LCTF-based multispectral fluorescence imaging: System development and potential for real-time foreign object detection in fresh-cut vegetable processing

Abstract

Ensuring the supply of safe and contaminant-free fresh-cut vegetables is of importance to consumers and suppliers worldwide. The present research aimed to develop an online inspection system, making use of fluorescence and color imaging for detection of potential foreign materials (FMs) unintentionally added to fresh-cut vegetables. A multispectral fluorescence imager incorporating a liquid crystal tunable filter (LCTF) was developed to sequentially acquire selected band images of fresh-cut vegetables. Custom-built software was developed to synchronize the LCTF with the camera exposure to collect the fluorescence images of selected spectral bands and to collect the digital color images of the same samples using a color camera. Image processing algorithms were developed for both fluorescence and color images to detect a wide range of potential FMs in two different fresh-cut vegetables, namely, cabbage and green onion. The obtained results showed that the combined use of the multispectral fluorescence technique and color imaging can detect most FMs with accuracy > 95%; however, non-fluorescent tiny dark FMs could not be detected. The potential of the developed online detection system was further tested in an industrial environment by installation in a fresh-cut processing unit. All hardware parts were enclosed in a black box and the software program was modified to programmatically control conveyor belt movement and facilitate real-time image processing for FM visualization. FMs mixed with fresh-cut vegetables were manually fed onto the conveyor belt; fluorescence and color images of fresh-cut vegetables were acquired simultaneously while moving through the conveyor belt. The developed online system performed almost identically in the industrial environment, and has the potential to scan an area as large as 24 × 24 cm2 in approximately 1.5 s. Thus, its application in commercial setting may be feasible.