Evoluzione compositiva dell’olio durante il processo di frittura

Blue fish is the main dietary source of long chain polyunsaturated omega-3 fatty acids, which are known to be among the fatty acids most prone to oxidative degradation. The deep-frying process is therefore critical in the preparation of seafood products. On the other hand, deep-frying is a very popular method of cooking fish and is particularly appreciated by the consumer, as it is a quick procedure and leads to a nourishing and filling food, due to the absorption of oil by the fried food. The extremely pleasant texture of a fried product is of primary importance, thanks to the crispy properties, partially due to the evaporation of free water. This results in the formation of a surface crust containing Maillard reaction products with well appreciated sensory characteristics. The conditions of deep frying (oil quality and origin, temperature and duration of frying, re use of frying oils from previous treatments) represent a critical factor for the formation of compounds with anti nutritional properties in the fried fish. The aim of this study was the evaluation of the influence of the operating parameters in the case of domestic frying on the quality of both fresh oil, oil subjected to frying and sardines (Sardina pilchardus) used as raw material in the process. The main changes produced in oils and fish during the frying process were monitored. Three types of oils were obtained from local shops: extra virgin olive oil, conventional sunflower oil and high oleic sunflower oil. The frying temperature was 160° C. Ten fishes for each experimental point were fried for 5 min in an electric fryer, capacity 2 L, in a closed environment. The fried fish was sampled after the following frying time intervals: 10 min, 30 min, 1 h and 2 h. Afterwards, deep frying was carried out with the same frying oils and the same operating conditions, but using the residual oil from the previous test, which was performed 24 hours before. A third test was performed by re using the residual frying oil which had been stored into a closed bottle and kept at room temperature in the dark for one week. The determinations made on the frying oils were the forced oxidation test (Rancimat test), free acidity, peroxide number, spectrophotometric parameters and fatty acid composition. The fried fish were analysed to determine the fat and water content, the fatty acid composition and the composition of the molecular species of phosphatidylcholine