Changes in the Frying Medium During Deep‐frying of Food Rich in Proteins and Carbohydrates

Changes in the frying medium (rapeseed oil) during controlled deep‐frying of sliced potatoes and cod fillets and oil heated without them were compared. Fifteen frying cycles were conducted each day for five days. Results showed that oil after frying of cod fillets contained 10% less triacylglycerol (TAG) polymers and 40% less TAG dimers than other oils. Other parameters (iodine and anisidine values and absorption value at 233nm) showed that less thermooxidative products formed during frying of food rich in proteins. Oil after frying of cod fillets was darker and its acid value was significantly higher than that for other oils. Content of TAG polymers and dimers for oil after frying of sliced potatoes and oil heated without food was equal. The relative loss of C18:2 acid and decrease in iodine value showed that oil after heating without food underwent more intensive thermooxidative transformation than other oils.