Research On Electricial Mechanism Of Postharvest Lingwu Long Jujubes’ Physiological Changes

The prediction and theoretical exploration on quality and freshness of Ling-Wu long jujube were carried out based on dielectric properties. The main results were as follows:(1)Correlation studies on the relative dielectric constant and quality parameters:Quality parameters such as soluble solids, moisture, pulp firmness and brittleness were monitored dynamically, and the relative dielectric constant ε’ was calculated by testing. The good correlation was showed under five appropriate test frequencies (3.16 kHz,3.98kHz,5.01 kHz,6.31 kHz and 7.94 kHz). For the highest correlation was found under 3.16 kHz, therefore it was determined as the characteristic frequency for Long jujube quality prediction. Under the characteristic frequency, the determination coefficient R2 of regression equation established between ε’ and jujube pulp firmness, brittleness, TSS and water were 0.9721,0.9626,0.8891 and 0.906. The PLS prediction model was established for jujube pulp firmness, brittleness, TSS and water based on relative dielectric constant ε’. Correlation coefficient R between the predicted values and real values were 0.95,0.93,0.92 and 0.92 orderly.(2) Correlation studies on loss factor and freshness of long jujube: Gradually, the total sugar content was escalating, total acid content declining as the storage time extending, and the freshness gradually reduced. Sugar-acid ratio was determined for its freshness index TI which was divided into 3 classes according to local standards. A good linear relationship was found between the loss factor ε" and TI under characteristic frequency, and R2=0.96. Long jujube freshness prediction model was established by BP-ANN neural network, ε" as input, and TI as output. The class identification accuracy reached 94%.(3) The establishment and analysis of long jujube electromagnetic theory equation: On the basis of preliminary experiments, the electromagnetic model curve was drawn on the complex plane and fitted, ε’ as horizontal axis, ε" as vertical axis. The model shape parameters were worked out by Hannai theory (a was 0.13, β was 0.65), and Long jujube electromagnetic equation established:ε*=εh+△ε/[1+(j ω)0.87]0.65. Long jujube internal electrical parameters were obtained by parsing electromagnetic equation (free water conductivity κa was 0.58, cell volume fraction Φ0.32, cell dielectric constant εi 184.2, the cell electrical conductivity κi 0.36), and therefore the experimental basis was provided for the development, popularization and application of rapid Long jujube nondestructive testing technology.