Kajian spektroskopi impedansi listrik untuk evaluasi kualitas buah jeruk keprok garut secara nondestruktif

Abstract

Garut citrus fruit is a local agriculture commodity, which have the opportunity to developed as a superior agriculture product. The productivity and quality of this product should be increased in order to meet market demand. Commonly quality of this fruit is evaluated by visual judgement ratio subject to error. This method also only evaluated the external quality of fruit. Internal quality of this fruit such as sugar content is determined by refractometer that is belong to a destructive method, and is not suitable for online quality measurement. So an objective and nondestructive method is required to evaluate quality of Garut citrus fruit. In this research, the potential of electrical impedance spectroscopy to determine quality of Garut citrus fruit was investigated. The electrical properties of Garut citrus have been investigated on frequency variation from 50 Hz to 5MHz. The fruits are placed between two plate electrodes, and treated as dielectric material. The study was conducted in four stages. The first stage is a study of the electrical circuit modeling to represent the electrical properties of citrus. This step is performed as an initial step study of the electrical properties of citrus fruit as nondestructive method for quality evaluation. Electrical models of citrus fruit constructed from circuit of resistors and capacitors. The electric models are built on the series and parallel configurations were adopted from the literature. Orange model development has also been carried out based on the internal structure of the fruit. Simulation and measurement results on citrus fruit shows a good match for certain values of resistors and capacitors. The correlation between measured data and simulations has been done by regression techniques. The best result is shown by the high value of the coefficient deterministic. Best correlation occurs in the new model. Changes in physicochemical properties during fruit maturation made changes in the value of the resistor and capacitor internal parameters of the model. If the pH increases, the capacitance value increases while the resistance value decreases. Changes in hardness and electrical resistance of the component models show a positive relationship, although not linearly correlated. However, an increase in hardness values correlate with a reduction in electrical capacitance value of the component in the model. In the second stage, Garut Orange fruit was assessed on its electrical properties associated with the spectrum or frequency variation of electrical signal. All electrical parameters divided by the amount of compensation parameters i.e. weight, volume and diameter of the fruit. The measurement results showed that the electrical impedance, resistance, reactance, capacitance, inductance per weight, per volume, and per diameter showed a similar phenomenon. Electrical impedance, resistance, reactance, capacitance, inductance per weight, per volume, and per diameter of citrus fruits will decrease if the frequency is increased. Citrus fruits, in general, are a weak electrical conductor, especially at low frequencies. However, when the frequency increased the ability of the electrical conductivity is relatively increased. Results in the second stage are used as the reference data to validate the model in the first stage. The third stage is the study of Garut citrus fruit quality based on physico-chemical properties. The quality parameters were correlated with electrical parameters. The quality parameters of the fruit such as hardness, total soluble solids (TSS), pH, vitamin C, and the concentration of hydrogen ions were correlated with electrical properties such as impedance, resistance, reactance, capacitance, inductance per weight. Electrical parameters per weight of the fruit were used in this study to compensate for variations in weight. Value of resistance, impedance, inductance, and reactance per fruit weight decreased during ripening. While the capacitance per weight of Garut Citrus fruits increased during fruit ripening. Correlations between electrical and physicochemical properties of citrus were also investigated. Highest consistency of the correlation occurs at a frequency of 1 MHz. Electrical parameters have a significant response to acidity, hardness, and indexes TSS / hydrogen ion concentration of Garut Citrus fruits. The correlation between quality and electrical parameters were estimated by using multiple regression equations. The estimation equation is the main basis for nondestructive quality determining of citrus Garut by using electrical impedance measurements. pH value could be predicted by both linear regression and nonlinear multiple regression equation in the form of the logarithm of the electrical parameters. TSS values / concentration of hydrogen ions can be only estimated by nonlinear multiple regression equation in the form of logarithms of all parameters. The fourth stage is grading on fruit quality parameters based on the prediction results of the electrical parameters. Basic assessment at this stage is the result of the best equation obtained from the study on the third phase. In this study, electrical parameters of Garut citrus fruit related to fruit quality based on the pH value and the ratio of sweetness to the concentration of hydrogen ions were analyzed. Organoleptic testing used in this stage is test score. The result shows that citrus fruits was classified to three classes. The grading results are validated by measurement results refraktormeter and pH meter. Results showed 91.94% accuracy for parameter estimation of sweetness to acidity ratio, and 93.55% for the estimation of pH values. This study provides information about the potential of impedance spectroscopy technique for non-destructive quality testing of fruits. More comprehensive study will be very useful to increase knowledge and further applications.