Non-destructive optical characterization of fruit and vegetables by non-contact time-resolved reflectance spectroscopy

Abstract

A non-contact time-resolved reflectance spectroscopy (TRS) laboratory prototype is presented, which non-invasively probes highly scattering media, retrieving their bulk absorption and reduced scattering coefficients. The performance of the prototype was assessed according to an established procedure for the characterization of diffuse optics devices. Results comparable with those obtained by state-of-the-art TRS devices were achieved for absorption coefficients up to 0.4 cm⁻¹ and reduced scattering coefficients up to 15 cm⁻¹. 150 ‘Abate Fetel’ pears were probed, sorted into three maturity classes based on their absorption coefficient at 671 nm (${\mu }_{a}671$) retrieved by a state-of-the-art TRS device. After ninety days of storage at 1 °C, the non-contact prototype monitored the fruit throughout seven days of shelf-life at 20 °C, successfully distinguishing less, medium, and more mature pears, and detecting the expected decrease of ${\mu }_{a}671$. This prototype, featuring a customized collection optical system, performs non-contact measurements at approximately 10 cm distance from the sample. Thus, it represents a step towards application of TRS technology at industry level in the horticultural sector.