Hi Helen
Welcome to the Forum, We are really glad your 2 wormeries are so successful
To answer your question...
It is beneficial to chop the food up first, as this makes it compost down quicker.
This is because the surface area is greatly increased, and the bacteria and microbes can work on it better.
However - if the food has been cooked or frozen this also helps break it down.
In a well established wormery like yours, even big pieces of food will be broken down quickly
Hope that helps
Ronnie