Ms Tan: not expert - just did my fair share of reading up =)
initially when I gave my girl solids, I started off with sweet potatoes and avocados. give a little mix with BM. then I tried also brown rice cereal (Healthy Times) mix with BM for my gal. So initially very small portion - about 2 tablespoon or so. Now she's on 2 cubes - sweet potato, papaya, avocado, pumpkin, cooked apple per day with 4 tablespoon of cereal per day.
You just need to start little, same single food for 4 days in a row, observe if any allergies. then you start on a new food. Recommended testing portion is 1/2 cube / 1/2 ounce - I think about 1/2 to 1 teaspoon of the food before it's mixed with other stuff. So like 1 teaspoon of sweet potato before it's mixed with milk.
I hope this helps