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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.

Analizirali smo kemijsko sestavo ekstraktivov v beljavi, jedrovini, grčah in vejah bele jelke (Abies alba Mill.) ter preučili njihove fungistatične, antimikrobne in antioksidativne lastnosti. Preiskali smo variabilnost v vsebnosti ekstraktivov v centripetalni smeri, torej od perifernega dela debla proti strženu, ter v longitudinalni smeri. Izolirali smo vzorce lesa debla, grč in vej. Jelovino smo ekstrahirali pri povišani temperaturi in tlaku s cikloheksanom in acetonom. Vsebnosti ekstraktivov in celokupnih fenolov smo določili z gravimetrično in s spektrofotometrično metodo. Fenolne ekstraktive smo identificirali s tankoplastno kromatografijo in s tekočinsko kromatografijo visoke ločljivosti. Fungistatične, antimikrobne in antioksidativne lastnosti ekstraktivov smo ocenili z difuznim testom in z metodo lovljenja difenilpikrilhidrazilnega radikala. Ugotovili smo, da največ hidrofilnih ekstraktivov vsebuje les grč in vej, manj jedrovina, najmanj pa beljava. Med identificiranimi spojinami so lignani, fenolne kisline in flavonoidi. V živih grčah in vejah je bilo največ sekoizolaricirezinola, v jedrovini pa matairezinola. Največ fenolnih spojin smo ekstrahirali iz delov grč, ki so vključene v beljavo ter delov vej tik ob deblu. Jedrovina je vsebovala več lignanov v njenih starejših delih. Značilne variabilnosti v vsebnosti ekstraktivov v longitudinalni smeri debla nismo ugotovili. Hidrofilni ekstrakti grč in vej so inhibirali razvoj gliv razkrojevalk lesa ter plesni, vendar pa inhibicija ni bila močna. Ekstrakti grč in vej so izkazali dobre antioksidativne lastnosti. Ugotovili smo, da so ekstrakti grč in vej boljši lovilci prostih radikalov kot ekstrakti jedrovine. Rezultati pričujoče raziskave opisujejo les grč in vej kot najbogatejši vir fenolnih ekstraktivov in lignanov v drevesu bele jelke. Rezultati testov bioloških aktivnosti kažejo na to, da lahko zaščitno funkcijo fenolnih ekstraktivov v lesu bele jelke pojasnimo tudi z njihovimi antioskidativnimi lastnostmi. We analysed the chemical composition of extracts in the sapwood, heartwood, knots and branches of silver fir (Abies alba Mill.) and examined their fungistatic, antimicrobial and antioxidative properties. We investigated the variability in extract content in the centripetal direction, that is, from the periphery of the trunk towards the pith, and in the longitudinal direction. We isolated wood samples from the trunk, knots and branches. The wood was extracted at an elevated temperature and pressure. Cyclohexane and acetone were used as solvents. Extract and total phenol content were determined by the gravimetric and spectrophotometric methods. Phenolic extracts were identified using thin-layer chromotography and high-resolution liquid chromatography. Fungistatic, antimicrobial and antioxidative properties of the extracts were assessed with a diffusion test and the diphenylpicrylhydrazyl radical scavenging method. We found that knot and branch wood contains the highest amount of hydrophilic extracts, heartwood less so and sapwood the least. Among the identified compounds are lignans, phenolic acids and flavonoids. Secoisolariciresinol was predominent in live knots and branches, while matairesinol was prevalent in heartwood. The largest amount of phenolic compounds was extraced from sections of knots included in the sapwood and from parts of branches closest to the trunk. Heartwood contained more lignans in its older sections. A characteristic variability in extract content in the longitudinal direction of the trunk was not found. Hydrophilic extracts from knots and branches inhibited the growth of wood-decay fungi and molds, but the inhibition was not strong. Knot and branch extracts exhibited good antioxidative properties. We found that knot and branch extracts are better free radical scavengers than heartwood extracts. The results of this study describe knot and branch wood as the richest sources of phenolic extracts and lignans in a silver fir tree. Results of biological activity tests indicate that the protective function of phenolic extracts in silver fir wood can also be explained by their antioxidative properties.