Assessing multiple quality attributes of peaches using spectral absorption and scattering properties

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

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/17/2012
Publication Date: 5/21/2012
Citation: Cen, H., Lu, R., Mendoza, F., Ariana, D.P. 2012. Assessing multiple quality attributes of peaches using spectral absorption and scattering properties. Transactions of the ASABE. 55(2):647-657.

Interpretive Summary: Fruit maturity determines when to harvest and how the harvested fruit should be stored, handled and marketed. Peach maturity is commonly assessed using multiple destructive techniques, including Magness-Taylor penetrometric measurement for flesh firmness, refractometric measurement for soluble solids content, and colorimetric measurement for fruit skin and flesh. This research was aimed at nondestructively assessing multiple maturity/quality parameters of peaches using a newly in-house developed optical property measuring instrument. The instrument provides fast, nondestructive measurement of the absorption and scattering coefficient spectra, two fundamental spectral properties that characterize light transport in biological materials like fruit. Five hundred ‘Redstar’ peaches were harvested in 2010 and their optical absorption and scattering properties for the wavelengths of 515-1,000 nm were measured. The firmness of the peaches was measured nondestructively using a commercial acoustic and impact sensor. Standard destructive tests were then performed for measuring the fruit firmness, soluble solids content, and fruit skin and flesh color of the peaches. Mathematical models were developed to predict the maturity parameters of peaches using the optical property data. The absorption and scattering properties of peaches were influenced by the ripening and development of pigments in the fruit. The measured optical properties were correlated with the firmness, soluble solids content, and skin and flesh color of the peaches with values of the correlation coefficient being equal to 0.749, 0.504, 0.898 and 0.741, respectively. The optical firmness prediction results, although not quite satisfactory, compared favorably to acoustic and impact firmness measurements, whose correlation with destructive measurements was 0.639 and 0.631, respectively. This research demonstrated that the optical property measuring technique can be potentially useful for assessing multiple maturity/quality parameters of peaches.

Technical Abstract: The objective of this research was to measure the spectral absorption and reduced scattering coefficients of peaches, using a hyperspectral imaging-based spatially-resolved method, for maturity/quality assessment. A newly developed optical property measuring instrument was used for acquiring hyperspectral reflectance images of 500 ‘Redstar’ peaches. Spectra of absorption and reduced scattering coefficients for 515-1,000 nm were extracted from the spatially-resolved reflectance profiles using a diffusion model coupled with an inverse algorithm. The absorption spectra of peach fruit were marked with absorption peaks around 525 nm for anthocyanin, 620 nm for chlorophyll-b, 675 nm for chlorophyll-a, and 970 nm for water, while the reduced scattering coefficient decreased monotonically with the increasing wavelength for most of the tested samples. Both absorption and reduced scattering coefficients were correlated with peach firmness, soluble solids content (SSC), and skin and flesh color parameters. Better correlation results for partial least squares models were obtained using the product of absorption and scattering coefficients or the effective attenuation coefficient which is a function of absorption and scattering coefficients. The results were further improved using least squares support vector machine models with values of the best correlation coefficient for firmness, SSC, skin lightness and flesh lightness being 0.749 (standard error of prediction or SEP = 17.39 N), 0.504 (SEP = 0.92 °Brix), 0.898 (SEP = 3.45), and 0.741 (SEP = 3.27), respectively. These results compared favorably to acoustic and impact firmness measurements whose correlations with destructive measurements were 0.639 and 0.631, respectively. Hyperspectral imaging-based spatially-resolved technique is useful for measuring the optical properties of peach fruit, and it also has potential for assessing fruit maturity/quality attributes.