Abstract
Post-harvest change in the colour of green field pea (Pisum sativum L.) is undesirable as this impacts the visual quality and market value of the seed. To date, there is no standard, objective method to determine bleaching. Therefore, the aim of this study was to develop an objective method for scoring bleaching based on colour reflectance spectra, measured both by spectrophotometer and multispectral Image Analysis (IA). Green field pea seeds were sorted into samples of uniform colour and these were used to train the model. Spectra calculated from multispectral images (with colour bands at 405,470,530,590,660 and 850nm) were matched to the spectrophotometer output through multiple linear regression. All spectra were transformed to emphasize the wavelength regions most impacted during bleaching, following which two critical reflectance values were scaled to a single bleaching score. The bleaching assessment method was tested in a time-course experiment comprising seeds from five green-pea genotypes stored for six months. Each sample was divided into two so that half of the seeds were stored in the dark and the remainder were exposed to controlled light to exaggerate bleaching. Throughout this period, the samples were imaged at six-weekly intervals. Assessment of bleaching by the IA method agreed well with spectrophotometer measurements, achieving a Lin’s concordance statistic of 0.99 and 0.96 for the calibration and time-course samples respectively. The IA method proved more versatile because assessments could be made on individual seeds enabling the computation of bleaching uniformity within each sample. This method captured differences between genotypes in the extent, rate and uniformity of bleaching. All genotypes exhibited susceptibility to bleaching when stored under the controlled light conditions. Excell was observed to be the most susceptible genotype with the greatest bleaching-rate and OZB1308 displayed the most colour-stability.
Highlights
Green pea is one of the major market classes of the Pisum sativum L. pulse grain family [1] and commonly used as a high-protein food source for human consumption as well as livestock feed
The aims of this study were to: (1) Develop an objective model based on visible reflectance spectral analysis to determine bleaching scores for green field pea samples; (2) Develop an image analysis method, based on multispectral images, to replicate the spectral analysis bleaching scores and enable assessment of bleaching at a single seed level; and (3) Apply the image analysis method to quantify bleaching score, rate and uniformity of five green pea genotypes subjected to exaggerated bleaching conditions over a period of six months
Digital-image spectral-reflectance values calculated through Multiple Linear Regression (MLR) models highly correlated with the spectrophotometer output for both the colour-sorted sample set and the time-course sample set (Table 2)
Summary
Green pea is one of the major market classes of the Pisum sativum L. pulse grain family [1] and commonly used as a high-protein food source for human consumption as well as livestock feed. Quantifying bleaching in green field pea Canadian Grain Standards Guide [3], field pea is classified as either ‘green pea’ or ‘other than green pea’ and subsequently assessed for other quality traits. This classification emphasises the relative importance of the green pea type in comparison with the other field pea market classes. Australian guidelines indicate a maximum of 1% off-colour seed for a field pea sample to achieve No 1 grade [11] and in Canada the maximum allowance is 2% bleached seed [3]. It is generally thought that bleaching has no effect on the seed viability [12], Atak, Kaya [13] conducted a study of three green pea genotypes and found that the darker seed had a higher vigour and germination rate than lighter seed
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