Basic introduction Chinese name: Starch hydrolysis belongs to: high molecular compound pathway: dilute sulfuric acid or heating: scientific inquiry of glucose, experimental articles, experimental methods, matters needing attention, problem thinking, preparation methods, scientific inquiry design experimental scheme, whether experimental starch can be hydrolyzed, and what are the conditions and products of hydrolysis? How to judge whether starch is hydrolyzed? Experimental supplies: starch, water, iodine solution, 20% sulfuric acid, 10% sodium hydroxide, 2% copper sulfate, alcohol lamp, test tube holder, test tube, etc. Experimental method 1. Add 0.5g starch and 4ml water to test tube 1, and add 0.5g starch and 4ml 20% sulfuric acid solution to test tube 2. Heat the test tubes for 3 ~ 4 minutes respectively. 2. Pour part of the solution in test tube 2 into test tube 3 for the next experiment. 3. Add a few drops of iodine solution into test tube 1 and test tube 2, and observe the phenomenon. It was found that the solution of test tube 1 was blue (starch turned blue when it met iodine), and there was no obvious phenomenon in test tube 2. 4. Drop 10% sodium hydroxide solution into the test tube 3, and adjust the pH value of the solution to about 9~ 10. 5. Add 3ml of sodium hydroxide solution into another test tube 4, and drop 4 drops of 2% copper sulfate solution, and blue copper hydroxide will precipitate immediately. Drop 65438 0 ml of hydrolysate into test tube 3, shake well, and heat it with alcohol lamp until it boils. The color of the solution often changes from blue to yellow and then to green (yellow and blue mixed) and then to red. Finally, a red precipitate is formed. The reason is that copper hydroxide is reduced to produce red cuprous oxide, which is insoluble in water. Experimental conclusion: Starch can be hydrolyzed under the catalysis of acid. Hydrolysis process of starch: dextrin with small molecular weight (the product of incomplete hydrolysis of starch) is formed, and dextrin continues to hydrolyze to form maltose, and the final hydrolysis product is glucose. Note: Dextrin, the intermediate product of starch hydrolysis (including red dextrin with larger molecular weight and white dextrin with smaller molecular weight) changes color when it reacts with iodine: purple-brown-yellow. If starch is not completely hydrolyzed, different colors will appear. Question: Why do 1 and test tube 1 turn blue? Why is there no obvious phenomenon in test tube 2? Why? (The starch in the test tube 1 does not hydrolyze, but turns blue when it meets iodine; The starch in test tube 2 is hydrolyzed under the catalysis of acid, and there is no obvious phenomenon; The reason for the different phenomena is that starch is hydrolyzed under acidic conditions and heating conditions. 2. How to verify that starch cannot be reduced? (Hint: Silver mirror reaction cannot occur or copper hydroxide cannot be reduced) 3. Experimental extension design: How to verify the catalytic effect of sialidase on starch hydrolysis? (Note: When using saliva as a catalyst to hydrolyze starch, the temperature should not exceed 45℃, because sialidase will lose its activity if the temperature is too high, and the most suitable temperature is 37-40℃. Some bacteria can secrete amylase (extracellular enzyme), hydrolyze starch into maltose and glucose, and then be absorbed and utilized by bacteria. Starch will not turn blue when it meets iodine after hydrolysis. (1) Melt the conical flask containing starch culture medium in boiling water bath, then take it out, cool it to about 50℃, pour it into a Petri dish, and make it into a flat plate after solidification. (2) Turn the flat plate so that the back of the bottom dish faces upwards, and divide it into two halves on the back glass with a marker pen, one half is used for inoculating Bacillus subtilis as a positive control bacteria, and the other half is used for inoculating test bacteria Escherichia coli or Enterobacter aerogenes. During inoculation, take a small amount of bacteria with an inoculation ring and mark "+"on both sides of the plate. (3) The inoculation plate was inverted in a constant temperature box at 37℃ for 24 hours. (4) When observing the results, you can open the dish cover, drop a small amount of iodine solution on the flat plate, and gently rotate it to make the iodine solution evenly spread over the whole flat plate. If there are colorless and transparent circles around the bacteria, it means that the starch has been hydrolyzed. The size of the transparent circle indicates the ability of the strain to hydrolyze starch. Preparation method 1. Acid hydrolysis is to hydrolyze starch into glucose at high temperature and high pressure with acid (inorganic acid or organic acid) as catalyst. Advantages: simple production, the whole chemical reaction process of gradually hydrolyzing starch into glucose is only carried out in a high-pressure container, the hydrolysis time is short, and the production capacity of the equipment is large. If starch with the concentration of 10oBe' is used, it will take 20 minutes under the pressure of 0.294 Mpa; It only takes 7- 10min under the pressure of 0.343 Mpa. Disadvantages: 1) Because hydrolysis is carried out at high temperature and high pressure, the equipment is required to be corrosion-resistant and resistant to high temperature and high pressure; 2) In the process of acid hydrolysis, besides the hydrolysis reaction of starch, there are side reactions, which will reduce the utilization rate of starch; 3) Acid hydrolysis method requires strict starch raw materials, uniform particle size, and the starch concentration should not be too high. 2. Enzymatic hydrolysis (double enzyme hydrolysis method) Enzymatic hydrolysis is to hydrolyze starch into glucose with amylase. Enzymatic hydrolysis can be divided into two steps: the first step: starch is converted into dextrin and oligosaccharide by-amylase, which increases the solubility of starch. This process is called "liquefaction"; If-amylase of BF7658 is used, the reaction temperature is 85-90℃ and the pH is 6.0-7.0; Using glucoamylase, the reaction temperature is 50-60℃ and the pH is pH3.5-5.0. Step 2: Further hydrolyze dextrin or oligosaccharide with glucoamylase to convert it into glucose. This process is called "saccharification". "Liquefaction" and "saccharification" are both completed under the action of enzymes, hence the name. Acid hydrolysis is generally 10- 12 be' (containing 18-20% starch), and double enzyme method is generally 20-23 be' (containing 34-40% starch). 3. Acid-enzyme combination method Some starches, such as corn and wheat, have solid starch particles. For example, acid can be used to hydrolyze starch to glucose values 10- 15, then the hydrolysate is cooled, neutralized and saccharified by adding glucoamylase. Glucose values (DE value; Glucose equivalent value)-refers to the percentage of glucose sugar (all measured reducing sugars are regarded as glucose) in dry matter, which is used to indicate the degree of starch hydrolysis and saccharification.