iRule: 'Switch -glob' does not work with HTTP::payload, it works using 'if-elseif' logic.

It will work, but I'm guessing you need to allow for some padding:

when HTTP_REQUEST {
    if { [HTTP::method] equals "POST" }{
        HTTP::collect [HTTP::header Content-Length]
    }
}
when HTTP_REQUEST_DATA {
    switch -glob [HTTP::payload] {      
        "*apple*" {
            pool apple_pool
        }
        "*orange*" {   
            pool orange_pool
        }
    }
}

You shouldn't need to issue the HTTP::release command because you're explicitly defining the amount of payload to collect using the Content-Length header.