What you’re really asking for is a safe way of representing arbitrary binary data as text and then converting it back again. The fact that it stores a serialized object is irrelevant.
The answer is almost to use Base 64 (e.g. Convert.ToBase64String and Convert.FromBase64String). Do not use Encoding.UTF8.GetString or anything similar – your binary data is not encoded text data, and shouldn’t be treated as such.
However, does your database not have a data type for binary data? Check for BLOB, IMAGE and BINARY types…