There are some food (like pizza) where we can find 0.5 % of alcohol, is it forbidden to eat it ?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

If the water or the flour is mixed with alcohol, it becomes forbidden to drink or eat that mixture.

Allah Says (what means): {O you who have believed, indeed, intoxicants, gambling, [sacrificing on] stone alters [to other than Allah], and divining arrows are but defilement from the work of Satan, so avoid it that you may be successful.} [Quran 5:90]
There is no difference between drinking alcohol or putting it in the food, nor is there a difference between its amount, be it small or big.

Ibn ‘Umar narrated that the Prophet said: “Everything that causes drunkenness is wine, and all kinds of wine are prohibited.” [Abu Daawood]

Besides, Jaabir narrated that the Prophet said: “If a big amount of something can cause drunkenness, then any little amount of that thing is forbidden." [Abu Daawood]

‘Aa’ishah said: “I heard the Prophet saying: “Anything that causes drunkenness is forbidden. And if a Faraq (8 liters approximately) of something can cause drunkenness, so a handful of it is forbidden.”

So, Muslims should be cautious of taking such foods and should advise their brothers to stay away from such foods, above all those brothers who live in the West.

For more benefit on the existence of a small percentage of alcohol in food or other substances, please refer to Fataawa 382309, 327754, 299059, 301753, and 81423.

Allah knows best.