Effect of Presence and Absence of Three different Foods on the Degradation of Two different Oils during Frying 
S. Exarhopoulos1,  A. Papastathopoulos1, C. Karastogiannidou2 & E. P. Kalogianni1*
1Department of Food Technology, Alexander Technological Educational Institute (ATEI) of Thessaloniki, Thessaloniki, Greece
2 Department of Nutrition and Dietetics, ATEI of Thessaloniki, Thessaloniki, Greece
*e-mail: elekalo@food.teithe.gr

Frying is a complex process where the oil is exposed to the simultaneous and prolonged effect of high temperatures, atmospheric oxygen, as well as moisture and several components coming from the food being fried. This results in extensive oxidation, oligopolymer formation and hydrolysis in the oil. Although there has been extensive work on the effect of the frying process on oil/fat oxidation and other degradation reactions there is only limited information on how different foods affect oil/fat degradation during frying.
This work focuses on the effect of food type vs oil type on oil degradation during frying. To this end extensive experimental work has been performed including 9 series of repeated frying experiments of 45 frying batches each where the oils have been degraded reaching or surpassing legislation limits. Two oil types were selected differing in the degree of unsaturation (sunflower oil and palm oil). Each oil type was used for frying three different foods. Potato was used as a representative of foods rich in starch. Zucchini was selected as a legume poor in starch but very rich in water. Finally, bovine minced meat was selected as a representative of protein rich foods. Control, thermo-oxidation (heating-quenching) experiments were performed in the absence of food. In order to have comparable results all series of frying and heating–quenching experiments were conducted under the same/similar time-temperature profiles by means of temperature controlled fryers. The food-to-oil ratio was constant for all series and all batches and the dimensions of food samples were all the same. The whole oil and its polar fraction were analyzed using high performance size exclusion chromatography followed by quantitative and statistical analysis. The interaction of the food type and oil type on oil degradation are discussed with special focus on the concentration of different classes of oligopolymers of tryacylglycerols and the composition of the polar fraction of the oils.