Chlorophyll fluorescence imaging for early visual detection and measurement of postharvest discoloration: Potato greening and broccoli yellowing.

Chlorophyll serves as both physiological basis and fundamental pigment underlying healthy coloration of numerous fruits and vegetables. Yet conventional visual inspection, point-level color measurement, and destructive chlorophyll assays lack sensitivity for early, non-destructive detection of discoloration driven by abnormal chlorophyll metabolism in postharvest produce. This study developed a simple chlorophyll fluorescence imaging system to enable early detection and measurement of two representative postharvest discoloration phenomena: light-induced greening in potatoes and senescence-driven yellowing in broccoli. By focusing on dark-adapted fluorescence parameters of Fo, Fm, and Fv/Fm, this imaging system utilizes semantic pseudo-color mapping to visualize discoloration severity and spatial distribution. Results demonstrated that potato greening was accompanied by increasing trends in Fo, Fm, and Fv/Fm (from 0.15 to 0.60), while broccoli yellowing showed declines in Fo, Fm, and Fv/Fm (from 0.7 to 0.6). The chlorophyll fluorescence imaging detected potato greening initiation 1-2 days before visible color changes (ΔE = 1.34-3.30) and yellow-green hues appear (h° = 86.5-88.4), while accurately tracked spatial progression of chlorophyll degradation during broccoli yellowing. Crucially, the full-field imaging capability sensitively detects heterogeneous discoloration patterns-such as spots or patches-thereby overcoming the risk of missed detections caused by biased local sampling. This work demonstrates the value of chlorophyll fluorescence imaging as a physiologically informative approach for probing chlorophyll metabolism underlying postharvest discoloration. The approach offers a useful analytical tool for non-destructive freshness and discoloration monitoring in produce with active chlorophyll metabolism.