Different types of salads have been analyzed. As shown in Fig. 1, UV spectra were highly reproducible for the same type of lettuce, and that was recorded with the Anthelie spectrophotometer. But the UV shapes were quite different for the common lettuce as compared to the curly lettuce and the oak-leaf ones. The UV shape of lettuce was mainly due to the a higher nitrate content (see below) , that explained the large peak at 206 nm, while the suspensions of curly and oak-leaf lettuces contained less nitrates but more pigments, that were analyzed in global DOC , and provided a higher UV absorption at about 250 nm . First we focused on the common lettuce that are supposed to contain higher amounts of nitrate