Will cross-contamination not happen when deep frying breaded chicken and battered fish in the same oil?

Question

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.

EDIT:

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?)

Answer 1

Pasteurization is usually done between 63-90 °C, (145 - 194 °F) steam sterilization at 120-130 °C (248 - 266 °F). So you can consider long frying oil at 150-200 °C (245 - 392 °F) safely to be free from any microbes.

For flavours it depends, some will vanish even at temperatures far below the boiling point, some will change and some will reman stable even at high temperatures. Also many flavours are very well soluble in fats, so there is a possibility of carrying over the flavour of one food to another. And while you probably don´t want to prapare donuts in an oil that was used for fish and onions it remains a question of personal taste if this is neccessarily is a bad thing.

Gluten needs a temperature of at least 300 °C (572 °F) to denaturate, which is beyond the temperature used for frying. Also note that as long as the dough also contains some water it will not surpass the boiling point.

Parvalbumin the proteine which is the main reason for fish allergy seems to be relatively stable against high temperatures, so it might be an issue. If you have a reason to fear it as a serious hazard for your health it probably is safer to avoid it. But for advice on personal health threats and how to deal with an allergy you better should consult a doctor or another professional with an deeper insight into your specific situation and its reguirements than this community can provide.