Append comma to markup

[Jay Anderson]

\version "2.15.41"

title = \markup{Piece in \concat { E \hspace #0.25 \flat } }

\markup { \fill-line { \huge \larger \bold \line { \concat { \title
"," } opus} } }
\markup { \fill-line { \huge \larger \bold \line { \title "," opus} } }

Essentially I want to append a comma to an existing markup. In the
above two examples the first smushes all the words in the title
together with the comma. In the second there is extra space between
the title and the comma. Any suggestions on how to do this? Thanks.

-----Jay