Nondestructive Food Quality Monitoring Using Phase Information in Time-Resolved Reflectance Spectroscopy

A rapid and affordable method is desired by the food industry to monitor the quality of the food. A nondestructive and noninvasive testing is desired to determine the optimum harvesting time, monitor changes during storage, and asses the internal quality of the fruits. Time-resolved reflectance spectroscopy (TRS) is used for noninvasive simultaneous measurement of the scattering and the absorption properties of turbid media. In this article, a time-resolved phase reflectance-based nondestructive and noninvasive method is proposed to monitor the internal quality of the fruits. The time-resolved reflectance is determined by the number of internal scatterers based on the mean-free path length of the incident light. The change in the mean-free path due to change in the pigmentation of the internal pulp changes the order of the scatters and, therefore, affects the scattering profile of the reflected light. The scattering profile is monitored using the Stokes degree of linear polarization. As an example, the Red Star and Granny Smith apples are considered, and the degradation in the apples due to storage is correlated with the changes in the degree of polarization (DoP). The change in the DoP after seven days is 0.26% and 11.4% for a time resolution of 300 ps, while for 500 ps, it is 2% and 2.3% for Red Star and Granny Smith, respectively. The differential variations in the DoP help in monitoring the internal pulp quality of the two variants of the apples considered. This proposed method can also be used in all agro-based products for internal quality monitoring.