A Freshness Indicator for Leafy Greens

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Freshness is a very desirable but somewhat elusive characteristic for leafy greens. Leafy greens contain a significant amount of protein, and accumulation of ammonia as a byproduct of protein metabolism can occur when products lose freshness and begin to deteriorate. In this project we demonstrated the relationship between ammonia accumulation and the deterioration of spinach and arugula (loss of visual quality, yellowing, decay, off-odors) in relation to storage temperatures and degree of leaf damage. Ammonia was measured in a destructive spectrophotometric assay. This method is not practical for commercial operations, so the main objective of this project was to compare the performance of a nondestructive volatile ammonia sensor to the laboratory method. Volatile ammonia sensors using nanotechnology ammonia sensitive films were constructed and tested for response to quality changes in leafy products. In one experiment, ammonia was measured by both methods on the same arugula and spinach samples. The methods compared favorably, especially for spinach. Although the sensors need further work to make them practical for commercial application, they appear to have potential for assessment of postharvest quality changes and freshness in leafy greens. 


Marita Cantwell
Gyunghoon Hong
Judy Song
California Leafy Greens Research Program