Different fruits have different optimum conditions. If it is for biological experiments, you must add (pectinase) slowly and record it at any time. Experimental design and implementation of "the role of pectinase in fruit juice production" [turn] 29-3-21 21:35 1. Introduction In fruit juice processing, pectin not only affects the juice yield, but also makes the fruit juice turbid. Pectinase is a kind of enzymes that decompose pectin, which can make it easier to extract juice and make the juice clearer. "The Role of Pectinase in Fruit Juice Production" is the first topic in the fourth topic "Research and Application of Enzymes" in the standard experimental textbook of Biotechnology Practice (Elective 1) for senior high schools published by People's Education Press. The topic requires students to design experiments to explore the effects of temperature and pH on the activity of pectinase and the optimal dosage of pectinase. This content is closely related to students' daily life, and it is based on the compulsory "Exploring the conditions that affect the activity of enzymes", so it is not difficult for students. However, the subject pays more attention to the design of experimental scheme, considering relatively many variables, and also involves the gradient design of experimental variables. In order to obtain ideal results, repeated experiments and explorations must be carried out. In the process of inquiry, students discussed the experimental design and scheme in the teaching materials and reference materials, and put forward different problems and improvement measures. The author selected a more reasonable case, which is summarized as follows for reference only. 2, experimental materials and experimental methods 2.1 Experimental materials In this experiment, apples were selected as experimental materials and used after being squeezed into juice; The pectinase used in the experiment was purchased from Shanghai Lanji Biotechnology Co., Ltd., and was used after being prepared into a solution with a mass fraction of 2%. 2.2 experimental method 2.2.1 overall design of the experiment

fig. 1 this experimental design scheme 2.2.2 method of preparing fruit juice a medium-sized apple (about 2g) is selected, washed, peeled, cut into small pieces, put into a juicer, add about 2mL of water, and squeeze for 2min to obtain apple puree. Measure a certain volume of apple puree, treat it under different conditions, and filter it with filter paper to get juice. 2.2.3 Detection index of pectinase activity Pectinase can decompose pectin into small molecules, which can pass through filter paper and the volume of apple juice reflects the ability of pectinase to catalyze pectin decomposition. By measuring the volume of the filtered apple juice, the pectinase activity was detected. 2.2.4 Determine the most suitable amount of pectinase Take five test tubes, add 1mL apple puree after numbering, add water, .5mL, 1mL, 2mL and 4 ml of 2% pectinase solution in turn, add water to make the final volume of each test tube reaction system 14mL, act for a long time at room temperature, filter for 15min, measure the volume of filtered apple juice, and determine the most suitable amount of pectinase. 2.2.5 Determine the action time of pectinase Take six test tubes, add 1mL of apple puree to each tube after numbering, add 1mL of water to one tube as a blank control, and add 1 ml of 2% pectinase solution to the other five tubes, and treat the five test tubes with enzyme at room temperature for 1min, 5min, 1min, 15min and 2min in turn. After treatment, the enzyme was inactivated by boiling water bath, filtered for 15min, and the volume of filtered apple juice was measured to determine the action time of pectinase. 2.2.6 Explore the influence of different temperatures on pectinase activity. Set the temperature gradient: 1℃, 2℃, 3℃, 4℃, 5℃, 6℃, 7℃. Take 7 test tubes, add 1mL of apple puree after numbering, and add 1 ml of 2% pectinase solution after numbering. Firstly, the apple puree and pectinase solution were kept in water bath at 1℃, 2℃, 3℃, 4℃, 5℃, 6℃ and 7℃ for 1min, then the apple puree and pectinase solution treated at the same temperature were evenly mixed and kept at the corresponding temperature for 5min. After treatment, the enzyme was inactivated in boiling water bath, filtered for 15min, and the volume of filtered apple juice was measured to determine the influence of different temperatures on pectinase activity. If there is no constant-temperature water bath pot in the laboratory, different proportions of cold water and hot water can be added to the big beaker of the water bath, and the temperature of the water bath can be controlled by a thermometer (appropriate amount of hot water can be added from time to time to maintain the temperature). When the room temperature is greater than 1℃, the temperature of the water bath at 1℃ can be controlled by ice cubes or the cold room of the refrigerator. 2.2.7 Explore the influence of different pH values on pectinase activity. Set pH gradient: 2, 3, 4, 5, 6, 7, 8, 9. Take 8 test tubes, add 1mL apple puree after numbering, and take 8 test tubes, add 1 ml of 2% pectinase solution after numbering. Using .1moL/L HCl solution and 1% NaOH solution, the pH values of apple puree and pectinase solution were set to eight pH gradients: 2, 3, 4, 5, 6, 7, 8, 9, etc. The pH values were determined by pH test paper or pH meter, and then the apple puree and pectinase solution with the same pH value were mixed to obtain eight reaction systems with different pH gradients. Adjust the volume of the solution in eight test tubes with distilled water (the total volume of the reaction solution in this experiment is 16mL), keep the temperature at room temperature for 5 minutes, inactivate the enzyme with boiling water bath after treatment, filter for 15 minutes, measure the volume of the filtered apple juice, and determine the influence of different pH values on pectinase activity. 3. Experimental results 3.1 It takes about 1mL of 2% pectinase solution to completely treat 1mL of apple puree, and the volume gradient of 2% pectinase solution is set to catalyze the same volume of apple puree (1mL) respectively, and the volume and clarity of the obtained apple juice are shown in Table I.. Table Ⅰ. Effect of enzyme amount on the filtration amount of apple juice. Test tubeNo. 123452% pectinase solution .5mL1mL2mL4mL The volume of apple juice after filtration is 5.4ml 8.5ml 9.5ml 9.5ml Clarification Clarification Clarification Clarification From Table Ⅰ and Figure 2(A), it can be seen that 1mL apple puree is treated with different amounts of pectinase for a long time at room temperature. In 1 ~ 4 test tubes, the volume of apple juice increases with the increase of pectinase content, but when the 2% pectinase solution reaches 1mL, the volume of apple juice hardly increases, indicating that the substrate has been exhausted, and the most suitable amount of pectinase solution for treating 1mL apple puree should be about 1mL. 3.2 At room temperature, it only takes 5 ~ 1 minutes for 1 ml of 2% pectinase solution to completely treat 1mL of apple puree. Take 1 ml of 2% pectinase solution to catalyze the same volume of apple puree (1mL) for different time, and the volume and clarity of apple juice obtained are shown in the following table. Table Ⅱ. Effect of enzyme action time on apple juice filtration. Test tube number 123456 Pectinase action time 1min5min1min15min2min. The volume of apple juice after filtration is 4.5mL5.9 mL7.8 mL8. mL8. mL8.1 mL Clarity of apple juice after filtration is clarified by Table Ⅱ. And fig. 2(B) show that in 1 ~ 4 test tubes, the volume of apple juice increases with the increase of pectinase action time, but when the enzyme action time is increased to 1min, the volume of apple juice almost does not increase, indicating that the substrate has been exhausted. When the enzyme action time is 5min (test tube 3), the volume of apple juice almost reaches the maximum, so 1mL of 2% pectinase solution is completely.