Characterization of the Optical Properties of Normal and Defective Pickling Cucumbers and Whole Pickles

Authors: Lu, Renfu; ARIANA, DIWAN - Michigan State University; CEN, HAIYAN - Michigan State University

Submitted to: Proceedings of SPIE
Publication Type: Proceedings
Publication Acceptance Date: 4/23/2010
Publication Date: 5/13/2010
Citation: Lu, R., Ariana, D.P., Cen, H. 2010. Characterization of the Optical Properties of Normal and Defective Pickling Cucumbers and Whole Pickles. Proceedings of SPIE. April 5-9, 2010, Orlando, Florida. 76760:76760G. p. 1-8.

Interpretive Summary: Internal defect in pickling cucumbers can cause bloater damage during brining, which lowers the quality of final pickled products and results in economic loss for the pickle industry. Currently, automated inspection technology is not available for detecting internal defects in pickling cucumbers, and pickle processors still rely on human inspectors to remove defective cucumbers or pickles. This research was aimed at determining the optical properties of normal and defective cucumbers, and of whole pickles, in order to provide useful information for the design of an effective optical inspection system. Fifty fresh pickling cucumbers of commercial size 3 (37-55 mm in diameter) were harvested in the summer of 2008 and their optical absorption and scattering properties for the spectral region of 700-1,000 nm, a region that is most useful for internal defect detection, were measured using an optical property measuring system developed in our laboratory. Thereafter the cucumbers were subjected to rolling under mechanical load to induce internal tissue damage. The damaged cucumbers were measured again within one hour and one day after the treatment to determine the effect of mechanical damage and post-damage time on the optical properties. Likewise, the optical properties of 20 whole pickles each of normal and bloated class were also measured. It was found that mechanical damage had different effects on the optical absorption properties than on the scattering properties for the pickling cucumbers. Within one hour after mechanical damage, small to no changes in the absorption and scattering properties were observed in the cucumbers. One day later, the damaged cucumbers showed increased absorption abilities for 700-920 nm, while their scattering abilities for 700-1,000 nm decreased more significantly. Whole pickles had markedly different optical properties than pickling cucumbers; their light scattering abilities were greatly diminished after brining. The research findings suggest that to more effectively detect internal defect in cucumbers, it is desirable to enhance optical scattering features.

Technical Abstract: Internal defect in pickling cucumbers can cause bloater damage during brining, which lowers the quality of final pickled products and results in economic loss for the pickle industry. Hence it is important to have an effective optical inspection system for detection and segregation of defective pickling cucumbers. This research was intended to measure the spectral absorption and scattering properties of normal and internally defective pickling cucumbers and whole pickles, using hyperspectral imaging-based spatially-resolved technique. Spatially-resolved hyperspectral scattering images were acquired from 50 freshly harvested ‘Journey’ pickling cucumbers in the summer of 2008. The cucumbers were then subjected to rolling under mechanical load to induce internal damage. The damaged cucumbers were imaged again one hour and one day after the mechanical stress treatment. In addition, 20 whole pickles each of normal and defective (bloated) class were also measured by following the same procedure as that for pickling cucumbers. Spectra of the absorption and reduced scattering coefficients for pickling cucumbers and whole pickles were extracted from the spatially-resolved scattering profiles, using an inverse algorithm for a diffusion theory model, for the spectral range of 700-1,000 nm. It was found that within one hour after mechanical damage, changes in the absorption and reduced scattering coefficients for the cucumbers were minimal. One day after mechanical damage, the absorption coefficient for the cucumbers increased noticeably for the wavelengths of 700-920 nm, whereas the reduced scattering coefficient decreased more significantly for the wavelengths of 700-1,000 nm. Overall mechanical damage had greater impact on the scattering properties than on the absorption properties. After brining, pickles became translucent and scattering was greatly diminished. Thus the diffusion theory model was no longer valid for determining the optical properties of whole pickles. This research suggests that effective defect detection may be achieved by enhancing scattering features in the optical evaluation of cucumbers.