The aim of this study was to investigate flavonoids and other polyhenols in Australian grown and made tea, and in Australian floral honey. Phenolic compounds in fresh tea leaves collected from a tea farm in north Queensland were analysed. This field study was conducted on different commercial harvests from April 2000 to May 2001, using both hand plucking and mechanical harvesting to collect the fresh tea leaves in order to determine seasonal variations. The analysis of Australian made tea was conducted on the samples collected off the processing line of a black tea processing factory in north Queensland, Australia at three month interval from April 2000 to January 2001, so the process could be evaluated in terms of its effects on tea flavonoids. The study of flavonoids and other polyphenols in Australian honey was done to determine floral markers for a number of Australian honeys. Prior to this study, no published research has been
conducted on the flavonoids and other polyphenols of Australian tea, and little on the flavonoids and other polyphenols in Australian honey.
Fresh tea leaves, consisting of one apical bud and two adjunct leaves, were hand plucked just before each mechanical harvest during the sampling period. The samples were packed in dry ice and delivered to the laboratory by overnight transport and stored in a freezer at -80 °C before analysis. The phenolic compounds were extracted with methanol using a method developed and optimised for this study, and were analysed using an HPLC with photodiode array detection. Four catechins, six catechin gallates, five flavonoid glycosides, and seven phenolic acids were identified and quantified. The main flavonoids found in the fresh tea leaves were epigallocatechin gallate (EGCG), epicatechin gallate (ECG) and epigallocatechin (EGC).
The major findings of the analysis of the
fresh tea leaves from the field are that there were lower levels of catechins gallates in the tea leaves harvested in the cooler months of July to September 2000 (EGCG, 92.94 mg/g; ECG, 33.41 mg/g; total catechin gallates, 132.61 mg/g), and higher levels in the tea leaves harvested during the warmer months of November 2000 to February 2001 (EGCG, 112.37 mg/g; ECG, 37.13 mg/g; total catechin gallates, 159.34 mg/g). For the catechin levels in the harvested tea samples, higher and constant levels were found in those harvested in the cooler months (EGC, 50.50 mg/g; total catechins 89.67 mg/g) and lower levels were found in those harvested in the warmer months (EGC, 44.86 mg/g; total catechins, 79.26 mg/g). This is probably due mainly to the more active biochemical synthesis of catechin gallates during the warmer months. On comparing the hand plucked samples with the mechanically harvested tea leaves, it was found that the levels of catechins and catechin gallates was lower in the
mechanically harvested leaves probably due to more mature leaves being in these samples than in the hand plucked ones.
The samples from the processing line were collected during three sessions of black tea processing in April, July, and October 2000, and January 2001. The in-line samples were collected at each of the main processing steps from the initial field green leaves to the final black tea. The samples were also packed in dry ice and delivered to the laboratory by overnight transport and stored in a freezer at -80 °C before analysis. The phenolic compounds in these in-line tea samples were extracted using methanol and aqueous methanol, and analysed using a HPLC with photodiode array detection. Catechins, catechin gallates and theaflavins were the main flavonoids quantified for the in-line samples.
Analysis of the results for the in-line tea samples shows that the main decreases in the individual
and total catechins and catechin gallates due to oxidation occurred at the early stages of the fermentation period. Correspondingly, formation of individual and the total theaflavins occurred at the early stages of the fermentation period, suggesting the individual theaflavins are oxidation products of the catechins, catechin gallates and other phenolic acids such as gallic acid. The only seasonal variation that can be explained is that higher levels of the catechin gallates in the fresh leaves in January 2001 corresponded with higher levels of the oxidation products, theaflavins, in the resulting black tea. However, other seasonal variations in the formation of theaflavins and reduction in the levels of the catechins and their gallates showed no regular patterns throughout the black tea processing. This could be due mainly to factory factors, such as the high processing capacity and the poor drying capacity and drying efficiency of the fermented tea leaves.
Therefore, it can be concluded from this tea study that tea leaves harvested in the warmer months, such as January, when processed, would contain the highest level of theaflavins, and produce a correspondingly higher quality black tea.
The flavonoids and other polyphenols in various unifloral Ausfralian honeys were analysed using a HPLC with photodiode array detection, and related to thefr floral origin. These honeys included various species-specific types of Eucalyptus honeys, and jelly bush (Leptospermum polygalifolium), tea tree (Melaleuca quinquenervia), crow ash (Guioa semiglauca) and heath (Banksia ericifolia) honeys. Luteolin, quercetin, tricetin and quercetin 3-methyl ether were found to be floral markers for Australian Eucalyptus honeys, while the individual phenolic acids such as ellagic acid and the
profile of phenolic acids may be used as potential floral markers. The main flavonoid found in jelly bush honey is myricetin. This honey is also rich in phenolic acids.
Overall, analysis of phenolic compounds in Australian grown and made tea is useful in producing quality Australian tea, particularly in optimising the fermentation stage. In addition, analysis of phenolic compounds in Australian floral honey is a promising chemical technique for honey authentication.