You cannot do simple serialization here because the class itself is not marked with the [Serializable] attribute.
However, looking at the docs , it seems that the class is indeed an assistant for building and managing strings of the "text / Javascript" type. And based on the documentation of the ToString method, you can bypass the ContentType object using the ToString method and constructor.
Example:
ContentType ctype = ....;
String serialized_form = ctype.ToString();
...
ContentType ctype2 = new ContentType(serialized_form);
Debug.Assert(ctype.Equals(ctype2));
, , ( ... ).