I've written about it few times before,

To put it simply, the Iberians just wanted to get to the source of spices and buy them cheap and sell expensive in Europe, Ottoman actions and fall of Constantiniople don't really matter in this decision process.

• r/badhistory - 'Spice must flow' a.k.a 'Ottomans stopped the spice trade and started Age of Discovery' myth

also:

• How much did the Fall of Constantinople influence the Age of Discovery?
• Did the fall of Constantinople stop the spice trade and cause the Age of Discoveries? Answer: no and no.
• To what degree was the Ottoman conquest of Constantinople responsible for Iberian interest in a new route to Asia? With data about Venetian spice imports prior and after 1453

I recommend reading all of the links as some provide more data and sources than the others, but to sum some of the sources here:

Sources on Egypt being the main trade route, in no particular order (maybe chronological by publishing):

• The Ottoman Turks and the Routes of Oriental Trade (1915) by Albert H. Lybyer, available in full here
• Pepper Prices Before Da Gama (1968) by Frederic C. Lane , available on jstor, login with google needed
• The Changing Pattern of Europe's Pepper and Spice Imports, ca 1400-1700 (1979) by Christopher Wake, available in full here
• The Volume of European Spice Imports at the Beginning and End of the XVth Century (1986) by Christopher Wake, available in full here

Sources on Afonso V and his crusade is mentioned in:

• Foundations of the Portuguese empire in Asia 1415 -1580 by Diffie, Winius has a small section titled: Portugal and the Fall of the Byzantine Empire which says that Afonso V responded to the crusade call and started preparations
• Prince Henry the Navigator: A Life by Peter Russel