A perfect example is cow's milk, which contains quite a few proteins which act as allergens, such as lactoglobulin, casein, bovine serum albumin (or BSA), and lactalbumin. (verywellfamily.com)
The β - lactoglobulin protein fraction has been selectively hydrolysed and the α - lactalbumin protein fraction has been largely retained. (kerry.com)
Food allergens in cow's milk, such as B lactoglobulin, casein, and whey, can be transferred in the breast milk (19). (journals.lww.com)