Calibration of visible and near infrared spectrums for measuring freshness of vegetables

A new nondestructive methods based on optical properties at multiple, wavelengths is being applied to measure the freshness of some vegetables. The principle; of this method is to determine the absorbance and the reflectance of a sample in visible and near infrared region. When a light beam is illuminated upon a piece of vegetable sample, the majority of the lights penetrate into the sample tissue. Upon entering the tissue, photons scatter in different directions. Some are absorbed, some pass-through to the whole sample and emerge from the opposite side, and some scatter back and reemerge from the region adjacent to the incident center. While the absorption is related to certain chemical constituent of the sample, scattering is influenced by the density, compositions, cells and intercellular structures of samples and therefore can be useful for measuring samples freshness. Our objectives are to investigate the spectral behavior of some vegetables and to develop an algorithm for a non-destructive freshness sensor system using visible and near infrared light sources. The preliminary results of the study showed that the freshness of green mustard leaf and onion using a red (lambda = 633 nm) and green (lambda = 808 nm) light sources were closely related.