Why my index don’t update?

I have created this index

ORACLE/VIDEO# create index titolo_index
  2  on titolo(titolo)
  3   indextype is ctxsys.context
  4  ONLINE
  5  ;

I do a research

select * from generale where CONTAINS(titolo, '%ragazzi%')>0 order by titolo;

   159|I ragazzi della roma violenta                   |1976   |Drammatico    |1:30    |Vhs       |Italiano

I change from roma to Roma

update titolo set titolo = 'I ragazzi della Roma violenta' where idtitolo = 159;

And it disappear from index!
Why?

Indexing with Oracle Text

3.3.6.1 CONTEXT Index and DML

A CONTEXT index is not transactional. When you perform inserts,
updates, or deletes on the base table, you must explicitly synchronize
the index with CTX_DDL.SYNC_INDEX.