You should try 'Initiacion'. Quite rare to find though (I could upload it to bittorrent if you like ..)
Its a story about, the cotton plantations and how a white family, a husband with his wife and two younger daughters end up being made hostage by their own rebellious slave-workers. The family house is out in the middle of nowhere somewhere down South, and after half a dozen slaves set themselves free, by killing guards etc they make the owners "Slaves".
Its not an actual soft porno.
Its pretty violent but it has shit loads of fucking and full frontal nudity.
The husband is chained down in a cellar while, one by one, first his wife and then his two pretty daughters get to know what dark meat actually feels and tastes like as well as experiencing the humiliating life of servants to the newlyfreed blacks.
Its an excellent choice cuz you get to see how the wife, who was initially afraid of the black slaves, ends up knuckling under without resistance.
Message me if you want to the file.
You could also try Emanuelle in Africa.