U ovome radu ispitivano je voltametrijsko ponašanje galne kiseline (GK) i glavnih katehinskih spojeva ili katehina epigalokatehin galat (EGCG), epigalokatehin (EGC), epikatehin (EC) i epikatehin ...galat (ECG) prisutnih u zelenim i crnim čajevima. Također, razvijena je nova elektroanalitička metoda za karakterizaciju katehina u vodenim ekstraktima odnosno suhom lišću zelenih i crnih čajeva.
Podaci o katehinskom profilu zelenih i crnih čajeva dobiveni su primjenom tekućinske kromatografije visoke djelotvornosti u kombinaciji s elektrokemijskim detektorom (HPLCECD).
Ustanovljeno je da su glavni katehini u zelenim i crnim čajevima EGCG i EGC, koji čine 84-89 % ukupnih katehina zelenog i 53-89 % ukupnih katehina crnog čaja.
Voltametrijska mjerenja pravokutnovalna voltametrija (SWV) i ciklička voltametrija (CV) na elektrodi od staklastog ugljika (GCE) pokazala su da je elektrokemijska oksidacija katehina difuzijom kontrolirani kvazireverzibilni proces. Voltametrijska svojstva katehina funkcija su koncentracije katehina, pH i brzine polarizacije. Utvrđeni su optimalni uvjeti i validirana je SWV kao metoda za karakterizaciju katehina u zelenim i crnim čajevima.
Analizirani su uzorci zelenih i crnih čajeva primjenom SWV metode na GCE i određen je sadržaj katehina u vodenim ekstraktima čajeva. Koncentracije katehina dobivene SWV metodom gotovo su identične onima dobivenima HPLC-ECD analizom. Stoga, SWV metoda predstavlja vrlo dobru alternativnu metodu analize katehinskih spojeva u ekstraktima zelenih i crnih čajeva u odnosu na zahtjevnu i skupu HPLC analizu.
Kao dodatna metoda karakterizacije katehina korištena je abrazivna SWV s anodnim otapanjem uzorka imobiliziranog na površini parafinom impregnirane grafitne elektrode (PIGE). Ova metoda pokazala se kao brza i jednostavna semikvantitativna metoda za detekciju elektroaktivnih katehina u suhom lišću zelenih i crnih čajeva.
The voltammetric behaviour of gallic acid (GA) and the main catechins epigallocatechin
gallate (EGCG), epigallocatechin (EGC), spicatechin (EC), and epicatechin gallate (ECG) found
in green and black teas was investigated. In addition, novel electroanalytical procedure for
characterization of catechins in tea extracts and dry tea leaves was developed.
The concentrations of individual catechins in green and black teas were determined using
high-performance liquid chromatography with electrochemical detection (HPLC-ECD). EGCG
and EGC were the major catechins in green and black tea samples, representing 84-89% and 53-
89% of total catechins, respectively.
Square-wave and cyclic voltammetry experiments showed that the oxidation of catechins
on glassy carbon electrode (GCE) is a quasireversible and diffusion controlled process. It has
been shown that voltammetric properties of catechins depend on pH, scan rate and catechin
concentration. A new SWV method for characterization of catechins has been established,
optimized and validated. The proposed method was applied to characterize the catechins in green
and black teas.
Water extracts of green and black teas were analysed using SWV on GCE. Amounts of
catechins in green and black teas obtained using SWV were in good agreement to those obtained
using HPLC-ECD. Accordingly, SWV has been shown to be a good alternative compared to
more expensive, laborious and time-consuming HPLC methods.
In addition, the abrasive stripping SWV of microparticles of tea leaves immobilized on
the surface of paraffin-immpregnated graphite electrode (PIGE) was used for characterization of
catechins as well. This semiquantitative method enabled a fast and simple screening of catechins
in dry leaves of green and black teas.
U ovom radu je, primjenom HPLC i spektroskopskih metoda, provedena karakterizacija
polifenolnih spojeva: antocijanina, flavonola (kvercetin, miricetin, kemferol), flavanola ((+)-
katehin, ...(-)-epikatehin), hidroksibenzojevih (p-hidroksibenzojeva, elaginska), hidroksicimetnih
kiselina (p-kumarinska, kafeinska, ferulicna); koji su prisutni u borovnici, bobicama bazge,
kupini, malini, višnji, trešnji, crnom i crvenom ribizu, jagodi i aroniji. Antioksidacijska aktivnost
voća određena je primjenom DPPH i ABTS metode, a utjecaj polifenola na antioksidacijsku
aktivnost voća ispitan je traženjem korelacije izmedu količine polifenola i antioksidacijske
aktivnosti voća.
Rezultati analiza pokazali su da se u ispitivanom voću nalaze vrlo velike količine
ukupnih polifenola (od 1763 mg kg-1 u malini do 7194 mg kg-1 u aroniji) od kojih su
najznačajniji antocijanini (od 169 mg kg-1u jagodi do 4069 mg kg-1 u borovnici). Sadržaj
flavonola (od 4 mg kg-1 u malinama do 183 mg kg-1 u borovnici), flavanola (0-256 mg kg-1)
hidroksicimetnih (12-92 mg kg-1) te hidroksibenzojevih kiselina (0-121 mg kg-1) znatno je manji.
Iako se voće značajno razlikuje po količini, vrsti i rasprostranjenosti polifenola, aronija,
borovnica, bobice bazge i crni ribiz mogu se izdvojiti po vrlo velikoj količini polifenolnih
spojeva i vrlo visokoj antioksidacijskoj aktivnosti te bi ove vrste voća mogle poslužiti kao dobra
sirovina u proizvodnji funkcionalne hrane. Visoke korelacije između antioksidacijske aktivnosti i
sadržaja ukupnih polifenola, ukupnih antocijanina, ukupnih flavonola, ukupnih hidroksicimetnih
kiselina te pojedinih polifenolnih spojeva (kafeinska kiselina, derivati cijanidina, p-kumarinska
kiselina i kvercetin) pokazuju da ovi polifenolni spojevi imaju snažan utjecaj na ukupnu
antioksidacijsku aktivnost voća, dok ostali istraživani polifenoli nisu značajni za ukupnu
antioksidacijsku aktivnost. Ovi rezultati pridonose boljem objašnjenju antioksidacijske aktivnosti
polifenola iz voća koji su bitni za pozitivno djelovanje voća u ljudskom organizmu.
In this study, the characterization of polyphenolic compounds: anthocyanins, flavonols
(quercetin myricetin, kaempferol), flavanols ((+)-catechin, (-)-epicatechin), hydroxybenzoic
acids (p-hydroxybenzoic, ellagic) and hydroxycinnamic acids (p-coumaric, caffeic, ferulic;
which are present in blueberry, elderberry, blackberry, red raspberry, sour cherry, sweet cherry,
black currant, red currant, strawberry and chokeberry was carried out by using HPLC and
spectroscopic methods. DPPH and ABTS assays were used to determine antioxidant activity of
fruits. The correlation between the amount of polyphenols and antioxidant activity of fruits was
investigated in order to examine the influence of polyphenols on antioxidant activity.
The results showed that investigated fruits contained high amounts of polyphenols (from
1763 mg kg-1 in red raspberry to 7194 mg kg-1 in chokeberry) among which anthocyanins were
the most important ones (from 169 mg kg-1 in strawberry to 4069 mg kg-1 in blueberry). The
amount of flavonols (from 4 mg kg-1 in red raspberries to 183 mg kg-1 in blueberries), flavanols
(0-256 mg kg-1), hydroxycinnamic (12-92 mg kg-1) and hydroxybenzoic acids (0-121 mg kg-1)
was considerably lower. Fruits differ greatly in the amount, species and distribution of
polyphenols but chokeberry, blueberry, elderberry and black currant stand out in high amounts of
polyphenolic compounds and in strong antioxidant activity and could be used as a good raw
material in production of functional foods. High correlations between antioxidant activity and
amount of total polyphenols, total anthocyanins, total flavonols, total hydroxycinnamic acids, or
the amount of individual polyphenolic compounds (caffeic acid, cyanidin derivatives, pcoumaric
acid and quercetin) showed that these polyphenols have strong influence on total
antioxidant activity of fruits whereas other investigated polyphenols were not significant for total
antioxidant activity of fruits. Overall results are a contribution to better understanding of
antioxidant activity of fruit’s polyphenols, the compounds that are important for positive action
of fruits in human organism.
