1. †
To whom correspondence should be addressed.
E-mail: 1201058@rgu.ac.uk
Student copy
Determination of the polyphenols and caffeine contents recovered from spent
coffee grounds and their antioxidant capacities.
Gareth Fenn BSc
Department of Analytical Chemistry, School of Pharmacy and Life Sciences, Robert Gordon University, The Sir Ian
Wood Building, Garthdee Road, Aberdeen, AB10 7GJ, Scotland
Abstract
The feasibility of utilizing spent coffee grounds (SCGs) as a natural antioxidant resource was
determined. A solvent extraction was performed to extract the polyphenols and antioxidants
present in Costa® Robusta and Nandos Arabica SCG. The antioxidant capacities of the SCGs
were determined using the FRAP and DPPH assays. The Robusta mix displayed higher
scavenging and electron transfer abilities (EC50 = 20.70 +/- 1.49 µg/ml and a trolox equivalent
(TE) of 495.11 TE/100µg) compared to the Arabica sample (EC50 = 24.36 +/- 1.24µg/ml and
326.06 TE/100µg). The FC assay was used to determine the total polyphenol count (expressed
as Gallic acid equivalent GAE/100mg) for the Robusta and Arabica samples obtaining values of
7.40+/-1.68 GAE/100mg and 6.25+/-1.22 GAE/100mg. Finally, the caffeine and
neochlorogenic acid levels were determined by HPLC-DAD using an Agilent C18 5µm column
at 233nm for caffeine, (obtaining values of 70.01mg/ml and 67.18mg/ml respectively), and a
Phenomenex C18 3µm column at 325nm for Neochlorogenic acid obtaining values of 9.02mg/ml
and 8.91mg/ml. These values provide promising results for the feasibility of utilizing SCGs as a
source of natural antioxidants.
Keywords: Spent coffee grounds, Chlorogenic acid, polyphenols, Caffeine, DPPH, FRAP,
Folin–Ciocalteau.
Introduction
Thought to have originated in Ethiopia over
1000 years ago, coffee is now the world’s 2nd
most traded commodity1
with Coffea Arabica
and Coffea Canephora varieties (commonly
known as Robusta coffee) holding the most
economic value2
.
Spent Coffee Grounds (SCG).
The International coffee organisation’s (ICO)
world consumption report 20153
estimated
that in 2014 over 8.9 billion Kg of green
coffee bean (GCB) were consumed,
generating the equivalent waste in the form
of spent coffee grounds (SCG). This
generated waste is equivalent to 1.25Kg of
coffee per person in the world or 86
espressos per person per annum.
Due to the health benefits associated with
coffee, many studies have focused on the
extraction and identification of these
beneficial compounds. However, in recent
years the SCGs produced have become of
great interest due to the presence of these
beneficial compounds and the mass of SCG
produced.
Health benefits associated with coffee
consumption.
In the past decade there has been an increase
in reports focusing on the harmful effects of
coffee consumption. However, a thorough
review of these reports4
refutes most of the
studies based on uncontrolled variables and
irreproducible results.
In contrast to these challenged reports, there
have been numerous studies investigating the
health benefits related to the consumption of
coffee, more specifically the polyphenols
within the coffee. The antioxidants and
polyphenols in coffee are of great interest due
to the well documented health benefits of

2. 2
other plant polyphenols. Most of these
benefits relate to the scavenging capabilities
and metal chelating abilities of these
compounds5. These abilities have been linked
to the prevention of oxidative related stress
diseases and degenerative brain diseases such
as Alzheimer’s and Parkinson’s.
This paper will focus on two of the major
components of coffee and the benefits
associated with them, caffeine
(1,3,7-Trimethylpurine-2,6-dione) and a
group of polyphenols named Chlorogenic
acids (CGAs) more specifically
Neochlorogenic acid6
(5-CQA).
Health benefits associated with caffeine
The stimulant effects of caffeine commonly
known and thought to be linked to the
popularity of coffee as a beverage, this is
however only one of the positive benefits of
caffeine. In a review4
conducted by Higdon
and Frei, the authors concluded that in
moderate doses caffeine has been shown to
reduce the risk of cardiovascular diseases and
helped prevent type 2 diabetes as well as
Parkinson’s. Caffeine’s role as an adenosine
antagonist is thought to be the pathway
through which it helps prevent neurological
degeneration and diseases such as
Alzheimer’s, Huntington’s, Parkinson’s and
schizophrenia7
.
The metal chelating abilities of caffeine
become clearer upon reviewing the
relationship between caffeine and
osteoporosis. In high doses, caffeine was
found to reduce the calcium concentration
within the test subjects increasing the
subjects risk of developing osteoporosis.
Nevertheless, a review published in 20128
suggested that caffeine was not solely
responsible for the prevention of type 2
diabetes as decaffeinated coffee also reduced
the risk suggesting polyphenolic
involvement.
Health benefits associated with CGAs
CGAs have been of great scientific interest
due to their antioxidant and biological
properties. According to Ky et al.9
the three
main sub groups of CGAs are caffeoylquinic
acids (CQAs), feruloylquinic acids (FQA)
and dicaffeoylquinic acids (diCQAs) (Fig
1.1). with 5-CQA being the most abundant. It
was also noted that Robusta coffee contained
a higher percentage of these components on a
dry mass basis (%dmb) compared to Arabica.
Table 1.1- Comparison of CGA
components between species (%dmb)
Component Arabica
(%dmb)
Robusta
(%dmb)
CQA 3.26 7.66
diCQA 0.19 1.43
FQA 0.60 2.31
* figures adapted from Ky et al.9
Fig. 1.1 Chemical structures of: CQAs1, FQAs2 and
diCQAs3 in coffee10
Research suggests that the antioxidant and
the radical scavenging properties of the
CGAs found in coffee play a role in
preventing degenerate brain diseases11
.These
scavenging properties are split into the
following sub groups: metal chelating
scavengers, nitrous oxide (NO) scavengers
and reactive oxygen scavengers (ROX), each
group responsible for its unique preventative
abilities. Although essential for bodily
functions, reactive oxygen species (ROS)
such as peroxides can, if allowed to
accumulate, cause cell damage and disease
due to free radical attack. If allowed to
accumulate, these species can cause cancers
and degenerate neurological diseases12
.
Moreover, a review conducted by
Nichenametla et al.13
suggested that although
CGAs possess anti-carcinogenic properties,
these properties are highly dose dependant,
with too high a dose stimulating certain types
of tumour cells. Nevertheless, further studies
have shown caffeic acid, a minor CGA
component, to be a highly effective
chemosensitizer. Caffeic acid has been
shown to dramatically increase the efficiency

3. 3
of certain breast cancer treatments reducing
the IC50 of the treatment drug from 10.8µM
to just 0.83 µM13
. This reduction not only
reduces the adverse effects of the treatment
for the patient, it also reduces the overall cost
of the treatment.
It is clear from the above studies that the
polyphenols and antioxidants in coffee, are
beneficial to the health of the consumer.
Hence, if we consider that in procedure
associated with making coffee, as only water
is passed through the ground beans, it is
logical to assume, that the resulting SCGs
would contain some of these compounds.
This assumption suggesting that SCGs are a
possible source for antioxidant recovery.
Many studies14-18
have focused on optimising
extraction procedures in order to recover
these compounds from SCG. Experimental
work carried out by Nayak et al.19
showed
that ultrasonic assisted extraction (UAE)
increases the extraction efficiency of CGAs.
Hence, UAE was factored into the
experimental work of this paper.
Determination of the antioxidant and
polyphenolic activity of the SCG
To determine if SCGs are indeed a viable
source for antioxidant recovery, and to assess
the effect of the extraction method on the
antioxidants, the activity of the sample
extract must be investigated. As previously
mentioned, the antioxidants, caffeine and
polyphenols in coffee have specific beneficial
qualities, whether that be metal ion chelation
or NO scavenging. These abilities are
exploited in order to assess the health
benefits of the extract. The following assays
are known to be the most common methods
of assessing antioxidant and polyphenolic
activity in samples. This is not only due to
the simplicity of the colorimetric
determination, but as each of these assays
react via a different mechanism20-23
it allows
a more accurate determination of the overall
health benefits. The total polyphenolic count
(TPC) is determined by the Folin-Ciocalteu
(FC) assay while the antioxidant activity is
determined by the DPPH and FRAP assays.
DPPH assay (2,2-Diphenyl-1-picrylhydrazyl)
The DPPH assay measures the antioxidants
radical quenching ability. The purple DPPH*
radical reacts with the antioxidant (Ao)
converting it to the yellow DPPH-H22
. (Eq. 1).
The results are commonly expressed as the
EC50. This is the concentration required to
reduce the absorbance and hence the
concentration of DPPH* molecule by 50 %.
FRAP assay (Ferric Reducing Antioxidant
Power)
The FRAP assay determines the antioxidants
electron transfer ability by assessing its
ability to reduce the Fe(III) complex
(ferric-tripyridyltriazine) to the Fe(II)
complex (ferrous-tripyridyltriazine). This
reduction (Eq. 2) prompts the colour change
from pale yellow to blue. FRAP results are
expressed as an antioxidant equivalent per
100µg with Trolox being the favoured
standard.
FC assay (Folin-Ciocalteau)
The FC assay, like the FRAP assay, relies on
the antioxidants electron transfer abilities.
However, unlike the FRAP assay, the FC
mechanism requires the oxidation of the
yellow molybdenum (VI) complex to form
the blue molybdenum (V) complex (Eq. 3).
The FC assay is however non-specific,
allowing the Mo(VI) to react with
non-polyphenolic compounds23
, which in
turn would lead to a higher TPC. Again,
similar to the frap assay the FC results are
expressed as an antioxidant equivalent per
100mg with Gallic acid (GA) being the
favoured standard.
DPPH*(purple)+AH→DPPHH(yellow)+Ao (1)
Fe(III)(yellow)+Ao→Fe(II)(blue)+Ao (-) (2)
Mo(VI)(yellow)+Ao→Mo(V)(blue)+Ao(+) (3)
It was the purpose of this paper to determine
the antioxidant capacities of two different
species of coffee in order to assess the
feasibility of utilising SCG extract as a
natural source of antioxidants.
Experimental
Reagents and chemicals
The chemicals and reagents used were
obtained from three suppliers.
Acetonitrile (HPLC grade), Acetic Acid
(Analytical grade), Citric Acid monohydrate
(Analytical grade), Ethanol (HPLC grade),
HCl (Analytical grade), Methanol (HPLC
grade), Sodium acetate trihydrate (Analytical
grade) were all purchased from Fisher
scientific (Loughborough, UK). Caffeine
(99%) was purchased from Alfa Aesar
(Heysham, Lancaster). With

4. 4
DPPH(2,2-Diphenyl-1-picrylhydrazyl),
FC-reagent, Gallic acid (97%),
Iron(III)chloride hexahydrate (97%),
Neochlorogenic acid (>98% HPLC), sodium
carbonate (97%), TPTZ
[2,4,6-Tris(2-pyridyl)-s-triazine (98%)]
Trolox
[(±)-6-Hydroxy-2,5,7,8-tetramethylchromane
-2-carboxylic acid (97%)] all purchased from
Sigma Aldrich (Dorset,UK).
Preparation of SCGextracts
SCG samples were donated by Costa®
(Robusta mocha mix) and Nandos (Arabica).
These samples were reduced to a dry mass by
freezing the samples (-30o
C) then the ice was
removed by dry freezing (Edwards
Cryogenics, UK). The extraction process for
the SCGs was based on an optimised
method18
with the following modifications.
Extraction temp. 47°C, extraction time- 150
min, solvent/sample ratio- 48mL/g and a 58%
aqueous ethanol solvent. For each method
samples were prepared in triplicate. This first
set of extractions were aided by agitation
from magnetic stirring with the second set
aided by UAE.
A third set of samples were prepared in a
closed container conditions. This time, the
first set was agitated by magnetic stirring
(150 min) the second set by UAE (15 min).
After the extraction, the samples were
transferred into centrifuge tubes (50ml) and
centrifuged at 3000rpm for 5 min (IEC
Centra-4x centrifuge, Bedfordshire, UK). The
supernatants were transferred into
pre-weighed round bottom flasks then the
solvent removed by rotary evaporation
(Buchi, Switzerland). The samples were then
frozen and freeze dried to obtain a dry
extract.
It was from this resulting dry mass which
1mg/ml standards were created by dissolving
the samples in methanol. These were
prepared fresh daily.
Determination of caffeine and 5-CQA
HPLC data was obtained with a Shimadzu
LC-20AD Prominence Liquid
Chromatograph fitted with a Shimadzu
DGU-20A5 Prominence Degasser, Shimadzu
SIL-20A Prominence Autosampler and a
Shimadzu SPD-M20A Prominence DAD
(USA). The buffers were 10mM Citric acid
(Solvent A) and 50:50 Methanol:Acetonitrile
(Solvent B).
For the determination of caffeine, the
samples were dissolved in methanol and the
conditions were set as follows. The flow rate
was set at 1.5mL/min and solvent ratio of
70:30 (A:B). The column for the
determination of caffeine was an Agilent C18
5µm column (4.6x150mm) at 233nm.
For the determination of 5-CQA, the samples
were dissolved in the mobile phase in a ratio
of 85:15 and the conditions were set as
follows, flow rate of 0.5mL/min and solvent
ratio of 85:15 (A:B). The column for the
determination of 5-CQA was a Phenomenex
C18 3µm column (4.6x150mm) at 325nm.
Determination of the Total Polyphenol
content (TPC)
To determine the TPC the FC assay was
performed on a 96 well plate. GA standards
along with the samples were prepared in
methanol with serial dilutions of standard
prepared to create a calibration curve. This
allowed the TPC of each sample to be
expressed as the GAE. Samples and
standards were repeated in triplicate with
samples also being used at 1mg/ml and
0.5mg/ml
Briefly, the FC assay was performed as
follows, 270µL of dH2O was pipetted into the
outer wells while 25µL of sample of interest
along with 200µL of dH2O were pipetted into
the inner wells. To the inner wells 20µL of
FC reagent was added and the plate incubated
at room temperature (3 min). Finally, 25µL
of 20% sodium carbonate solution was added
(total volume for each well was 270µL) and
the plate incubated at 37°C (30 min) before
the absorbance was determined using a
BIO-RAD iMark plate reader (Japan).
Methanol was used as a control.
Antiradical activity of SCG extracts
The antiradical scavenging ability of the SCG
samples (EC50) were determined by the
DPPH assay. As with the FC assay, the
DPPH assay was performed on a 96 well
plate and values determined by a BIO-RAD
iMark plate reader (Japan). Serial dilutions of
each sample along with a serial dilution of
GA were carried out. A 50 µL sample of each
dilution was pipetted into the desired well
along with 100 µL of 0.1mM DPPH solution.
The outer wells contained 150 µL methanol
with the negative controls consisting of 50
µL methanol and 100 µL of 0.1mM DPPH
solution (total well volume 150 µL). The
plate was incubated in the dark at room
temperature (30 min) before the absorbance
was read at 490nm. The linear range of the
calibration was extracted and the IC50
calculated. Samples and standards were
repeated in triplicate.

5. 5
Reducing power of SCG
The FRAP values, expressed as trolox
equivalent (TE), were used to assess the
reducing power of the samples. The Frap
reagent was prepared by mixing 25 mL of
300mM acetate buffer at pH3.6 with 2.5 mL
of 10mM TPTZ dissolved in 40mM HCL and
2.5 mL of 20mM FeCl3.3H2O. Serial
dilutions of the trolox standard were prepared
and the wells of the 96 well plate set up as
follows. The outer wells contained 10µL of
dH2O and 190 µL FRAP reagent with the
inner wells containing 10 µL of the sample or
standard and 190 µL FRAP reagent (total
volume of well 200 µL).
Statistical analysis of results
F, T and Q tests were carried out on the raw
data to determine the validity and remove any
outliers. The data was analysed using Excel
Analysis ToolPak.
Results and Discussion
Effect of UAE on extraction efficiency of SCG
The effect of UAE on the antioxidant
capacities, as well as the caffeine and 5-CQA
concentrations, were investigated. It is clear
from the results obtained as seen in Table 1.2
(for samples 1-4) that prolonged exposure
(150 min) to UAE had a negative impact on
the antioxidants scavenging abilities as well
as the extraction of caffeine and 5-CQA.
However, in agreement with Nayak et al.19
if
we compare samples 5 and 3, we can see that
short term exposure (15 min) to ultrasonic
agitation increases the caffeine and 5-CQA
yields by around 50% (Refer to table 1.2).
If we compare samples 4 and 6, it is clear that
the open container extraction method had
very little impact on the extraction yields.
Taking into account that the closed container
differences are minimal, if we then compare
samples 3 (UAE 150 min) and 5 (UAE 15
min), the decrease in antioxidant capacity,
given that the TPCs are similar, can be
related to the length of time exposed to
ultrasonic waves. It is not clear how UAE
interferes with the antioxidant capacities nor
how it effects the extraction yield of caffeine
and CGA. However, the similar TPCs could
be explained by the fact that the oxidation of
the Mo(VI) complex is not very specific23
, it
could be suggested that UAE causes the
analytes to collide slightly altering their
chemical structure, reducing their scavenging
and electron transfer abilities but still
allowing the oxidation of the Mo(VI). This
could also explain the low caffeine and
5-CQA yield.
FC assay results
The FC assay was used to determine the TPC
of each of the samples. A gallic acid standard
calibration curve was created (500, 250, 100,
50 and 25µgml-1
respectively) (Fig. 3.1). The
resulting equation of the line was used to
determine the sample count expressed as the
GAE. The GAEs were then converted to the
GAE/100mg to allow for comparison (Eq. 4,
5). Due to the nature of this work the
calibration was determined to be valid based
on it adhering to the equation of a straight
line with acceptable y-intercept and R2
value.
(Refer to table 1.2).
𝑆𝑎𝑚𝑝𝑙𝑒 𝐺𝐴𝐸 =
𝑆𝑎𝑚𝑝𝑙𝑒 𝐴𝑏𝑠− 𝑐
1.8308
(𝟒)
𝐺𝐴𝐸
100𝑚𝑔
=
𝑋(𝐺𝐴𝐸)
[𝐶𝑜𝑛𝑐. 𝑜𝑓 𝑠𝑎𝑚𝑝𝑙𝑒]
(𝟓)
It can be clearly seen from the results that
both Nandos Arabica and Costa® Robusta
SCGs contain a small quantity of
polyphenolic compounds. These results are
lower than those cited in the literature9,15,18 24
.
However, as the extraction methods between
these papers are different, as well as the
species of SCGs investigated, no true
statistical comparison can be made. Again,
by referring to the samples aided by UAE
comparisons if we compare the sonicated
samples to the stirred samples little
difference is seen suggesting that the UAE
has no positive effect on the TPC.
Figure 3.1 TPC determination of SCG samples by
UV absorption using iMark plate reader at 750nm
(Gallic acid calibration).

6. 6
Table 1.2 Summary of results from SCG extract
* All errors expressed as SD
a-
Extraction aided by magnetic stirring
(150min).
b
- Extraction by UAE (150min).
c
-Closed container extraction by UAE
(15min).
d
-Closed container extraction aided by
magnetic stirring (150min)
DPPH scavenging abilities of SCG sample
extracts
The DPPH radical scavenging capabilities of
each of the six samples along with the GA
standard are depicted in Figure 3.2. The EC50
of 5-CQA was also determined (72.7 +/- 1.23
µg/ml) however this is not shown as, due to
its weak antioxidant capacity a further
standard point at (100µg/ml) was introduced.
The EC50 of each sample was determined by
extrapolation using the equation of the line
relating the linear range of the sample in
question (Eq. 6). GA was used as a standard
for the samples and 5-CQA
Figure 3.2 DPPH* scavenging capacities of SCG
samples and GA standard by UV absorption using
iMark plate reader at 490nm
However, it is clear that due to the gradual
slope decrease of the SCG samples, they
possess only weak scavengers hence a
weaker standard could be used to reduce any
error and increase the accuracy of the assay.
It should also be pointed out that the ƛmax for
DPPH* is 520 nm. However, the Bio-Rad
iMark plate reader used was unable to scan at
this range hence the closest wavelength
490nm was used instead. For this reason,
the results could not be compared directly to
literature values.
Figure 3.3 FRAP determination of SCG samples
by UV absorption using iMark plate reader at
595nm (Trolox calibration).
.
Sample Species
TPC
GAE/100mg
EC50 µg /ml TE/100µg caffeine (µg /ml) 5-CQA (µg /ml)
1 Arabica a
6.25+/-1.22 24.36 +/-1.24 362.06 67.18 8.91
2 Arabica b
6.49+/-1.22 32.68 +/-1.92 304.7 56.17 5.98
3 Robustab
5.39+/-1.00 33.81 +/-0.93 251.34 38.75 4.88
4 Robustaa
7.4+/-1.68 20.7 +/-1.49 495.11 70.01 9.02
5 Robustac
5.09+/-0.78 20.56 +/-0.42 350.07 78.52 9.64
6 Robustad
7.3+/-1.95 20.7 +/-0.45 388.86 64.61 8.89

7. 7
𝐸𝐶50 =
50 − 𝑐
𝑀
(6)
Upon evaluation of results, it is clear that
both samples 2 and 3 have a higher than
expected value yielding a 34% and 63%
increase when compared to samples 1 and 4
respectively. This again could potentially be
explained by the prolong exposure to the
ultrasonic waves although due to insufficient
data this cannot be confirmed. Nevertheless,
we can see from sample 5 that UAE used for
15 min has no apparent negative effects
suggesting that the negative effects are time
dependent.
FRAP capacities of SCGsample extract
To determine the TE values a Trolox
calibration curve was prepared (fig. 3.3).
Based on the nature of this work, as the
calibration followed the equation of a straight
line, with an acceptable y-intercept and R2
value the calibration was deemed to be valid.
To allow for comparison the TE values were
converted to TE/100µg. This was performed
in a similar fashion to Eq. 4-5. Sample 4
(Table 1.2) appeared to have a value of
almost twice that of its sonicated counterpart
(495.11 and 251.34 TE/100µg, respectively).
However, when compared to the closed
container sample 6 (388.86 TE/100µg) as we
already established the open container had a
limited effect, the large TE value suggests an
error.
It has been reported24
that a correlation
between the TPC and the trolox equivalents
exists, suggesting the electron transfer
abilities are directly proportionate to the
concentration of the active compounds. The
findings of this report are in agreement with
the literature. Similar to the DPPH results, it
is clear that the 150 min sonication had a
negative impact on the results whilst the
negative effect was limited in the 15 min
sample. This again provides further evidence
that the benefits of UAE are highly time
dependent.
HPLC capacities of SCGsample extract
The HPLC parameters were chosen from a
comparison of literature25-26
. A citric acid
organic phase was chosen with the 50:50
ACN:MeOH solvent B.
A caffeine calibration graph was created and
the resulting equation of the line used to
calculate the sample concentrations. However,
to determine and overcome interference
caused by the coffee browns, the method of
standard addition was applied. (Fig. 3.4).
Figure 3.4 Determination of Caffeine content of
SCG samples by HPLC-DAD at 233nm (1)
method of standard addition (2) method of
determination using caffeine calibration curve.
It is clear from the comparison (results
unpublished) of the two methods that the
coffee browns did create some interference.
These browns lead to the concentration
obtained using the calibration curve to be on
average 20ug/ml lower than the alternate
method.
Due to the nature of the CGAs and the high
degree of similarity between structures10
it
was decided that a 3µm column would help
resolve the CGAs more efficiently. As with
caffeine, standards were used to aid
optimization. To help reduce interference, the
samples were dissolved in 15% A: 75% B.
(fig. 3.5). Due to the low levels of 5-CQA
present and the high level of noise on the
baseline, manual integration was used to
create a base line for the 5-CQA.
Figure 3.5 Absorbance chromatogram of the
CGAs present in SCG by HPLC-DAD at
325nm.5-CQA (1) Rt=4.1 min
1

8. 8
Contrary to literature, which states that
5-CQA should be the most abundant analyte9
,
figure 3.5 suggests otherwise. However, upon
analysing the absorbance signature, it was
suggested that the peak could be a member of
the di-CQA or, more likely, the co-elution of
two different sub-group CGAs. However,
given the limited data obtained, and as no
standards were available for all subgroups the
larger peak could not be identified.
Again, in referring to the literature, the
results obtained are consistent with those of
Ky et al.9
showing that the Robusta SCGs
contain a higher concentration of caffeine
and 5-CQA than the Arabica SCG.
Although the caffeine and 5-CQA
concentrations are substantially lower than
those found in a fresh coffee beverage, this is
to be expected. The lower yields can be
related to the fact that the grounds have
already been through a filtration stage during
the preparation of the beverage.
When the results (table 1.2) are compared it
is clear that the UAE (150 min) dramatically
reduces the extraction yield. That being said,
the highest values for caffeine and 5-CQA
were obtained from UAE (15 min) yet this
was the sample with the lowest TPC.
Conclusions
It is clear from the results that agitation by
magnetic stirring provided a higher TPC as
well as a better quality yield displaying
higher antioxidant activity. However,
although a lower TPC, and TE value was
obtained by UAE (15 min), there was a
notable increase in the levels of caffeine and
5-CQA extracted. Although these extraction
yields are relatively low for both species,
(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.
Future work
As mentioned, the results of this paper
suggest that the benefits of UAE are highly
time dependent, given the slight variances
between the stirring for (150 min) and the
UAE (15 min). An optimized UAE method
would not only increase the yield of the
products it would reduce the extraction time
increasing efficiency. Hence future work
should be focused on developing and
optimizing an UAE method for the use on
SCG. Further work should also compare the
activities and concentrations of brewed
beverage against the associated SCG. This
would allow for a true comparison between
the coffee and the SCG.
Acknowledgments
This work was funded by the Robert Gordon
University, Aberdeen. Another vote of thanks
is extended to Costa® and Nandos Chicken
Land for the donation of the SCGs.
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66, 45-58
2. L. R. Cagliani, G. Pellegrino, G.
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2013,106,169-173.
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“World coffee consumption report”,
Last accessed 20/04/16, from
http://www.ico.org/prices/new-consu
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4. J. V. Higdon and B. Frei, Critical
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