Study On The Characteristics Of Electrical Impedance Spectrum And The Relationship With Quality Of Pork In Different Storage

The economic benefits and customer's acceptance of meat are correlated significantly with the quality traits and it is the focus for the consumers and producers.For this reason,it is important to control and monitor the quality during storage.While the traditional methods are time-consuming,it is particularly important to establish a fast detection method in order to meet the requirements in the fast-paced life.The purpose of this study is to explore relationship of electrical impedance spectrum characteristics,texture and freshness of pork during storage.The main research content is as follows:Lean pork tenderloins 12 h after slaughter were purchased from a local supermarket.Each muscle was divided into 5 pieces for impedance,texture and freshness measurement at 1 day,2 days,4 days,6 days,8 days post mortem,respectively.1.Impedance measurementEach observation consisted of the acquisition of an impedance spectrum of 601 points(logarithmic frequency intervals)over the frequency range from 20 Hz to 5 MHz.The values of frequency,impedance magnitude Z and phase angle ? were recorded by the system.The measured impedance values were analyzed with equivalent circuit models consisting of several electrical components.Intracellular fluid resistance RS,extracellular fluid resistance Rp and membrane capacitance C were calculated.It is shown significant dependence of impedance on the frequency within certain frequency ranges,and highly correlated with storage time(p < 0.05).The measured impedance values were analyzed with equivalent circuit models consisting of several electrical components.In order to model the complex pork tissues accurately,a constant phase element(CPE)was introduced instead of Cm in the conventional Fricke model to reflect the capacitance of cell membrane.R2 values of the real part of impedance were within the range between 0.961 and 0.999,and those for the imaginary part were between 0.730 and 0.999.The modified model with CPE can be further developed to monitor tissues conductivity changes and to evaluate cell physiological status of heterogeneous pork tissues in storage.2.Relationship of texture and freshness with electrochemical properties of porkTextural properties were measured by double compression using a Texture Analyzer CT3(Brookfield,US)equipped with a flat-ended cylindrical plunger(12.7mm).The force(N)was recorded continuously during compression in a texture profile curve with a preload of 0.07 N.Cubical samples(20×20×20 mm)were compressed with a constant cross-head speed of 4 mm/s.From the TPA curves,the following texture parameters were calculated: hardness(g),cohesiveness(dimensionless),springiness(dimensionless),adhesiveness and chewiness(g).There are significant differences among five mechanics characteristic parameters(p < 0.05),and they are highly correlated with storage time except springiness(p < 0.05).Volatile basic nitrogen content was determined with Semimicro-quantitative nitro gent method and TVB-N content was taken as the freshness criteria,highly correlated with electrochemical parameters(p < 0.05).3.Regression analysis and the establishment of modelElectrochemical index characteristics were screened through the principal component analysis.And the most representative principal components,PC1 and PC2,whose cumulative contribution rate reached 83.051%,were selected for multivariate linear regression modeling.Multivariate linear regression modeling was performed with PC1 and PC2,and the R2 of TVB-N,hardness,cohesiveness,springiness and chewiness were 0.91,0.552,0.801,0.528 and 0.725,respectively.Partial least squares regression analysis was used to establish the prediction model for the screened electrical parameters.The training set coefficients RC2 of the partial least-squares regression model for predicting the pork quality indicators were over 0.7(except cohesion)and the RMSECV value is also lower.So the model is seen which has better prediction ability and is suitable for the prediction of pork tissue quality indexes.This research is the first time to analyze the complex inhomogeneous pork tissues with the modified model.The modified model with CPE can be further developed to monitor tissues conductivity changes and to evaluate cell physiological status of heterogeneous pork tissues in storage.Control and evaluation of meat maturation state with electrical impedance spectroscopy from microscopic scale,which is a convenient and inexpensive method,is feasible and applicable.