Effects of different varieties and shelf storage conditions of chicory on deteriorative color changes using digital image processing and analysis

This study established a method of evaluating the color change during the shelf storage of different varieties of chicory. The RGB system was used for digitizing the color images. Four colored areas, white, red, yellow and brown, were segmented according to the Hierarchical Classification using Projection Pursuit (HICUPP) decision tree. Experiments were conducted with six varieties of chicory. In the experiments, a comprehensive index, Sc, was presented and used for estimating the unfavorable color change (turning to brown and red). The index is based on comprehensive consideration of the colored area and degree of the color change. The translation among the segmented color areas has been discussed, to explain why the rgb values decrease during the shelf storage. The effects of red and brown separately on the color change as well as changing temperature on Sc are discussed. Finally, the effect of different varieties on the yellow leaf growth and the effect of a commercial cut on Sc have been analyzed. The results indicate that two commercial varieties, Focus and Sigma, and a test variety, Pax, have better characteristics for the red and brown colors of the core. The results also show that the segmented areas translate with time. In the first 4 days the red area increases more rapidly than the brown; while from the fourth day on the brown increases more prominently. Higher temperatures (T10-18 degrees C) during the first 2 days of shelf storage lead to more serious red and brown coloring compared with the lower temperatures (T2-5 degrees C) for both Sigma and Focus. The lower the humidity, the slower the color change is. The recommended humidity range for shelf storage is between 50 and 65%RH. The higher temperature also leads to stronger leaf-growth; the effect of humidity on the leaf-growth is small. Changing temperatures during storage often lead to a serious red and brown coloring. So avoiding to change temperature during shelf storage is reasonable.