"This is the final ingredient," he said before heating the soup in a microwave oven and giving it to the elderly cleaners - four women and one man.

Anton Fisher , a university spokesman, said the cleaners, some very old, may have been tricked.
  
"They obviously got the workers to participate under false pretence, something innocuous, and when it was put together it was not what they told the workers [it would be]."
  
The video was reportedly made in protest against a new university integration policy that would see black and white students mix more in residences, such as the Reitz hostel, which was once a white-only accommodation.
  
The video also shows the workers drinking alcohol and dancing.

Filmed last September, Fisher said he received a copy of the recording on Tuesday.
 
'Disgusting'
  
He said two of the students on the video had completed their studies and left. The other two have now been barred from campus.
  
Fisher said: "I viewed the video. I found it absolutely shocking and  disgusting and I was very angry with what I saw."

"There are other steps to follow still, we are in a disciplinary process and another step will be going to the police and laying a criminal charge."

Students and staff held a protest against racism on the campus.

Police used a stun grenade to disperse a group who threw stones at the Reitz hostel. Five students were arrested.

South African universities have undergone massive changes since the fall of the apartheid state 14 years ago.