Submitted to: Near Infrared Spectroscopy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2005
Publication Date: 5/1/2005
Citation: Lu, R., Peng, Y. 2005. Assessing peach firmness by multispectral scattering. Near Infrared Spectroscopy Journal. 13(1):27-36. Interpretive Summary: Currently, fruit are sorted for color and size, but not for firmness. Fruit firmness is an important quality parameter in grading peaches and a wide range of fruits, and it is routinely measured with the destructive Magness-Taylor (MT) penetration method. The MT testing renders the measured fruit no longer suitable for marketing. A sensing technique that can measure internal quality of fruit nondestructively and rapidly is important for assuring the eating quality of individual fruit delivered to the market. This research investigated a multispectral imaging system for nondestructive measurement of peach fruit firmness. The system allowed us to acquire spectral images from peaches at four selected wavelengths simultaneously in the visible and near-infrared (with wavelengths longer than the visible) region. A mathematical function was proposed for describing the scattering profiles in peaches accurately. Firmness prediction models were developed on relating light scattering to fruit firmness, as measured by the destructive MT method. The multispectral imaging technique gave good predictions of peach firmness. Firmness predictions were affected by orchard, but its effect was small. The multispectral scattering technique is nondestructive, fast, and easy to implement. The technique is useful for assessing the firmness of peaches and other fruits and can help the fruit industry in delivering better and more consistent fruit to the consumer.
Technical Abstract: The objective of this research was to investigate a multispectral scattering technique for measuring peach fruit firmness. A multispectral imaging system, which is capable of acquiring four spectral images simultaneously, was used to measure spectral scattering from ‘Red Haven’ peaches, harvested at different ripening stages from two orchards, at wavelengths of 680, 880, 905, and 940 nm. Soft peaches had broader scattering profiles than firmer ones, which was most pronounced at 680 nm, the wavelength that is related to chlorophyll absorption. An empirical model, the Lorentzian distribution function with three parameters, was proposed to fit the restructured (shifted) scattering profiles for all four wavelengths, with the mean coefficient of determination (r**2) equal to or greater than 0.998. Multi-linear regression models were developed on relating Lorentzian parameters to fruit firmness. The best firmness predictions (r**2=0.757 and the standard error for validation or SEV=14.57 N or Newtons) were obtained when separate models were developed for each orchard. When data from two orchards were pooled, the model was able to predict fruit firmness with r**2=0.672 and SEV=18.55 N. The multispectral scattering technique is nondestructive, fast and relatively easy to implement, and it provides a nondestructive means for measuring peach fruit firmness.