Capacitive Impedance Analysis for Noncontact Assessment of Fruit Quality and Ripening

This article presents a comprehensive examination of the development of a non-contact measuring technique for determining fruit quality. Capacitance measurements were performed on soap (reference), banana, and nectarine samples across a frequency range of 5 Hz–200 kHz for banana and soap, and 10 Hz–1 MHz for nectarine. The data analysis revealed consistent trends in series capacitance ($C_{s}$), indicating its suitability for future investigation. Additionally, temperature compensation improved data accuracy. Compensated capacitance data, obtained through linear fitting coefficients from the first 18 hours of data, showed distinct trends in banana samples, with a reduction of 6.76% on the first day and an additional 3.38% on the last day, illustrating the impact of aging. In contrast, the soap reference sample exhibited constant capacitance behavior over time. The response of the system to the presence and absence of the fruit sample and the effect of mass loss of the banana fruit on the Cs trends were also examined. The system's capacity to differentiate between undamaged and damaged samples was demonstrated after the investigation was expanded to include 51 nectarines. Following the impact damage, $C_{s}$ significantly increased, particularly one hour later, aligning with biochemical changes associated with mechanical damage. ANOVA, a type of multivariate analysis, highlighted the system's efficacy. The system demonstrated preserved damage detection even 24 hours after impact, despite temperature variations. This study provides valuable insights into non-contact measurement methods for potential industrial use, considering the effect of temperature and sample-specific analysis in the accurate evaluation of fruit quality.