It contains antioxidants and saccharin occasionally (4)
I believe the answer is:
acai
'it contains antioxidants' is the definition.
I know nothing about this answer so I cannot tell whether it can be defined by this definition.
'saccharin occasionally' is the wordplay.
'occasionally' means one should take alternating letters (letters taken at regular intervals or occasions).
The alternating letters of 'saccharin' are 'ACAI'.
'and' acts as a link.
Can you help me to learn more?
(Other definitions for acai that I've seen before include "South American palm tree" , "South American food product" , "fruit which is nutritious" , "something nutritional to eat" .)