Re-arranging merged lists items

Dim category As New List(Of String)
 Dim products As New List(Of String)

 'concantenate category
        For i As Integer = 0 To Me.dgvData.Rows.Count - 1
            If dgvData.Rows(i).Cells("chk").Value = True Then
                category.Add(dgvData.Rows(i).Cells("catName").Value)
            End If
        Next
        Dim combinedCategory As String = String.Join(", ", category)

        'concantenate products
        For i As Integer = 0 To Me.dgvData.Rows.Count - 1
            If dgvData.Rows(i).Cells("chk").Value = True Then
                products.Add(dgvData.Rows(i).Cells("ProdName").Value)
            End If
        Next
        Dim combinedProducts As String = String.Join(", ", products)

descriptive = combinedCategory  & ", " & combinedProducts