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Physicochemical Analysis of Cold Brew and Hot Brew Peaberry Coffee

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Peaberry coffee is the result of a natural mutation of coffee beans, and they make up only about 5–7% of coffee crops. A typical coffee cherry contains two seeds that are developed against each other, resulting in the distinctive half-rounded shape of coffee beans. However, failing to fertilize both ovules of one of the seeds or failure in endosperm development can cause only one of the seeds to develop, resulting in smaller, denser beans with a more domed shape. Peaberry coffees are said to be sweeter, lighter, and more flavorful since the peaberry beans receive all nutrients from the coffee cherry. Due to its exclusive nature, the chemical characteristic of peaberry coffee is not well understood. This study explores the acidities and antioxidant activity of peaberry coffee sourced from multiple regions. Total antioxidant capacity, total caffeoylquinic acid (CQA), total caffeine concentration, and pH levels were evaluated for peaberry coffee extracts prepared by cold and hot brewing methods. Little correlation between antioxidant activity and the concentrations of caffeine and CQA in peaberry beans was shown. Six methods were performed for the characterization of total antioxidant capacity including cyclic voltammetry, ABTS assay, and FRAP assay. Peaberry bean extract demonstrated higher average total caffeine concentrations compared to traditional coffee bean extracts.
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Citation: Schwarzmann, E.T.;
Washington, M.P.; Rao, N.Z.
Physicochemical Analysis of Cold
Brew and Hot Brew Peaberry Coffee.
Processes 2022,10, 1989. https://
doi.org/10.3390/pr10101989
Academic Editors: Grzegorz Bartosz
and Izabela Sadowska-Bartosz
Received: 16 August 2022
Accepted: 28 September 2022
Published: 2 October 2022
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processes
Article
Physicochemical Analysis of Cold Brew and Hot Brew
Peaberry Coffee
Evan T. Schwarzmann, Marlena P. Washington and Niny Z. Rao *
Department of Biological and Chemical Sciences, College of Life Sciences, Thomas Jefferson University,
Philadelphia, PA 19144, USA
*Correspondence: niny.rao@jefferson.edu
Abstract:
Peaberry coffee is the result of a natural mutation of coffee beans, and they make up only
about 5–7% of coffee crops. A typical coffee cherry contains two seeds that are developed against each
other, resulting in the distinctive half-rounded shape of coffee beans. However, failing to fertilize
both ovules of one of the seeds or failure in endosperm development can cause only one of the seeds
to develop, resulting in smaller, denser beans with a more domed shape. Peaberry coffees are said
to be sweeter, lighter, and more flavorful since the peaberry beans receive all nutrients from the
coffee cherry. Due to its exclusive nature, the chemical characteristic of peaberry coffee is not well
understood. This study explores the acidities and antioxidant activity of peaberry coffee sourced
from multiple regions. Total antioxidant capacity, total caffeoylquinic acid (CQA), total caffeine
concentration, and pH levels were evaluated for peaberry coffee extracts prepared by cold and hot
brewing methods. Little correlation between antioxidant activity and the concentrations of caffeine
and CQA in peaberry beans was shown. Six methods were performed for the characterization of
total antioxidant capacity including cyclic voltammetry, ABTS assay, and FRAP assay. Peaberry bean
extract demonstrated higher average total caffeine concentrations compared to traditional coffee
bean extracts.
Keywords: peaberry coffee; cold brew; acidity; antioxidants; electrochemistry; chemical analysis
1. Introduction
Coffee remains one of the largest global industries with 166.3 million 60 kg bags
consumed internationally for the 2020–2021 year [
1
]. Within the global industry, a specialty
coffee market continues to grow providing consumers with access to unique and rare coffee
beans [
2
]. Civet coffee beans are one such variety that is unique because they undergo
digestion by the civet cat and are a luxury export of Indonesia with a comparatively high
price per pound [
3
]. While some specialty coffee beans occupy a high price range, market
prices for average coffee beans are insufficient to sustain farming operations causing many
farms to operate at a loss financially per the Specialty Coffee Association’s Price Crisis
Response Initiative [
4
]. As a result, sustainability, both in specialty and regular coffee
production, remains a major focus of the global industry to ensure continued industry
growth as predicted. Due to industry growth, peaberry coffee beans, a bean type previously
seen as waste, has grown in popularity enabling regular farmers to sell “deformed” beans
as specialty coffee to allow for an increase in financial profit and stability.
Research around the peaberry coffee bean is relatively limited compared to general
coffee research. Availability is a major limiting factor as roughly 7% of harvested farm
crops are identified as peaberry beans [
5
,
6
]. Peaberry coffee beans result from the abortion
of an ovary by a coffee plant leading to the fertilization and development of only one
bean [
7
]. Furthermore, researchers haveidentified three factors: unfavorable environmental
conditions, incompatibility of parent species, and insufficient pollination, which result
in either failure to fertilize one of two ovaries or failure of an ovary to develop into an
Processes 2022,10, 1989. https://doi.org/10.3390/pr10101989 https://www.mdpi.com/journal/processes
Processes 2022,10, 1989 2 of 17
endosperm [
8
]. Peaberry is not a genetic mutation and thus cannot be selectively bred
by farmers for production or elimination. The primary difference between peaberry and
regular coffee beans is the shape and size of the beans with peaberries appearing smaller
and rounder compared to regular, flat-sided beans. Prior to the recent economic interest
in peaberry coffee, farmers would typically sort peaberries from regular coffee beans and
discard them. This was done to maintain even roasting in coffee bean batches since the
smaller peaberries roast more quickly. Techniques for the separation of peaberry beans by
features such as color and shape for an automated system are under development, while
they are currently sorted by hand [
9
,
10
]. Despite its recent popularity as a class of specialty
coffee in recent years, the physicochemical profile of peaberry coffee extracts has not been
fully characterized.
Coffee bean extract is the traditional product of coffee bean fruits which, through exten-
sive research, has been shown to positively impact health. Extracts contain approximately
one thousand types of biologically active molecules including caffeine and chlorogenic
acid derivatives which are principal compounds [
11
,
12
]. Other compounds present in the
extract include phenolic compounds, diterpenes, melanoidins, and trigonelline [
13
]. In
isolated studies, caffeine and chlorogenic acid have been shown to have antimicrobial and
anti-inflammatory activity, as well as protective effects against neurodegenerative and hep-
atic diseases [
14
,
15
]. Interestingly, chlorogenic acid positively correlates to anticarcinogenic,
anti-hypertensive, and anti-diabetic effects [
15
]. Antioxidant activity further contributes to
these beneficial effects by reducing the effects of oxidative stress through the removal of
free radicals from bodily systems [16].
A variety of colorimetric assays are frequently used for the determination of to-
tal antioxidant capacity (TAC) in food extract samples, including ABTS (2,2-azinobis
(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt), DPPH (2,2-diphenyl-1-
picrylhydrazy), FRAP (Ferric Ion Reducing Antioxidant Power), Folin–Ciocalteu Phenolic,
and Flavonoids Assays. Unfortunately, limitations to each assay prevent TAC to be accu-
rately reflected by an individual assay [
17
]. As a result, assays utilize different mechanisms
to quantify antioxidant concentrations, enabling a more complete identification. ABTS as-
says require the development of an ABTS radical cation through the oxidation of ABTS and
measure antioxidant ability to scavenge the radical cation [
18
]. Radical scavenging ability
is determined by quantifying the decolorization of solution from a control. Decolorization
assays beyond ABTS include the use of the stable radical DPPH. The scavenging ability of
antioxidants is determined by the hydrogen electron transfer of antioxidants to the nitrogen
radical of DPPH [
19
]. FRAP assays measure the reduction in a Fe(III)-TPTZ complex to a
Fe(II)-TPTZ complex [
20
]. This assay measures TAC by analyzing color generation by a
reducing agent (antioxidant) and comparing it to a known standard such as chlorogenic
acid. The Folin–Ciocalteu assay is a measurement of the reductive capacity of antioxidants
through the quantification of total polyphenols. This reduction/oxidation reaction gener-
ates color through the oxidation of phenols present reducing phosphotungstic acid and
phosphomolybdic acid to tungsten oxide and molybdenum oxide [
21
,
22
]. To determine
total flavonoid capacity, an aluminum chloride-based assay is used. In this assay, sodium
nitrite oxidizes the flavonoid to form an aluminum ion chelation before the complex is
treated with a reducing agent forming a radical [23,24].
Beyond the spectrophotometric assays, electrochemical techniques can also be utilized
to give insight into TAC. Cyclic voltammetry (CV) is an electrochemical technique used in
the analyses of electron transfer reactions in which an applied potential is “swept” through
the sample and the change in current is observed as the species undergoes a redox process.
This technique looks at the reduction and oxidation processes of a molecular species, of
which the gaining and losing of electrons can be determined. When looking at the data
obtained from this technique, one can determine any number of different outcomes, such as
the number of transferable electrons, the concentration of relevant species, and molecular
orbital energetics [
25
]. Beyond the spectrophotometric assays, electrochemical techniques
have garnered attention for their use in correlating and corroborating results of the other
Processes 2022,10, 1989 3 of 17
assays, especially regarding the focus of this paper, phenolic antioxidants [
26
30
]. It was
determined that looking at the oxidation potential allows for further understanding of
antioxidant concentration in samples, where a decrease in potential results in a higher
concentration. Using a technique such as CV, the determination of TAC within the food
and beverage industry has garnered much interest [
31
50
]. Through these studies, the
characterization of phenolic antioxidants was carried out.
The rich antioxidant content of peaberry coffee is not well-documented [
51
]. This
study aims to perform novel characterization of the physicochemical profile of peaberry
coffee from multiple geographic origins using both cold and hot brew methods. Selection
of brewing methods was based on general popularity and accessibility. The TAC of cold
and hot brew peaberry coffee extracts were assessed using a suite of spectrophotometric
assays, including ABTS radical cation decolorization assay, DPPH free radical decoloriza-
tion assay, FRAP assay, Folin–Ciocalteu assay for total phenolic content (TPC), and total
flavonoids content (TFC) assay. Cyclic voltammetry techniques were also employed to
further elucidate the TAC of cold and hot brew peaberry coffee extracts.
2. Materials and Methods
2.1. Materials
5-Caffeoylquinic acid (5-CQA, CAS: 327-97-9), Caffeine (CAS: 58-08-02), 2,2 -azinobis(3-
ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS, CAS: 30931-67-0), 6-hydroxy-
2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox, CAS: 53188-07-1), Potassium Persul-
fate (CAS: 7727-21-1), Sodium Acetate Trihydrate (CAS: 6131-90-4), Glacial Acetic Acid
(CAS: 64-19-7), Methanol (CAS: 67-56-1), Iron (II) Sulfate Heptahydrate (CAS: 7782-63-0),
2,4,6-Tris(2-pyridyl)-s-triazine (TPTZ, CAS: 3682-35-7), Folin–Ciocalteu Reagent (MDL:
MFCD00132625), Sodium Carbonate (CAS: 497-19-8), Caffeic Acid (CAS: 331-39-5), and
Standardized 0.1 M and 1 M Sodium Hydroxide (CAS: 1310-73-2) were purchased from
Sigma-Aldrich (Milwaukee, WI, USA). 2,2-diphenyl-1-picrylhydrazy (DPPH, CAS: 1898-
66-4), Iron (III) Chloride Hexahydrate (CAS: 10025-77-1), and 3,4,5-trihydroxybenzoic
acid (Gallic Acid, CAS: 149-91-7) were obtained from Alfa Aesar (Ward Hill, MA, USA).
Hydrochloric Acid (CAS: 7647-01-0), Sodium Nitrite (CAS: 7632-00-0), and Aluminium
Chloride Hexahydrate (CAS: 7784-13-6) were purchased from Thermo Scientific/Fischer
Chemical (Nazareth, PA, USA). HPLC-grade Rutin Hydrate was acquired from Tokyo
Chemical Industry (Tokyo, Japan). Britton-Robinson pH 4.10 buffer was manufactured by
the Ricca Chemical Company.
2.2. Coffee Bean Preparation
Unroasted Tanzania peaberry coffee beans were purchased from Golden Valley Coffee
Roasters located in West Chester, PA, USA. Unroasted peaberry coffee beans from Kenya,
Sumatra, and Papua New Guinea were purchased from Sweet Maria’s Home Coffee
Roasting Retailer. Green coffee beans samples, 250 g, were roasted until after the first
crack in a Hottop coffee roaster (Model No. KN-8828B-2K, HotTop, Hottop Coffee Roaster,
Cranston, RI, USA) using the manufacturer’s default temperature-time setting. Beans were
ejected from the roaster at a final temperature of 188
C for a medium roast. Roasts were
placed on baking sheets, covered, and allowed to rest in a room temperature environment
until the beans external temperature reached 20
C. The roasted beans were then frozen
for a minimum of 12 h at
19
C [
52
] before grinding while frozen using a Capresso
conical burr coffee grinder (Model No. 560.01, Capresso, Montvale, NJ, USA) at the highest
Medium coarseness setting as designated by the manufacturer. Three sieves were used
with mesh openings of 500
µ
m, 710
µ
m, and 1000
µ
m to separate and retain particles in
increments of <500
µ
m, 500–710
µ
m, and 710–1000
µ
m. Sieved grounds were stored at
approximately
18
C before brewing. Particle sizes ranging from 500
µ
m to 710
µ
m were
retained for this study [53].
Processes 2022,10, 1989 4 of 17
2.3. Coffee Bean Extract Preparation
Cold brew coffee was prepared by placing a sample of 10 g of coffee grounds with
100 mL deionized (DI) water at room temperature in a French press coffee maker for 24 h,
after which the coffee solution was obtained by depressing the plunger. Hot brew coffee
was prepared by pouring 100 mL DI water at 100
C over 10 g of coffee grounds in a
French press coffee maker. After 6 min, the coffee was obtained by depressing the plunger.
All brewed coffee was filtered using a 0.20
µ
m Acrodisc
®
Syringe Filter with a Universal
PTFE Membrane (Pall, New York, NY, USA) [
54
]. All coffee samples were stored at 4
C
until analysis. Three batches of coffee were brewed per brewing method per bean origin.
The extracts were then combined based on bean origin and brewing method before being
analyzed (n= 8).
2.4. pH and Total Titratable Acidity
Using a ThermoScientific OrionStar T910 titrator, 30 mL of each coffee brew was
analyzed under the same titration method following an initial pH reading using an Orion
Ross Sure-Flow pH electrode (Catalog #: 8172BNWP). Titrator was set for two endpoints,
pH = 6 and pH = 8, to record the volume of titrant required to reach each pH. The titrant
used was standardized 0.1 N NaOH. Three batches of coffee were brewed and analyzed
per brewing method per bean origin (n= 3).
2.5. Total Antioxidant Capacity Measurements
2.5.1. ABTS Assay
Methodology for ABTS
+
radical cation decolorization assay was previously described
by Rao et al. [
55
]. To prepare a stock solution, 7 mM ABTS and 2.45 mM potassium
persulfate solutions were combined in a 1:1 ratio and incubated for at least 16 h in a dark
room. A working solution was prepared by diluting the stock ABTS radical solution with
DI water to obtain an absorbance within the range of 0.8 to 0.9 at 734 nm. Dilution factor
in this experiment was roughly 500
µ
L of stock solution to 20 mL of DI water. A total of
5
µ
L of extract sample was added to 3000
µ
L of the working solution in a covered vial.
The resulting solution was mixed for 1 min and incubated for 6 min at room temperature.
The absorbance of the solution was then measured at 734 nm using a Thermo Scientific
Evolution 201 spectrophotometer. Trolox was used as a standard and results were expressed
in mmol of Trolox equivalence (TE) per liter of extract. Each extract was analyzed 6 times,
n= 6.
2.5.2. DPPH Assay
Methodology for DPPH radical scavenging activity assay was adapted from Odžakovi´c
et al. and Muzykievicz et al. [
56
,
57
]. In brief, a working solution was prepared by diluting
0.3 mM DPPH methanolic solution with methanol to obtain an absorbance 1.000
±
0.020
at 517 nm using a Thermo Scientific Evolution 201 spectrophotometer. A 5
µ
L aliquot
of extract was added to 2850
µ
L of the DPPH working solution. Solution was vortexed
for 1 min using a VWR Vortexer 2 before incubation for 30 min in a dark room at room
temperature. The absorbance of the solution was then measured at 517 nm. Trolox was
used as a standard, and results were expressed in mmol of Trolox equivalence (TE) per liter
of extract. Each extract was analyzed 6 times, n= 6.
2.5.3. Folin–Ciocalteu Assay (TPC)
Methodology for the Folin–Ciocalteu method for the determination of total phenolic
content (TPC) was adopted from Muzykiewicz et al. [
57
]. Then, 10% v/v Folin–Ciocalteu
reagent and 5 mM Na
2
CO
3
aqueous solutions were prepared and incubated for 1 h prior
to the assay. Next, 2700
µ
L of 5 mM Na
2
CO
3
, 150
µ
L of 10% Folin–Ciocalteu, and 15
µ
L
of extract were mixed and incubated in a dark room. After 30 min, the absorbance of the
solution was measured at 750 nm using UV-VIS spectroscopy. Gallic acid was used as
Processes 2022,10, 1989 5 of 17
standard and results were expressed in mg gallic acid equivalence (GAE) per liter of extract.
Each extract was analyzed 6 times, n= 6.
2.5.4. Ferric Ion Reducing Antioxidant Power (FRAP)
Methodology for a reducing capacity assay, ferric ion reducing antioxidant power
(FRAP) assay, was adapted from Benzie and Strain, and Muzykievicz et al. [
20
,
57
]. To
prepare a working solution, 1 part 10 mM TPTZ in 40 mM HCl, 1 part 20 mM iron (III)
chloride hexahydrate, and 10 parts 300 mM acetate buffer of pH 3.6 were combined. The
acetate buffer was prepared using 3.1 g sodium acetate trihydrate and 16 mL glacial acetic
acid into a 1 L volumetric flask and filled with DI water. In a wrapped vial, 3 mL of
working solution was mixed with a 100
µ
L sample (5
µ
L extract + 95
µ
L DI water). The
absorbance of the solution was measured at 593 nm after 15 min of incubation. Iron (II)
sulfate heptahydrate and ascorbic acid were used as standards with results expressed in
mg FeSO4per liter of extract. Each extract was analyzed 6 times, n= 6.
2.5.5. Total Flavonoid Capacity Assay
To assess total flavonoid content, the aluminum chloride method was adapted from
Saeed et al. [
58
]. Then, 150
µ
L of 0.5 M NaNO
2
, 3.4 mL of 30% methanol, 150
µ
L of 0.3 M
aluminum chloride hexahydrate, and 50
µ
L of coffee extract were mixed for one minute.
After 5 min, 1 mL of 1 N NaOH was added and mixed for one minute. Sample absorbance
was measured at 506 nm using UV-VIS spectroscopy. Rutin was used as a flavonoid
standard and results were expressed in mg rutin equivalents/g spent coffee extract. Each
extract was analyzed 6 times, n= 6.
2.5.6. Cyclic Voltammetry Analysis
A BASi Epsilon Eclipse Potentiostat was utilized for all cyclic voltammetry (CV) mea-
surements. A three-electrode system was set up consisting of a glassy carbon working
electrode, platinum wire counter electrode, and silver-silver chloride reference electrode.
The glassy carbon working electrode was polished with 0.05 micron alumina (BASi
PK-4
polishing kit), thoroughly cleaned of any residue, and dried before use. Glassware was
cleaned and oven-dried overnight before use. All scans were performed at a scan rate of
0.1 V/s with a potential window of
0.2 V to +1.1 V (based on scans of longer ranges
showing degradation of the solvent) at room temperature, unless for variable scan rate
measurements to determine reversibility in the case of the caffeic acid standard. Deionized
(DI) water was used in all aspects of CV analyses. Due to the chemical nature of the
antioxidants present in the coffee samples, pH considerations were accounted for whereby
all measurements were performed in buffered solutions acting as the supporting electrolyte
with a pH of 4.10 (Britton-Robinson Buffer: adjusted to a 0.5 M ionic strength with a com-
position of water, potassium chloride, phosphoric acid, acetic acid, boric acid, and sodium
hydroxide). A CV scan of the buffer supporting electrolyte alone under the conditions
and parameters to mimic the coffee samples was obtained and subtracted from all scans to
account for reactive species present in the buffer. To aid with the standardization of the
measurements, a stock solution (5 mg/L) of caffeic acid was prepared and measured via
CV at variable scan rates. A Levich plot was prepared to illustrate the reversible nature
of the caffeic acid standard solution before coffee samples were analyzed and produced
a goodness-of-fit of 0.99 which can be found in the Supporting Information [
25
]. Coffee
samples analyzed were made to obtain a final concentration of 50 mg/L and analyzed
under the same parameters as the caffeic acid standard.
2.6. HPLC Analysis
Methodology for the analysis of standard solutions and coffee extracts was adapted
from GL Sciences Technical Note No. 67 using an Agilent 1200 series high-performance
liquid chromatography (HPLC) system [
59
]. The HPLC system is fitted with a Supelco C-18,
5
µ
m column (15 cm
×
4.6 cm) (Supelco, Bellefonte, PA, USA), and a C-18 guard column at
Processes 2022,10, 1989 6 of 17
25
C with a mobile phase mixture of 80% mobile phase A and 20% mobile phase B (A: 95%
2.0 mM phosphoric acid and 5% methanol; B: 95% methanol and 5% 2.0 mM phosphoric
acid). The mobile phase flow rate was set at 1.0 mL/min with an injection volume of
10.0
µ
L. CQA isomers were detected using a diode array detector at 325 nm and 280 nm,
respectively. Concentrations of 5-CQA were quantified via standard calibration curves. The
retention time of 3-CQA and 4-CQA isomers was determined using standard solutions and
quantitation of these two isomers was accomplished using the area of the 5-CQA standard
combined with the respective molar extinction coefficients of the other two isomers as
reported previously [6062]. Each extract was analyzed 6 times, n= 6.
2.7. Statistical Analysis
Two-way ANOVA analysis with Tukey’s Honest Significant Difference (HSD) test was
performed using an R script by Wessa [
63
]. Differences between means were considered
significant at p< 0.05.
3. Results and Discussion
3.1. pH and Total Titratable Acidity
The pH and total titratable acidity (TTA) results are shown in Figure 1. The pH of all
samples analyzed ranged from 5.10 (cold brew Sumatra peaberry, and hot brew Papua New
Guinea peaberry) to 5.29 (cold brew Tanzania peaberry) (see Table S1). Cold brew Tanzania
was observed to have the lowest TTA value (2.26 mL of 0.1 N NaOH per 30 mL of coffee),
while cold brew Sumatra was observed to have the highest TTA value (2.87 mL of 0.1 N
NaOH per 30 mL of coffee) as shown in Figure 1. The pH of extracts from the present study
is comparable to previously reported values of extracts of regular coffee beans [
64
66
].
Although the pH of cold brew extracts was generally higher than that of the hot brew
extract, the differences were minimal and agree with previous studies [
64
67
]. The total
titratable acidity (TTA) of cold brew extracts was found to be lower than that of the hot
brew counterparts, in general, suggesting that additional acids or higher concentrations of
acids were found in hot brew extracts. This finding is in agreement with a previous study
by Rao and Fuller, in which they reported significant differences between hot and cold
brew coffee extracts using beans from various regions [64].
Processes 2022, 10, x FOR PEER REVIEW 6 of 17
of 10.0 µL. CQA isomers were detected using a diode array detector at 325 nm and 280
nm, respectively. Concentrations of 5-CQA were quantified via standard calibration
curves. The retention time of 3-CQA and 4-CQA isomers was determined using standard
solutions and quantitation of these two isomers was accomplished using the area of the 5-
CQA standard combined with the respective molar extinction coefficients of the other two
isomers as reported previously [6062]. Each extract was analyzed 6 times, n = 6.
2.7. Statistical Analysis
Two-way ANOVA analysis with Tukey’s Honest Significant Difference (HSD) test
was performed using an R script by Wessa [63]. Differences between means were consid-
ered significant at p < 0.05.
3. Results and Discussion
3.1. pH and Total Titratable Acidity
The pH and total titratable acidity (TTA) results are shown in Figure 1. The pH of all
samples analyzed ranged from 5.10 (cold brew Sumatra peaberry, and hot brew Papua
New Guinea peaberry) to 5.29 (cold brew Tanzania peaberry) (see Table S1). Cold brew
Tanzania was observed to have the lowest TTA value (2.26 mL of 0.1 N NaOH per 30 mL
of coffee), while cold brew Sumatra was observed to have the highest TTA value (2.87 mL
of 0.1 N NaOH per 30 mL of coffee) as shown in Figure 1. The pH of extracts from the
present study is comparable to previously reported values of extracts of regular coffee
beans [6466]. Although the pH of cold brew extracts was generally higher than that of
the hot brew extract, the differences were minimal and agree with previous studies [64
67]. The total titratable acidity (TTA) of cold brew extracts was found to be lower than that
of the hot brew counterparts, in general, suggesting that additional acids or higher con-
centrations of acids were found in hot brew extracts. This finding is in agreement with a
previous study by Rao and Fuller, in which they reported significant differences between
hot and cold brew coffee extracts using beans from various regions [64].
Figure 1. (a) pH and (b) total titratable acidity titrated to pH of 6.0 (TTA) of cold and hot brew
peaberry coffee samples from four different regions. Error bars represent standard deviation (SD).
Letters ad, denote significant differences as analyzed by two-way ANOVA and the TUKEY HDS
post-test. Samples without a common letter differ (p < 0.05).
Previous studies have attempted to better understand the acidity of coffee by at-
tempting to correlate pH measurements with other chemical and/or sensory metrics and
Figure 1.
(
a
) pH and (
b
) total titratable acidity titrated to pH of 6.0 (TTA) of cold and hot brew
peaberry coffee samples from four different regions. Error bars represent standard deviation (SD).
Letters a–d, denote significant differences as analyzed by two-way ANOVA and the TUKEY HDS
post-test. Samples without a common letter differ (p< 0.05).
Processes 2022,10, 1989 7 of 17
Previous studies have attempted to better understand the acidity of coffee by at-
tempting to correlate pH measurements with other chemical and/or sensory metrics and
have found that total titratable acidity (TTA) is a better indicator for coffee acidity than
pH [
64
,
68
74
]. As detailed by Rao and Fuller, pH values indirectly quantify the amount
of deprotonated acids in a sample at the time of analysis, while total titratable acidity
(TTA) measures both dissociated and non-dissociated acidic protons in a sample via a
neutralization reaction with a strong base [
64
]. As a result, pH values do not paint a
complete picture with regard to acids present in coffee extracts [
74
]. This work found
little correlation between pH and TTA for hot brew coffee (r =
0.46 for TTA titrated to
pH 6, r = 0.07 for TTA titrated to pH 8), and a strong correlation between pH and TTA
for cold brew coffee (r =
0.9 and
0.95 for TTA titrated to pH 6 and pH 8, respectively;
p< 0.05
). The lack of correlation between pH and TTA for hot brew is in agreement with
findings by
Gloess et al
. [
74
]. The strong correlation between pH and TTA in cold brew
extracts contradicts previous findings by Rao and Fuller, in which they found that pH of
both cold and hot brew correlated poorly with TTA [
64
]. To date, only one study attempted
to identify the acids present in peaberry coffee in organic solvent extracts [
75
]. The result
from the current study implies that the majority of acids present in cold brew extracts of
peaberry coffee exist in their deprotonated forms. Moreover, higher TTA values of hot brew
extracts indicated that additional non-deprotonated acids were extracted using hot brew
methods than cold brew methods, suggesting that the solubility of these acids is low at low
temperatures and can only be extracted more readily with high water temperature.
3.2. Total Caffeine and CQA Concentrations
The chlorogenic acid concentrations of both cold and hot brew extracts of the peaberry
coffee included the three major isomers of caffeoylquinic acid (CQA), namely, 5-CQA,
4-CQA, and 3-CQA. The total CQA concentration ranged from 1845 mg per liter of coffee to
2294 mg per liter of coffee (see Table S2). As shown in Figure 2, the Tanzania peaberry hot
brew extract was found to have the highest CQA concentration while Papua New Guinea
cold brew extract was found to have the lowest CQA concentration. Cordoba et al. reported
higher levels of 5-CQA and 4-CQA concentration in cold brew extracts of Columbian coffee
made from an immersion method compared to extracts made from the hot brew French
press method [
67
]. However, Rao et al. reported comparable CQA concentrations among
cold and hot brew Columbian coffee extracts [
55
]. Previous studies also reported that
CQA concentration of the cold brew extracts varied with bean origin [
64
,
76
]. The data
from this work indicates that the CQA concentrations of peaberry beans also vary with the
bean origin. Data reported in the current study is not indicative of a consistent correlation
between total CQA concentration and brewing methods in peaberry beans.
The caffeine concentration of cold and hot brew extract of the peaberry coffee ranged
from 1108 mg per liter of coffee to 1315 mg per liter of coffee (see Table S2). Kenya cold brew
extract was observed to have the highest caffeine concentration, while Tanzania cold brew
extract was found to have the lowest caffeine concentration (see Figure 2). In general, the
caffeine concentrations in the cold brew extracts of peaberry coffee were found to be com-
parable to those in the hot brew extracts, in agreement with recent studies
[55,66,67,7679]
.
Variation of caffeine content with bean origin has been reported previously [
80
84
]. Caf-
feine concentrations from previous studies of regular coffee beans using similar brewing
methods ranged from 960 mg/L [
55
] to 1250 mg/L [
85
] for cold brew extracts [
67
,
76
,
83
],
and 520 mg/L [
85
] to 1140 mg/L [
77
] for French press hot brew extracts [
55
,
67
,
83
]. Caffeine
concentrations in peaberry coffee reported in the current study are higher than previously
reported values, hinting at the possibility that peaberry coffee beans may have higher
caffeine content than regular beans.
Processes 2022,10, 1989 8 of 17
Processes 2022, 10, x FOR PEER REVIEW 7 of 17
have found that total titratable acidity (TTA) is a better indicator for coffee acidity than
pH [64,6874]. As detailed by Rao and Fuller, pH values indirectly quantify the amount
of deprotonated acids in a sample at the time of analysis, while total titratable acidity
(TTA) measures both dissociated and non-dissociated acidic protons in a sample via a
neutralization reaction with a strong base [64]. As a result, pH values do not paint a com-
plete picture with regard to acids present in coffee extracts [74]. This work found little
correlation between pH and TTA for hot brew coffee (r = 0.46 for TTA titrated to pH 6, r
= 0.07 for TTA titrated to pH 8), and a strong correlation between pH and TTA for cold
brew coffee (r = 0.9 and 0.95 for TTA titrated to pH 6 and pH 8, respectively; p < 0.05).
The lack of correlation between pH and TTA for hot brew is in agreement with findings
by Gloess et al. [74]. The strong correlation between pH and TTA in cold brew extracts
contradicts previous findings by Rao and Fuller, in which they found that pH of both cold
and hot brew correlated poorly with TTA [64]. To date, only one study attempted to iden-
tify the acids present in peaberry coffee in organic solvent extracts [75]. The result from
the current study implies that the majority of acids present in cold brew extracts of pea-
berry coffee exist in their deprotonated forms. Moreover, higher TTA values of hot brew
extracts indicated that additional non-deprotonated acids were extracted using hot brew
methods than cold brew methods, suggesting that the solubility of these acids is low at
low temperatures and can only be extracted more readily with high water temperature.
3.2. Total Caffeine and CQA Concentrations
The chlorogenic acid concentrations of both cold and hot brew extracts of the pea-
berry coffee included the three major isomers of caffeoylquinic acid (CQA), namely, 5-
CQA, 4-CQA, and 3-CQA. The total CQA concentration ranged from 1845 mg per liter of
coffee to 2294 mg per liter of coffee (see Table S2). As shown in Figure 2, the Tanzania
peaberry hot brew extract was found to have the highest CQA concentration while Papua
New Guinea cold brew extract was found to have the lowest CQA concentration. Cordoba
et al. reported higher levels of 5-CQA and 4-CQA concentration in cold brew extracts of
Columbian coffee made from an immersion method compared to extracts made from the
hot brew French press method [67]. However, Rao et al. reported comparable CQA con-
centrations among cold and hot brew Columbian coffee extracts [55]. Previous studies also
reported that CQA concentration of the cold brew extracts varied with bean origin [64,76].
The data from this work indicates that the CQA concentrations of peaberry beans also
vary with the bean origin. Data reported in the current study is not indicative of a con-
sistent correlation between total CQA concentration and brewing methods in peaberry
beans.
Figure 2.
(
a
) Total CQA concentration and (
b
) caffeine concentration of cold and hot brew extract
of peaberry coffee from four different regions. Error bars represent standard deviation (SD). Letters
a–e, denote significant differences as analyzed by two-way ANOVA and the TUKEY HDS post-test.
Samples without a common letter differ (p< 0.05).
3.3. Total Antioxidant Capacity (TAC)
The total antioxidant capabilities (TAC) of cold and hot extracts of peaberry coffee
from multiple origins are shown in Figure 3. The TAC of coffee has been studied exten-
sively using various methods [
86
,
87
]. However, there is no universal method to quantify
TAC accurately [
17
,
88
]. The free radical scavenging activities were assessed using ABTS
and DPPH assays. The extracts’ ability to reduce Fe
3+
ions was evaluated using FRAP
(Ferric Reducing Antioxidant Power) assay. Total phenolic content (TPC) was assessed
using the Folin-Ciocalteau assay. The basic mechanism of the Folin–Ciocalteu assay is an
oxidation/reduction reaction, and can, therefore, be considered a metric for antioxidant
activities. Flavonoids are a group of phenolic compounds with antioxidant activities [
89
,
90
].
The total flavonoid content (TFC) was assessed as an additional TAC indicator. In all
five assays, Papua New Guinea peaberry cold brew extract was found to have the lowest
TAC values, while Kenya peaberry hot brew extract was observed to have relatively high
TAC values. Direct comparison of TAC values among studies is somewhat difficult due
to a lack of standardized TAC testing methods [
17
]. The ABTS values from this study
are comparable to the ABTS values of cold brew extracts previously reported by Rao and
Fuller, in which the ABTS values for cold brew extract ranged from 13.36 mmol of Trolox
equivalence (TE)/L to 17.45 mmol TE/L [
64
], whereas ABTS values from this study ranged
from 15.39 mmol TE/L to 18.10 mmol TE/L (see Table S3). The DPPH values from the
current study are also higher than those previously reported by Milek et al. The values
from this study ranged from 15.39 mmol TE/L to 16.84 mmol TE/L (see Table S3), whereas
values reported by Milek et al. ranged from 10.12 mmol TE/L to 11.74 mmol TE/L [
91
]. It
is worth noting that Kenya coffee extracts exhibited high DPPH values in the current study,
similar to the finds from Milek et al. [91].
Processes 2022,10, 1989 9 of 17
Processes 2022, 10, x FOR PEER REVIEW 9 of 17
Figure 3. Total antioxidant capabilities (TAC) of cold and hot extracts of peaberry coffee from four
different regions assessed using (a) ABTS assay, (b) DPPH assay, (c) FRAP assay, (d) Folin-Ciocal-
teau assay for total phenolic content (TPC), and (e) total flavonoid content (TFC). Error bars repre-
sent standard deviation (SD). Letters ad, denote significant differences as analyzed by two-way
ANOVA and the TUKEY HDS post-test. Samples without a common letter differ (p < 0.05).
In general, results from the present study showed that the differences in TAC values
between cold brew and hot brew peaberry coffee extracts were relatively small and there
was no conclusive evidence to suggest that brewing temperature strongly impacted the
TAC values of peaberry coffee extracts (see Figure 3). Hot brew methods have been shown
to have higher radical scavenging activities than cold brew methods [6466,76]. However,
a study by Kang et al., showed that cold brew coffee extracted using a steeping method at
20 °C had higher ABTS values than the hot brew extracts studied [92]. While studies of
TPC extraction from other botanicals have demonstrated that the TPC values were sensi-
tive to extraction temperature [9396], the effect of brewing temperature on the phenolic
content of coffee extracts was somewhat disputable. While some studies reported a rela-
tively high concentration of phenolic compounds in hot brew extracts [53,76], other stud-
ies observed that cold brew methods were more effective at the extraction of phenolic
compounds [66,92]. Results from this work showed that TPC values were somewhat in-
sensitive to extraction temperature, in agreement with a previous study by Bilge, in which
the author noted that the TPC values for cold brew and French press coffee extracts were
similar [65]. Muzykiewicz-Szymańska et al., also noted that some cold brew extracts ex-
hibited higher radical scavenging activities and iron reducing power (FRAP) than their
hot brew counterparts and concluded that it might be difficult to fully assess how brewing
temperature affects the extraction of antioxidants from coffee [66].
Previous studies by Vignoli et al. reported significant correlations between TPC val-
ues and ABTS, DPPH, and FRAP measurements [97,98]. A study by Sánchez-Gonzálex et
al., also reported that TPC values correlated strongly with ABTS and FRAP values. Similar
correlations were observed from data collected from this work. The Pearson correlation
coefficients between TPC values and ABTS, DPPH, and FRAP were 0.82 (p < 0.05), 0.74 (p
Figure 3.
Total antioxidant capabilities (TAC) of cold and hot extracts of peaberry coffee from four
different regions assessed using (
a
) ABTS assay, (
b
) DPPH assay, (
c
) FRAP assay, (
d
) Folin-Ciocalteau
assay for total phenolic content (TPC), and (
e
) total flavonoid content (TFC). Error bars represent
standard deviation (SD). Letters a–d, denote significant differences as analyzed by two-way ANOVA
and the TUKEY HDS post-test. Samples without a common letter differ (p< 0.05).
In general, results from the present study showed that the differences in TAC values
between cold brew and hot brew peaberry coffee extracts were relatively small and there
was no conclusive evidence to suggest that brewing temperature strongly impacted the
TAC values of peaberry coffee extracts (see Figure 3). Hot brew methods have been
shown to have higher radical scavenging activities than cold brew methods [
64
66
,
76
].
However, a study by Kang et al., showed that cold brew coffee extracted using a steeping
method at 20
C had higher ABTS values than the hot brew extracts studied [
92
]. While
studies of TPC extraction from other botanicals have demonstrated that the TPC values
were sensitive to extraction temperature [
93
96
], the effect of brewing temperature on the
phenolic content of coffee extracts was somewhat disputable. While some studies reported
a relatively high concentration of phenolic compounds in hot brew extracts [
53
,
76
], other
studies observed that cold brew methods were more effective at the extraction of phenolic
compounds [
66
,
92
]. Results from this work showed that TPC values were somewhat
insensitive to extraction temperature, in agreement with a previous study by Bilge, in
which the author noted that the TPC values for cold brew and French press coffee extracts
were similar [
65
]. Muzykiewicz-Szyma ´nska et al., also noted that some cold brew extracts
exhibited higher radical scavenging activities and iron reducing power (FRAP) than their
hot brew counterparts and concluded that it might be difficult to fully assess how brewing
temperature affects the extraction of antioxidants from coffee [66].
Previous studies by Vignoli et al. reported significant correlations between TPC values
and ABTS, DPPH, and FRAP measurements [
97
,
98
]. A study by Sánchez-Gonzálex et al.,
also reported that TPC values correlated strongly with ABTS and FRAP values. Similar
correlations were observed from data collected from this work. The Pearson correlation
Processes 2022,10, 1989 10 of 17
coefficients between TPC values and ABTS, DPPH, and FRAP were 0.82 (p< 0.05), 0.74
(p< 0.05), and 0.97 (p< 0.05), respectively. The TPC values were determined by Folin-
Ciocalteau assay, the basic mechanism of which is an oxidation-reduction reaction. The
strong correlations between TPC values and other AA methods suggest that the phenolic
compounds are the major contributor to the antioxidant activities of peaberry coffee extracts
and are also involved in radical scavenging and exhibit iron-reducing power. Additionally,
TFC values also correlated with TPC (r = 0.87, p< 0.05) and FRAP (r = 0.80, p< 0.05). Since
TFC measures flavonoids, a class of phenolic compounds, a high correlation between TFC
and TPC was expected. The significant correlation between TFC and FRAP, in conjunction
with the lack of strong correlations between TFC and radical scavenging AA assays, implied
that the dominant antioxidant activity mechanism of flavonoids in peaberry coffee extract
was likely a redox reaction [17].
Coffee extracts with high caffeine content have been noted to have high antioxidant
activities [
97
100
]. Strong correlations between caffeine concentrations and TAC methods
were not observed in this study, however, suggesting that caffeine was not a major contribu-
tor to the AA of peaberry coffee extracts. Moreover, the CQA concentrations did not exhibit
strong correlations with any TAC methods. Rao and Fuller previously reported that 5-CQA
concentration positively correlated with ABTS values for cold brew coffee extracts [
64
].
No significant correlations were observed in this study between TAC methods and CQA
concentrations regardless of the brewing temperature. This suggested that at low extraction
temperatures, CQAs are not the chemical species that contribute to the antioxidant activities
of peaberry coffee extracts. There is an abundance of additional chemical species highly
soluble at low extraction temperature present in peaberry coffee. The results from current
work also suggest that peaberry coffee beans contain a variety of bioactive compounds
with a wide range of solubility.
The geographical origins of the coffee beans have been shown to affect the con-
centration of bioactive compounds [
51
,
53
,
64
66
,
84
,
101
]. Other factors, such as growing
conditions [
102
], agricultural practices [
103
,
104
], processing [
105
,
106
], storage [
107
], and
genetic varietals [108], may also impact the physicochemical profile of the coffee extract.
3.4. Cyclic Voltammetry
Cyclic voltammograms of cold and hot extracts of peaberry coffee from the four global
regions can be seen in Figure 4, with redox data seen in Table 1. The voltammograms
feature distinct reversible waves with an average redox potential (E
1/2
) of 0.407 and 0.406 V
vs. Ag/AgCl for cold and hot extracts, respectively. The reversible nature is due to the two-
electron redox process of key diphenolic antioxidants, such as caffeic and chlorogenic acid
to their quinone forms. These values are in good agreement with similar studies performed
by Yildirim et al., Kilmartin and Hsu, Ziyatdinova et al., Juárez-Gómez et al., Yardim,
Takahashi et al. 2020, Pilipczuk et al., and Oliveira-Neto et al. with coffee. Similar work on
phenolic antioxidants in different beverages of varying pH values found an increase in pH
by 1 will cause the potential to decrease by 0.035 V [
27
,
31
34
,
38
,
40
,
41
,
43
45
,
48
,
49
,
109
111
].
Despite the differences in pH within the different studies, the values presented here are
within the range of values reported elsewhere.
The average E
1/2
of 0.407 and 0.406 V vs. Ag/AgCl for cold and hot extracts, respec-
tively, are slightly higher than the E
1/2
value for the standard caffeic acid solution studied of
0.374 V vs. Ag/AgCl with a buffered solution. The difference can be attributed to a variety
of possibilities. One such possibility is the phenolic antioxidants within the coffee extracts
are undergoing a structural change during the CV scan from the presence of hydroxyl
groups on the aromatic ring to quinones. With these changes to multiple substances, the
stability of the quinone is called into question, which results in very slight differences in
potential, current, and reversibility owing to the slight shouldering within the traces seen
in Figure 4. Another possibility is the radical species formed during the redox processes of
the antioxidants can cause other reactions resulting in the shouldering seen as byproduct
contamination or even decomposition within the trace. Lastly, the change in potential
Processes 2022,10, 1989 11 of 17
between caffeic acid and the coffee extracts could be the result of particulates within the
coffee extracts of which the caffeic acid standard would not be assumed as a suspended
solution, which can cause changes in resistance during the scans.
Processes 2022, 10, x FOR PEER REVIEW 11 of 17
Figure 4. Cyclic voltammograms of cold and hot extracts of peaberry coffee from four (4) different
regions (a) Kenya, (b) Papua New Guinea, (c) Sumatra, and (d) Tanzania. Samples were prepared
in 50 mg/L solutions with pH 4.10 buffer acting as supporting electrolyte at a scan rate of 0.1 V/s.
Individual scans of each sample can be found in the Supporting Information.
Table 1. Redox values of cold and hot extracts of peaberry coffee from four (4) different regions.
Coffee Samples
Reduction Potential
(V)
Oxidation Potential
(V)
E1/2
(V)
Oxidation Current
(A)
Cold Brew
Kenya
0.424
0.391
0.408
−5.94 107
Papua New Guinea
0.426
0.391
0.409
−7.70 107
Sumatra
0.424
0.385
0.405
−7.42 107
Tanzania
0.427
0.385
0.406
−7.25 107
Hot Brew
Kenya
0.436
0.389
0.413
−8.28 107
Papua New Guinea
0.426
0.397
0.412
−7.78 107
Sumatra
0.420
0.385
0.403
−7.99 107
Tanzania
0.412
0.382
0.397
−7.85 107
The average E1/2 of 0.407 and 0.406 V vs. Ag/AgCl for cold and hot extracts, respec-
tively, are slightly higher than the E1/2 value for the standard caffeic acid solution studied
of 0.374 V vs. Ag/AgCl with a buffered solution. The difference can be attributed to a va-
riety of possibilities. One such possibility is the phenolic antioxidants within the coffee
extracts are undergoing a structural change during the CV scan from the presence of hy-
droxyl groups on the aromatic ring to quinones. With these changes to multiple sub-
stances, the stability of the quinone is called into question, which results in very slight
differences in potential, current, and reversibility owing to the slight shouldering within
the traces seen in Figure 4. Another possibility is the radical species formed during the
redox processes of the antioxidants can cause other reactions resulting in the shouldering
seen as byproduct contamination or even decomposition within the trace. Lastly, the
change in potential between caffeic acid and the coffee extracts could be the result of
Figure 4.
Cyclic voltammograms of cold and hot extracts of peaberry coffee from four (4) different
regions (
a
) Kenya, (
b
) Papua New Guinea, (
c
) Sumatra, and (
d
) Tanzania. Samples were prepared
in 50 mg/L solutions with pH 4.10 buffer acting as supporting electrolyte at a scan rate of 0.1 V/s.
Individual scans of each sample can be found in the Supporting Information.
Table 1. Redox values of cold and hot extracts of peaberry coffee from four (4) different regions.
Coffee
Samples
Reduction
Potential
(V)
Oxidation
Potential
(V)
E1/2
(V)
Reduction
Current
(A)
Oxidation
Current
(A)
Cold Brew
Kenya 0.424 0.391 0.408 9.71 ×107
5.94
×
10
7
Papua New
Guinea 0.426 0.391 0.409 1.06 ×106
7.70
×
10
7
Sumatra 0.424 0.385 0.405 9.56 ×107
7.42
×
10
7
Tanzania 0.427 0.385 0.406 1.09 ×106
7.25
×
10
7
Hot Brew
Kenya 0.436 0.389 0.413 1.24 ×106
8.28
×
10
7
Papua New
Guinea 0.426 0.397 0.412 8.95 ×107
7.78
×
10
7
Sumatra 0.420 0.385 0.403 1.06 ×106
7.99
×
10
7
Tanzania 0.412 0.382 0.397 1.00 ×106
7.85
×
10
7
The redox data gives a strong correlation to the data from the spectrophotometric
assays. As seen in Figure 3for the ABTS and DPPH assays, coffee extracts from the four
regions behaved similarly when looking at the anodic current values. The same pattern is
Processes 2022,10, 1989 12 of 17
seen where the higher anodic current corresponds to a higher TAC value, of which the same
trend is seen in the assays with Kenya being highest and Papua New Guinea being lowest.
This similarity is manifested in the CV data due to the structure of the phenolic antioxidants,
specifically caffeic and chlorogenic acids, where the stabilization of the quinone formed
during the redox process due to electron delocalization and the donation of hydrogen to act
as radical scavengers is seen [
34
,
112
]. When comparing brewing temperatures, there is no
conclusive evidence that temperature had an impact on the TAC, as the values presented
do not show measurable differences. This correlates to the results of the TAC assays
mentioned earlier.
4. Conclusions
Peaberry coffee has been gaining popularity in recent years. Originally considered a
defect, coffee producers have been marketing peaberry coffee as flavorful with a complex
aroma and sweeter taste. To date, the physicochemical profile and antioxidant activity of
peaberry coffee extracts have not been reported. Results from the current work demon-
strated peaberry coffee extracts contain higher levels of caffeine than regular coffee reported
in the literature. Comparisons of hot and cold brewing techniques demonstrated that cold
brew peaberry coffee extracts have comparable pH and generally lower titratable acidity
than their hot brew counterparts. However, the current work showed no significant differ-
ence in total antioxidant capacity between hot and cold brew extracts. The total phenolic
content (TPC) of peaberry coffee extracts was observed to have a strong correlation with
other total antioxidant capacities (TAC) assays, suggesting that the phenolic compounds
in peaberry extracts have different modes of antioxidant activity mechanism. Moreover,
the current work found that the TAC values of peaberry coffee extracts did not correlate
to either caffeine concentration or CQA concentration, indicating that neither compounds
were a major contributor to the antioxidant activities of peaberry coffee extract. While CV
data did show expected two-electron reversibility of the phenolic antioxidants present in
coffee, it did not show a significant difference in TAC between cold and hot brew peaberry
coffee extracts, as further noted by TAC assay data. CV studies also resulted in the cor-
roboration of ABTS and DPPH studies for TAC based on the different regions studied for
peaberry coffee origin with Kenya having the highest TAC and Papua New Guinea having
the lowest. In general, peaberry coffee is a plentiful source of antioxidants independent of
brewing style.
Supplementary Materials:
The following supporting information can be downloaded at: https://
www.mdpi.com/article/10.3390/pr10101989/s1, Table S1: Physicochemical characteristics of cold
and hot brew peaberry coffee samples from four regions; Table S2: 5-CQA, 4-CQA, 3-CQA, total
CQA, and caffeine concentration of cold and hot brew peaberry coffee samples from four regions;
Table S3: Antioxidant activities, total phenolic content (TPC), and total flavonoid content (TFC) of
cold and hot brew peaberry coffee samples from four regions.
Author Contributions:
Conceptualization, N.Z.R., E.T.S. and M.P.W.; data curation, E.T.S.; formal
analysis, N.Z.R., E.T.S. and M.P.W.; investigation, N.Z.R., E.T.S. and M.P.W.; methodology, E.T.S. and
M.P.W.; project administration, N.Z.R.; writing—original draft, N.Z.R., E.T.S. and M.P.W.; writing—
review and editing, N.Z.R., E.T.S. and M.P.W. All authors have read and agreed to the published
version of the manuscript.
Funding:
This work was supported by Thomas Jefferson University and in part by the Improving
Food Quality 2019-67018-29187/1018488 from the USDA National Institute of Food and Agriculture.
Data Availability Statement: Not applicable.
Acknowledgments:
The authors would like to thank our friends at Golden Valley Coffee Roasters
in West Chester, Pennsylvania for their constant support. The authors would also like to thank
Brian G. Yust for his insightful discussions and suggestions. NZR would like to thank Mark Shapiro
for catalyzing this work. Publication made possible in part by support from the Thomas Jefferson
University Open Access Fund.
Processes 2022,10, 1989 13 of 17
Conflicts of Interest: The authors declare no conflict of interest.
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