Research On The Electrical Characteristics Of Orange Juice Based On Electric And Magnetic Field

Bacterial concentration is an important criterion for evaluating the quality of orange juice products.Based on impedance measurement technology and induced electromotive force measurement,a rapidly testing system was established for determining the colony forming units in orange juice products.The change rule of the electrical characteristics of juice derived from satsuma mandarin and navel orange during storage was investigated according to single chip microcomputer and LabVIEW technology with double electrode incentives and constant temperature incubator thermostatic control mode.The optimal measurement parameters and condition measurement of orange juice was ascertained.Furthermore,the freshness evaluation index of juice evaluation index was established.On this basis,the method of determining the total number of juice colonies was established by using the dielectric loss angle and viscosity parameters.The measurement system of dielectric loss of citrus juice was constructed by using two electrode measurement system and LabVIEW technology.The main results were as follows:1.The impedance spectrum of satsuma mandarin and navel orange juice during storage obviously presents as cole circle and cole-cole plots measured at different time and temperature in the measurement range of 100 Hz-100 KHz.The result characteristics provide a theoretical foundation to evaluate freshness of orange juice based on the characteristics of impedance.2.Based on single chip microcomputer technology and LabVIEW technology with the two electrode excitation mode and constant temperature incubator monitoring and control,the measurement system for juice biological impedance was innovatively proposed.The system consists of two hardware components,namely,constant current source signal generator,pre-signal conditioning filter amplifier circuit and signal generation module,data acquisition module,signal analysis and processing module and file saving module under LabVIEW software platform.The system has a high degree of automation and can quickly get the measured citrus juice electrical impedance amplitude and phase value with the excitation frequency in the range of 100 Hz to 100 kHz.3.Based on two different voltage-controlled constant current source(VCCS),the signal stimulus module is evaluated by measuring the resistance of the internal resistance of the constant current source module.The maximum output resistance source of VCCS excitation signal designed with chip AD844 can be obtained 1211k?,which is lagher than that of VCCS excitation signal designed with AD620 VCCS(320k?).It is proved that the output current signal performance of VCCS excitation signal source based on AD844 is stable.Meanwhile,the addition of DC feedback module circuitn this design circuit was use to further ensure the stability of signal source excitation module output current.4.Three different algorithms about the phase difference are designed and analyzed.The results showed that the impedance phase angle error obtained by the orthogonal digital modulation and demodulation algorithm is the smallest in the actual measurement process.In the process of simulation experiment,the three algorithms can realize the calculation of standard sinusoidal phase difference proving the operability of the algorithm.For the signal with white noise,the research on the phase difference measurement was realized based on three phase difference algorithm.The results showed that,the maximum error rate of the phase difference was only 0.8%and that of the actual display phase angle is less than 0.03 degrees accordingly to quadrature digital modulation and demodulation algorithm.5.Considering the interference of the temperature,humidity and frequency in the whole measuring environment to the impedance measuring device,it is confirmed through the experiment that the outside temperature and the environment humidity will not cause the measurement interference to the measuring system.The error caused by the measurement frequency phase shift can be compensated using the system itself.The results confirmed that the juice impedance measurement system itself has excellent accuracy.The maximum error of measured impedance amplitude is only 0.11%,the maximum error of phase angle is less than 0.07 degree and the maximum standard deviation is 0.39 degree in the range of excitation frequency 100Hz-100kHz.6.Based on the orthogonal digital demodulation algorithm,the determination of dielectric loss angle can be realized by the graphical programming module.Using the dielectric loss angle can be more intuitive to determine the initial concentration of colonies at different concentrations of detection time.The shortest detection time came in initial colony 105 of navel orange juice.The detection time is 292 min and detection threshold is 106.There is a high correlation between the initial number of colonies and detection time(R2=0.9781).7.Based on the rheometer,the detection of colony number in juice can be completed in 30min when the apparent viscosity was scanned in the range of 0.001-1 s-1 with the measured temperature 37?.When the number of colonies is less than 102 cfu/mL3 the linear regression equation is y=1.221n(x)+1.05(R2=0.94)and the detection limit of bacterial concentration is greater than 10 cfu/mL.However,the detection range was selsected in range of 102cfu/mL-107cfu/mL taking into account the existence of the actual error.