Near-infrared imaging equipment that detects small organic substances in thick foods

Abstract

ABSTRACT We have developed near-infrared imaging equipment that can detect small organic substances in foodstuffs with thicknesses of more than 1 mm. The equipment is composed of a high output laser diode and a CMOS camera. The irradiated light power distribution was highly uniform with a maximum optical density of 1.3 W/cm 2 . A 0.3-mm-diameter wooden stick covered with a 2-mm-thick layer of ha m can easily be distinguished in the images. The bones in fish and in chicken wing sticks could also be distinguished. The thicknesses of the fish and the chicken wing sticks were approximately 30 mm and 20 mm, respectively. We eliminated the low spatial frequency components from the images to improve the image contrast. Keywords: near-IR imaging, optical equipment, food contaminan t detection, foreign substance, spatial frequency filter 1. INTRODUCTION In our daily lives, foreign substances in foods can cause se rious problems because they can badly affect human health 1 . Various systems, including X-ray computed tomography and metal detectors, have been used to detect these contaminant substances. In mass production lines in food processing factories, X-ray computed tomography is generally used to detect foreign substances in foods, including metal articles and high-density materials such as stones. However, organic materials, such as hairs and wooden sticks, are difficult to detect when using X-ray computed tomography or metal detectors. A contaminant detection technique that uses near-i nfrared (NIR) light has been a ttracting attentio n because the technique enables transmission images to be monitored at high speed. For example, detection systems based on NIR hyperspectral imaging spectroscopy can detect impurities in cereals