| Abstract | Zeleni čaj, dobiven iz lišća biljke Camellia sinensis, jedno je od najpopularnijih pića na svijetu. Razlozi popularnosti su organoleptička svojstva i mogući pozitivni utjecaji na ljudsko zdravlje. Pozitivni učinci vezuju se uz njegov kemijski sastav, posebice visok udjel polifenola koji posjeduju jako antioksidativno djelovanje. Cilj ovog istraživanja bilo je ispitivanje sastava polifenola i metilksantina u 13 zelenih čajeva te određivanje njihove antioksidativne aktivnosti. Četiri zelena čaja (Matcha, Gyokuro, Twinings of London i Longjing), odabrana kao reprezentativni uzorci, razlikovala su se načinom primjene (rinfuza, filter-vrećice) i načinom proizvodnje. Promjene udjela ukupnih fenola i flavonoida ovisno o različitim uvjetima pripreme čajeva (temperatura, duljina trajanja ekstrakcije, višestruko ponovljanje ekstrakcije istog uzorka), kao i tijekom jednodnevnog stajanja pripremljenih čajeva na sobnoj temperaturi, praćene su spektrofotometrijskim metodama. Udjeli pojedinačnih fenolnih sastojaka i metilksantina određeni su primjenom metoda tekućinske kromatografije visoke djelotvornosti (HPLC-PDA). Antioksidativna svojstva čajeva određena su primjenom triju metoda: reakcijom s 1,1-difenil-2-pikrilhidrazil radikalom (DPPH), reakcijom s 2,2'-azino-bis(3-etilbenzotiazolin-6-sulfonskom kiselinom) (ABTS- radikal) te reakcijom s Fe3+-2,4,6-tripiridil-S-tirazin kompleksom (FRAP). Kod većine čajeva udjel ispitivanih sastojaka povećao se povišenjem temperature, duljim trajanjem ekstrakcije te duljim stajanjem pripremljenih uzoraka na sobnoj temperaturi. Višestrukim ponavljanjem ekstrakcija istog uzorka udjeli istih su se smanjili. Pokazalo se da su najznačajniji fenolni sastojci zelenog čaja katehini posebice (-)-epigalokatehin-galat (EGCG). Od metilksantina najzastupljeniji je kafein. Svi čajevi posjeduju visoku antioksidativnu aktivnost. |
| Abstract (english) | Green tea, a pale tea, made from leaves of Camellia sinensis, that have been dried but not fermented, is one of the most consumed drinks in the world. A fact that makes it right are its organoleptic properties as well as its health benefits. It is reputed to contain the highest concentration of polyphenols, chemicals, that act like powerful antioxidants. It has been extensively studied and the results from these studies suggest that concentration of polyphenols and methylxanthines in thirteen green teas, may be useful for the health conditions. Four green tea varieties (Matcha, Gyokuro, Twinings of London i Longjing) differ from one another in way of appliance (loose tea and tea bags) and in their processing and in its country of origin (Longjing – Chinese tea). Participation changes of phenols and flavonoids in different types of processing tea ( rise in temperature, duration of extraction and multiple repetition of extraction of the same kind), and keeping samples at room temperature, daily, are defined by spectrophotometrycal methods. Participations of individual phenols and methylxanthines are defined by application of High Performance Liquid Chromatography (HPLC-PDA). Antioxidant properties of teas are defined by application of three methods: reaction with 1,1-diphenil-2-pichrylhydrasyl radical (DPPH), reaction with s 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS- radical) and reaction with Fe3+-2,4,6-tripyridyl-S-tirazine complex (FRAP). Taken from a larger amount of samples, the participation of examined ingredients has become higher by rising of temperature, longer duration of tea extraction and longer keeping of processed samples. By multiple repetition of extractions of the same sample,their participation lessened. It has shown that the most important phenol ingredients of green tea are catechins i.e. (-)-epigallocatechin-gallate (EGCG). Caffeine is the largest in amount among methylxanthines. All teas had shown powerful antioxidant activity. |
