A comparison of hyperspectral reflectance and fluorescence imaging techniques for detection of contaminants on spinach leaves

Abstract

Ensuring the supply of safe, contaminant free fresh fruit and vegetables is of importance to consumers, suppliers and governments worldwide. In this study, three hyperspectral imaging (HSI) configurations coupled with two multivariate image analysis techniques are compared for detection of fecal contamination on spinach leaves (Spinacia oleracea). Fluorescence imaging in the visible region with ultra violet (UV) and violet excitation sources, and reflectance imaging in the visible to near-infrared regions were investigated. Partial least squares discriminant analysis and two band ratio analysis techniques were used to compare these HSI configurations. High detection accuracy was found for the two fluorescence HSI configurations compared to the visible/near infrared HSI. Both fluorescence HSI configurations had 100% detection rates for fecal contamination up to 1:10 dilution level and violet HSI had 99% and 87% detection rates for 1:20 and 1:30 levels, respectively. Results indicated that fluorescence imaging with the violet excitation performed superior to HSI with UV excitation for detection of a range of diluted fecal contamination on leafy greens. 5% or less false positives were observed for the fluorescence HSI configurations and were associated with yellow hue on the leaves. On-line detection of fecal contamination on leaves has the potential to reduce the cases of food borne illnesses and their associated costs.