Change HeaderText from a columngroup radgrid da telerik

I have a radgrid of the telerik component and inside it I made a columngroup like this:

<ColumnGroups>
    <telerik:GridColumnGroup HeaderText="Folha Mensal" Name="FOLHA" HeaderStyle-HorizontalAlign="Left" HeaderStyle-BackColor="Lavender">
    </telerik:GridColumnGroup>
</ColumnGroups>

I want to dynamically change HeaderText, I tried with the following code:

RadGrid.MasterTableView.ColumnGroups[0].HeaderText = "TESTE";

But I got the error:

  

Error "CS1010 Newline in constant"

Any other way?