Multicolor fluorescence images and fluorescence ratio images of green apples at harvest and during storage

Abstract

With a multicolor fluorescence imaging system the fluorescence images of freshly harvested light-green apples were measured in the four major fluorescence bands of green plant tissue, i.e., the fluorescence bands F440 (blue), F520 (green), F690 (red), and F740 (far-red). By a pixel-to-pixel division of the fluorescence images we also determined the fluorescence ratio images blue/green (F440/F520), blue/red (F440/F690), and blue/far-red (F440/F740), as well as the chlorophyll fluorescence ratio red/far-red (F690/F740). In addition, the changes of fluorescence yield in the four fluorescence bands and of the fluorescence ratios were studied during the storage and ripening of Braeburn apples during 2,3, and 6 months at standard conditions of 4 °C and 90% relative humidity. The blue and green fluorescence bands increased during storage and ripening, whereas the far-red band continuously declined with decreasing chlorophyll content. In contrast, the intensity of the red chlorophyll fluorescence band F690 slight...