Determination Of α-amylase Activity In Rice Based On Rapid Visco-Analyser

α-amylase can be used as an important index to judge the change of rice quality.At present,colorimetry is the method for determiningα-amylase activity in rice according to the national standard.However,this method has a complicated operation process,which is easy to lead to the deviation of measurement results and needs further improvement.Therefore,a fast and accurate detection method can effectively solve this problem.To solve this problem,this paper explores a detection method based on rapid vissimeter（RVA）,that is,the silver nitrate solution can passivate the activity ofα-amylase in rice.The difference of peak viscosity before and after the treatment of silver nitrate in the rapid vissimeter is used to characterize and reflect the activity ofα-amylase in rice,which is referred to as RVA method for short in this paper.The factors influencing the determination ofα-amylase activity in rice by RVA method were explored.The unit conversion formulas of colorimetric method and RVA method were established based on the difference of amylopectin content in non-waxy rice and waxy rice respectively.The main research contents and results are as follows:（1）The influence factors ofα-amylase activity in rice determined by RVA method showed that 4 m M was the optimal concentration of Ag NO₃ solution for the determination ofα-amylase activity in rice.The peak viscosity of glutinous rice starch measured by different concentrations of silver nitrate solution instead of ultra-pure water was not much different from that obtained by ultra-pure water treatment,indicating that different concentrations of silver nitrate solution had little effect on the peak viscosity of glutinous rice starch itself.The peak viscosity of rice starch and glutinous rice starch changed little after treatment with 4 m M silver nitrate solution,so the effect of silver nitrate solution on starch itself could be ruled out.The change of peak viscosity of rice flour before and after adding silver nitrate solution under different RVA heating procedures is as follows:with the extension of heating time,the peak viscosity of rice flour shows a downward trend.The experimental results show that the difference of peak viscosity of rice flour under national standard procedures before and after treatment of silver nitrate solution is the largest.The national standard is the best procedure for determiningα-amylase activity of rice flour by RVA method.The results of the same amount ofα-amylase on the peak viscosity of different types of starch showed that the difference of peak viscosity of different types of starch after adding water and enzyme was different,indicating that the same amount ofα-amylase on different types of starch have different effects.When matching amylose and amylopectin,the peak viscosity of amylose showed a significant decrease trend with the increase of amylose content in the mixing powder of amylose and amylopectin,indicating that the different proportion of amylose and amylopectin would have an important impact on the paste characteristics of starch.（2）Theanalysisof thecorrespondingrelationshipbetweencolorimetricmethodand RVA methodforthedeterminationofα-amylaseactivityinriceshowedthatthe accuracy of colorimetric methodand RVA methodfor thedeterminationofα-amylaseactivity in rice is higher,and theimproved RVA method hasahigherprecision,which has realized the basic exploration ofthe possibility ofusing the rapid viscosity analyzerto analyze and determine theα-amylaseactivity inrice.（3）Using 30 non-waxy rice purchased from different parts of China as raw materials,theα-amylase activity of 30 non-waxy rice determined by RVA method as independent variable（x）,and theα-amylase activity of non-waxy rice determined by colorimetric method as dependent variable（y）.The optimal unit conversion formula between colorimetric method and RVA method for 30 non-waxy rice was established,and the fitting result was y=1.012×10^-6x^2.044-0.03121.The formula has a good fitting effect,with R² reaching 0.8476.In addition,the real and predicted values ofα-amylase activity of non-waxy rice were analyzed by t test.The results showed that there was no significant difference between the predicted values and the real values,which indicated that the established formula was reasonable and verified the reliability of the established formula.（4）The optimal unit conversion formula between waxy rice colorimetric method and RVA method was established by taking 30 kinds of waxy rice purchased from different parts of China.The fitting result was y=4.045×10^-6x^1.679+0.2628.Among them,y value representsα-amylase activity measured by colorimetric method,and x value representsα-amylase activity measured by RVA method.The formula fits well,and the R² reaches 0.9153.In addition,t-test analysis was made on the real value and predicted value of the established formula,and the test showed that there was no significant difference between the predicted value and the real value of waxy riceα-amylase activity,which indicated that the established formula was reasonable and verified the reliability of the established unit conversion formula.