Study On The Electrical Properties Of Cucumber During Pickling

The traditional measurements of quality indices of pickled vegetable products are usually time-consuming, complicated and destructive. In this research, the electrical property of pickled cucumber was investigated in the frequency range of 100 Hz ~ 10 MHz and 10 k Hz ~ 120 MHz respectively based on a parallel-plate capacitor system. Then the regression equations and prediction models for quality indices of pickled cucumber were established by the correlation analysis between the electrical parameters and quality indices. Results facilitate a successful and alternative application for rapid and nondestructive assessment of quality indices in pickled vegetable products.The main quality indices of cucumber during pickling were measured. It indicated that, during the 5 days period, the salt content of cucumber increased with pickling time while the water content decreased, resulting a decrease in firmness and toughness of cucumber. The nitrite content of cucumber exhibited a rapid increase during the initial pickling periods, then decreased on the later period with a maximum of 42.05 mg/kg. And nitrite content in cucumber decreased to safe content range for consuming on the fourth day with a content of 24.63 mg/kg.By analyzing the tissue characteristics of cucumber, the equivalent circuit and circuit discription code R(CR)(CR) of cucumber during pickling were investigating. The electrical property of pickled cucumber was studied, and the results demonstrated that the impedance(Z), equivalent parallel resistance(Rp) and equivalent parallel capacitance(Cp) of cucumber declined as the frequency increased since capacitive characteristics of the membrane changed with respect to the pickling time. The changes trend of conductance(G) and admittance(Y) were different with those of Z value. The dielectric constant(ε’) and loss factor(ε’’) obtained a monotonous recline as the frequency, and had a continuous increase with the pickling time. No regular trend between quality factor(Q) and pickling time was observed, and Q value was larger in low frequency region(at 100 Hz) than in high frequency region(at 1 MHz).Through the correlation analysis between the electrical parameters and quality indices, Z and R value of pickled cucumber at optimal frequencies were found to be positively correlated with moisture content and p H(P<0.01), and be negatively correlated with salt content, total acidity, firmness and toughness(P<0.01). On the contrary, ε’ and ε’’of pickled cucumber turned to be negatively correlated with moisture content and p H(P<0.05), and be positively correlated with salt content, total acidity(P<0.05). Furthermore, obvious linear correlations between Z, R and moisture and salt content of pickled garlic were observed due to the ionic conduction. The most favorable estimations for moisture and salt content are characterized by y = 0.0352x+88.736(R at 10.63 k Hz) and y =- 0.0104 x +6.5898(Z at 100 Hz). The R value of pickled cucumber at 10.63 k Hz have been found which predominantly contribute to the prediction of moisture content, and Z value at 100 Hz could be applied to the prediction of salt content, firmness and toughness, while G values at frequencies of 100 Hz and 9.42 MHz were properly employed to model total acidity content and p H value respectively, as the highest regression coefficients in corresponding model equations. No obvious correlations between electrical parameters and nitrite content, free amino acid content were observed which indicating that electrical parameters could not be application on detection of microelement in the pickled garlic. Selected optimal prediction models for moisture content, salt content, firmness, toughness and p H were verified to be suitable for the detection of corresponding quality indices of pickled cucumber owing to higher precision.Electrical simulation was performed by COMSOL Multiphysics, and the simulative values of Z, R, Y and G of pickled cucumber were validated to be close to the measured values.