I had a lot of interest in the topic but found the book hard going. In the first half, Opie establishes that Africans were already familiar with American foods like corn and black-eyed peas before the slave trade really got under way. He goes on to cite (I can't say "incorporate") various sources which produce factoids about the slaves' cuisine. The first half of the book reads like a dissertation that has been adapted into a book, common enough in academia.
The book does get interesting in Chapter 7, "The Chitlin Circuit." Here Opie clarifies the origin of the term "soul food" as something that grew out of the civil rights struggle, particularly in the 1960s. Opie acknowledges that the hog jowls, grits, chitlins, greens and so on represent the same food eaten by white southerners, especially poor white southerners. He quotes Amari Baraka, Pearl Bowser and many others to show their effort to claim this cuisine as a central part of African-American culture.
There's a lot of info in this book (although it is too focused on New York City), but the great, sweeping STORY of black people's eating is still waiting for a writer.