The Mechanism Of Enzymatic Browning In Potato

Potato(Solanum tuberosum L) has many characteristics such as high yield, strong adaptability, nutrition-rich, extensive used and so on. Potato has become one of the four major food crops after rice, wheat and corn in the world. Potato processing is the most important part of the high value of agricultural products. Browning is a serious problem which impact on the quality of potato processed products and market competitiveness during processing. That is to say, enzymatic browning must be solved in potato processing industry. This research studied the mechanism of enzymatic browning in potato during processing, fit the mathematical model, and provided a theoretical basis for the control of browning in the potato processing. The main contents and conclusions of this paper are induced as follows:Firstly, to obtain the correlation of polyphenol oxidase, phenolics acid and the degree of browning in potato tuber, the dominant factors which leading color to inferior in processing was determine. Spectrophotometry and HPLC were applied to test the degree of browning, polyphenol oxidase activity and phenolic content. The correlation of the three during processing was analysed by SPSS software. The results show that:The correlation significantly differences with different temperature, the correlation coefficient (r) of polyphenol oxidase, phenols and chlorogenic acid in30℃:-0.972,-0.947,-0.966respectively;-0.924,-0.605,-0.856in45℃and-0.794,-0.715,-0.858in60℃. it show that the correlation between degree of browning and polyphenol oxidase activity, phenolic acid content was negatively, the higher the temperature is, the correlation worse. Conclusion:Enzymatic browning was the main reason leading color deterioration in low heat processing. Phenolic compounds were closely related with browning, and chlorogenic was the important substrate to potato tuber enzymatic browning.Secondly, to fit the thermal stability model of polyphenol oxidase from potato, and to predict the tendency of polyphenol oxidase activity in processing. Method: Residual activity of PPO in different heating temperature and time was detected by Spectrophotometry. Matlab software was used to fit the polynomial model. Result: Goodness of fit of the bivariate cubic polynomial model was high, R2=0.981, P<0.01, it show that the model was very significant. The equation is as follows:Z=24.54+6.116X+3.406Y-0.02689X2-0.2361XY-0.03509Y2-0.0002836X3+0.001326X2Y+0.0012XY2. Validation experiments show that when residual activity within30%-80%, the error was about5%. Conclusion:the bivariate cubic polynomial model could be more accurately predict the tendency of polyphenol oxidase activity in the thermal processing.Then, to study the enzyme kinetics of polyphenol oxidase, including the enzyme kinetics equation, the specificity of substrate and the activation energy of browning. Method:Hanes-Woolf was used to calculate the kinetic parameters:Vmax and Km, activation energy of browning was calculated by Arrhenius. Result:The Vmax of chlorogenic acid, caffeic acid, L-dopa and tyrosine was0.2060,0.2897,0.1251and0.0098mol/L-min respectively, The Km was10.3845,15.8274,18.0205and5.5913mmol/L respectively, and the activation energy of browning was37.165,20.716,37.877,31.269KJ/mol respectively, hydroquinone and ferulic acid was not catalysised by PPO. Conclusion:the affinity was different with different substrate: chlorogenic acid> caffeic acid> L-dopa> tyrosine. Chlorogenic acid was the optimal substrate of potato PPO. It is mainly catalyzed the substrate of ortho phenolic hydroxyl structure.Finally, to research double-dip substrates browning model and predict the effect of substrate composition on the enzymatic browning. Method:Spectrophotometry was used to the degree of browning in different substrates, Matlab software was used to fit the quadratic polynomial:(Y=b0+b1X2+b2Y2+b3XY+b4X+b5Y), the regression analysis coefficients of the quadratic polynomial equation was analyzed by SPSS. Result:the R2of three analog systerm was as follows:0.990,0.985,0.993respectively, P<0.01, it showed that the fitting equation is highly significant. Conclusion:the goodness of quadratic polynomial regression equationted was very high, and could be accurately reflect the substrates composition on the degree of browning, chlorogenic acid and caffeic had significant impact on browning degree, while chlorogenic acid and L-dopa had no significant impact, and chlorogenic acid and tyrosine inhibited when they exist together.