Analysis of absorption and scattering spectra for assessing apple fruit internal quality after harvest and storage

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

Submitted to: Acta horticulturae
Publication Type: Proceedings
Publication Acceptance Date: 8/18/2011
Publication Date: 4/1/2012
Citation: Cen, H., Lu, R., Mendoza, F. 2012. Analysis of absorption and scattering spectra for assessing apple fruit internal quality after harvest and storage. In: Proceedings of the Fourth International Conference Postharvest Unlimited, May 22-26, 2011, Leavenworth, Washington. p. 181-188.

Interpretive Summary: Optical absorption and scattering properties are useful for studying light transport in horticultural products, as well as for potential nondestructive assessment of their internal quality. Research was carried out to measure the optical absorption and scattering properties of two cultivars of apple, i.e., ‘Golden Delicious’ (GD) and ‘Delicious’ (RD), using an optical property measuring instrument newly developed in a USDA/ARS lab at East Lansing, Michigan. A total of 1039 GD apples and 1040 RD apples were tested within one day after they were harvested or after the fruit had been kept in refrigerated air for various periods up to 12 weeks. Optical absorption and scattering properties were determined for GD apples for the wavelengths of 500-1,000 nm and for RD apples for 515-1,000 nm, using a mathematical model coupled with an inverse algorithm. These optical property data were then used to predict the firmness and soluble solids content (SSC) of the apples. While both absorption and scattering properties were related to the fruit firmness and SSC, the former had better correlation than the latter in predicting both firmness and SSC. Better firmness and SSC predictions were obtained when the two optical property parameters were combined, with the best correlations of 0.892 and 0.863 for firmness and of 0.778 and 0.825 for the SSC of GD and RD apples, respectively. This research showed that the optical absorption and scattering properties are related to the physiological changes in apples and thus their internal quality attributes. The technique provides a new means for assessing internal quality of horticultural products like apple.

Technical Abstract: Optical absorption and scattering properties are useful for quantifying light interaction with plant tissue, as well as for quality assessment of horticultural products. The aim of this research was to measure the absorption and reduced scattering coefficient spectra of two cultivars of apple (Malus×domestica), i.e., ‘Golden Delicious’ (GD) and ‘Delicious’ (RD), for the wavelengths of 500-1,000 nm for their internal quality assessment. A newly developed hyperspectral imaging-based spatially-resolved instrument was used to acquire reflectance images for 1039 GD apples and 1040 RD apples immediately after harvest or after they had been kept in refrigerated air for various periods for up to 12 weeks. Absorption and reduced scattering coefficient spectra of the apples were then determined from the spatially-resolved reflectance profiles using a diffusion model coupled with an inverse algorithm. The spectra of absorption and reduced scattering coefficients, and their combinations were used for predicting the firmness and soluble solids content (SSC) by partial least squares method. The combinations of absorption and scattering spectra improved prediction results, compared with individual spectra. The best correlations (r) for firmness prediction for GD and RD apples were 0.892 and 0.863 with the standard errors of prediction (SEP) of 7.89 N and 8.94 N, and were 0.778 and 0.825 for SSC with the SEP of 0.82 Brix and 0.85 Brix, respectively, when all samples were pooled. This research showed that optical absorption and scattering properties are useful for assessing internal quality of apples.