Fast Evaluation Freshness Of Freshwater Fish Based On Bioimpedance Characteristics And Electronic Nose

Freshness makes a major contribution to the quality of fish and fishery products. While,fish is a product of preservation intolerance and is easily deteriorated,the spoilage fish would lead to food poisoning.It is important to enhance hygienic examination to ensure the safety of fish products.Therefore,fast and accurate evaluation of fish freshness has a scientific and practical value to preservation,deposit and further processing of fish.Bioimpedance and electronic nose measurement technology was employed to research on fast evaluation freshness of freshwater fish.Based on bioimpedance and virtual instrument measurement technology,based on four-electrode and sweep frequency method,a freshwater fish bioimpedance measurement system was established.Crucian and silver carp was taken as study object,measurement method of bioimpedance spectrum and change rule of bioimepdance of freshwater fish during storage was investigated,the optimal measurement parameters and condition for the bioimpedance measurement of freshwater fish was ascertained.Futhermore,freshness index was constructed based on freshwater fish bioimpedance characteristics and BP-ANN (back-propagation artificial neural networks) method was used to improve the evaluation accuracy.A freshwater fish electronic nose measurement system was constructed based on artificial olfactory system and virtual instrument technology.Then,silver carp meat during storage was investigated by electronic nose measurement system.Experiment parameters of the system was optimized by PCA(Principal Component Analysis) method, and the optimal measurement condition was ascertained,finally,PCR(Principal Component Regression),PLS(Partial Least Square) and ANN(Artificial Neural Network) methods were employed and compared to build mathematic model,the most optimal method of model identification was ascertained,furthermore,the gas sensor array was optimized by model comparison.The main conclusions are as follows.1.The bioimpedance spectrum of crucian and silver carp during storage presents as cole circle and the cole-cole plots measured at different post-mortem time differentiated obviously,the result provides a theoretical foundation for using bioimpedance technology and bioimpedance characteristics to evaluate freshness of freshwater fish.2.Measurement method and measurement system of bioimpedance characteristics of freshwater fish was firstly brought forward and constructed.The system consists of two parts,one is the hardware which includes self-design four-electrode,voltage control current source(VCCS),signal processed circuit,and the other is software which includes signal generator,data acquisition and file auto-save model based on LabVIEW development environment.The result indicated that the system has high intelligence and accuracy,at the range of 100Hz～100 kHz,the maximum error of impedance is 0.58%,at the range of 50kHz～100kHz,the maximum error of phase is 0.31°;While at the frequency range lower than 50 kHz,the maximum error of phase is 0.07°.At the range of 100Hz～100kHz for 10 points every decade,it cost only 30s～50s for the system to calculate the impedance and phase changing with frequency,which establishes a theoretical foundation and technical parameters for other bio-tissue research on bioimpedance characteristics.3.Two VCCS based on AD844 and AD620 were designed to solve the problem of measurement accuracy of bioimpedance;the result indicated that the performance of VCCS based on AD844 is better,which has 1155 kΩfor inner impedance,while the inner impedance of VCCS based on AD620 is only 500 kΩ,in additional,a DCFB(Directed Current Feed Back) circuit was added to the VCCS to ensure the stability of current source.Aimed at solving the problem of phase accuracy of bio-tissue bioimpedance measurement,five different phase measurement methods was designed and then compared at the condition of white noise,the result indicated that the digital demodulation method(add standard sine and cosine method) has the highest accuracy,the maximum error is lower than 0.03°.4.The effect of excitation current,measurement electrode,excitation frequency, measured direction and measured position of crucian and silver carp during fish storage was first systematically investigated based on bioimpedance technology,the optimal measurement condition for freshwater fish bioimpedance measurement are as follows: 0.3mA for excitation current,composite electrode for measurement electrode,1kHz～5kH for excitation frequency and measured parallel to the lateral line of gill for measured direction and position.The result indicated that different measured positions lead to different impedance,the biggest impedance of measured position is tail,and then is belly and gill,however,the difference of impedance of measured position decreases with post-mortem time.At the same post-mortem time,the impedance decreases with the increase of frequency,while phase increases with frequency.The impedance changing rule conforms to the frequency dispersion of bio-tissue.At the same post-mortem time, the impedance measured paralleled to the lateral line is bigger than the impedance measured vertical to the lateral line of fish,which conforms to the anisotropy characteristics of bio-tissue,however,the anisotropy decreases with post-mortem time, when the ration of impedance measured parallel and vertical to the lateral line fish is lower than 1.05,it can indicate the deterioration of freshwater fish.5.Taking the TVB-N(Total Volatile Basic Nitrogen) as the compared index of freshwater fish freshness,the freshness index of bioimpedance characteristics of crucian and silver carp was constructed at 1 kHz and ANN method was used to build predicted model.When the impedance of crucian is less than 129.79Ωand phase of crucian is less than 5.43°,and when the impedance of silver carp is less than 91.26Ωand phase of silver carp is less than 1.48°,it can indicate the deterioration of freshwater fish.Taking the impedance and phase as input parameters and the TVB-N value as the output parameter for building the ANN predicted model,the result indicated that the optimal net layer structure for crucian ANN is 2-11-1,the model's correlation coefficient of predicted and measured TVB-N is 0.95621,the test accuracy of the modle is 94.44%;while for silver carp,the optimal net layer structure is 2-10-1,the model's correlation coefficient of predicted and measured TVB-N is 0.99282,the test accuracy of the model is 97.44%.6.A freshwater fish electronic nose was firstly brought forward and constructed based on artificial olfactory system and virtual instrument method,the measurement system includes electronic nose gas collection container,four-gas sensor array(TGS822 for ethanol;TGS825 for H₂S;TGGS826 for NH₃ and aime,TGS832 for halocarbon) and its signal processed circuit for hardware,and data acquisition,data analysis and file saving model based on LabVIEW for software.The result indicated that the response of electronic nose correlated with freshness loss of fish.A new air sample method(free air diffused method) was improved on the basis of traditional static headspace air analysis, which can simplify the sample equipment and provide theoretical foundation and technical parameters for constructing easy-carried electronic nose.7.Taking silver carp as the research object and PCA as the analysis method,the optimal measurement condition for electronic nose are as follows:headspace for 5min, 60g for sample weight.8.ANN was the most optimal model identification method for electronic nose,the three gas sensors,TGS822,TGS826 and TGS832,were the optimal gas sensor array for electronic nose.PCR,PLS and BP-ANN was used to build the predicted model,the result indicated their correlation coefficient of predicted and measured-N value are 0.89778, 0.92250 and 0.97613,which indicated that the ANN method has higher accuracy and is the optimal method,the optimal net layer of ANN structure is 4-11-1.On this basis,gas sensor array response were analyzed,the result showed that the three gas sensor(TGS822,TGS826 and TGS832) has the same correlation coefficient of predicted and measured-N value with the four gas sensor array(TGS822,TGS 825,TGS826 and TGS832),the correlation coefficient is 0.976.The three gas sensors were ascertained as the optimal gas sensor array.9.The optimal net layer structure is 3-11-2,the accuracy of ANN model of optimal three gas sensor array is 97.32%to identify fresh,semi-fresh,semi-deteriorated and deteriorated fish samples.When using the bioimpedance index for assistant judgement of the freshness of fish,the accuracy can be improved to 100%.Innovations:1.Bioimpedance measurement technology was firstly brought forward to evaluate the freshness of freshwater fish and was proved to be able to evaluate the freshness of freshwater fish.On this basis,biomimpedance measurement system was constructed based on LabVIEW environment and has high accuracy.The maximum error of impedance of the system is 0.58%;the maximum error of phase is 0.31°and 0.07°during 50 kHz～100 kHz and 100 Hz～50 kHz.2.A large numbers of crucian and silver carp was used to investigate the factors affecting on bioimpedance characteristics,and the optimum measurement conditions were ascertained as follows:0.3mA for excitation current,composite electrode for measurement electrode,1 kHz～5 kHz for excitation frequency and measured parallel to the lateral line of gill for measured direction and position.Freshness index was constructed based on bioimpedance characteristics and BP-ANN method was used to construct evaluation freshness model to improve the accuracy,the model accuracy for crucian and silver carp is 94.44%and 97.44%.3.A new air sample method(free air diffused method) was improved on the basis of traditional static headspace air analysis,which simplified the sample equipment.Based on artificial olfactory technology and virtual instrument technology,electronic nose of freshwater fish was firstly brought forward and constructed with four gas sensor array and was proved validity.Experiment factors for electronic nose system was investigated, headspace for 5min and 60g for sample weight were ascertained as the optimum measurement conditions.On this basis,BP-ANN method was employed to build predicted model for freshness level,the accuracy is 97.32%to identify fresh,semi-fresh, semi-deteriorated and deteriorated fish samples.And when using the bioimpedance index for assistant judgement of the freshness of fish,the accuracy can be improved to 100%.4.PCR,PLS and BP-ANN was employed to build the predicted model and their model accuracy was compared,the result indicated that BP-ANN method was the optimum method for electronic nose system.On this basis,the gas sensor array was optimized by comparing the predicted accuracy,finally the three gas sensor(TGS822, TGS826 and TGS832) was ascertained as the optimum gas sensor array,which provides a ness method for optimizing gas sensor array.