Vol. 56, Issue 1, pp. 103-119 (2026)

Abstract

In this work, a reflectance polarimetry imaging system based on liquid crystal polarization rotator is proposed for the assessment of ripening process of mangoes. A low-cost voltage-controlled liquid crystal polarization rotator and a wire-grid polarizer were integrated into input ray path of a digital camera, enabling selective acquisition of horizontally or vertically polarized (0° and 90°) input images. Unripe Chokanan mango samples were subjected to the illumination of linearly polarized LED light at different wavelength. Digital images at two polarization states were recorded daily until the mangoes were fully ripened on the eighth day. Average reflectance intensity and Degree of Linear Polarization (DoLP) and the findings indicate the dynamic correlation between the varying reflectance intensity, illumination wavelength and the associated dominant pigments (e.g. carotenoids, anthocyanins and chlorophylls) in the fruit epidermis during the ripening process. In addition, the DoLP at different wavelengths have shown different variation characteristics with ripening. Notably, DoLPs at 593 and 660 nm decrease with ripening, due to decreasing moisture content in the fruit epidermis that promises light scattering and depolarization in the epidermis tissues. The study demonstrates the potential of reflectance polarimetry as a non-invasive method for assessing the ripeness and storage condition of fruits.