|Noh, Hyun Kwon|
Submitted to: ASABE Annual International Meeting
Publication Type: Proceedings
Publication Acceptance Date: 6/26/2006
Publication Date: 7/12/2006
Citation: Noh, H., Peng, Y., Lu, R. 2006. Integration of hyperspectral reflectance and laser-induced fluorescence imaging for assessing apple maturity. ASABE Annual International Meeting. Paper No. 066182. Interpretive Summary: The maturity of apple fruit is an important indicator in determining harvest time and planning apple storage regimes. Apple maturity measurements include skin and flesh color, fruit firmness, sugar or soluble solids content, starch, acid, and ethylene production. Methods for measuring these maturity parameters are largely destructive. Moreover, these methods are inefficient or time consuming and prone to operational error. Hence a nondestructive sensing technique that can measure multiple maturity parameters at the same time would be of significant value to fruit growers and packers in determining the optimal harvest time and ensuring high quality, consistent fruit for the consumer. The objective of this research was to develop a technique integrating hyperspectral reflectance and fluorescence imaging for better measurement of multiple maturity parameters of apples. Fluorescence refers to a phenomenon that plant tissue emits light of longer wavelengths after it absorbs light of short wavelengths, whereas reflectance is a different form of light interaction with the plant tissue and does not involve wavelength changes. It is hypothesized that fluorescence and reflectance are complementary and the integration of the two sensing modes can lead to improved measurement of apple maturity. A hyperspectral imaging system, which provided both spectral and spatial information, was used to acquire fluorescence and reflectance from freshly harvested apples. Mathematical methods were developed for the integrated data of the two sensing modes. Results showed that reflectance had consistently better measurements of individual maturity parameters than did fluorescence. The integrated method led to improved measurements of all maturity parameters; the improvements were up to 12% in terms of the correlation coefficient, and even greater in the standard error, when compared to the reflectance sensing mode. The hyperspectral imaging system allows for rapid acquisition of both reflectance and fluorescence and, thus, will be useful for assessing apple maturity and postharvest quality. The research represents a first effort in using the integrated sensing technique for maturity/quality assessment of apples. Further development of the technique would allow fruit growers and packers to better monitor and control fruit maturity and/or quality, thus providing better quality fruit for the consumer.
Technical Abstract: Fluorescence and reflectance are two different forms of light interaction with matter, and they can be complementary in measuring fruit quality and condition. The objective of this research was to develop an integrated hyperspectral reflectance and fluorescence imaging system for measuring apple maturity. Experiments were performed to acquire hyperspectral laser induced fluorescence and reflectance scattering images and measure multiple maturity parameters (flesh and skin color, firmness, soluble solids, starch, and acid) from 'Golden Delicious' apples harvested over a 4-week period. Fluorescence and reflectance scattering profiles were described by a two-parameter Lorentzian function. Multi-linear regression prediction models were developed relating Lorentzian parameters to individual maturity parameters for each sensing mode and their combined data. The fluorescence prediction models had consistently lower correlations with individual maturity parameters than did reflectance. The integration of reflectance and fluorescence improved maturity measurements over either reflectance or fluorescence; the improvements in correlation were noticeable for most parameters (up to 12% for titratable acid). Since fluorescence and reflectance measurements can be performed with the same imaging system in real time, the integrated technique provides an effective means for better assessment of apple fruit maturity and quality.