Detection of decay in fresh-cut lettuce using hyperspectral imaging and chlorophyll fluorescence imaging

Abstract

Fresh-cut lettuce sold in modified atmosphere packaging (MAP) is a desirable, but highly perishable product. Decay of tissue can start a few days after processing and may be difficult to detect by quick visual observation. A system for early detection of decay and gradual evaluation of its progress is important both for lettuce processing industry and for breeding companies and institutions assessing quality of new cultivars and breeding lines. We have developed two lettuce decay indices (LEDI) that can be used to detect decay of leaf tissue. One of the indices (LEDI4) is based on three wavelengths identified from hyperspectral imaging, while the second index (LEDICF) is based on chlorophyll fluorescence imaging. In addition to detecting lettuce decay, the indices identified tissue damaged by freezing temperatures. LEDI4 and LEDICF showed almost 97% accuracy in classifying tissue as being fresh or decayed when tested on red, dark green, green, light green, and yellow leaves. Specificity of the indices decreased when tested on fresh tissue with a very limited amount of chlorophyll that visually appeared to be almost white. Both indices detected lettuce decay without opening plastic MAP bags. The non-destructive nature of the methods thus allows rapid and repeated evaluation of samples over time and presents the opportunity for development of a commercial, high throughput scanner for evaluation of bagged, fresh-cut lettuce quality.