'College grade textbooks' is very difficult. Many of which were written some time ago... (I know my well recognized textbook for veterinary studies had one one chapter on nutrition- the information was dated back to 1972!). Beyond that- every species is different (macaws vs eclectus vs cockatiels.. all extremely different diets even though they are all psittacine).
A great deal of the 'book' information is written by Avian enthusiests who only have personal anectdoytal data and reach a wide range of conclusions. Many of which can be disproved by recent published scientific data. I only look at recent studies of wild birds and NCBI, etc and apply that to companion birds. Much of those documents are in science-eez (closely related to legaleez). I enjoy reading it, but even I find deciphering the code (and that algebraic calculating!) a headache at times.
Here on AA you will find a vast knowledge of all things birds- housing, care, diet, husbandry. Try to utilize people here- but without a specific 'species'' were are going to be hard pressed to help. Which 'parrot' are you talking about?