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Citation: Chang, X.; Ye, Y.; Pan, J.;
Lin, Z.; Qiu, J.; Peng, C.; Guo, X.; Lu,
Y. Comparative Analysis of
Phytochemical Profiles and
Antioxidant Activities between Sweet
and Sour Wampee (Clausena lansium)
Fruits. Foods 2022,11, 1230. https://
doi.org/10.3390/foods11091230
Academic Editors: Andrei Mocan
and Simone Carradori
Received: 24 March 2022
Accepted: 21 April 2022
Published: 25 April 2022
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foods
Article
Comparative Analysis of Phytochemical Profiles and
Antioxidant Activities between Sweet and Sour Wampee
(Clausena lansium) Fruits
Xiaoxiao Chang 1, Yutong Ye 2, Jianping Pan 1, Zhixiong Lin 1, Jishui Qiu 1, Cheng Peng 1, Xinbo Guo 2, *
and Yusheng Lu 1,*
1Institute of Fruit Tree Research, Guangdong Academy of Agricultural Sciences, Key Laboratory of South
Subtropical Fruit Biology and Genetic Resource Utilization, Ministry of Agriculture and Rural Affairs,
Guangdong Provincial Key Laboratory of Tropical and Subtropical Fruit Tree Research,
Guangzhou 510640, China; xxchang6@163.com (X.C.); panjianping_2003@163.com (J.P.);
lzxf200@126.com (Z.L.); rgxoii307@126.com (J.Q.); pengcheng2007@foxmail.com (C.P.)
2School of Food Science and Engineering, South China University of Technology, Guangzhou 510640, China;
yytaw95@mail.ubc.ca
*Correspondence: guoxinbo@scut.edu.cn (X.G.); luyusheng6702746@126.com (Y.L.)
Abstract:
As a local medicine and food, wampee fruit, with abundant bioactive compounds, is loved
by local residents in Southern China. Titratable acid (TA), total sugar (TS), and total phenolic and
flavonoid contents were detected, and phytochemical profiles and cellular antioxidant activities
were analyzed by the HPLC and CAA (cellular antioxidant activity) assay in five sweet wampee
varieties and five sour wampee varieties. Results showed that the average TS/TA ratio of sweet
wampee varieties was 29 times higher than sour wampee varieties, while TA content was 19 times
lower than sour wampee varieties. There were much lower levels of total phenolics, flavonoids,
and antioxidant activities in sweet wampee varieties than those in sour wampee varieties. Eight
phytochemicals were detected in sour wampee varieties, including syringin, rutin, benzoic acid,
2-methoxycinnamic acid, kaempferol, hesperetin, nobiletin, and tangeretin, while just four of them
were detected in sweet wampee varieties. Syringin was the only one that was detected in all the sour
wampee varieties and was not detected in all sweet wampee varieties. Correlation analysis showed
significant positive correlations between TA with phenolics, flavonoids, and total and cellular (PBS
wash) antioxidant activities, while there were significant negative correlations between TS/TA with
phenolic and cellular (no PBS wash) antioxidant activities. This suggested that the content of titratable
acid in wampee fruit might have some relationship with the contents of phenolics and flavonoids.
Sour wampee varieties should be paid much attention by breeders for their high phytochemical
contents and antioxidant activities for cultivating germplasms with high health care efficacy.
Keywords: wampee fruit; titratable acid; phenolics; flavonoids; antioxidant activities
1. Introduction
Clausena lansium (Lour.) Skeels, commonly known as wampee, is indigenous to and
commonly cultivated in Southern China—such as in the provinces of Guangdong, Fujian,
Hainan, Guangxi, and occasionally in Sri Lanka, Australia, India, America, and South
Asia [
1
]. Because wampee leaves, stems, and seeds contain functional compounds such as
clausenamide, carbazole alkaloids, and essential oils, they are used as traditional medicines
and food ingredients for cough [
2
], viral hepatitis [
3
], and dermatological and gastro-
intestinal diseases [
4
] due to the following properties: antioxidant [
5
], antidiabetic [
6
,
7
],
antimicrobial [
8
,
9
], anti-inflammatory [
10
], hepatoprotective [
11
], anticancer [
12
], and
nootropic and cerebral protective [
13
,
14
], etc. The wampee fruits have a pleasant flavor
and are consumed either fresh or served with meat dishes and in preserves. Although less
studies have focused on wampee fruits, they were reported containing high phytochemicals
Foods 2022,11, 1230. https://doi.org/10.3390/foods11091230 https://www.mdpi.com/journal/foods
Foods 2022,11, 1230 2 of 11
(including phenolics and flavonoids), and the extracts from fruits show high antioxidant,
anti-inflammation, and anticancer activities [10,15,16].
Epidemiological studies have highlighted that a phytochemical-rich diet protects
against chronic diseases [
17
]. Phytochemicals, such as phenolic acids, flavonoids, antho-
cyanidins, and tannins, are rich in plant foods [
18
], which possess remarkable antioxidant
and anticancer activities [
19
], and they can protect against chronic diseases such as car-
diovascular diseases, cancers, diabetes, and neurodegenerative diseases [
17
,
18
]. Phenolic
compounds in fruits have been reported as being positively related to antioxidant activity
and have potential health benefits [20,21]. Superfruits contain more bioactive compounds
and are consumed regionally; they are gaining popularity in the marketplace due to their
nutritional and therapeutic values, including acai, acerola, camu-camu, goji berry, and
jaboticaba, among others [
22
]. Wampee fruits are typically tropical and subtropical fruits
and are consumed in Southern Asia as traditional and folk fruits and medicine, which are
rich in polyphenols and exhibit high antioxidant activities, as reported [23].
The phenolics and antioxidant activities of different varieties of wampee fruit were
analyzed in recent years by our research team, and results showed that the sweet wampee
varieties CCTHP and THP, with high soluble solids content and little content of titratable
acid, contained less flavonoids and phenolics and had lower antioxidant activities than the
sour wampee varieties, YSDH and JFHP [
23
,
24
]. Further, we analyzed the phenolic and
flavonoid contents and antioxidant activities of wampee fruits of more than one hundred
and fifty different germplasms, and we found that sweet wampee varieties contained less
phenolics and flavonoids and showed lower antioxidant activities than those of the sour
wampee varieties. The hypothesis was that the titratable acid and/or sugar contents might
have some relationship with phytochemical compounds such as phenolics and flavonoids
in wampee fruits. In order to study this phenomenon, five sweet wampee varieties and
five sour wampee varieties were selected in this study, and their titratable acid, total sugar,
phenolic and flavonoid contents, and antioxidant activities were analyzed. This work will
provide an insight into the relationship between sugars, acids, and phenolic compounds in
wampee fruit.
2. Materials and Methods
2.1. Sample Preparation
The fruits of ten varieties of wampee (Clausena lansium (Lour.) Skeels) were collected
from the wampee resources nursery in the Institute of Fruit Tree Research, Guangdong
Academy of Agricultural Sciences, Guangzhou, China. The cultivars were five sweet
wampee varieties (
THP
: TianHuangPi;
ZFHP
: ZaoFengHuangPi;
CCTP
: CongChengTianPi;
LTDH
: LuTianDuHe;
TXTP
: TaXiaTianPi) and five sour wampee varieties
(
M3H
: Min3Hao;
JZP
: JiZiPi;
M4H
: Min4Hao;
TXSP
: TaXiaSuanPi;
JXHP
: JiXinHuangPi),
as shown in
Figure 1
. The fruits were harvested freshly in the fully matured stage. Fifty
fruits of each variety, without pests and diseases, were selected for handling. The seeds
were removed from the fruit, and the residues (pulp and peel) were stored at
−
20
◦
C
until analysis.
2.2. Determination of Titratable Acid and Total Sugar
Total sugar was determined by the anthrone method [
20
]. Total sugar was determined
from the standard curve prepared using glucose and was expressed as “g/100 g FW”.
Titratable acid was measured according to the AOAC 962.12 method (AOAC, 2012) with
an Automatic Potentiometric Titrator (TITRALAB TIM840, Loveland, Colorado, USA) and
was expressed as “g/100 g FW”.
Foods 2022,11, 1230 3 of 11
Foods 2022, 11, x FOR PEER REVIEW 3 of 12
THP
ZFHP
CCTP
LTDH
TXTP
M3H
JZP
M4H
TXSP
JXHP
Figure 1. The varieties of wampee fruits. THP: TianHuangPi; ZFHP: ZaoFengHuangPi; CCTP:
CongChengTianPi; LTDH: LuTianDuHe; TXTP: TaXiaTianPi; M3H: Min3Hao; JZP: JiZiPi; M4H:
Min4Hao; TXSP: TaXiaSuanPi; JXHP: JiXinHuangPi.
2.2. Determination of Titratable Acid and Total Sugar
Total sugar was determined by the anthrone method [20]. Total sugar was deter-
mined from the standard curve prepared using glucose and was expressed as “g/100 g
FW”. Titratable acid was measured according to the AOAC 962.12 method (AOAC, 2012)
with an Automatic Potentiometric Titrator (TITRALAB TIM840, Loveland, Colorado,
USA) and was expressed as “g/100 g FW”.
2.3. Phytochemical Extraction
Phytochemical contents of the wampee fruits were extracted by the following
method, as reported earlier [20,23]. Briefly, 50 g of wampee fruit was homogenized with
400 mL of 80% cold acetone for 3 min. The homogenate was extracted stationary over-
night, followed by filtration under reduced pressure. The filtrate was evaporated using a
rotary evaporator at 45 °C and redissolved by 70% methanol. All the extracts were stored
at −20 °C for the following analysis.
2.4. Determination of Total Phenolic and Flavonoid Content
The total phenolics of the wampee fruit extracts were determined by using the Folin-
Ciocalteu method [25], and gallic acid was used as the standard for calculation. Total phe-
nolic content was expressed as milligrams of gallic acid equivalents per 100 g of fresh
weight (mg GAE/100 g FW). The total flavonoids of wampee fruit extracts were tested by
the sodium borohydride/chloranil colorimetric method [26], and catechin was used as the
standard for calculation. Total flavonoid content was expressed as milligrams of catechin
equivalents per 100 g of fresh weight (mg CE/100 g FW). All the data were reported as
mean ± SD for three replicates.
Figure 1.
The varieties of wampee fruits. THP: TianHuangPi; ZFHP: ZaoFengHuangPi; CCTP:
CongChengTianPi; LTDH: LuTianDuHe; TXTP: TaXiaTianPi; M3H: Min3Hao; JZP: JiZiPi; M4H:
Min4Hao; TXSP: TaXiaSuanPi; JXHP: JiXinHuangPi.
2.3. Phytochemical Extraction
Phytochemical contents of the wampee fruits were extracted by the following method,
as reported earlier [
20
,
23
]. Briefly, 50 g of wampee fruit was homogenized with 400 mL of
80% cold acetone for 3 min. The homogenate was extracted stationary overnight, followed
by filtration under reduced pressure. The filtrate was evaporated using a rotary evaporator
at 45
◦
C and redissolved by 70% methanol. All the extracts were stored at
−
20
◦
C for the
following analysis.
2.4. Determination of Total Phenolic and Flavonoid Content
The total phenolics of the wampee fruit extracts were determined by using the Folin-
Ciocalteu method [
25
], and gallic acid was used as the standard for calculation. Total
phenolic content was expressed as milligrams of gallic acid equivalents per 100 g of fresh
weight (mg GAE/100 g FW). The total flavonoids of wampee fruit extracts were tested by
the sodium borohydride/chloranil colorimetric method [
26
], and catechin was used as the
standard for calculation. Total flavonoid content was expressed as milligrams of catechin
equivalents per 100 g of fresh weight (mg CE/100 g FW). All the data were reported as
mean ±SD for three replicates.
2.5. Determination of Phytochemical Profiles
Phytochemical profiles were determined on a Waters HPLC system (Waters Corp.,
Milford, MA, USA), consisting of a binary pump (model 1525), a micro degasser, an
autosampler (model 2707), a thermostatically-controlled column apartment (model 1500),
and a photodiode array detector (model 2998). Sample separation was employed with a
gradient elution program at the flow rate of 1 mL/min and the column temperature of
30
◦
C in a Waters HSS T3 C18 column (150 mm
×
4.6 mm, 5
µ
m). The chromatographic
data were recorded and processed by Waters software. The mobile phase consisted of 0.1%
trifluoroacetic acid solution (aqueous) (A) and acetonitrile (B) using a gradient elution of
10% B at 0–2 min, 10–25% B at 2–7 min, 25–30% B at 7–15 min, 30–58% B at 15–17 min,
58–100% B at 17–18 min, 100% B at 18–19 min, and 100–10% B at 19–20 min. The flow rate
of the mobile phase was kept at 1 mL/min. The UV absorbance at 280 nm and 370 nm was
Foods 2022,11, 1230 4 of 11
monitored for phenolic acids and flavonoids, respectively. Chromatographic peaks were
identified by comparing the retention times in specific UV spectra with those of authentic
standards. Data were reported as mean ±SD (n= 3).
2.6. Determination of Antioxidant Activities
The total antioxidant activity of samples was determined using the oxygen radical
absorbance capacity (ORAC) assay [
27
]. Fluorescein disodium salt was used as the flu-
orescence probe, and 2,2
0
-azobis (2-amidinopropane) dihydrochloride (ABAP) was used
as the free radical donor in this assay. The total antioxidant activity value was calculated
by standard Trolox, and the data were expressed as mean
±
SD millimole of the Trolox
equivalents (TE) per 100 g in fresh weight (mmol TE/100 g FW) for three replicates.
The cellular antioxidant activity (CAA) assay was applied in this study to deter-
mine the cellular antioxidant ability of the wampee fruit samples [
20
,
28
]. Human live
cancer cell line HepG2 (ATCC HB-8065) was used as the cellular model in this assay;
quercetin was used as the standard to calculate the cellular antioxidant activity value, while
2
0
,7
0
-Dichlorofluorescin diacetate (DCFH-DA) was used as the fluorescence probe. ABAP
was used as the free radical donor. PBS wash and no PBS wash treatments were used in
this assay. Fluorescence intensity was measured at the excitation of 485 nm and emission of
535 nm for a dynamic fluorescein intensity analysis by the Multi-mode microplate reader
(Molecular Devices, Sunnyvale, CA, USA). CAA value was calculated from the integrated
area under the fluorescence versus time curve, and the results were expressed as micro-
mole of quercetin equivalents (QE) per 100 g in fresh weight (
µ
mol QE/100 g FW) for
three replicates.
2.7. Statistical Analysis
Statistical analyses were performed using SigmaPlot software 12.3 (Systat Software,
Inc., Chicago, IL, USA). The significance of relationships was calculated by the multivariate
method. Data were analyzed among groups using one-way analysis of variance (ANOVA)
and Duncan’s multiple comparison post-test using SPSS software 18.0 (SPSS Inc., Chicago,
IL, USA). P-values less than 0.05 were regarded as statistically significant. All data were
reported as mean ±SD of triplicate analyses.
3. Results
3.1. Titratable Acid and Total Sugar Contents in Sweet and Sour Wampee Fruits
Five sweet wampee (THP, ZFHP, CCTP, LTDH, and TXTP) and five sour wampee
varieties (M3H, JZP, M4H, TXSP, and JXHP) were selected for analysis. According to
Table 1, for the five sweet wampee varieties, the titratable acid contents were all below
0.100 g/100 g FW
, and the total sugar contents were all above 10.00 g/100 g FW; meanwhile,
the TS/TA ratios were all higher than 200, as compared to sour wampee samples. The
variety of ZFHP had the lowest titratable acid content of 0.020
±
0.002 g/100 g FW and
the highest TS/TA ratio up to 817. For the five sour wampee varieties, the titratable
acid contents were all above 0.700 g/100 g FW, and total sugar contents were between
8.00 g/100 g FW
and 13.00 g/100 g FW; meanwhile, the TS/TA ratios were all lower than
20. JXHP had the lowest total sugar content of 8.810
±
0.490 g/100 g FW, while M4H had
the highest titratable acid content of 1.220
±
0.030 g/100 g FW and the lowest TS/TA ratio
of 9.94 among all the wampee samples.
The average titratable acid content, total sugar content, and TS/TA ratio of five sweet
wampees were 0.045 g/100 g FW, 13.93 g/100 g FW, and 395.9, respectively, while those of
the five sour wampees were 0.895 g/100 g FW, 11.25 g/100 g FW, and 13.07, respectively.
The results showed that the average titratable acid content of the sour wampee samples
was 19 times higher than those of the sweet wampee samples. On the contrary, the average
TS/TA ratio of the sweet wampee samples was 29 times higher than those of the sour
wampee samples. However, the average total sugar content between sweet and sour
wampee fruits did not show major difference, as did that of titratable acid and TS/TA ratio.
Foods 2022,11, 1230 5 of 11
Table 1. Titratable acid and total sugar contents of sweet and sour wampee varieties.
Variety Titratable Acid (TA)
(g/100 g FW)
Total Sugar (TS)
(g/100 g FW) TS/TA
Sweet
wampee
THP 0.047 ±0.002 fg 10.42 ±0.38 ef 222.0 ±14.1 c
ZFHP 0.020 ±0.002 g 15.99 ±0.20 b 817.1 ±75.7 a
CCTP 0.027 ±0.005 g 11.65 ±0.67 de 438.6 ±109.4 b
LTDH 0.049 ±0.001 fg 13.90 ±0.68 c 283.8 ±6.4 c
TXTP 0.081 ±0.003 f 17.71 ±0.73 a 218.1 ±15.9 c
Sour
wampee
M3H 0.927 ±0.010 b 10.16 ±1.71 f 10.97 ±1.89 d
JZP 0.719 ±0.060 e 12.84 ±0.39 cd 17.92 ±1.17 d
M4H 1.220 ±0.030 a 12.12 ±0.22 d 9.940 ±0.150 d
TXSP 0.770 ±0.010 d 12.33 ±0.87 d 16.01 ±1.31 d
JXHP 0.839 ±0.020 c 8.810 ±0.490 g 10.50 ±0.35 d
Values with no letter in common in each column are significantly different (p< 0.05).
3.2. Total Phenolic Content in Sweet and Sour Wampee Fruits
The total phenolic content of ten different wampee varieties varied greatly from
49.25
±
0.08 mg GAE/100 g FW (THP) to 829.1
±
1.6 mg GAE/100 g FW (JXHP), according
to Figure 2. The total phenolic contents of five sweet wampee varieties were all under
90.0 mg GAE/100 g FW, and the average content was 73.80 mg GAE/100 g FW. The lowest
one was THP, which showed significant differences (p< 0.05) between the other four sweet
wampee varieties. However, the total phenolic contents of five sour wampee varieties
were all above 300.0 mg GAE/100 g FW, and there were significant differences between
each other. The average total phenolic content of five sour wampee fruits was 521.7 mg
GAE/100 g FW, which was six times higher than those of sweet wampee fruits. The results
showed that the total phenolic contents in sour wampee fruits were obviously higher than
sweet wampee fruits, which was a similar variation to the titratable acid contents in sour
and sweet wampee fruits.
Foods 2022, 11, x FOR PEER REVIEW 6 of 12
Figure 2. Total phenolic contents of five sweet and five sour wampee varieties. Bars with no letters
in common are significantly different (p < 0.05).
3.3. Total Flavonoid Contents in Sweet and Sour Wampee Fruits
According to Figure 3, THP contained the lowest value of total flavonoid content
(54.41 ± 1.41 mg CE/100 g FW) among the ten different varieties, while JXHP had the high-
est value of 909.9 ± 177.9 mg CE/100 g FW, which was 16 times higher than that of THP.
The total flavonoid contents of the five sweet wampee varieties were all lower than 150.0
mg CE/100 g FW, and there was no significant difference (p < 0.05) between each other.
The average total flavonoid value of the five sweet wampee fruits was 99.82 mg CE/100 g
FW. For the five sour wampee varieties, the total flavonoid contents showed major differ-
ences, and they could be classified into three levels. The low level was M3H with 281.3 ±
17.8 mg CE/100 g FW, and the medium levels were JZP, M4H, and TXSP, with the values
of 392.5 ± 22.40 mg CE/100 g FW, 387.2 ± 22.5 mg CE/100 g FW, and 433.7 ± 13.4 mg CE/100
g FW, respectively. In addition, JXHP had the highest flavonoid content, which was three
times higher than that of M3H. The average total flavonoid content of the five sour wam-
pee varieties was 480.9 mg CE/100 g FW, which was four times higher than those of the
sweet wampee varieties.
Figure 3. Total flavonoid contents of five sweet and five sour wampee varieties. Bars with no letters
in common are significantly different (p < 0.05).
Figure 2.
Total phenolic contents of five sweet and five sour wampee varieties. Bars with no letters in
common are significantly different (p< 0.05).
3.3. Total Flavonoid Contents in Sweet and Sour Wampee Fruits
According to Figure 3, THP contained the lowest value of total flavonoid content
(54.41
±
1.41 mg CE/100 g FW) among the ten different varieties, while JXHP had the
highest value of 909.9
±
177.9 mg CE/100 g FW, which was 16 times higher than that of
THP. The total flavonoid contents of the five sweet wampee varieties were all lower than
150.0 mg CE/100 g FW, and there was no significant difference (p< 0.05) between each other.
The average total flavonoid value of the five sweet wampee fruits was
99.82 mg CE/100 g FW
.
Foods 2022,11, 1230 6 of 11
For the five sour wampee varieties, the total flavonoid contents showed major differ-
ences, and they could be classified into three levels. The low level was M3H with
281.3 ±17.8 mg CE/100 g FW
, and the medium levels were JZP, M4H, and TXSP, with the
values of
392.5 ±22.40 mg
CE/100 g FW, 387.2
±
22.5 mg CE/100 g FW, and
433.7 ±13.4 mg
CE/100 g FW, respectively. In addition, JXHP had the highest flavonoid content, which
was three times higher than that of M3H. The average total flavonoid content of the five
sour wampee varieties was 480.9 mg CE/100 g FW, which was four times higher than those
of the sweet wampee varieties.
Foods 2022, 11, x FOR PEER REVIEW 6 of 12
Figure 2. Total phenolic contents of five sweet and five sour wampee varieties. Bars with no letters
in common are significantly different (p < 0.05).
3.3. Total Flavonoid Contents in Sweet and Sour Wampee Fruits
According to Figure 3, THP contained the lowest value of total flavonoid content
(54.41 ± 1.41 mg CE/100 g FW) among the ten different varieties, while JXHP had the high-
est value of 909.9 ± 177.9 mg CE/100 g FW, which was 16 times higher than that of THP.
The total flavonoid contents of the five sweet wampee varieties were all lower than 150.0
mg CE/100 g FW, and there was no significant difference (p < 0.05) between each other.
The average total flavonoid value of the five sweet wampee fruits was 99.82 mg CE/100 g
FW. For the five sour wampee varieties, the total flavonoid contents showed major differ-
ences, and they could be classified into three levels. The low level was M3H with 281.3 ±
17.8 mg CE/100 g FW, and the medium levels were JZP, M4H, and TXSP, with the values
of 392.5 ± 22.40 mg CE/100 g FW, 387.2 ± 22.5 mg CE/100 g FW, and 433.7 ± 13.4 mg CE/100
g FW, respectively. In addition, JXHP had the highest flavonoid content, which was three
times higher than that of M3H. The average total flavonoid content of the five sour wam-
pee varieties was 480.9 mg CE/100 g FW, which was four times higher than those of the
sweet wampee varieties.
Figure 3. Total flavonoid contents of five sweet and five sour wampee varieties. Bars with no letters
in common are significantly different (p < 0.05).
Figure 3.
Total flavonoid contents of five sweet and five sour wampee varieties. Bars with no letters
in common are significantly different (p< 0.05).
3.4. Phytochemical Profiles in Sweet and Sour Wampee Fruits
As shown in Table 2, eight phytochemical compounds were detected in sour wampee
varieties, including syringin, rutin, benzoic acid, 2-Methoxycinnamic acid, kaempferol,
hesperetin, nobiletin, and tangeretin, while just four of them were detected in sweet
wampee varieties, including rutin, hesperetin, nobiletin, and tangeretin, and the other four
were not detected (Supplementary materials). Syringin was the only one that was detected
in all the sour wampee varieties and not detected in all the sweet wampee varieties. Rutin
showed the highest level among the eight components in all the wampee varieties, but
there was no difference between sweet and sour wampee varieties.
Table 2. Phytochemical components of the sweet and sour wampee varieties (µg/g FW).
Syringin Rutin Benzoic acid
2-
Methoxycinnamic
acid
Kaempferol Hesperetin Nobiletin Tangeretin
THP ND 63.54 ±1.59 c ND ND ND 1.060 ±0.010 h 3.120 ±0.080 g 6.570 ±0.020 e
ZFHP ND 41.25 ±0.85 g ND ND ND 1.110 ±0.020 g 2.600 ±0.02 i 5.620 ±0.040 f
CCTP ND 38.41 ±0.36 g ND ND ND 1.050 ±0.010 g 9.520 ±0.060 b 13.79 ±0.02 c
LTDH ND 59.01 ±0.19 de ND ND ND 1.150 ±0.010 f 8.890 ±0.060 c 14.87 ±0.09 a
TXTP ND 70.97 ±5.74 a ND ND ND 1.580 ±0.010 c 11.78 ±0.08 a ND
M3H 0.11 ±0.01 c 68.14 ±0.43 ab ND ND 2.290 ±0.030 a 1.790 ±0.010 b 4.440 ±0.320 e 6.880 ±0.020 d
JZP 1.05 ±0.09 b 55.79 ±4.78 ef 27.87 ±1.49 b 4.370 ±0.290 a 1.090 ±0.040 c 1.180 ±0.030 e 2.810 ±0.170 h 3.840 ±0.420 h
M4H 0.24 ±0.03 c 53.04 ±0.95 f ND ND ND 1.330 ±0.010 d 6.500 ±0.050 d 14.21 ±0.10 b
TXSP 1.53 ±0.01 a 61.84 ±7.17 cd ND ND ND 1.100 ±0.020 g 3.740 ±0.240 f ND
JXHP 0.98 ±0.08 b 65.68 ±0.72 bc 35.01 ±1.51 a 2.910 ±0.150 b 2.070 ±0.001 b 2.090 ±0.010 a 3.910 ±0.020 f 4.820 ±0.080 g
ND: not detected; values with no letter in common in each column are significantly different (p< 0.05).
3.5. Total Antioxidant Activities of Sweet and Sour Wampee Fruits
The total antioxidant activities of ten different wampee varieties were determined by
the ORAC assay. According to Figure 4, the ORAC value varied from
1.080 ±0.140 mmol
TE/100 g FW (THP) to 8.230
±
0.920 mmol TE/100 g FW (JXHP). For the five sweet wampee
varieties, CCTP showed the highest ORAC value of 2.020
±
0.390 mmol TE/
100 g FW
and
Foods 2022,11, 1230 7 of 11
had significant differences (p< 0.05) with the lowest one, THP. The other three sweet
wampee varieties (ZFHP, LTDH, and TXTP) did not show any significant differences
between each other, either with CCTP or THP. The average ORAC value of the five sweet
wampee varieties was 1.540 mmol TE/100 g FW. In the case of the five sour wampee
varieties, the ORAC value could be divided into three levels: the high level of JXHP
(8.230
±
0.920 mmol TE/ 100 g FW), the medium levels of M3H (4.390
±
0.350 mmol
TE/100 g FW) and JZP (4.690
±
0.640 mmol TE/100 g FW), and the low levels of M4H
(3.380
±
0.230 mmol TE/100 g FW) and TXSP (2.920
±
0.470 mmol TE/100 g FW). There
were significant differences (p< 0.05) between these three different levels. The average
ORAC value of the five sour wampee varieties was 4.72 mmol TE/100 g FW, which was
two times higher than those of the sweet wampee varieties.
Foods 2022, 11, x FOR PEER REVIEW 8 of 12
Figure 4. Total antioxidant activities of the five sweet and five sour wampee varieties obtained by
the ORAC assay. Bars with no letters in common are significantly different (p < 0.05).
3.6. Cellular Antioxidant Activities of Sweet and Sour Wampee Fruits
The intracellular and cellular antioxidant activities were evaluated using the CAA
assay, with PBS wash and no PBS wash methods. According to Figure 5, it was obvious
that the CAA values of both the PBS wash and no wash methods in the sour wampee
varieties were much higher than the sweet wampee varieties, especially of the no PBS
wash samples. The CAA values in the no PBS wash samples of the five sour wampee
varieties varied from 292.7 ± 28.5 μmol QE/100 g FW to 366.6 ± 39.6 μmol QE/100 g FW,
and the average value of them was 335.9 ± 27.6 μmol QE/100 g FW, which was almost 15
times more than the average level of the five sweet wampee varieties. The CAA values in
the PBS wash samples of the five sour wampee varieties varied from 67.95 ± 8.57 μmol
QE/100 g FW to 188.3 ± 11.3 μmol QE/100 g FW, and the average value of them was almost
12 times higher than the average level of the five sweet wampee varieties.
Figure 5. The cellular activities of the five sweet and five sour wampee varieties obtained by the
ORAC assay. Bars with no letters in common are significantly different (p < 0.05).
Figure 4.
Total antioxidant activities of the five sweet and five sour wampee varieties obtained by the
ORAC assay. Bars with no letters in common are significantly different (p< 0.05).
3.6. Cellular Antioxidant Activities of Sweet and Sour Wampee Fruits
The intracellular and cellular antioxidant activities were evaluated using the CAA
assay, with PBS wash and no PBS wash methods. According to Figure 5, it was obvious that
the CAA values of both the PBS wash and no wash methods in the sour wampee varieties
were much higher than the sweet wampee varieties, especially of the no PBS wash samples.
The CAA values in the no PBS wash samples of the five sour wampee varieties varied
from 292.7
±
28.5
µ
mol QE/100 g FW to 366.6
±
39.6
µ
mol QE/100 g FW, and the average
value of them was 335.9
±
27.6
µ
mol QE/100 g FW, which was almost 15 times more than
the average level of the five sweet wampee varieties. The CAA values in the PBS wash
samples of the five sour wampee varieties varied from 67.95
±
8.57
µ
mol QE/100 g FW to
188.3
±
11.3
µ
mol QE/100 g FW, and the average value of them was almost 12 times higher
than the average level of the five sweet wampee varieties.
3.7. Correlation Analysis
As shown in Figure 6, TPC, TFC, ORAC, CAA-no wash, and CAA wash values all
showed significant positive correlations with TA, especially TPC and CAA. The TPC and
CAA-no wash values showed significant negative correlations with TS/TA. In addition,
there was a significant strong positive correlation between TFC and TPC (r = 0.972, p< 0.01).
The ORAC value positively correlated with TPC (r = 0.902, p< 0.01) and TFC (r = 0.945,
p< 0.01
). The CAA-no wash value positively correlated with the TPC, TFC, and ORAC
values. The correlation analysis suggested that the titratable acid could be an important
factor that affected the contents of phenolics and flavonoids and the antioxidant activities
of wampee fruits; furthermore, the total phenolic and flavonoid contents were major
contributors to the antioxidant activities of wampee fruits. For the phenolic components,
Foods 2022,11, 1230 8 of 11
the correlation analysis showed that the syringin content was positively correlated with
the TPC, TFC, and CAA values and that the benzoic acid content was positively correlated
with the TPC, TFC, and ORAC values.
Foods 2022, 11, x FOR PEER REVIEW 8 of 12
Figure 4. Total antioxidant activities of the five sweet and five sour wampee varieties obtained by
the ORAC assay. Bars with no letters in common are significantly different (p < 0.05).
3.6. Cellular Antioxidant Activities of Sweet and Sour Wampee Fruits
The intracellular and cellular antioxidant activities were evaluated using the CAA
assay, with PBS wash and no PBS wash methods. According to Figure 5, it was obvious
that the CAA values of both the PBS wash and no wash methods in the sour wampee
varieties were much higher than the sweet wampee varieties, especially of the no PBS
wash samples. The CAA values in the no PBS wash samples of the five sour wampee
varieties varied from 292.7 ± 28.5 μmol QE/100 g FW to 366.6 ± 39.6 μmol QE/100 g FW,
and the average value of them was 335.9 ± 27.6 μmol QE/100 g FW, which was almost 15
times more than the average level of the five sweet wampee varieties. The CAA values in
the PBS wash samples of the five sour wampee varieties varied from 67.95 ± 8.57 μmol
QE/100 g FW to 188.3 ± 11.3 μmol QE/100 g FW, and the average value of them was almost
12 times higher than the average level of the five sweet wampee varieties.
Figure 5. The cellular activities of the five sweet and five sour wampee varieties obtained by the
ORAC assay. Bars with no letters in common are significantly different (p < 0.05).
Figure 5.
The cellular activities of the five sweet and five sour wampee varieties obtained by the
ORAC assay. Bars with no letters in common are significantly different (p< 0.05).
Foods 2022, 11, x FOR PEER REVIEW 9 of 12
3.7. Correlation Analysis
As shown in Figure 6, TPC, TFC, ORAC, CAA-no wash, and CAA wash values all
showed significant positive correlations with TA, especially TPC and CAA. The TPC and
CAA-no wash values showed significant negative correlations with TS/TA. In addition,
there was a significant strong positive correlation between TFC and TPC (r = 0.972, p <
0.01). The ORAC value positively correlated with TPC (r = 0.902, p < 0.01) and TFC (r =
0.945, p < 0.01). The CAA-no wash value positively correlated with the TPC, TFC, and
ORAC values. The correlation analysis suggested that the titratable acid could be an im-
portant factor that affected the contents of phenolics and flavonoids and the antioxidant
activities of wampee fruits; furthermore, the total phenolic and flavonoid contents were
major contributors to the antioxidant activities of wampee fruits. For the phenolic compo-
nents, the correlation analysis showed that the syringin content was positively correlated
with the TPC, TFC, and CAA values and that the benzoic acid content was positively cor-
related with the TPC, TFC, and ORAC values.
Figure 6. Heat map of the correlation analysis among titratable acid, total sugar, total phenolics,
total flavonoids, phytochemical components, and antioxidant activities. TA: titratable acid; TS: total
sugar; TSTA: total sugar/titratable acid; TPC: total phenolic content; TFC: total flavonoid content;
ORAC: the oxygen radical absorbance capacity; CAANW: CAA value without PBS wash; CAAW:
CAA value with PBS wash; SY: syringin; RU: rutin; BE: benzoic acid; ME: 2-methoxycinnamic acid;
KA: kaempferol; HE: hesperetin; NO: nobiletin; TG: tangeretin. * p < 0.05, ** p < 0.01.
4. Discussion
Figure 6.
Heat map of the correlation analysis among titratable acid, total sugar, total pheno-
lics, total flavonoids, phytochemical components, and antioxidant activities. TA: titratable acid;
TS: total sugar;
TSTA: total sugar/titratable acid; TPC: total phenolic content; TFC: total flavonoid
content; ORAC: the oxygen radical absorbance capacity; CAANW: CAA value without PBS wash;
CAAW: CAA
value with PBS wash; SY: syringin; RU: rutin; BE: benzoic acid; ME: 2-methoxycinnamic
acid; KA: kaempferol; HE: hesperetin; NO: nobiletin; TG: tangeretin. * p< 0.05, ** p< 0.01.
Foods 2022,11, 1230 9 of 11
4. Discussion
In this study, the five sweet wampee varieties, with an average TS/TA ratio 29 times
higher and an average titratable acid content 19 times lower than the five sour wampee
varieties, showed significantly much lower levels of total phenolics, flavonoids, and an-
tioxidant activities than the sour wampee varieties. Thus, the hypothesis was if there were
any relationship between TS/TA and TA with TPC, TFC, and antioxidant activities. The
correlation analysis showed significant positive correlations between TA with TPC, TFC,
ORAC, and CAA values, while it showed significant negative correlations between TS/TA
with TPC and CAANW values. These results suggested that the content of titratable acid in
wampee fruit might have some relationship with the content of phenolics and flavonoids.
In previous studies about fruit phenolics, flavonoids, and antioxidant activities, there was
little focus on the relationship between titratable acid and these phytochemicals and an-
tioxidant activities. In the research of the phenolic metabolism of the red currant through
fruit ripening, the authors found that the phenolic contents slightly decreased in all three
cultivars, while the sugar/acid ratios increased during development, and the average total
phenolic values of four development stages of three cultivars were positively correlated
with the average values of total organic acids [
29
]. Kim et al. analyzed the fruit quality and
phenolic contents of 45 commercial cultivars of blueberry fruits grown in Korea [
30
], and
Yilmaz et al. detected the total phenolic, acidity, and sugar contents of 31 edible wild pear
fruits [
31
], while the relationship between total phenolics and acid and/or sugar were not
analyzed in both papers. According to the data in the two papers about blueberry and pear
fruits, the content of total phenolics and total acidity did not show a positive relationship,
which was not consistent with the results of the wampee fruit.
As TA and TS/TA both significantly correlated with TPC and CAA values in this study,
the question is if there were any phytochemicals correlated with TA or TS/TA? According
to the correlation analysis in this study, among the eight chemicals detected from wampee
fruits, only rutin (the one with the most content) showed a significant negative correlation
with TS/TA (r =
−
0.671) but no significant correlation with TA; the others showed no
significant correlation with TA or TS/TA. This may explain the relationship between TS/TA
and total phenolics. However, if there is any relation between TA and TPC and TFC, or if
they are just two parallels with no intersection, should be analyzed in further studies.
Phytochemical profiles of different wampee varieties in this study showed that sweet
wampee varieties contain less phenolics and flavonoids because there were four more
phytochemical compounds detected in sour wampee varieties than sweet wampee vari-
eties. The four undetected chemicals in sweet wampee varieties of syringin, benzoic acid,
2-methoxycinnamic
acid, and kaempferol may be the main factors that caused the differ-
ences of TPC and TFC between sweet and sour wampee varieties. The correlation analysis
showed that syringin positively correlated with TPC, TFC, and CAA values (
r > 0.6
); ben-
zoic acid positively correlated with TPC, TFC and ORAC values (r > 0.7); and kaempferol
positively correlated with ORAC and CAA values (r = 0.83 and 0.64). However, benzoic acid
and kaempferol were only detected in two or three sour wampee varieties, while syringin
was detected in all the five sour wampee varieties but not in all the sweet wampee varieties.
This suggested that syringin might be the key factor that caused the differentiation of TPC
and TFC between the sweet and sour wampee varieties.
5. Conclusions
Sour wampee varieties analyzed in this study showed more total phenolic and
flavonoid contents and higher antioxidant activity and cellular antioxidant activity than
sweet wampees. The titratable acid content in the sour wampee fruits was significantly
higher than in the sweet wampee fruits, while the total sugar content between the sour
and sweet wampee varieties did not show significant differences. The titratable acid
content may be the main factor that causes the taste difference between sour and sweet
wampee fruits.
Foods 2022,11, 1230 10 of 11
The correlation analysis showed significant positive correlations between TA with
TPC, TFC, ORAC, and CAA values, which suggested that the content of titratable acid in
wampee fruit might have some relationship with the content of phenolics and flavonoids.
This study will provide an insight into the relationship between sugars, acids, and phenolic
compounds in wampee fruit. Sour wampee varieties with high phenolics and antioxidant
activity should be paid much attention by breeders to cultivate germplasms with high
health care efficacy.
Supplementary Materials:
The following supporting information can be downloaded at: https:
//www.mdpi.com/article/10.3390/foods11091230/s1.
Author Contributions:
Conceptualization, X.C., X.G. and Y.L.; methodology, Y.Y.; software, Y.Y.;
validation, J.P., Z.L. and J.Q.; formal analysis, Y.Y.; investigation, C.P.; resources, J.P.; data curation,
X.C. and Y.Y.; writing—original draft preparation, X.C.; writing—review and editing, X.C. and X.G.;
visualization, X.C.; supervision, X.G.; project administration, Y.L.; funding acquisition, Y.L. All
authors have read and agreed to the published version of the manuscript.
Funding:
This research was funded by the National Natural Science Foundation of China [grant
number: 31501730]; Modern Agricultural Industry Technology System in Guangdong Province of
China [grant number: 2021KJ116]; National Tropical Plants Germplasm Resource Center [grant
number: NTPGRC2022-009]; the Special Financial Fund of Foshan-Guangdong Agricultural Science
and Technology Demonstration City Project (2021).
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement:
The data presented in this study are available on request from the
corresponding author.
Conflicts of Interest: The authors declare no conflict of interest.
References
1.
Liu, Y.-P.; Guo, J.-M.; Liu, Y.-Y.; Hu, S.; Yan, G.; Qiang, L.; Fu, Y.-H. Carbazole Alkaloids with Potential Neuroprotective Activities
from the Fruits of Clausena lansium.J. Agric. Food Chem. 2019,67, 5764–5771. [CrossRef] [PubMed]
2. Lin, J.-H. Cinnamamide derivatives from Clausena lansium.Phytochemistry 1989,28, 621–622. [CrossRef]
3.
Liu, G.T.; Li, W.-X.; Chen, Y.-Y.; Wei, H.-L. Hepatoprotective action of nine constituents isolated from the leaves of Clausena
lansium in mice. Drug Dev. Res. 1996,39, 174–178. [CrossRef]
4.
Zaman, W.; Ye, J.; Saqib, S.; Liu, Y.; Shan, Z.; Hao, D.; Chen, Z.; Xiao, P. Predicting potential medicinal plants with phylogenetic
topology: Inspiration from the research of traditional Chinese medicine. J. Ethnopharmacol. 2021,281, 114515. [CrossRef]
5.
Liu, J.; Li, C.-J.; Du, Y.-Q.; Li, L.; Sun, H.; Chen, N.-H.; Zhang, D.-M. Bioactive Compounds from the Stems of Clausena lansium.
Molecules 2017,22, 2226. [CrossRef]
6.
Shen, S.; Liao, Q.; Huang, L.; Li, D.; Zhang, Q.; Wang, Y.; Lee, S.M.-Y.; Lin, L. Water soluble fraction from ethanolic extract of
Clausena lansium seeds alleviates obesity and insulin resistance, and changes the composition of gut microbiota in high-fat diet-fed
mice. J. Funct. Foods 2018,47, 192–199. [CrossRef]
7.
Kong, F.; Su, Z.; Guo, X.; Zeng, F.; Bi, Y. Antidiabetic and Lipid-Lowering Effects of the Polyphenol Extracts from the Leaves
of Clausena lansium (Lour.) Skeels on Streptozotocin-Induced Type 2 Diabetic Rats. J. Food Sci.
2018
,83, 212–220. [CrossRef]
[PubMed]
8.
He, X.; Zhang, L.; Chen, J.; Sui, J.; Yi, G.; Wu, J.; Ma, Y. Correlation between Chemical Composition and Antifungal Activity of
Clausena lansium Essential Oil against Candida spp. Molecules 2019,24, 1394. [CrossRef] [PubMed]
9.
Liu, X.-Y.; Fu, X.-X.; Li, Y.-Y.; Xiong, Z.-H.; Li, B.-T.; Peng, W.-W. The sesquiterpenes from the stem and leaf of Clausena lansium
with their potential antibacterial activities. Nat. Prod. Res. 2021,35, 4887–4893. [CrossRef]
10.
Huang, G.; Li, J.; Li, W.; Liu, T.; Jiang, G.; Wu, T.; Zou, Y.; Huang, J.; Tao, L.; Zhu, Z.; et al. Suppression of inflammation by
ethanol extract of Clausena lansium via modulation of TLR4/MYD88/TRAF6 signaling pathway in RAW 264.7 macrophages. Eur.
J. Inflamm. 2019,17, 2058739219841973. [CrossRef]
11.
Adebajo, A.C.; Iwalewa, E.O.; Obuotor, E.M.; Ibikunle, G.F.; Omisore, N.O.; Adewunmi, C.O.; Obaparusi, O.O.; Klaes, M.;
Adetogun, G.E.; Schmidt, T.J.; et al. Pharmacological properties of the extract and some isolated compounds of Clausena lansium
stem bark: Anti-trichomonal, antidiabetic, anti-inflammatory, hepatoprotective and antioxidant effects. J. Ethnopharmacol.
2009
,
122, 10–19. [CrossRef] [PubMed]
12.
Prasad, K.N.; Hao, J.; Yi, C.; Zhang, D.; Qiu, S.; Jiang, Y.; Zhang, M.; Chen, F. Antioxidant and Anticancer Activities of Wampee
(Clausena lansium (Lour.) Skeels) Peel. J. Biomed. Biotechnol. 2009,2009, 612805. [CrossRef] [PubMed]
Foods 2022,11, 1230 11 of 11
13.
Li, B.-Y.; Yuan, Y.-H.; Hu, J.-F.; Zhao, Q.; Zhang, D.-M.; Chen, N. Protective effect of Bu-7, a flavonoid extracted from Clausena
lansium, against rotenone injury in PC12 cells. Acta Pharmacol. Sin. 2011,32, 1321–1326. [CrossRef]
14.
Feng, Z.; Li, X.; Zheng, G.; Huang, L. Synthesis and activity in enhancing long-term potentiation (LTP) of clausenamide
stereoisomers. Bioorganic Med. Chem. Lett. 2009,19, 2112–2115. [CrossRef] [PubMed]
15.
Peng, W.-W.; Fu, X.-X.; Xiong, Z.-H.; Wu, H.-L.; Chang, J.-W.; Huo, G.-H.; Li, B.-T. Taxonomic significance and antitumor activity
of alkaloids from Clausena lansium Lour. Skeels (Rutaceae). Biochem. Syst. Ecol. 2020,90, 104046. [CrossRef]
16.
Zhu, T.; Zuo, W.; Yan, J.; Wen, P.; Pei, Z.; Lian, H.; Yang, H.-C. Comparative Assessment of the Antioxidant Activities among
the Extracts of Different Parts of Clausena lansium (Lour.) Skeels in Human Gingival Fibroblast Cells. Evid.-Based Complementary
Altern. Med. 2020,2020, 3958098. [CrossRef] [PubMed]
17.
Luca, S.V.; Macovei, I.; Bujor, A.; Miron, A.; Skalicka-Wo´zniak, K.; Aprotosoaie, A.C.; Trifan, A. Bioactivity of dietary polyphenols:
The role of metabolites. Crit. Rev. Food Sci. Nutr. 2020,60, 626–659. [CrossRef] [PubMed]
18.
Batiha, G.E.-S.; Beshbishy, A.M.; Ikram, M.; Mulla, Z.S.; El-Hack, M.E.A.; Taha, A.E.; Algammal, A.M.; Elewa, Y.H.A. The
Pharmacological Activity, Biochemical Properties, and Pharmacokinetics of the Major Natural Polyphenolic Flavonoid: Quercetin.
Foods 2020,9, 374. [CrossRef]
19.
Di Lorenzo, C.; Colombo, F.; Biella, S.; Stockley, C.; Restani, P. Polyphenols and Human Health: The Role of Bioavailability.
Nutrients 2021,13, 273. [CrossRef]
20.
Li, Q.; Chang, X.-X.; Wang, H.; Brennan, C.S.; Guo, X.-B. Phytochemicals Accumulation in Sanhua Plum (Prunus salicina L.) during
Fruit Development and Their Potential Use as Antioxidants. J. Agric. Food Chem. 2019,67, 2459–2466. [CrossRef] [PubMed]
21.
Wang, H.; Guo, X.; Hu, X.; Li, T.; Fu, X.; Liu, R.H. Comparison of phytochemical profiles, antioxidant and cellular antioxidant
activities of different varieties of blueberry (Vaccinium spp.). Food Chem. 2017,217, 773–781. [CrossRef] [PubMed]
22.
Chang, S.K.; Alasalvar, C.; Shahidi, F. Superfruits: Phytochemicals, antioxidant efficacies, and health effects—A comprehensive
review. Crit. Rev. Food Sci. Nutr. 2019,59, 1580–1604. [CrossRef] [PubMed]
23.
Ye, Y.; Chang, X.; Brennan, M.A.; Brennan, C.S.; Guo, X. Comparison of phytochemical profiles, cellular antioxidant and
anti-proliferative activities in five varieties of wampee (Clausena lansium) fruits. Int. J. Food Sci. Technol.
2019
,54, 2487–2493.
[CrossRef]
24.
Chang, X.; Ye, Y.; Pan, J.; Lin, Z.; Qiu, J.; Guo, X.; Lu, Y. Comparative assessment of phytochemical profiles and antioxidant
activities in selected five varieties of wampee (Clausena lansium) fruits. Int. J. Food Sci. Technol. 2018,53, 2680–2686. [CrossRef]
25.
Guo, X.; Li, T.; Tang, K.; Liu, R.H. Effect of Germination on Phytochemical Profiles and Antioxidant Activity of Mung Bean
Sprouts (Vigna radiata). J. Agric. Food Chem. 2012,60, 11050–11055. [CrossRef]
26.
He, X.; Liu, D.; Liu, R.H. Sodium Borohydride/Chloranil-Based Assay for Quantifying Total Flavonoids. J. Agric. Food Chem.
2008,56, 9337–9344. [CrossRef]
27.
Kohri, S.; Fujii, H. Modified Oxygen Radical Absorbance Capacity Assay that can be Implemented at Low Temperatures: A pilot
study. Food Sci. Technol. Res. 2013,19, 269–276. [CrossRef]
28. Wolfe, K.L.; Liu, R.H. Cellular Antioxidant Activity (CAA) Assay for Assessing Antioxidants, Foods, and Dietary Supplements.
J. Agric. Food Chem. 2007,55, 8896–8907. [CrossRef]
29.
Zorenc, Z.; Veberic, R.; Koron, D.; Miosic, S.; Hutabarat, O.S.; Halbwirth, H.; Mikulic-Petkovsek, M. Polyphenol metabolism in
differently colored cultivars of red currant (Ribes rubrum L.) through fruit ripening. Planta 2017,246, 217–226. [CrossRef]
30.
Kim, J.G.; Kim, H.L.; Kim, S.J.; Park, K.-S. Fruit quality, anthocyanin and total phenolic contents, and antioxidant activities of
45 blueberry cultivars grown in Suwon, Korea. J. Zhejiang Univ. Sci. B 2013,14, 793–799. [CrossRef]
31.
Ugurtan Yilmaz, K.; Ercisli, S.; Cam, M.; Uzun, A.; Yilmaztekin, M.; Kafkas, E.; Pinar, H. Fruit Weight, Total Phenolics, Acidity
and Sugar Content of Edible Wild Pear (Pyrus elaeagnifolia Pall.) Fruits. Erwerbs-Obstbau 2015,57, 179–184. [CrossRef]
