The administrative user has the ability to configure which metadata fields are included when the system performs freetext search.
From version 5.7 this can be done from the Media Manager UI. Navigate to ‘Settings’ (1) → ‘General settings’ (2) → ‘Asset seacrh’ (3) → ‘Freetext search fields’ (4)
...
Navigate to Administration → Portals → [Your portal] → Asset search → Freetext search fields
...
Now click in the field ‘Add fields’ under ‘Freetext search fields’ section and select metadata fields from the dropdown list.
...