar under low-temperature conditions, reducing energy consumption, retaining more natural minerals, improving product purity and nutritional value, while simultaneously enabling the recycling of mother liquor, reducing pollutant emissions, and making it suitable for large-scale industrial production.

[0008] A method for producing refined white sugar by low-temperature enzymatic hydrolysis of raw sugar includes the following steps: S10: Raw sugar pretreatment: Crush the raw sugar to a particle size of 40-60 mesh, add deionized water to prepare a raw sugar solution with a mass concentration of 30-40%, stir and dissolve at 30-40℃ for 20-30 minutes, then add activated carbon with a mass fraction of 0.05-0.1%, stir and adsorb for 15-20 minutes, filter to remove impurities, and obtain refined raw sugar solution; S20: Compound enzymatic hydrolysis: The refined raw sugar solution obtained from S10 is heated to 50-60℃, the pH value is adjusted to 6.0-6.5, a compound enzyme preparation is added, and enzymatic hydrolysis is carried out for 3-5 hours under a stirring speed of 100-150 r / min to obtain the enzymatic hydrolysate; the compound enzyme preparation is composed of α-amylase and saccharifying enzyme, the amount of α-amylase added is 0.02-0.05% of the mass of raw sugar solution, the amount of saccharifying enzyme added is 0.03-0.06% of the mass of raw sugar solution, and the activity ratio of α-amylase to saccharifying enzyme is 1:1.2-1:1.5; S30: Enzyme inactivation: After the enzymatic hydrolysis is completed, the hydrolysate is heated to 75-80℃ and kept at that temperature for 10-15 minutes to inactivate the compound enzyme preparation. Then the temperature is lowered to 50-55℃. S40: Step-by-step low-temperature crystallization: The inactivated enzymatic hydrolysate obtained from S30 is transferred to a crystallization tank. First, the temperature is lowered from 50-55℃ to 40-45℃ at a cooling rate of 0.5-1℃ / h, and crystallization is maintained at this temperature for 8-10h. Then, the temperature is lowered to 30-35℃ at a cooling rate of 0.3-0.5℃ / h, and crystallization is maintained at this temperature for 12-15h. Finally, the temperature is lowered to 20-25℃ at a cooling rate of 0.1-0.3℃ / h, and crystallization is maintained at this temperature for 18-20h, resulting in a mixture of sugar crystals and mother liquor. S50: Solid-liquid separation: The mixture obtained in S40 is centrifuged at a speed of 3000-4000 r / min for 10-15 min to obtain wet sugar crystals; S60: Drying and sieving: Place the wet sugar crystals obtained from S50 into a vacuum drying oven and dry them for 3-4 hours under a vacuum of -0.08~-0.09MPa and a temperature of 40-45℃. After drying, sieve them through a 100-120 mesh screen to obtain the finished white sugar product.

[0009] Beneficial effects (1) Significantly reduced energy consumption: This process uses low-temperature enzymatic hydrolysis and low-temperature crystallization at 50-60℃, which reduces energy consumption and significantly lowers production costs compared to traditional high-temperature processes (100-120℃).

[0010] (2) Excellent product quality: The finished white sugar has a purity of over 99.9%, retains more natural minerals, and has higher nutritional value. The crystal particle size is uniform, the sensory quality is good, and it is suitable for use in the high-end food industry.

[0011] (3) Green and environmentally friendly: The mother liquor is recycled, and the utilization rate of raw sugar reaches more than 98%, reducing raw material loss and wastewater discharge. The low-temperature process avoids thermal pollution caused by high-temperature emissions, which is in line with the green and low-carbon development trend.

[0012] (4) High production efficiency: The compound enzymatic hydrolysis has high efficiency and fast crystallization rate. The entire process cycle is shortened by more than 20% compared with the traditional process, and continuous large-scale industrial production can be realized.

[0013] (5) Wide applicability: It is applicable to different raw materials such as cane sugar raw sugar and beet sugar raw sugar, with strong process stability and easy to promote and apply. Detailed Implementation

[0014] An embodiment of the present invention provides a method for producing refined white sugar by low-temperature enzymatic hydrolysis of raw sugar, comprising the following steps: S10: Raw Sugar Pretreatment: Crush the raw sugar to a particle size of 40-60 mesh, add deionized water to prepare a raw sugar solution with a mass concentration of 30-40%, stir and dissolve at 30-40℃ for 20-30 minutes, then add 0.05-0.1% activated carbon, stir and adsorb for 15-20 minutes, filter to remove impurities, and obtain a refined raw sugar solution. Crushing the raw sugar to 40-60 mesh increases the contact area between the raw sugar and water, improving the dissolution rate; adding deionized water to prepare a 30-40% raw sugar solution ensures sufficient dissolution of the raw sugar while avoiding excessive concentration that could hinder subsequent enzymatic hydrolysis; adding activated carbon for adsorption effectively removes pigments, colloids, and other impurities from the raw sugar, improving the purity of the raw sugar solution; filtration using a precision filter membrane (pore size 0.22-0.45μm) further removes fine impurities, providing pure raw materials for subsequent enzymatic hydrolysis.

[0015] S20: Compound enzymatic hydrolysis: The refined raw sugar solution obtained from S10 is heated to 50-60℃, the pH value is adjusted to 6.0-6.5, a compound enzyme preparation is added, and enzymatic hydrolysis is carried out for 3-5 hours under the condition of stirring speed of 100-150r / min to obtain the enzymatic hydrolysate; the compound enzyme preparation consists of α-amylase and saccharifying enzyme, the amount of α-amylase added is 0.02-0.05% of the mass of raw sugar solution, the amount of saccharifying enzyme added is 0.03-0.06% of the mass of raw sugar solution, and the activity ratio of α-amylase to saccharifying enzyme is 1:1.2-1:1.5. A compound enzyme preparation consisting of α-amylase and glucoamylase is selected. α-amylase can break down the starch macromolecules in raw sugar, while glucoamylase can break down glucan. The two enzymes work synergistically to achieve the full conversion of raw sugar. The enzymatic hydrolysis temperature is controlled at 50-60℃, which is the optimal operating temperature for both enzymes, ensuring high enzyme activity while avoiding increased energy consumption due to high temperature. The pH value is precisely controlled at 6.0-6.5 using a citrate-sodium citrate buffer solution to maintain pH stability and ensure smooth enzymatic hydrolysis. By controlling the amount and activity ratio of the enzymes, the enzymatic hydrolysis efficiency is improved and the hydrolysis time is shortened.

[0016] S30: Enzyme Inactivation: After enzymatic hydrolysis, heat the hydrolysate to 75-80℃ and hold for 10-15 minutes to inactivate the compound enzyme preparation, then cool to 50-55℃. Inactivation at 75-80℃ for 10-15 minutes after hydrolysis completely inactivates the compound enzyme preparation, preventing changes in the sugar solution composition due to continued enzyme action. Rapid cooling to 50-55℃ provides a suitable initial temperature for subsequent crystallization processes, preventing excessively high temperatures from affecting the crystallization effect.

[0017] S40: Step-by-step low-temperature crystallization: The inactivated enzymatic hydrolysate obtained from S30 is transferred to a crystallization tank. First, the temperature is lowered from 50-55℃ to 40-45℃ at a rate of 0.5-1℃ / h, and crystallized at this temperature for 8-10 hours. Then, the temperature is lowered to 30-35℃ at a rate of 0.3-0.5℃ / h, and crystallized at this temperature for 12-15 hours. Finally, the temperature is lowered to 20-25℃ at a rate of 0.1-0.3℃ / h, and crystallized at this temperature for 18-20 hours, yielding a mixture of sugar crystals and mother liquor. Step-by-step cooling crystallization gradually reduces the temperature, allowing the sugar crystals to grow slowly and avoiding uneven crystal size and decreased purity caused by rapid cooling. Seed crystals are added at each cooling stage to promote directional growth of the sugar crystals, improving the crystallization rate and crystal purity. Controlling the stirring speed ensures uniform dispersion of the seed crystals, preventing crystal agglomeration and resulting in white granulated sugar crystals with a uniform particle size distribution.

[0018] S50: Solid-liquid separation: The mixture obtained in S40 is centrifuged at a speed of 3000-4000 r / min for 10-15 min to obtain wet sugar crystals.

[0019] S60: Drying and Sieving: The wet sugar crystals obtained in S50 are placed in a vacuum drying oven and dried for 3-4 hours at a vacuum of -0.08~-0.09 MPa and a temperature of 40-45℃. After drying, the sugar is sieved through a 100-120 mesh sieve to obtain the finished white sugar product. Vacuum drying is carried out at a low temperature to avoid mineral loss and caramelization caused by high-temperature drying, thus improving product quality. After drying, the sugar is cooled to room temperature, vacuum-packed, and the ambient humidity is controlled to prevent the white sugar from absorbing moisture and clumping, thereby extending the product's shelf life.

[0020] The above method defines a complete process flow for low-temperature enzymatic hydrolysis of refined white sugar. Impurities are removed through raw sugar pretreatment, providing pure raw materials for subsequent enzymatic hydrolysis. The compound enzymatic hydrolysis utilizes the synergistic action of α-amylase and saccharifying enzyme to achieve efficient hydrolysis of raw sugar at a low temperature of 50-60℃, reducing energy consumption compared to traditional high-temperature refining processes (typically 100-120℃). Precise control of the hydrolysis pH value between 6.0 and 6.5, the optimal pH range for synergistic effect of the two enzymes, significantly improves hydrolysis efficiency and shortens hydrolysis time. Step-by-step low-temperature crystallization achieves slow crystal growth through gradual cooling, avoiding problems such as uneven crystal size and decreased purity caused by rapid cooling, ultimately yielding high-purity white sugar. The entire process is coherent, with parameters synergistically matched in each step, achieving low-energy, high-quality white sugar refining, suitable for industrial production.

[0021] In some embodiments, the purity of raw sugar in S10 is 90-95%, the reducing sugar content is ≤1.5%, and the moisture content is ≤0.5%. By screening the raw sugar, the difficulty of pretreatment can be reduced, and the enzymatic hydrolysis effect and the quality of the final product can be avoided due to excessive impurities and high moisture content in the raw sugar. At the same time, raw sugar within this range is readily available in the market, balancing raw material cost and product quality, and improving the practicality and economy of the process.

[0022] In some embodiments, the α-amylase activity in S20 is 2000-3000 U / g, and the saccharifying enzyme activity in S20 is 3000-4000 U / g. During the enzymatic hydrolysis of S20, the reducing sugar content of the hydrolysate is checked every 1 hour, and the hydrolysis is stopped when the reducing sugar content reaches 35-40%. The combination of 2000-3000 U / g α-amylase and 3000-4000 U / g saccharifying enzyme, with an activity ratio controlled at 1:1.2-1:1.5, achieves synergistic effects between the two enzymes, increasing the hydrolysis efficiency by more than 30% compared to single-enzymatic hydrolysis. By controlling the hydrolysis endpoint by detecting the reducing sugar content, the low utilization rate of raw sugar due to insufficient hydrolysis or the excessive production of byproducts due to over-hydrolysis can be avoided, ensuring the stability of the hydrolysate quality and laying a good foundation for the subsequent crystallization process.

[0023] In some embodiments, the pH adjuster used in S20 is a citrate-sodium citrate buffer solution with a concentration of 0.1-0.2 mol / L. This buffer solution has good pH stability, maintaining a stable pH value of 6.0-6.5 during enzymatic hydrolysis, preventing pH drop due to the generation of organic acids during hydrolysis, thereby ensuring stable enzyme activity. Compared to single acid or base adjusters, the buffer solution provides more precise adjustment and does not introduce additional impurities, thus improving product purity.

[0024] In some embodiments, during the step-by-step low-temperature crystallization process in S40, the stirring speed in the crystallization tank is 50-80 r / min, and 0.01-0.02% by mass of seed crystals are added before the start of each cooling stage. The seed crystals are granulated sugar crystals with a particle size of 80-100 mesh. The stirring speed of 50-80 r / min can ensure uniform dispersion of the seed crystals and avoid crystal agglomeration; the 80-100 mesh seed crystals can act as crystallization nuclei, promoting the directional growth of sugar crystals and improving the crystallization rate and crystal purity; adding seed crystals at each cooling stage can ensure uniform crystallization at each stage, resulting in granulated sugar crystals with a uniform particle size distribution.

[0025] In some embodiments, the mother liquor obtained after centrifugation in S50 is returned to S10 for preparing raw sugar solution, and the mother liquor is recycled no more than 5 times. High-speed centrifugation is used to quickly separate sugar crystals from the mother liquor, improving separation efficiency; the mother liquor is returned to the pretreatment process for recycling, improving raw sugar utilization, reducing raw material loss, reducing pollutant emissions, and achieving resource recycling.

[0026] In some embodiments, the dried granulated sugar product in S60 is cooled to room temperature and then vacuum-packed, with the ambient humidity controlled to ≤60% during the packaging process. This prevents the granulated sugar from absorbing moisture and clumping, extending the product's shelf life from 12 months in traditional processes to over 18 months, thus improving the product's storage stability.

[0027] In some embodiments, the raw sugar in S10 includes one or more of sucrose raw sugar and beet raw sugar.

[0028] In some implementations, the white granulated sugar has a purity of ≥99.9%, a reducing sugar content of ≤0.05%, a moisture content of ≤0.03%, and an ash content of ≤0.02%. All these indicators are superior to the requirements for Grade A white granulated sugar in the national standard (GB / T317-2018) (purity ≥99.5%, reducing sugar content ≤0.10%, moisture content ≤0.05%, ash content ≤0.04%). At the same time, it retains natural minerals such as potassium, calcium, and magnesium. Compared with the traditional high-temperature process (mineral loss rate of 60-70%), the mineral loss rate of this process is ≤30%, which improves the nutritional value of the product and meets consumers' demand for high-quality, healthy sugar products.

[0029] The following are examples and comparative examples.

[0030] The relevant raw materials involved in the examples and comparative examples are as follows: raw sugar (cane sugar, purity 92%, reducing sugar content 1.2%, moisture content 0.4%); α-amylase (enzyme activity 2500U / g); saccharifying enzyme (enzyme activity 3500U / g); citric acid-sodium citrate buffer solution; activated carbon (food grade); deionized water; seed crystals (white granulated sugar crystals, particle size 90 mesh).

[0031] Example 1 The method for refining white sugar in this embodiment includes: S101: Raw sugar pretreatment: Crush the raw sugar to 50 mesh, add deionized water to prepare a raw sugar solution with a mass concentration of 35%, stir and dissolve at 35℃ for 25 min, then add activated carbon with a mass fraction of 0.08%, stir and adsorb for 18 min, and filter through a 0.3μm precision filter to obtain refined raw sugar solution.

[0032] S102: Compound enzymatic hydrolysis: The purified raw sugar solution was heated to 55℃, and the pH was adjusted to 6.2 with 0.15mol / L citric acid-sodium citrate buffer solution. A compound enzyme preparation was added (α-amylase was added at 0.03% of the raw sugar solution mass, saccharifying enzyme was added at 0.045% of the raw sugar solution mass, and the activity ratio of α-amylase to saccharifying enzyme was 1:1.3). Enzymatic hydrolysis was carried out for 4 hours with a stirring speed of 120r / min. The reducing sugar content was checked every 1 hour during the enzymatic hydrolysis process. Enzymatic hydrolysis was stopped when the reducing sugar content reached 38%. S103: Enzyme inactivation: After the enzymatic hydrolysis is completed, the enzymatic hydrolysate is heated to 78°C, kept at this temperature for 12 minutes, and then cooled to 52°C. S104: Step-by-step low-temperature crystallization: The inactivated enzyme hydrolysate was transferred to a crystallization tank, and the stirring speed was controlled at 60 r / min. First, the temperature was lowered from 52℃ to 42℃ at a cooling rate of 0.8℃ / h, and 0.015% of seed crystals were added. The mixture was kept at this temperature for 9 h. Then, the temperature was lowered to 32℃ at a cooling rate of 0.4℃ / h, and 0.015% of seed crystals were added. The mixture was kept at this temperature for 13 h. Finally, the temperature was lowered to 22℃ at a cooling rate of 0.2℃ / h, and 0.015% of seed crystals were added. The mixture was kept at this temperature for 19 h to obtain a mixture of sugar crystals and mother liquor. S105: Solid-liquid separation: Place the mixture into a high-speed centrifuge and centrifuge at 3500 r / min for 12 min to obtain wet sugar crystals; return the mother liquor after centrifugation to step S101 for preparing the original sugar solution; S106: Drying and sieving: Place the wet sugar crystals into a vacuum drying oven and dry them for 3.5 hours under a vacuum of -0.085 MPa and a temperature of 42°C. After drying, sieve them through a 110-mesh sieve, cool them to room temperature, and vacuum package them under an ambient humidity of 55% to obtain the finished white sugar product.

[0033] Example 2 The method for refining white sugar in this embodiment includes: S101: Raw sugar pretreatment: Crush the raw sugar to 40 mesh, add deionized water to prepare a raw sugar solution with a mass concentration of 30%, stir and dissolve at 30℃ for 20 min, then add activated carbon with a mass fraction of 0.05%, stir and adsorb for 15 min, and filter through a 0.22μm precision filter to obtain refined raw sugar solution; S102: Compound enzymatic hydrolysis: The purified raw sugar solution was heated to 50℃, and the pH was adjusted to 6.0 with 0.1mol / L citric acid-sodium citrate buffer solution. A compound enzyme preparation was added (α-amylase was added at 0.02% of the raw sugar solution mass, saccharifying enzyme was added at 0.036% of the raw sugar solution mass, and the activity ratio of α-amylase to saccharifying enzyme was 1:1.2). Enzymatic hydrolysis was carried out for 3 hours with a stirring speed of 100r / min. The reducing sugar content was checked every 1 hour during the enzymatic hydrolysis process. Enzymatic hydrolysis was stopped when the reducing sugar content reached 35%. S103: Enzyme inactivation: After the enzymatic hydrolysis is completed, the enzymatic hydrolysate is heated to 75°C, kept at this temperature for 10 minutes, and then cooled to 50°C. S104: Step-by-step low-temperature crystallization: The inactivated enzyme hydrolysate was transferred to a crystallization tank, and the stirring speed was controlled at 50 r / min. First, the temperature was lowered from 50℃ to 40℃ at a cooling rate of 0.5℃ / h, and 0.01% of seed crystals were added. The mixture was kept at this temperature for 8 hours. Then, the temperature was lowered to 30℃ at a cooling rate of 0.3℃ / h, and 0.01% of seed crystals were added. The mixture was kept at this temperature for 12 hours. Finally, the temperature was lowered to 20℃ at a cooling rate of 0.1℃ / h, and 0.01% of seed crystals were added. The mixture was kept at this temperature for 18 hours to obtain a mixture of sugar crystals and mother liquor. S105: Solid-liquid separation: Place the mixture into a high-speed centrifuge and centrifuge at 3000 r / min for 10 min to obtain wet sugar crystals; return the mother liquor after centrifugation to step S101 for preparing the original sugar solution; S106: Drying and sieving: Place the wet sugar crystals into a vacuum drying oven and dry them for 3 hours under a vacuum of -0.085 MPa and a temperature of 42°C. After drying, sieve them through a 100-mesh sieve, cool them to room temperature, and vacuum package them under an ambient humidity of 50% to obtain the finished white sugar product.

[0034] Example 3 The method for refining white sugar in this embodiment includes: S101: Raw sugar pretreatment: Crush the raw sugar to 60 mesh, add deionized water to prepare a raw sugar solution with a mass concentration of 40%, stir and dissolve at 40℃ for 30 min, then add activated carbon with a mass fraction of 0.1%, stir and adsorb for 20 min, and filter through a 0.45μm precision filter to obtain refined raw sugar solution; S102: Compound enzymatic hydrolysis: The purified raw sugar solution was heated to 60℃, and the pH was adjusted to 6.5 with 0.2mol / L citric acid-sodium citrate buffer solution. A compound enzyme preparation was added (α-amylase was added at 0.05% of the raw sugar solution mass, saccharifying enzyme was added at 0.06%, and the activity ratio of α-amylase to saccharifying enzyme was 1:1.5). Enzymatic hydrolysis was carried out for 5 hours with a stirring speed of 150r / min. The reducing sugar content was checked every 1 hour during the enzymatic hydrolysis process. Enzymatic hydrolysis was stopped when the reducing sugar content reached 40%. S103: Enzyme inactivation: After the enzymatic hydrolysis is completed, the hydrolysate is heated to 80°C, kept at that temperature for 15 minutes, and then cooled to 55°C. S104: Step-by-step low-temperature crystallization: The inactivated enzyme hydrolysate was transferred to a crystallization tank, and the stirring speed was controlled at 80 r / min. First, the temperature was lowered from 55℃ to 45℃ at a cooling rate of 1℃ / h, and 0.02% (w / w) of seed crystals were added. The mixture was kept at this temperature for 10 h. Then, the temperature was lowered to 35℃ at a cooling rate of 0.5℃ / h, and 0.02% (w / w) of seed crystals were added. The mixture was kept at this temperature for 15 h. Finally, the temperature was lowered to 25℃ at a cooling rate of 0.3℃ / h, and 0.02% (w / w) of seed crystals were added. The mixture was kept at this temperature for 20 h to obtain a mixture of sugar crystals and mother liquor. S105: Solid-liquid separation: Place the mixture into a high-speed centrifuge and centrifuge at 4000 r / min for 15 min to obtain wet sugar crystals; return the mother liquor after centrifugation to step S101 for preparing the original sugar solution; S106: Drying and sieving: Place the wet sugar crystals into a vacuum drying oven and dry them for 4 hours under a vacuum of -0.085 MPa and a temperature of 42°C. After drying, sieve them through a 120-mesh sieve, cool them to room temperature, and vacuum package them under an ambient humidity of 60% to obtain the finished white sugar product.

[0035] Comparative Example 1 This comparative example uses a traditional high-temperature refining process. The methods for refining white sugar include: S101: Raw sugar pretreatment: Crush the raw sugar to 50 mesh, add deionized water to prepare a raw sugar solution with a mass concentration of 35%, stir and dissolve at 35℃ for 25 min, add activated carbon with a mass fraction of 0.08%, stir and adsorb for 18 min, and filter to obtain refined raw sugar solution. S102: High-temperature clarification: Heat the refined raw sugar solution to 110℃, add lime milk to adjust the pH value to 7.5, keep it at this temperature for 30 minutes to clarify, and then filter to remove the precipitate; S103: High-temperature evaporation: The clarified sugar solution is heated to 115°C and vacuum evaporated to a syrup with a mass concentration of 60%. S104: High-temperature crystallization: Transfer the syrup to a crystallization tank, heat it to 105℃, keep it at that temperature for 24 hours, and then let it cool naturally to room temperature to obtain a mixture of sugar crystals and mother liquor; S105: Solid-liquid separation: Centrifuge the mixture (3500 r / min, 12 min) to obtain wet sugar crystals; S106: Drying and Packaging: The wet sugar crystals are dried with hot air at 70°C for 3.5 hours, sieved, and then vacuum-packed to obtain the finished white sugar product.

[0036] Comparative Example 2 Compared with Example 1, this comparative example differs in step S102. This comparative example uses a single enzymatic hydrolysis low-temperature process.

[0037] The comparative example S102 is as follows: S102: Enzymatic hydrolysis: Heat the refined raw sugar solution to 55℃, adjust the pH to 6.2 with 0.15mol / L citric acid-sodium citrate buffer solution, add enzyme preparation (the amount of saccharifying enzyme added is 0.075% of the mass of raw sugar solution), and enzymatically hydrolyze for 4 hours under the condition of stirring speed of 120r / min; during the enzymatic hydrolysis, the reducing sugar content is detected every 1 hour, and the enzymatic hydrolysis is stopped when the reducing sugar content reaches 38%.

[0038] Comparative Example 3 Compared to Example 1, this comparative example differs in step S104. This comparative example uses non-stepwise low-temperature crystallization.

[0039] The comparative example S104 is as follows: S104: One-time cooling crystallization (directly cooling from 52℃ to 22℃ at a cooling rate of 0.5℃ / h, and holding the temperature for crystallization for 41h).

[0040] Comparative Example 4 Compared to Example 1, this comparative example differs in that S102 is different. The pH value of S102 is different.

[0041] The comparative example S102 is as follows: S102: Compound enzymatic hydrolysis: The purified raw sugar solution was heated to 55℃, and the pH was adjusted to 5.5 with 0.15mol / L citric acid-sodium citrate buffer solution. A compound enzyme preparation was added (α-amylase was added at 0.03% of the raw sugar solution mass, saccharifying enzyme was added at 0.045% of the raw sugar solution mass, and the activity ratio of α-amylase to saccharifying enzyme was 1:1.3). Enzymatic hydrolysis was carried out for 4 hours with a stirring speed of 120r / min. The reducing sugar content was checked every 1 hour during the enzymatic hydrolysis process. Enzymatic hydrolysis was stopped when the reducing sugar content reached 38%.

[0042] Test case (1) Purity determination of finished white sugar: High performance liquid chromatography was used for determination, referring to the standard method of GB / T317-2018 "White Sugar".

[0043] (2) Determination of reducing sugar content in finished white sugar product: Fehling's reagent titration method was adopted, referring to the standard method of GB / T317-2018.

[0044] (3) Determination of moisture content of finished white sugar: Karl Fischer method, referring to GB / T317-2018 standard method.

[0045] (4) Determination of ash content of finished white sugar: The ignition method was adopted, referring to the standard method of GB / T317-2018. (5) Determination of mineral content in finished white sugar product: Potassium, calcium and magnesium content were determined using an elemental analyzer. (6) Determination of crystal particle size of finished white sugar: The average particle size was calculated by using a particle size analyzer. (7) Determination of raw sugar utilization rate of finished white sugar product: Calculate the raw sugar utilization rate based on the quality of finished white sugar and the amount of raw sugar fed. (8) Shelf life test of finished white sugar: Store finished white sugar at 25°C and 60% humidity, regularly test the moisture content and clumping, and record the shelf life.

[0046] The test results are shown in Table 1.

[0047] Table 1

[0048] As shown in Table 1, the purity of the white granulated sugar products prepared in each embodiment is above 99.9%, with reducing sugar content ≤0.05%, moisture content ≤0.03%, and ash content ≤0.018%. All indicators are superior to the comparative example and national standards. Regarding mineral content, the potassium, calcium, and magnesium contents of the embodiments are significantly higher than those of comparative example 1 (traditional high-temperature process), indicating that the low-temperature process can effectively retain natural minerals. The average crystal particle size is between 102-110 mesh, with uniform particle size, while the crystal particle size of comparative example 3 (non-step crystallization) is only 75 mesh, and the particle size distribution is uneven, indicating that step-type low-temperature crystallization can significantly improve crystal quality. The shelf life of the white granulated sugar products in the embodiments is 17-19 months, longer than that of the comparative example, indicating that low-temperature drying and vacuum packaging processes can effectively extend the product's shelf life and improve its storage stability.

[0049] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

[0050] For those skilled in the art, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A method for producing refined white sugar by low-temperature enzymatic hydrolysis of raw sugar, characterized in that, Includes the following steps: S10: Raw sugar pretreatment: Crush the raw sugar to a particle size of 40-60 mesh, add deionized water to prepare a raw sugar solution with a mass concentration of 30-40%, stir and dissolve at 30-40℃ for 20-30 minutes, then add activated carbon with a mass fraction of 0.05-0.1%, stir and adsorb for 15-20 minutes, filter to remove impurities, and obtain refined raw sugar solution; S20: Compound enzymatic hydrolysis: The refined raw sugar solution obtained from S10 is heated to 50-60℃, the pH value is adjusted to 6.0-6.5, a compound enzyme preparation is added, and enzymatic hydrolysis is carried out for 3-5 hours under a stirring speed of 100-150 r / min to obtain the enzymatic hydrolysate; the compound enzyme preparation is composed of α-amylase and saccharifying enzyme, the amount of α-amylase added is 0.02-0.05% of the mass of raw sugar solution, the amount of saccharifying enzyme added is 0.03-0.06% of the mass of raw sugar solution, and the activity ratio of α-amylase to saccharifying enzyme is 1:1.2-1:1.5; S30: Enzyme inactivation: After the enzymatic hydrolysis is completed, the hydrolysate is heated to 75-80℃ and kept at that temperature for 10-15 minutes to inactivate the compound enzyme preparation. Then the temperature is lowered to 50-55℃. S40: Step-by-step low-temperature crystallization: The inactivated enzymatic hydrolysate obtained from S30 is transferred to a crystallization tank. First, the temperature is lowered from 50-55℃ to 40-45℃ at a cooling rate of 0.5-1℃ / h, and crystallization is maintained at this temperature for 8-10h. Then, the temperature is lowered to 30-35℃ at a cooling rate of 0.3-0.5℃ / h, and crystallization is maintained at this temperature for 12-15h. Finally, the temperature is lowered to 20-25℃ at a cooling rate of 0.1-0.3℃ / h, and crystallization is maintained at this temperature for 18-20h, resulting in a mixture of sugar crystals and mother liquor. S50: Solid-liquid separation: The mixture obtained in S40 is centrifuged at a speed of 3000-4000 r / min for 10-15 min to obtain wet sugar crystals; S60: Drying and sieving: Place the wet sugar crystals obtained from S50 into a vacuum drying oven and dry them for 3-4 hours under a vacuum of -0.08~-0.09MPa and a temperature of 40-45℃. After drying, sieve them through a 100-120 mesh screen to obtain the finished white sugar product.

2. The method for producing refined white sugar by low-temperature enzymatic hydrolysis of raw sugar according to claim 1, characterized in that, The purity of the raw sugar in S10 is 90-95%, the reducing sugar content is ≤1.5%, and the moisture content is ≤0.5%.

3. The method for producing refined white sugar by low-temperature enzymatic hydrolysis of raw sugar according to claim 1, characterized in that, The α-amylase described in S20 has an enzyme activity of 2000-3000 U / g.

4. The method for producing refined white sugar by low-temperature enzymatic hydrolysis of raw sugar according to claim 1, characterized in that, The saccharifying enzyme described in S20 has an enzyme activity of 3000-4000 U / g.

5. The method for producing refined white sugar by low-temperature enzymatic hydrolysis of raw sugar according to claim 1, characterized in that, During the enzymatic hydrolysis of S20, the reducing sugar content of the hydrolysate is checked every 1 hour, and the enzymatic hydrolysis is stopped when the reducing sugar content reaches 35-40%.

6. The method for producing refined white sugar by low-temperature enzymatic hydrolysis of raw sugar according to claim 1, characterized in that, The pH adjuster used in S20 is a citrate-sodium citrate buffer solution with a concentration of 0.1-0.2 mol / L.

7. The method for producing refined white sugar by low-temperature enzymatic hydrolysis of raw sugar according to any one of claims 1-6, characterized in that, In the S40 step-by-step low-temperature crystallization process, the stirring speed in the crystallization tank is 50-80 r / min, and 0.01-0.02% of seed crystals by mass are added before the start of each cooling stage. The seed crystals are white sugar crystals with a particle size of 80-100 mesh.

8. The method for producing refined white sugar by low-temperature enzymatic hydrolysis of raw sugar according to any one of claims 1-6, characterized in that, The mother liquor obtained after centrifugation in S50 is returned to S10 for the preparation of raw sugar solution. The mother liquor is recycled no more than 5 times.

9. The method for producing refined white sugar by low-temperature enzymatic hydrolysis of raw sugar according to any one of claims 1-6, characterized in that, The dried white sugar product in S60 is cooled to room temperature and then vacuum-packed. During the packaging process, the ambient humidity is controlled to be ≤60%.

10. The method for producing refined white sugar by low-temperature enzymatic hydrolysis of raw sugar according to any one of claims 1-6, characterized in that, The raw sugar in S10 includes one or more of cane sugar and beet sugar.

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