$em = $this->createQueryBuilder('i');
        $libelle = $em->expr()->lower('i.libelle');

        $moningredientPk =  $em
                ->where($em->expr()->like($libelle, ':ing'))
                ->setParameter('ing', $em->expr()->literal(strtolower($ingredient)))
                ->getQuery()
                ->getSQL();
                //->getResult();
       var_dump($moningredientPk);
*****************************************************
Et le dump :
"SELECT i0_.ingredients_pk AS ingredients_pk_0, i0_.photo AS photo_1, i0_.libelle AS libelle_2, i0_.unite_mesure_pk AS unite_mesure_pk_3 FROM ingredients i0_ WHERE LOWER(i0_.libelle) LIKE ?"