3.4. Determination of FOG in green tea, oolong tea and black tea
samples by UHPLC vs. HPLC
Based on the identifications of FOG compounds on the UHPLC
and HPLC method, we analyzed 3 green tea, 2 oolong tea samples
and 3 black tea samples. The total amounts of the FOG in these teas
were 2.32–5.67 g/kg dry weight, and there is no significant difference
for the total FOG content between green tea, oolong tea and
black tea (Table 2). The highest was one black tea sample KEBT
from Kenya, but one green tea sample SBXT from China had the
similar content, and one oolong tea sample FSOT from China had
a little less content. However, we could find that the lowest was
from one green tea sample LSYW from China, and one black tea
sample ASBT from India had a lower content. It might show that
the big difference of FOG content could be sourced from the
producing area, and could be affected from some related factors
like tea cultivars, soil, rainfall and local climate. The small difference
between 2 oolong tea samples of DAOT and FSOT from the
same area in Fujian, China, might show that processing could also
influence the FOG content in some way.
The proportion of the corresponding aglycones was also investigated.
Table 3 shows that there are much kaempferol glycosides
in green teas, more quercetin glycosides and myricetin glycosides
in oolong teas, while quercetin glycosides dominate in all 3 blacktea samples with more than half of the total aglycone content. The
content of all flavonol glycosides is shown in Table 4.
From the results, both black tea and oolong tea samples had the
highest content of quercetin types of FOG, and green tea samples
had the highest content of kaempferol types of FOG. Referring to
the classification of 6 tea classes in the world, both black tea and
oolong tea were mostly manufactured from the Large-leaved species
and with the process of fermentation, while green tea was
mostly manufactured from the Small-leaved species and without
the process of fermentation, tea cultivar and processing method
might be the uppermost factors for the FOG content in tea samples.
This should be further studied
3.4. Determination of FOG in green tea, oolong tea and black teasamples by UHPLC vs. HPLCBased on the identifications of FOG compounds on the UHPLCand HPLC method, we analyzed 3 green tea, 2 oolong tea samplesand 3 black tea samples. The total amounts of the FOG in these teaswere 2.32–5.67 g/kg dry weight, and there is no significant differencefor the total FOG content between green tea, oolong tea andblack tea (Table 2). The highest was one black tea sample KEBTfrom Kenya, but one green tea sample SBXT from China had thesimilar content, and one oolong tea sample FSOT from China hada little less content. However, we could find that the lowest wasfrom one green tea sample LSYW from China, and one black teasample ASBT from India had a lower content. It might show thatthe big difference of FOG content could be sourced from theproducing area, and could be affected from some related factorslike tea cultivars, soil, rainfall and local climate. The small differencebetween 2 oolong tea samples of DAOT and FSOT from thesame area in Fujian, China, might show that processing could alsoinfluence the FOG content in some way.The proportion of the corresponding aglycones was also investigated.Table 3 shows that there are much kaempferol glycosidesin green teas, more quercetin glycosides and myricetin glycosidesin oolong teas, while quercetin glycosides dominate in all 3 blacktea samples with more than half of the total aglycone content. Thecontent of all flavonol glycosides is shown in Table 4.From the results, both black tea and oolong tea samples had thehighest content of quercetin types of FOG, and green tea sampleshad the highest content of kaempferol types of FOG. Referring tothe classification of 6 tea classes in the world, both black tea andoolong tea were mostly manufactured from the Large-leaved speciesand with the process of fermentation, while green tea wasmostly manufactured from the Small-leaved species and withoutthe process of fermentation, tea cultivar and processing methodmight be the uppermost factors for the FOG content in tea samples.This should be further studied
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