Two restaurants I know fry battered fish and breaded chicken in the same oil. I asked one of them how they prevent cross-contamination in that case and I received the following reply:
Our fish is hand battered which helps lock in the flavours and juices and we have not seen any leaching of flavour from the fish into other products. Foods are typically fried between 300 and 400 degrees (depending on product and stage of cooking) which is a very harsh environment for flavours or contaminants to survive. Even celiacs are generally fine eating products from a fryer that had other flour based products fried in the oil.
They essentially said that the heat will kill contaminants and hence cross-contamination won't happen. Is this correct? Please comment on the above claim.
By cross-contamination, I mean one food simply affecting or mixing with another (e.g. should someone with a fish allergy be concerned about chicken fried in the same oil?)