Application Of The Nanocomposites Modified Electrodes Array For Identifying The Aging Time Of Rice Wines

The rice wines,as a real Chinese specialty,called the world's three major fermentation wines together with French wine and German beer.It has a history of more than 5000 years and is also a characteristic of Zhejiang Province.About several years natural storage is necessary for the aging of newly-produced liquor.For now at least,the rice wine base liquor has become a scarce resource in the market.Due to factors such as stock and market expansion,the cost of base liquor is relatively high.There is a phenomenon in the rice wine market that some unscrupulous merchants attach the more aged labels on the packaging for profiteering,which encroaches up the rights and interests of consumers seriously.Therefore,it is particularly significant to explore a new detection method to identify rice wine ages correctly and efficiently.Chemically modified electrode has developed rapidly for their characteristics of rapid,comprehensive and nondestructive testing,which reached a new height in the field of wine quality testing.Excellent electrochemical properties of polymers and metal nanoparticles have attracted our attention,and we decided to explore the possibility of using the polymers as carriers to deposit metal nanoparticles in order to fabricate nanocomposites modified electrodes.The nanocomposites enlarged the surfaces area of electrodes and provided more active sites for catalyst than bare glassy carbon electrode and the single material modified electrodes.In the rice wine industry,the quality of wine is generally judged by its aging time,and the content of flavoring substances in wines is constantly changing during the aging process.Therefore,there is a certain relationship between the aging time of rice wine and flavoring substance contents,mainly including organic acids,amino acids,sugars and so on.In this paper,we focuses on the development of the conductive polymer nanocomposite materials and its applicability in the identification of the aging time of rice wines.Lactic acid,glutamic acid and glucose were the typical chemicals that have high correlations with wine ages and represented the diversified taste.Three nanocomposites modified electrodes were fabricated and exhibited high sensitivity to lactic acid,glutamic acid and glucose,respectively.The electrode processes and chemical reaction kinetics in single solute solutions were analyzed to explain the electrochemical reaction mechanism.Then,three electrodes were assembled into an array to collect comprehensive "taste" information in the "NvErHong " rice wines with 1-8 years of aging time.Then through feature extraction,feature selection,data visualization and modeling,the classification and prediction of the aging time of rice wines were realized.The main research contents,methods and conclusions are as follows:(1)Sour taste is a basic taste of rice wine.It has the effect of increasing the richness of the wine flavor and reducing the sweetness,so appropriate acid could make the taste of rice wine softer.In this work,poly cobalt phthalocyanine/multiwalled carbon nanotube nanocomposites modified electrode(CoPPc/MWCNTs/GCE)was fabricated and exhibited high sensitivity to lactic acid that has a great change in the content of rice wine during the aging process.SEM,TEM,FT-IR,UV-Vis and XPS were used to Characteristic the modified nanocomposites,and CoPPc/MWCNTs/GCE has good catalytic property to lactic acid.The experimental parameters after optimization are as follows:CoPPc/MWCNTs concentration of the composite is 2 mg/ml and the amount of modidier is 5 ?l,pH 4.0,scanning rate is 100 mV/s,and the accumulation time is 240 s.The detection limit was found to be 4× 10-7 mol/L(S/N=3)under optimal conditions.The electrokinetic equation of the electrode process might be:CH3CH(OH)COOH + H+ + e-?CH3CH(OH)CHO + H2O,in which the number of electrons and protons involved in the reaction were both 2,and the true electrochemical surface area of the electrode A = 0.49 cm2,and the diffusion Coefficient D = 9.22 × 10-5 cm2/s.(2)The umami taste is an important feature distinguishing rice wine from other wines.It is usually derived from amino acids,which could give people a refreshing and delicious feeling.Among all umami amino acids,glutamic acid has a great change in the content of rice wine during the aging process and plays a major role.In this work,poly neutral red/copper nanocomposites modified electrode(PNR/GU/GCE)was prepared and showed high sensitivity to glutamic acid.The morphology and structure of the nanocomposites were characterized by SEM,XRD and XPS,and PNR/Cu greatly enhances the catalytic performance of the electrode for glutamic acid.Finally,under optimal conditions of pH 4.0 and scan rate of 100 mV/s,the detection limit was found to be 3×10-6 mol/L(S/N=3).Based on the theoretical analysis and a large number of experimental results,the electrocatalytic equation could be:(HOOC)CH2CH2CH(NH2)COOH + H2O-e-?HOOCCH2CH2CH(NO2)COOH + H+.The number of electrons participating in the reaction was 2,and the number of protons was 4.It could be given by formulas that the true electrochemical surface area of the electrode A = 0.56 cm2,and the diffusion Coefficient D = 3.72 × 10-4 cm2/s.(3)Sweetness is one of the main flavors in rice wine,which derived from the decomposition of starch and protein in wine.Glucose,as a sweet substance with the greatest change in the content of rice wine during aging process,has a great influence on the overall taste of the wine.In this work,poly aspartic acid/nickel oxide nanocomposites modified electrode(PASP/NiO/GCE)was used to detect the concentration of glucose in single solute solution.The modified electrode was characterized by SEM,XRD and XPS.PASP/NiO/GCE reduced the energy barrier that needs to be overcome during the electrocatalysis of glucose,and then reduced the electrocatalytic voltage.In an alkaline solution(pH 10.0),the detection limit of glucose is 2 x 10-6 mol/L(S/N=3)under the condition of scan rate is 100 mV/s and accumulation time is 180 s.The electrokinetic equation of the electrode process probably was:CH2OH(CHOGCE were assembled into an array to collect comprehensive "taste" information in the "NvErHong H)4CHO + NiO + OH-? CH(OH)5CH2OH+ H+,in which the number of electrons and protons involved in the reaction were both 2,and the true electrochemical surface area of the electrode A = 0.71 cm2,and the diffusion Coefficient D =1.06 × 10-4 cm2/s.(4)CoPPc/MWCNTs/GCE,PNR/Cu/GCE and PASP/NiO/" rice wines with different aging time of 1-8 years.Chronoamperometry was adopted to record taste information of wine samples.Both the multi-frequency rectangle pulse voltammetry(MRPV)and the multi-frequency staircase pulse voltammetry(MSPV)were carried out as potential waveforms,with three different frequency fragments(1 Hz,10 Hz,and 100 Hz),respectively.The area under the corresponding response curves were taken as eigenvalues.Then the coefficient of variation analysis,multi-collinearity analysis and variance analysis were adopted to obtain the optimal feature subsets.Three dimensionality reduction methods(Principal Component Analysis(PCA),Locally Linear Embedding(LLE)and Locality Preserving Projection(LPP))and three classification algorithms(Logistical Regression(LR),Extreme Learning Machine(ELM)and Support Vector Machine(SVM))were employed and the best combination of dimensionality reduction method and classification algorithms was determined.The results showed that LPP-ELM model and LLE-SVM model reached 100%classification accuracy of rice wines.Besides,LPP-ELM model had the best regression effect on the aging time of "NvErHong " rice wines with R2 = 0.9985,RMSE=0.0892 in training set,and R2 = 0.9905,RMSE = 0.1733 in prediction set.