I tested the code and the separator didn’t show up
\mainlanguage[sv]
\setupbodyfont[12pt]
\defineitemgroup
[fooditems]
\setupitemgroup
[fooditems]
[each]
[none,text]
[textseparator=,]
\starttext
\startfooditems
\item fish
\item eggs
\item milk
\stopfooditems
\stoptext