interjection. Because "yum" can't always get the job done.
Real citation: "@bruisinales Yum! Or: YAAAAAA-ummmm!"
(April 28, 2010, Maureen Ogle, Twitter, http://twitter.com/maureenogle/status/13024535878)
Made-up citation: "Can I tell you how I feel about bao, the Chinese steamed bun? One way I feel is YAAAAAA-ummmm. Another way is: I'd trade my children to pirates for them. I think I've said enough."