How green is green? Long-term relationships between green seeds and chlorophyll in canola grading

Chlorophyll is undesirable in canola seeds because it is extracted into the oil resulting in problems during processing and utilization. In the Canadian grain grading system, and in similar systems in use in the United States and Australia, chlorophyll is estimated in canola seeds subjectively by crushing and counting the number of distinctly green seeds in a sample while simultaneously assessing the overall natural color of the crushed seeds. Chlorophyll contents of canola may be determined by extraction with solvent followed by spectrophotometric analysis or by using NIR instrumentation, capable of operating in the visible region and calibrated against samples with known amounts of chlorophyll. The relationship between the green seeds and chlorophyll content in canola export shipments from 1988 to 2001 was found to be linear, The intercept, referred to as the background chlorophyll, ranged from 6 to 16 mg/kg, and the slope ranged from 300 to 1000 mg/kg per green seed. In recent years, both the background chlorophyll and the slope have been increasing, resulting in an increase in the chlorophyll levels in top-grade canola exported from Canada. The increase may be partly a result of the change in proportion of species of canola grown in Canada, and also may result from changes in perception of what constitutes a green seed. The use of an objective measurement of chlorophyll is recommended to improve the consistency of the grading system.