Simultaneous Determination of Caffeine and Phenolic Compounds in Tea and Coffee - Caffeine: Chemistry, Analysis, Function and Effects - page 133

Concentration (mg g 21 ) of phenolic acids, catechins, flavones,
flavonols and caffeine determined in different samples.

Table 8.1

Compound Green Tea White Tea Black Tea Instant Coffee

d n 0 t 2 n g | 0

Caffeine 26.01 27.99 17.82 13.92

Gallic acid 0.86 1.12 1.63 --

Protocatechuic acid -- -- 0.08 -

Chlorogenic acid 1.39 0.49 0.24 12.09

Caffeic acid -- -- -- 0.91

Total phenolic acids 2.25 1.61 1.95 13.00

(-) Gallocatechin 5.86 2.22 0.15 --

(-) Catechin 6.28 5.67 0.25 --

(-) Epigallocatechin 13.28 8.91 0.32 --

(-) Epicatechin 2.44 1.92 0.84 --

(-) Epigallocatechin gallate 6.12 5.83 -- --

(-) Epicatechin gallate 2.96 4.39 0.11 --

Total catechins 36.94 28.94 1.67 --

Myricetin-3-O-rhamnoside 0.50 0.37 0.34 --

Quercetin-3-O-rutinoside 3.52 2.49 1.71 --

Quercetin-3-O-glucopyranoside 1.10 0.48 0.38 --

Kaempferol-3-O-rutinoside 0.89 0.30 0.33 --

Kaempferol-3-O-glucoside 0.76 0.43 0.38 --

Total flavonols 6.77 4.07 3.14

This table gives an example of the relative distribution of main polyphenols and caffeine in tea and
coffee. Adapted from Rostagno et al 2011 with permission from Elsevier.

In addition to the technique, extraction efficiency is also a function of
process conditions. Several factors affect the concentration of the desired
components in the extract, such as solvent type, temperature, sample to solvent
ratio, contact time, and particle size. When determining the content of
compounds in a sample, an extraction method with optimized conditions
should be employed. A survey of extraction methods and process conditions
available for caffeine and polyphenol recovery from coffee and tea is presented
in Table 8.2.
Conventional methods that employ only heating and-or stirring can be used
to extract caffeine and phenolic compounds; however, the disadvantages are
the loss of polyphenols due to thermal degradation and the long extraction
time. To overcome these drawbacks, various novel extraction techniques have
been developed, such as UAE, microwave-assisted extraction (MAE), SFE and
others. These techniques, in most cases, are an efficient alternative to reduce
the process time, its environmental impact and its cost.
It has been reported that UAE is of higher efficiency than simple infusion at
lower temperature for the extraction of tea; it also presents better results
compared to stirring (Wang et al 2008). On the other hand, although UAE
with methanol is theoretically a more preferable method for polyphenol
recovery compared to hot water maceration with stirring, UAE appears to be
less efficient in the case of non-fermented teas (Nov´ kov´ et al 2010).