Delta, like most major US carriers, uses a menu "cycle" dependent on route.. Within any one route there will be several menu options.. A cycle is usually between one month to as long as a few months -- cycles are shorter in the premium cabins than economy cabins due to smaller economies of scale in these premium cabins.
So, on any one day, the actual meal choices will vary.. but if you were to fly that same sector daily for several days in a row, you'd start to see the same meal choices coming up.. You'd see new options once a new menu cycle is implemented.
On Euro-sectors, the "norm" for US carriers is one will be a "meat" based protein entrée choice- beef or chicken being the norms... then a non-meat choice-- usually a pasta as your second option..
You tend not to see rice on Euro sectors when flown by non-Asian carriers and pork isn't usually the preferred protein option.
Delta's catering department will internally will assign the specific meal options for your flight usually at about 5 days out -- as that's about how far out the catering units take delivery of their immediate use perishable stocks... However, it's uncommon for this detail of information to be immediately accessible to your typical phone-based agent.