Study On Storage Time Discrimination Of Rice Based On Olfactory Visualization Technology

In the circulation and sales,with the prolongation of time and changes in environment,the rice became deteriorate,such as decreasing in nutritional value,darkening of color,and declining in the eating quality.While the conventional methods present some drawbacks such as low accuracy,complicated operation,high costs of implementation,and lengthy analysis time.There is no systemic standard and method for the quality identification of rice.With the improvement of people’s living standards and demands for food quality;it is imperative to establish a rapid and accurate identification method for the storage quality of rice.In this study,colorimetric sensor array was employed to identify rice samples with different storage times.The colorimetric sensor array of olfactory visualization system was constructed by sensitive and specific chemically responsive dyes that selected from a series of new dyes with different substituents in different positions.The main research contents of the paper are as follows:1.Biomarkers screening of rice at different storage time.SPME-GC-MS was used to analyze the changes of volatile components in rice during different storage periods.The results were analyzed by principal component analysis,loading factor analysis and variance analysis.The results showed that there were significant differences in volatile gases of rice during storage periods,and aldehydes were the most important volatiles in rice,which increased significantly during storage time;among them,the loading factor of hexanal was 0.7,contributed the most on the flavor changes of rice.The content of hexanal increased from 0%to 25%with the extension of storage time.Therefore hexanal was recognized as specific volatile organic component for aged rice.2.Identification of hexanal by colorimetric sensor array.Firstly,it was compared that the sensitivity of the traditional chemically responsive dyes（porphyrins）and novel chemically responsive dyes（fluoroborespyrrole compounds,BODIPYs）to hexanal（140 mg/L）.The results showed that BODIPYs performed more sensitive to hexanal.Then BODIPYs were exposed to different concentrations of hexanal for the measurement of identification,and exposed to rice for the detection of anti-interference ability.The results showed that BrBDP,NO₂BrBDP and NO₂Br₂BDP had good discrimination ability on different concentrations of hexanal and were not affect by other gases in rice samples.3.The mechanism of hexanal and chemically responsive dyes was investigated by quantum chemical calculation method based on the density functional theory.Firstly,it was analyzed that the difference of the coloration function between the porphyrins and the BODIPYs.The results showed that porphyrins were affected by steric repulsion in binding with hexanal.Then,binding energies,orbital energy levels,distances between atoms,charges and plane angles between hexanal and BODIPYs are analyzed.The results showed that the magnitude of the orbital energy difference had an important influence on their coloration function.The smaller the energy level difference,the more favorable the transition of electrons,which triggered coloration.Besides,the binding ability also exerted its coloration ability that can be expressed by the change in binding energy during the reaction.BrBDP,NO₂BrBDP and NO₂Br₂BDP had smaller orbital energy differences,and higher binding energy after combined with hexanal,which is benefit for the coloration function and consistent with the screening results of the chemically responsive dyes.4.The identification of rice storage time based on olfactory visualization technology.As the research objects,freshness rice,rice samples storage for two months,four months,six months and ten years,respectively were employed in this work.From 21 kinds of chemically responsive dyes（including 18 porphyrins and three fluoroborespyrrole compounds）,three manganese porphyrin compounds can characterize the whole VOCs of rice at different storage times.Combined with three sensitive dyes（BrBDP,NO₂BrBDP and NO₂Br₂BDP）to hexanal,a 2×3colorimetric sensor array was constructed for the identification of rice storage time.The pattern recognition methods were used to analyze the results.The results showed that when the principal components is 5,the LDA model obtains the best results with recognition rate of 98.0%.