Simultaneous Determination of Caffeine and Phenolic Compounds in Tea and Coffee - Caffeine: Chemistry, Analysis, Function and Effects - page 139

chosen as the best processing time (Wang et al 2008). In another study, the
extraction of polyphenols and caffeine increased as MAE time increased,
reaching a maximum at 4 min, with a decrease in caffeine extraction for longer
extraction times (Pan et al 2003).
Altogether, it is a difficult task to ensure quantitative recoveries are being
achieved. The differences in sample matrices and the profile and concentration
of phytochemicals present can influence the ability of certain processes and
their parameters to efficiently extract all compounds of interest, which means
that the extraction method and the optimal conditions for a particular sample
cannot always be extrapolated to other cases.
One conservative approach when quantifying compounds in coffee and tea is
multiple consecutive extractions that can include different extraction methods
and-or solvents. Up to four steps of stirring were used to extract catechins and
caffeine from green tea, and their cumulative recovery increased with each
subsequent extraction step (Perva-Uzunalic et al 2006).

d n 0 t 2 n g | 0

8.4 Analysis of Alkaloids and Polyphenols in Tea and
Coffee Samples
The last step in the analytical determination of the sample components is
usually carried out by instrumental analysis. High performance liquid
chromatography (HPLC) is the most common technique because it allows
simultaneous determination of both compound classes, requires simple pre-
analysis sample preparation and is highly sensitive and reproducible.
However, the correct separation of compounds present in complex samples
depends on several factors. Briefly, separation is determined by the number of
target compounds, column dimensions and characteristics, temperature,
mobile phase flow rate and composition, among other factors. In general,
the separation of a large number of alkaloids and polyphenols can be achieved
in relatively short times when employing optimal chromatographic conditions.
Most mobile phases are composed of water and methanol or acetonitrile,
with small amounts of acid (Table 8.3). Both methanol and acetonitrile have
advantages and disadvantages from analytical, economic and environmental
points of view. In general, it is feasible to assume that separation of
polyphenols and alkaloids is possible using both types of solvents, but the
ability of each mobile phase to effectively separate all sample components will
depend on several factors, such as the number and type of target analytes and
the analysis conditions.
Separation is usually performed in gradient mode, although several isocratic
separations have been reported. Gradient elution is generally used when a
larger number of compounds are analyzed, as higher resolution and separation
efficiency are required. Table 8.3 presents a survey of HPLC methods for the
separation of caffeine and other compounds from coffee and tea. There are
several reports of complex separations of the major polyphenols and alkaloids