Hlapljive tvari i senzorska svojstva djevičanskih maslinovih ulja istarskih sorti Buža, Črna i Rosinjola

The volatile compounds found in virgin olive oil, mainly C6 and C5 volatile compounds biogenerated from polyunsaturated fatty acids through the lipoxygenase pathway, are responsible for their particular aroma. The composition of volatile compounds in olive oil depends on the cultivar, the ripening degree of the fruits and processing conditions. Among many different autochthonous cultivars in Istria (Croatia), some of the most prevalent are Buža, Črna and Rosinjola. The volatiles and sensory characteristics of their monovarietal virgin olive oil are little known. Therefore, fruits from these three cultivars were handpicked at the same ripening degree and processed under the same conditions. Quantitative descriptive sensory analysis of monovarietal virgin olive oil was carried out by the panel. Volatile composition was evaluated by headspace solid phase microextraction-gas chromatography, previously optimized and validated. The main parameters affecting effectiveness, time and temperature of extraction were optimized. The extraction procedure showed detection and quantification limits, as well as linear ranges adequate for the analysis of selected volatile compounds. Good precision was obtained both in terms of intra-day repeatability (relative standard deviations generally lower than 7 %) and inter-day precision. The tested types of monovarietal olive oil showed different volatile profiles, although E-2-hexenal was the main compound in all samples. Buža oil was the richest in total C6 and C5 volatile compounds. The results show that the most important contributors to the olive oil aroma (odour activity value >1.0) were 1-penten-3-one, E-2-hexenal, hexanal, hexanol, Z-3-hexen-1-ol and Z-2-penten-1-ol. These chemical findings were compared with those provided by the panel test. Buža had the highest intensity of sensory characteristic 'other ripe fruits' and Rosinjola had the highest intensity of sensory characteristic 'bitter'. All results show that olive oil aroma compounds accumulate differently depending on the cultivar, indicating a close dependence on the enzymatic pool, which is genetically dependent.Specifičnu aromu djevičanskih maslinovih ulja određuju hlapljive tvari, a osobito C6 i C5 hlapljive tvari koje nastaju na lipoksigenaznom putu iz višenezasićenih masnih kiselina. Sastav hlapljivih tvari ovisi o sorti, stupnju zrelosti plodova i uvjetima prerade. Iako su Buža, Črna i Rosinjola jedne od najbrojnijih među različitim istarskim sortama, nedovoljno su poznate njihove hlapljive tvari i senzorska svojstva ulja. Plodovi tih sorti istog stupnja zrelosti brani su ručno i prerađeni pod istim uvjetima, a kvantitativnu deskriptivnu senzorsku analizu proizvedenih djevičanskih maslinovih ulja proveo je panel ocjenjivača. Prethodno optimiranom i validiranom metodom mikroekstrakcije na čvrstoj fazi iz para iznad ulja i plinskom kromatografijom određen je sastav hlapljivih tvari. Optimirani su vrijeme i temperatura, čimbenici koji najviše utječu na učinkovitost ekstrakcije. Metoda mikroekstrakcije prikladna je za analizu odabranih hlapljivih tvari, što je ustanovljeno granicama detekcije i kvantifikacije te linearnim odzivom detektora. Preciznost metode potvrđena je dnevnim mjerenjima (kada je relativna standardna devijacija bila većinom manja od 7 %) te onima u razmaku od tri dana. Analizirana sortna maslinova ulja imala su različit sastav hlapljivih tvari, iako je E-2-heksenala bilo najviše u svim uzorcima. Ulje Buže imalo je najviše ukupnih C6 i C5 hlapljivih tvari. Rezultati su pokazali da aromi maslinovih ulja najviše pridonose (vrijednost mirisne aktivnosti>1,0) 1-penten-3-on, E-2-heksenal, heksanal, heksanol, Z-3-heksen-1-ol i Z-2-penten-1-ol. Rezultati kemijskih analiza uspoređeni su s rezultatima panel testa. Najjači intenzitet senzorskog svojstva 'ostalo zrelo voće' imala je sorta Buža, a sorta Rosinjola najjači intenzitet senzorskog svojstva 'gorko'. Može se zaključiti da se hlapljive tvari arome maslinovih ulja akumuliraju različito u različitim sortama, tj. da ovise o genetski određenom enzimskom potencijalu