The analysis of tocopherol content in sunflower and olive oils before and after thermal treatment

Abstract

Vegetable oils have high vitamin E content. Depending on their production and consumption vitamin E can be preserved or diminished. There is an increasing number of vegetable oils offered in domestic market declared with tocopherol content; daily requirements in vitamin E are easily met to the significant extent with oil consumption. The purpose of the study was to determine tocopherol content in sunflower and olive oil from our market before and after their thermal treatment, using HPLC method. Retailed vegetable sunflower and olive oils of various origins and the way of production (the total of 16) were analyzed before and after temperature treatment for 20 minutes. For an accurate and reliable determination of vitamin E content in food of complex composition it is necessary to perform multiple sample purification, but for determination in vegetable oils a liquid/liquid extraction is recommended. The n-hexane extraction was applied after alkaline hydrolysis, extract vaporisation and reconstitution in methanol using membrane filtration. Separation was performed by using RP-HPLC method with fluorescent detector with changeable wavelengths. For tocopherol detection 95% ethanol was applied as mobile phase, with 1,2 ml/min of flow rate and measuring at λ = 295 nm wavelength for excitation and λ = 330 μm for emission. Fluorescence detector selectivity and sensitivity enabled detection of α-, β+γ and δ-tocopherols in analyzed oil samples. Tocopherol content determined in oil before the treatment corresponded to the values specified in legislative, with significant differences depending on origin and declared production modality. Thermal treatment of sample significantly affected vitamin E content.

Biljna ulja karakteriše visok sadržaj vitamina E. U zavisnosti od načina proizvodnje, obrade i upotrebe ta količina može biti očuvana ili umanjena. Na našem tržištu postoji sve raznovrsnija ponuda jestivih biljnih ulja. Pravilnom upotrebom ove namirnice moguće je u znatnoj meri zadovoljiti dnevne potrebe za vitaminom E. Cilj ovog rada bio je da primenom visoko efikasne tečne hroamtografije (HPLC ) odredimo sadržaj tokoferola u jestivom biljnom ulju suncokreta i masline, pre i posle termičkog tretmana. Analizirana su jestiva biljna ulja iz maloprodaje, različitog porekla i načina proizvodnje (ukupno 16), pre i nakon izlaganja temperaturi ključanja u trajanju od 20 minuta. Za tačno i pouzdano određivanje sadržaja vitamina E u namirnicama složenog sastava neophodno je višestruko prečišćavanje uzorka, dok se za određivanje u biljnom ulju preporučuje tečno/tečna ekstrakcija. Primenjena je ekstrakcija n-heksanom, nakon alkalne hidrolize, uparavanje ekstrakta i rekonstituisanje u metanolu uz membransku filtraciju. Razdvajanje je urađeno RP-HPLC metodom uz fluorescentni detektor sa promenljivim talasnim dužinama. Za detekciju tokoferola primenjen je 95%-ni metanol kao mobilna faza, sa protokom od 1,0 mL/min i talasnim dužinama: 295 nm za ekscitaciju i 330 nm za emisiju. Selektivnost i osetljivost fluorescentnog detektora omogućila je detekciju α, ß+γ i δ tokoferola u analiziranim uzorcima ulja. Određen sadržaj tokoferola u uljima pre tretmana je odgovarao zahtevu regulative, uz značajne međusobne razlike u zavisnosti od porekla i deklarisanog načina proizvodnje. Termički tretman uzoraka značajno je uticao na smanjenje početnog sadržaja vitamina E.