Strings by themselves don't contain any formatting - they're just a collection of characters. Whether you can add formatting to your email depends on the type of email you're creating. So if it's a plain text email, there's nothing you can do. If you're creating an HTML email then you can add HTML formatting (so you can put <b> tags around the text in question). This is going to be determined by how the email is getting sent, which isn't part of the code you're showing.