2009 Annual Report
1a.Objectives (from AD-416)
1) Evaluate NIR spectra in diffuse reflectance, transmittance, and scattering modes for determination of potato density/specific gravity.
2) Evaluate NIR spectra in diffuse reflectance, transmittance, and scattering modes for determination of specific sugars levels in potatoes.
3) Determine optimal sensing configuration (mode and wavelengths) for moving toward development of a prototype device for potential real-time field-based measurement.
1b.Approach (from AD-416)
Potatoes covering a range of density and sugar levels will be obtained from the potato industry. Samples will be collected and evaluated at multiple intervals over the length of the storage season. Each cleaned and intact potato tuber will be measured with the laboratory instrumentation set-up under the following three modes: diffuse reflectance over the visible and NIR region from 500-1700 nm; transmittance over the range of 500-1300 nm; and scattering over the range of 500-1300 nm. The transmittance and scattering ranges do not extend as far into the NIR range due to absorption. Following whole (intact) tuber measurement, a tissue sample will be cut from the same tuber and the same spectroscopic measurements will be obtained on this controlled and uniform sized sample. Additionally, each potato will be measured for density and specific sugars using conventional hydrometer and wet chemistry techniques to provide a baseline to which the spectroscopic measurements will be compared and correlated. A local company, Techmark Inc., specializes in potato handling and analysis and is supportive and willing to assist with conventional analysis (as a no cost collaborator). While the goal is to successfully measure whole/intact tubers, additionally evaluating samples of tissue will provide the opportunity to compare the results of this study against published results and also tissue versus whole tuber measurement. Several potato varieties will be included in the study to determine robustness or specificity of findings.
Data analysis will involve determining portions of the spectra and the mode, or combinations of spectra and modes, capable of best predicting density and sugars levels.
The progression of the research would include the first year of broad spectral measurement of whole tubers and tissue samples and critical analysis of data. A second year would be important (similar budget) to validate first year findings and, in parallel, focus on a particular sensing configuration based on what we learned from year 1. This sensing configuration would be a step toward a prototype device incorporating dedicated electronics for real-time in-field measurements.
The VIS/NIR spectra of whole and 12.7-mm thick perimedullary-potato-slice samples for the spectral ranges of 500-1100 nm and 500-1000 nm were acquired by a visible/near-infrared spectrometer in interactance mode and an in-house hyperspectral imaging system, respectively. The NIR spectra (900-1350 nm) of 12.7-mm thick perimedullary-potato-slices were acquired by the transmittance method. The evaluated constituents include leaf primordial, soluble solids, specific gravity, glucose and sucrose of potatoes. A total of 400 potatoes of two cultivars, Fritolay-1859 (FL) and Russet (RB) of varying status induced by storage temperature and duration, were used as experimental samples.
Different spectra pretreatment methods were evaluated and used to remove the variations in the spectra caused by unknown sources that tend to increase errors in calibration models. Partial least squares regression (PLSR) analysis was used to develop calibration models for each of the constituents per cultivar. After the calibration equations were established, samples in the validation group were used to assess the prediction accuracy of the calibration equations, as measured by the standard error of prediction (SEP), correlation coefficient (R), bias and the ratio of standard deviation of reference data in the prediction sample set to SEP (RPD).
Excellent predictions of leaf primordial was achieved using the interactance method on the sliced samples, with the R values of 0.97 and 0.95, the RPD of 4.03 and 3.90, and the SEP of 2.76 and 1.71 for cultivars FL and RB, respectively. These results show the potential of VIS/NIR technique as a means for nondestructive measurement of leaf primordial of potato with reasonable accuracy. Relatively good predictions of glucose was achieved using the interactance method on the sliced samples, with the R values of 0.85 and 0.92, RPD of 1.70 and 2.64, and SEP of 0.02 and 0.18 for FL and RB, respectively. Hence the VIS/NIR technique is potentially useful for nondestructive measurement of potato glucose concentration; however more studies are recommended to increase the method accuracy. Relatively poor predictions of sucrose were achieved using the interactance method on sliced samples, with the R values of 0.67 and 0.60, the RPD of 1.57 and 1.19, and the SEP of 0.01 and 0.13 for FL and RB, respectively. This demonstrated the limited potential of VIS/NIR technique for nondestructive measurement of potato sucrose concentration; however, further studies are recommended to possibly increase the method’s accuracy and/or validate this finding. Very poor prediction results were obtained in determining specific gravity and soluble solids, with the R values being lower than 0.5. This indicates that the evaluated techniques could not effectively measure potato soluble solids and specific gravity. Project progress was monitored via meetings, emails, and joint sessions on planning, execution, and analysis of research with the collaborating researchers.