I drop oak leaves for my shrimp and just let them hang out in the tank. The current one has been in there for two weeks with no sign of disintegration. Also, blanched veggies and fruit are great ... Just don't leave in more than a couple of hours. I feed spinach, broccoli, banana, apple, strawberry, just about anything I can get in the tank. Just make sure it doesn't have any pesticides.
Frozen should be thawed, fresh veggies I microwave in tank water and allow to cool so thy sink. Fruit I just drop in unless it floats. Shrimp only need supplemental feeding every 2-3 days (large planted tanks even less). They will benefit from the protein in fish food, but they are scavengers so any little bit of flake etc that makes it down will be found.