ROME — On the flight back to Rome after a papal trip to the United Arab Emirates last month, the Mexican journalist Valentina Alazraki got an unexpected surprise.

As the pope’s customary news conference with the reporters was winding down, a large square cake was wheeled into the cabin and placed next to him. “They told me we’re celebrating Valentina’s 150th birthday,” he said with a laugh, adding: “She doesn’t look so mummified to me.”

The celebration was actually for a milestone that even the most seasoned Vatican correspondents rarely reach: It was the 150th papal trip for Ms. Alazraki, who has covered Italy and the Vatican for Televisa, Mexico’s largest media conglomerate, since 1974.

After cutting the cake, she offered the first piece to the pope, but he declined, saying, “It will make me get fat.” Then the pope — and the cake — were whisked away.