External green light as a new tool to change colors and nutritional components of inner leaves of head cabbages

Abstract

The color and nutritional quality of vegetables directly affect the choices of consumers and thus affect the commercial value of the vegetable products. Green light can penetrate the outer leaves and reach the inner leaves to promote photochemical reaction of the overlapping leaves of head vegetables. However, whether this promotion can increase the nutritional components and change the color of the inner leaves of head cabbages, which is one of the major head vegetables largely produced worldwide, remains unclear. Therefore, we investigated the changes in the colors and the concentrations of chlorophyll (Chl) and carotenoid of the inner leaves of two types of cabbages by externally irradiating the cabbage with green light. The results showed that a short-term (48 h) irradiation with low light intensity (50 μmol m−2 s−1) of green light enhanced the Chl concentration and colors of the inner leaves of cabbages, and the positive changes of these indicators increased as the leaf layers approached the head center of the cabbage. Simultaneously, we also establish a method to effectively estimate the Chl concentration using luminosity (L*) and greenness (− a*) when the Chl concentration is so low that it is difficult or not possible to be measured by SPAD meter. Our findings demonstrated that green light, as a new tool, can be used to control the colors and nutritional components of the inner leaves of cabbages. The discoveries will help produce head vegetables with the preferred phenotype desired by consumers using a plant factory with artificial lighting.