1. Determination of the polyphenols and caffeine
contents recovered from spent coffee grounds and
their antioxidant capacities.
Gareth Fenn
Conclusion:
The feasibility of utilising SGCs as a natural antioxidant resource were assessed based upon the antioxidant properties of the extract.
Although agitation by magnetic stirring (150 min) yielded an extract with a higher TPC and greater antioxidant activities than UAE
(150 min), when these values are compared to UAE (15 min), although a lower TPC, obtained, there was a notable increase in the levels
of caffeine and 5-CQA extracted. Although these extraction yields are relatively low, (6-8% for caffeine and 0.8-0.9% for 5-CQA) if
applied to the annual SCG waste, 0.63 billion kg of caffeine and 71.92 million kg of 5-CQA are wasted each year. These figures along
with the antioxidant scavenging and electron transfer abilities provide substantial evidence that SCGs are indeed a feasible source of
natural antioxidants as well as caffeine.
References:
(1) International coffee organization, “World coffee consumption report”, Last accessed 5/4/16, http://www.ico.org/prices/new-consumption-table.pdf
(2) J. V. Higdon and B. Frei, Critical Reviews in Food Science and Nutrition, 2006, 46(2), 101-123
In 2014, the international coffee organisations (ICO) world
consumption report placed the consumed mass of green coffee
at around 8.9 billion Kg (1). The waste produced by this
consumption takes the form of spent coffee grounds (SCG).
SCG are known to contain caffeine, polyphenols and
antioxidants, like chlorogenic acids (CGAs). These chemicals
have a wide range of health benefits and have been linked to
cancer prevention and a reduced risk of developing
neurodegenerative diseases like Alzheimer's(2).
It was the purpose of this project to extract these compounds
using a solvent extraction, aided by UAE or magnetic stirring
(MS), in order to determine the activity of these antioxidants.
The antioxidant activities of these extracts were determined
via the FRAP, FC and DPPH assays. The levels of 5-CQA and
caffeine in the extracts were also determined by HPLC-DAD.
Background information Method
Figure 1.1 depicts the radical scavenging capacities of the
extracts as well as that of the gallic acid standard. It is clear
that although the samples possesses the ability to quench the
DPPH radical, the extent to which the do so is fairly weak..
Figure 1.1 DPPH* scavenging capacities of SCG samples and GA
standard by UV absorption using iMark plate reader at 490nm.
Results
Figure 1.2 shows a complete summary of results between the
3 experimental set-ups as seen in the method section. To
standardise the results a ratio between the UAE results and
the MS results have been used. Similar to the peak area ratio
with an internal standard this ratio comparison method helps
reduce any systematic errors seen between sets. This also
reduced any day to day variance caused by the sample sets
being prepared on different days.
Figure 1.2 Standardised ratio of UAE/MS showing a graphical
representation of all factors between all three data sets
It is clear from the results that a shorter exposure time to UAE (15
min) has a positive impact upon the extraction. This can be seen in
the antioxidant activity with the UAE (15 min) providing a lower
EC50 value ( better radical quenching ability) as well as a higher
Trolox equivalent. It can also be seen in the extraction yield of
caffeine and 5-CQA, however, a negative impact was seen on the
TPC. Another trend that can be seen is the benefits of Robusta coffee
over the more expensive Arabica coffee.
Preparation: The fresh samples were dry frozen before extraction
An optimised solvent extraction method was used to extract the
polyphenols, antioxidants and caffeine from the SCG samples.
3 different extractions were set.
6 samples were
aided by UAE for
150 min
(3 Arabica, 3
Robusta).
6 samples were
aided by MS for
150 min
(3 Arabica, 3
Robusta).
3 Robusta samples were
aided by UAE for 15 min
with another 3 aided by
MS for 150 min.
The solvent was evaporated and sample freeze dried with the
resulting dry mass used to determine the antioxidant activities by the
DPPH and FRAP assays with TPC determined by the FC assay (as
per lab S.O.P). A modified HPLC-DAD method was used to
determine the caffeine and 5-CQA levels.
All data was obtained in triplicate and F, T and Q tests performed to
determine the statistical validity of the results.