sudo apt-get install gstreamer0.10-plugins-ugly-multiverseThe mp3 option should now turn up in your Sound Juicer options. To adjust the bitrate try the following. Go into edit profiles or....
gnome-audio-profiles-propertiesAnd create a new profile with the following values.....
Profile name: mp3 192, Lossy
Profile Description: mp3 192
GStreamer Pipeline: audio/x-raw-int,rate=44100,channels=2 ! lame name=enc vbr=0 bitrate=128
File Extension: mp3
The bitrate value is changeable. Shut down Sound Juicer, fire it back up again, and it should now be available in your ripping options as a codec.