Safety Inspection of Cantaloupes and Strawberries Using Multispectral Fluorescence Imaging Techniques

Abstract

Fluorescence is widely used for investigation of biological materials, and in recent years ithas also been used to monitor food quality and safety. In this study the hyperspectral imaging systemdeveloped at the Instrumentation and Sensing Laboratory (ISL), United States Department ofAgriculture (USDA) was used to evaluate the potential for detection of animal fecal contamination oncantaloupes and strawberries. Samples obtained from a local store were rinsed and allowed to air dry.Subsequently, fresh cow feces collected from the USDA dairy were diluted 1:10, 1:50, and 1:100 byweight with H2O and applied to the samples. Samples were excited using a UVA source andfluorescence responses were measured from 430 to 770 nm. Results indicate that fluorescence imagesat 680nm exhibited the greatest contrast between treated and untreated surfaces. For cantaloupes,contrast was improved using ratio images where images at 660 nm were divided by images at 560 nm.For strawberries, contrast was improved using the ratio of images at 680 nm and 745 nm. When datawere analyzed for principle components (PC), the first four PC images exhibited useful results forcontamination detection. Leaves present a problem when trying to identify fecal contamination onstrawberries, however PC-3 provided contrast between them, creating ideal conditions for leafmasking. For cantaloupes, the PC-2 image differentiated contaminated regions. PC-1 presenteddistinctive differences between the contaminated spots and cantaloupe scarred tissue, suggestingpossible use for such discrimination.