Non-destructive assessment of mango attibutes using electrical impedance method = การประเมินคุณลักษณะของมะม่วงแบบไม่ทำลายด้วยวิธีอิมพีแดนซ์ทางไฟฟ้า


พนิดา บัลลพ์วานิช


วิทยานิพนธ์. (2017) 116 หน้า



The purpose of this study was to investigate a suitable type and design of electrodes that can be used of non-destructive assessment of mango attributes via the electrical impedance method. Twenty-four mangoes cv. Nam Dok Mai No.4 were stored at 28±2 °C for one week (days 0-7); 3 samples were taken daily to evaluate the mango ripening stage. The impedance and phase angle of the mangoes were measured using and LCR meter within the frequency range of 20-400 kHz. Quality attributes including, color (i.e., L*, a*, b*, h*, c* and ΔE), texture (i.e.,skin firmness, flesh firmness and stiffness), soluble solids content (SSC) and titratable acidity (TA) were measured as the standard attributes of mangoes. Effects of electrode type (i.e., copper rivet, ECG and copper plate) and size (i.e., small (12.5x90 mm), medium (25x90 mm), and large (50x90 mm) were studied in order to select a suitable electrode design for the mangoes. The results showed that when using copper rivet electrodes, no correlation between the mango impedance and the ripening stage could be obtained due to the effect of air gap between the electrodes and sample surface. Using ECG and small copper plates at a frequency between 20-100 kHz resulted in a significant decrease in the impedance as the storage time increased (p<0.05); above 100 kHz a slightly decrease in the impedance was observed. At 20-100 kHz, both electrodes could classify the ripening of mangoes into 3 stages. Since ECG has a limited lifetime due to gel dehydration, which affects the value of the impedance, the copper plate electrodes were selected based on its robustness. Although all sizes of copper plate electrodes could classify mango into 3 ripening stages, using the large electrodes at 20 kHz gave the best fit between the measured impedance and the changes in the main physical as well as chemical attributes of the mangoes (i.e., h* value, stiffness and TA) during ripening as indicated by R²=0.952-0.980 and RMSE=0.117-0.803