Manipulating an entity before saving to DB

I have an issue understanding something here. I'm trying to manipulate a field from an entity that is being created, but it is not working as expected.

In short I'm trying to change a field that has emails by splitting them and then adding a ; separator to distinguish the different emails before saving to the database.

This is my code:

public async Task<IActionResult> OnPost(Models.Requests.Request newRequest)
{
    newRequest.RequestStatusID = (int)RequestStatusEnum.Requested;
    newRequest.CreatedBy = User.Identity.Name;
    newRequest.CreatedDate = DateTime.Now;
    newRequest.LastRequestDate = DateTime.Now;

    if (!String.IsNullOrEmpty(newRequest.CCRecipients))
    {
        string[] emailSeparators;
        string ccRecipients = "";
        emailSeparators = newRequest.CCRecipients.Split(new Char[] { ' ', ',', ';' });

        foreach (var email in emailSeparators)
        {
            //ccRecipients.Concat(email + "; ");
            
            // I have tried two different ways to concatenate the string
            ccRecipients = email.Trim() + "; ";
        }

        // This is where I'm trying to manipulate the string into the field
        // To my understanding this is possible but I could be wrong
        newRequest.CCRecipients = ccRecipients;
    }

    await _changeControlContext.AddAsync(newRequest);
    await _changeControlContext.SaveChangesAsync();

    // Other code that is being done

    return new RedirectToPageResult("RedirectsToAnotherPage");
}

There's probably a better way to handle this but for now I want to understand why this is not working or what am I over looking.

In theory it should work but it is not. What could be the issue here?

EDIT: when I mean not working i mean that the values of CCRecipients field of said request are not being save in the database.

For example: RandomEmail@test.com; RandomEmail2@test.com. But in the database, nothing appears is stored. It's a white space instead of null. Sorry for the lack of clarity

Replace the existing line of code

ccRecipients = email.Trim() + "; ";

with

ccRecipients = ccRecipients + email.Trim() + "; ";

OR with a better approach (as mentioned by @Masoud Andalibi)

ccRecipients += email.Trim() + "; ";