פירוש על שבת 228:3

Rather for trimming vegetables: It seems to R[abbenu] Y[itzchok] that [this verse is used here] as a support [for a Rabbinic enactment], for if it is [prohibited] by Torah, it would be prohibited on Yom Kippur as well.  Even though it says in Chapter Klal Gadol (73b) "one who trims beets is liable twice", there it referring to [beets that are] attached [to the ground].  Here it is referring to harvested [vegetables], as Rashi explained. This is also not similar to what is said in Chapter Klal Gadol (74b) "One who minces beets is liable for [transgressing the Melachah of] Grinding", because there he is making very fine pieces whereas here he is making large pieces.