I visited the Galup factory in Pinarolo. They don't use any additives, but it's not very good.
I've now compared 5 brands of Panettone and there really is a difference, although it's not well represented by the price. Galup were the 2nd most expensive in my research and the worst quality. The best FYI were the deservedly famous Perbellini and my favorite local Turin bakery, Ficini, who is an expert in llevito madre which is the key thing to Panettone. Ficini was nearly indistinguishable from another local patisserie, Ghigo (known for cookies and cream puffs and the source of my absolute favorite savoiardi to which neither Ficini nor any other bakery's compare.)
Expense: Ghigo €30, Galup €25, Perbellini €22, Muzzi Tommaso €15, Ficini €15.
Deliciousness: Perbellini 10, Ficini 9, Ghigo 9, Galup 3, Muzzi 2. I have to also note with grave disappointment that I bought the Muzzi because they were sold at Eataly, but they do have additives and made me feel slightly sick.)
Thankfully, Perbellini ships internationally and is carried in the US by Formaggio Kitchen, who will ship domestically.