3.1 levels of total tea polyphenols, flavonoids and theaflavins
The total phenol contens of the tea infusions measured using Folin-Ciocalteu's reagent are summarized in Fig. 1A. TPC is always significantly higher in cold teas compared to hot teas and this is particularly evident for some African teas. Consistently significant lower TPC levels among the cold infusions were found in the Anji Needle Mao Feng, Yhin Zhen Bai Hao and Bvumbwe Bsp teas. Amongst the hot tea infusions, the highest TPC level was observed in the Bai Mu Dan Chinese tea while the lowest was found in the White Salima Peony.
The results on the total flavonoid content reported in Fig. 1B are in total agreement with the trend in TPC content shown in Fig. 1A as expected,since flavonoids constitute the most abundant group of polyphenols compounds in tea leaves. No significant differences were observed amongst the hot teas, whilst amongst the cold teas, Yhin Zhen Bai Hao, Anji Needle Mao Feng and Bvumbwe Bsp have the lowest content of flavonoids.
In hot and cold infusions, total theaflavin content was also determined. Theaflavin content should be very low in white teas which are considered as being slightly oxidized and actually, all the tested infusions show values lower than 10 umol/l, expect for cold White salima peony and bvumbwe bsp. These results are in accordance with the color of these two teas. which are darker compared to all rest.
3.2 Individual phenolics and caffeine content
Phenolic compounds and caffeine content were analyzed in hot and cold tea infusions and are reported in table 1. An example of the HPLC chromatographic profiles of the studied hot and cold tea infusion from Xue Ya with identification of the detected compounds is reported in Fig. 2. All the measured compounds are present in higher quantities in cold teas with respect to the hot tested infusions. Furthermore,the levels of EGC are exceptionally high in cold White lung ching and anji Needle Mao Feng Chinese teas and in all the cold African teas high levels of epigallocatechin-3-gallate are also found. Instead low levels of EGCGare observed in the remaining cold Chinese teas and in all the hot teas. Epicatechin-3-gallate levels are similar in all teas expect in the White Lung Ching and in the cold white salima peony which have the highest levels of this flavanol. The levels of catechin are highest in White salima peony while Bai Mu Dan,Yhin Zhen Bai Hao and White Salima Peony cold infusions have the highest levels of gallic acid.
Total catechin content is reported in Fig.3 and in Table 1: these are significantly higher in White Lung Ching, in Anji Needle Mao Feng and in cold White Salima Peony. Furthermore, a correlation was observed when comparing the data reported in Table 1 for total catechin content with TPC , TPF and antioxidants assay data, which resulted significant in all cases.
The caffieine levels are similar in all the teas, with cold infusions having higher levels. Moreover these levels are particularly high in White Lung Ching tea.
3.3 Antioxidant activity
The antioxidant activity of the tea infusions was assessed using two independent assays, ABTS and inhibition of LDL oxidation. The results obtained from the ABTS assay reported in Fig. 4A show that all cold teas have significantly higher antioxidant activity compared to their respective hot infusions. The highest activities were observed for cold Bai Mu Dan , Xue Ya and white salima peony , while the antioxidant activity of the Bvumbwe Bsp tea is
signficantly lower than all the others. Furthermore, a good correlation was found between the results obtained with the ABTS assay and TPC abd TPF reported in Fig. 1A and B.
The lag times reported in Fig. 4B concerning the ability of the teas to suppress copper-induced LDL oxidant, are in accordance with the trend of antioxidant activity evaluated using the ABTS assay reported in Fig. 4A. The results also show that cold tea infusions have a greater suppressive effect against LDL oxidation compared to hot tea infusions which did not significantly prolong the lag time compared to the control without tea. The lowest activities were observed for Yhin Zhen Bai Hao and Bvumbwe Bsp teas.
3.4 Metal chelating activity
The chelating activity of the tea infusions measures how effective the compounds in them can complete with ferrozine for ferrous ions. Fig. 5 shows that the hot teas have the lowest chelating activity with no differences among each other, except for Yhin Zhen Bai Hao that is significantly lower than White Lung Ching,White salima peony and Bvumbwe Bsp. Amongst the cold teas,Bvum bsp shows a significantly higher chelating power compared to all the others.
3.1 levels of total tea polyphenols, flavonoids and theaflavins
The total phenol contens of the tea infusions measured using Folin-Ciocalteu's reagent are summarized in Fig. 1A. TPC is always significantly higher in cold teas compared to hot teas and this is particularly evident for some African teas. Consistently significant lower TPC levels among the cold infusions were found in the Anji Needle Mao Feng, Yhin Zhen Bai Hao and Bvumbwe Bsp teas. Amongst the hot tea infusions, the highest TPC level was observed in the Bai Mu Dan Chinese tea while the lowest was found in the White Salima Peony.
The results on the total flavonoid content reported in Fig. 1B are in total agreement with the trend in TPC content shown in Fig. 1A as expected,since flavonoids constitute the most abundant group of polyphenols compounds in tea leaves. No significant differences were observed amongst the hot teas, whilst amongst the cold teas, Yhin Zhen Bai Hao, Anji Needle Mao Feng and Bvumbwe Bsp have the lowest content of flavonoids.
In hot and cold infusions, total theaflavin content was also determined. Theaflavin content should be very low in white teas which are considered as being slightly oxidized and actually, all the tested infusions show values lower than 10 umol/l, expect for cold White salima peony and bvumbwe bsp. These results are in accordance with the color of these two teas. which are darker compared to all rest.
3.2 Individual phenolics and caffeine content
Phenolic compounds and caffeine content were analyzed in hot and cold tea infusions and are reported in table 1. An example of the HPLC chromatographic profiles of the studied hot and cold tea infusion from Xue Ya with identification of the detected compounds is reported in Fig. 2. All the measured compounds are present in higher quantities in cold teas with respect to the hot tested infusions. Furthermore,the levels of EGC are exceptionally high in cold White lung ching and anji Needle Mao Feng Chinese teas and in all the cold African teas high levels of epigallocatechin-3-gallate are also found. Instead low levels of EGCGare observed in the remaining cold Chinese teas and in all the hot teas. Epicatechin-3-gallate levels are similar in all teas expect in the White Lung Ching and in the cold white salima peony which have the highest levels of this flavanol. The levels of catechin are highest in White salima peony while Bai Mu Dan,Yhin Zhen Bai Hao and White Salima Peony cold infusions have the highest levels of gallic acid.
Total catechin content is reported in Fig.3 and in Table 1: these are significantly higher in White Lung Ching, in Anji Needle Mao Feng and in cold White Salima Peony. Furthermore, a correlation was observed when comparing the data reported in Table 1 for total catechin content with TPC , TPF and antioxidants assay data, which resulted significant in all cases.
The caffieine levels are similar in all the teas, with cold infusions having higher levels. Moreover these levels are particularly high in White Lung Ching tea.
3.3 Antioxidant activity
The antioxidant activity of the tea infusions was assessed using two independent assays, ABTS and inhibition of LDL oxidation. The results obtained from the ABTS assay reported in Fig. 4A show that all cold teas have significantly higher antioxidant activity compared to their respective hot infusions. The highest activities were observed for cold Bai Mu Dan , Xue Ya and white salima peony , while the antioxidant activity of the Bvumbwe Bsp tea is
signficantly lower than all the others. Furthermore, a good correlation was found between the results obtained with the ABTS assay and TPC abd TPF reported in Fig. 1A and B.
The lag times reported in Fig. 4B concerning the ability of the teas to suppress copper-induced LDL oxidant, are in accordance with the trend of antioxidant activity evaluated using the ABTS assay reported in Fig. 4A. The results also show that cold tea infusions have a greater suppressive effect against LDL oxidation compared to hot tea infusions which did not significantly prolong the lag time compared to the control without tea. The lowest activities were observed for Yhin Zhen Bai Hao and Bvumbwe Bsp teas.
3.4 Metal chelating activity
The chelating activity of the tea infusions measures how effective the compounds in them can complete with ferrozine for ferrous ions. Fig. 5 shows that the hot teas have the lowest chelating activity with no differences among each other, except for Yhin Zhen Bai Hao that is significantly lower than White Lung Ching,White salima peony and Bvumbwe Bsp. Amongst the cold teas,Bvum bsp shows a significantly higher chelating power compared to all the others.
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