Today it's hard to imagine what people ate and how they cooked prior to the Columbian Exchange. Try to imagine Italian cooking and Italian food culture without tomatoes. Or Thai or Indian cooking without chili peppers. Or Brazilian food without limes or coconuts or mangoes. Impossible. Yet, until sometime after 1492 cooks in these cultures did not have these ingredients available, though today these ingredients are essential to the food culture of these countries. For an interesting chart of all the foods that were part of the Columbian Exchange, click on this link to a Wikipedia article - incidentally, the chart also shows the diseases that were part of this same exchange.
Recently a Portuguese scholar and historian, José Eduardo Mendes Ferrão, published a book on the Columbian Exchange, with particular emphasis on the role that Portuguese navigators and explorers played in this process. The book is entitled A Aventura das Plantas e Os Descobrimentos Portugueses (The Adventure of Plants a The Portuguese Discoveries) and was published by the Portuguese institute IICF - Instituto de Investigação Científica Tropical or Institute of Scientific Tropical Research. Sr. Ferrão's thesis is that because of the patterns and the history of Portuguese exploration and colonization in the 16th and 17th centuries, Portugal played a major role in the Columbian Exchange, a role that was far larger than might be expected. And because Brazil was Portuguese territory during those times, it played a large part in the Exchange as well.
Unlike Spanish colonization during those centuries which was centered on the New World, Portugal explored and colonized not only the Americas, but also Africa and Asia. According to Sr. Ferrão is it the geographically widespread nature of Portuguese exploration that makes Portugal such a major player in the Columbian Exchange. Another factor, as he points out, was that Portugal possessed islands in the Atlantic, such as Madeira, Porto Santo and the Cabo Verde archipelago. These semi-tropical islands allowed Portuguese planters to acclimatize new species to the cooler European climate prior to bringing them to mainland Portugal. They survived, whereas plants carried directly from the tropics to the Iberian peninsula might not have. In effect, these off-shore territories became botanical laboratories for the Europeanization of Asian, African and American foods.
A good example of the role Portugal played in the Columbian exchange is the dissemination of corn (maize) - milho in Portuguese. Although this plant did not originate in Brazil but came from Central America, it was already widespread in the indigenous cultures of Brazil prior to the arrival of Europeans in 1500. The Portuguese carried corn back to Europe with them, and from there, carried it to their colonies in Africa. From these colonies it spread throughout the continent, and today corn is the most widely-eaten staple food on the African continent. In the other direction, the Portuguese brought the coconut palm from Asia (either South Asia or Southeast Asia) to Africa and thence to Brazil. Brazilian food, particularly the African-based cuisine of Bahia, is unimaginable without the presence of coconut and coconut milk.
As far as I've been able to determine, Sr. Ferrão's book has not yet been translated into English. As the field of historic gastronomy grows and becomes a more prominent academic subject, I hope that this situation will be remedied. The Columbian Exchange is one of the fundamental shifts in the history of world gastronomy, and the Portuguese contribution to it should be made better known.