Effect of antioxidants on frying oils

Namen diplomske naloge je bil pregledati novejše znanstvene članke o vplivu prisotnih oz. dodanih antioksidantov na kakovost olja. Glede na pregledano literaturo cvrenje povzroča tvorbo številnih nezaželenih produktov, ki so škodljivi in povzročajo žarek okus in vonj. Nastali produkti v olju za cvrenje predstavljajo težavo, ker prehajajo tudi v živilo in s tem lahko zmanjšajo njegovo varnost, kakovost in prehransko vrednost. Stabilnost olja je odvisna predvsem od njegove maščobno kislinske sestave, vsebnosti antioksidantov ter pogojev cvrenja. Večkrat nenasičene maščobne kisline, odsotnost antioksidantov, visoka temperatura in čas cvrenja ter prisotnost kisika in drugih prooksidantov poslabšajo oksidativno stabilnost olja. Antioksidanti za zaščito olja med cvrenjem morajo biti v njem dobro topni in stabilni ob povišani temperaturi. Sintetični antioksidanti so primerni predvsem za zaščito olja v času skladiščenja, le nekateri sintetični antioksidanti so toplotno obstojni in primerni za uporabo v oljih za cvrenje. Med naravnimi antioksidanti so najučinkovitejši fenoli in polifenoli. Njihovo topnost in uporabnost v oljih za cvrenje poveča vlaga, ki v olje pride iz živil. Za povečanje topnosti oz. lipofilnosti (poli)fenolov so možne strukturne pretvorbe teh molekul. Za povečanje učinkovitosti predlagajo raziskovalci tudi uporabo zmesi različnih spojin, ki se med seboj dopolnjujejo.The purpose of the graduation thesis was to review the recent scientific literature about the effect of present or added antioxidants on quality of the oil. Based on the reviewed literature, frying causes formation of undesirable products that are harmful to health and cause rancidity. The products formed in frying oil pose a problem because they also pass into the food and thus reduce its safety, quality and nutritional value. Oil stability is mostly dependent on oil fatty acid composition, antioxidant content and frying conditions. Polyunsaturated fatty acids, the absence of antioxidants, temperature and time of frying, the presence of oxygen and other prooxidants all might affect the oxidative stability of oil. For oil protection during frying, antioxidants have to be well soluble and stable at elevated temperatures. Synthetic antioxidants are mainly suitable for protecting oil during storage, though only some synthetic antioxidants are stable at high temperatures and suitable for use in frying oils. Among natural antioxidants the phenols and polyphenols are the most effective. Their usefulness and solubility in frying oils is increased by the moisture that enters the oil from food. To increase the solubility or lipophilicity of (poly) phenols, structural transformations of these molecules are possible. To increase efficiency, researchers also suggest the use of a mixture of different compounds that complement each other