Generally with food we use du, de la, de l' and des according to the Gender and Number. In this case is, de+la=de la, or is it simply de+ la salade de tomates? What I mean to ask is that whether the "de" used in this context is strictly equivalent to "of" or does it have to do with what the "thing" is?
PS: I read the answers to this question but couldn't understand the answers. I would request the community to answer in English as I am still learning French.