Remplacez la chaîne si elle contient un pandas de substrat
df_a.loc[df_a.categories.str.contains('beverage'), 'categories'] = 'beverage'
categories product_name
0 beverage coca-cola
1 salty snacks salted pistachios
2 beverage fruit juice
3 beverage lemon tea
4 salty crackers roasted peanuts
Energetic Earthworm