Starch is the polymer of glucose. It is composed of hundreds or thousands of glucose units. It can also be regarded as consisting of many tiny particles, and each of particle has the rather complex internal structure. Under normal circumstances, these particles are insoluble.
The crystalline structure of starch particles has strong resistance to enzymes. For example, α-amylase hydrolyzes starch particles to hydrolyze gelatinized starch at the rate ratio of about 1:20,000.
Therefore, the amylase can not directly act on the starch.It is necessary to heat the starch milk firstly to make the starch particles absorb water and expand, gelatinize, and destroy its crystalline structure.
Starch milk gelatinization is the first necessary step in enzymatic process. Starch gelatinization has increased viscosity, poor fluidity, difficulty in stirring, and also affects heat transfer. It is difficult to obtain uniform gelatinization results,and it is difficult to conduct the operation especially in the case of high concentration and a large number of materials.
The α-amylase action on gelatinized starch has the strong catalytic hydrolysis effect, can quickly hydrolysis to dextrin and oligosaccharide range size of molecules, the viscosity rapidly declines, fluidity increases, while increasing a large number of
non-reducible end, this process of starch molecules is called "liquefaction"in the industry.
Another important purpose of liquefaction is to create favorable conditions for the next step of saccharification.
The glucamylase used for saccharification is an exoenzyme that hydrolyzes from the non-reducing tail end of the substrate molecule. In the liquefaction process, the molecules are hydrolyzed to the size of dextrin and oligosaccharide range, and the number
of substrate molecules increases, and the chances of saccharifying enzyme action increase, which is conducive to the saccharification reaction.
In the liquefaction process, starch is hydrolyzed by amylase into smaller molecules of the liquefied liquid of dextrin and oligosaccharides , and liquefaction liquid is further converted into glucose under the action of glucose amylase. This process is called saccharification.
Glucose amylase can catalyze the hydrolysis of starch and oligosaccharide molecules only α-1, 4 glucosidic bond, it cuts glucose units from the non-reducing end of the molecule, and stops the decomposition of glucose units near the branched chain α-1, 6 bond; However, it can continue to hydrolyze other only α-1, 4 bonds beyond the α-1, 6 bond.
Although glucose amylase can also hydrolyze the α-1, 6 bonds, the rate of hydrolysis is about ten times slower than that of severing the α-1, 4 bonds. When glucose amylase is used alone, there are a large number of α-1, 6 bond residues in the final saccharification solution, and these residues cannot produce glucose and ultimately affect the yield of glucose.
In order to increase the yield of glucose, in actual production, in addition to using glucose amylase, branched chain amylase which is also known as Pullulanase is also added. This enzyme can efficiently hydrolyze the α-1, 6 bond, and further hydrolyze the glucose unit near the α-1, 6 bond at the bifurcation point of the starch chain into glucose.
Of course, the Saccharifying enzyme preparations are actually used in most factories in the actual operation today ,and most of them are complex preparations of glucose amylase and branched chain amylase (also known as Pullulanase).
Therefore, in the actual production, as long as it is directly added according to the requirements of use, it can be used normally.
1. Process Flow
Starch milk → jet liquefaction → maintenance →thermal insulating layer flow → cooling to adjust pH value → saccharification
In the starch milk mixing tank, adjust the starch slurry milk to Be18 or so, use acid or alkali to adjust the pH to 5.4 ~ 5.8, add high temperature resistant α-amylase, then stir well, pump the starch slurry into the jet liquidator, through the injector, the slurry and steam are in direct contact, control the temperature 105℃ ~ 108℃, maintain for 3-5 minutes. Then it enters into the laminar flow tank, keep warm for 90 ~ 120 minutes, the measure DE value reaches 12-14%, and then start to cool down; After cooling, the liquefied liquid is quickly adjusted to the pH value of 4.2 ~ 4.4 with acid, and then the saccharifying enzyme is added, and the saccharification is kept warm at 60℃±2℃.
After the general control of 48 hours, DE value reaches or exceeds 98% (complex saccharification enzyme), the sampling is determined by HPLC to meet the requirements, the saccharification is ended, and then the saccharification liquid begins to enter the refining process.
2. Basic process conditions control
Starch milk:
Concentration: 30% ~ 32%.
pH: 5.4 ~ 5.8.
Starch milk protein content: ≤ 0.5%.
Liquefaction control:
Concentration: 32% ± 2%.
pH: 5.4 ~ 5.8.
Amount of enzyme: Add according to the recommended amount of enzyme model.
Injection temperature: 105℃ ~ 108℃(It can be adjusted slightly according to the actual situation)
Maintenance
time: 3-5 minutes.
Retention time of liquefaction: 90 ~ 120 minutes.
DE value at the end of liquefaction: 12% ~ 14%.
Iodine test: brown or brownish-red.
Saccharification:
pH: 4.2 to 4.4.
Amount of enzyme added: Refer to the recommended amount of enzyme.
Holding temperature: 60℃ ±2℃.
Saccharification time: 48 hours-60 hours.
DE value at the end of saccharification: ≥ 98%.
Dextrin test:qualified.
(This item is not required for check.)
3. High performance liquid phase analysis (saccharification liquid):
DP2: high, DP4+ low.
Possible cause: excessive saccharification.
Adjustment: Appropriately reduce the amount of saccharifying enzymes or shorten the time.
DP3 high.
Possible cause: Excessive liquefaction or uneven liquefaction.
Adjustment: Slightly adjust the liquefaction control conditions.
DP2 is low, DP4+ is high.
Possible cause: incomplete saccharification.