gistfile1.cs

      string xmlString = SerializeResultsToXmlString(response);

      return Content(xmlString, "application/xml", Encoding.UTF8);


    private string SerializeResultsToXmlString(ApiResponse response)
    {
      var memoryStream = new MemoryStream();
      var xs = new XmlSerializer(typeof(ApiResponse));
      var xmlTextWriter = new XmlTextWriter(memoryStream, Encoding.UTF8);
      xs.Serialize(xmlTextWriter, response);
      memoryStream = (MemoryStream)xmlTextWriter.BaseStream;
      return UtfByteArrayToString(memoryStream.ToArray());
    }

    private static String UtfByteArrayToString(Byte[] characters)
    {
      var encoding = new UTF8Encoding();
      return encoding.GetString(characters);
    }