From the list of supported formats here, it appears it does not.
However, here are some libraries that help you record to alternative formats:
Formats (Container.Codec): Ogg.Opus, WebM.Opus, WAV.PCM
Browsers: Chrome, Firefox, Safari, Edge
Note: Does not let you change the sampling rate for Opus recording from the default of 48000hz. (For example, this means its output can't directly be submitted to DialogFlow, since it requires Opus audio to have a sample rate of 16000hz.)
Formats: Ogg.Opus, WAV.PCM
Browsers: Chrome, Firefox, Safari, Opera, Edge
Formats: FLAC.FLAC
Browsers: (unknown, but probably same as the above)
See the speech-to-flac example for how to use with microphone input.
Formats: Ogg.Vorbis, MP3.MP3, WAV.PCM
Browsers: (unknown, but probably same as the above)
5) Libraries augmenting MediaRecorder with WAV/PCM support
A: https://github.com/muaz-khan/RecordRTC (recorderType: RecordRTC.StereoAudioRecorder)
B: https://github.com/streamproc/MediaStreamRecorder (mimeType: "audio/wav" or "audio/pcm")
6) Manual WAV.PCM encoding
For WAV.PCM, the format is simple enough you don't necessarily need a library. If you prefer a "lower level" approach, you can look through the examples here: https://mcmap.net/q/266964/-how-to-use-web-audio-api-to-get-raw-pcm-audio