Flavonoids in Grapefruit and Grapefruit Juice: Concentration, Distribution and
Potential Health Benefits
Executive Summary
John Zhang
Grapefruit and grapefruit juice products are one of the major components of Florida citrus industry.
Grapefruit fruit and grapefruit juice not only contain many essential human nutrients, but also contain
many other phytochemicals such as flavonoids. These phytochemicals are not essential nutrients for human
body, but they provide many health benefits. Flavonoids are a group of compounds among those
phytochemicals. Flavonoids are phenolic compounds with antioxidant activity and have been linked to the
reduced risk of many health problems.
More than 5,000 different flavonoid compounds have been identified in plants. Flavonoids found in fruit
and vegetables can be chemically divided into six subgroups, flavanones, flavonols, flavones, flavanols,
anthocyanidins and isoflavonoids. Grapefruit are rich in flavonoids. Flavonoids that have been identified in
grapefruit fall within the three subgroups (flavanones, flavones and flavonols). Flavanones are the
dominant flavonoids, and account for about 98% of the total flavonoids in grapefruit. Flavanones are
present as either flavanone aglycones (there is no sugar molecule attached) or flavanone glycosides (there
are sugar molecules attached). Major flavanones in grapefruit are present as flavanone glycosides.
Flavanone glycosides in grapefruit include flavanone neohesperidosides and flavanone rutinosides, which
are formed by the addition of sugars neohesperidose and rutinose, respectively, to the flavanone aglycones.
Flavanone neohesperidosides such as naringin, neohesperidin, neoeriocitrin and poncirin have a bitter taste,
while flavanone rutinosides such as narirutin, hesperidin, eriocitrin and didymin are tasteless.
In grapefruit and grapefruit juice, identified flavanone glycosides include didymin, dihydrokaempferol
glucoside, eriocitrin, naringin, poncirin, hesperidin, neohesperidin, neoeriocitrin, narirutin, narirutin-4’glucoside, naringin-6”-malonate (open form) and naringin-6”-malonate (closed form). The presence of
naringenin (a flavanone aglycone form) in grapefruit remains controversial. Flavones or flavonols found in
grapefruit include: apigenin 6,8-di-C-glucoside, apeigen 7-(malonylapiosy)-glucoside, kaempferol
1
glycoside, myricetin, neodiosimin, quercetin, rutin, and rhoifolin. Reported polymethoxylated flavones in
grapefruit include heptamethoxyflavone, nobiletin and tangeretin.
The major flavonoids in commercial grapefruit juices are naringin, narirutin, naringenin, poncirin,
hesperidin, neohesperidin, didymin and quercetin. Naringin is present at the highest concentration followed
by narirutin, hesperidin, poncirin, neohesperidin, didymin, and quercetin. Content of naringin varies among
the commercial grapefruit juice products, ranging from 10.1 to 86.7 mg/100 ml of juice. A recent study
showed that the mean content of naringin in commercial Ruby Red and pink grapefruit juice products is
significantly lower than white grapefruit juice products. Polymethoxylated flavones are not detectable in
commercial grapefruit juices.
Among different tissues within a grapefruit, the albedo generally contains higher concentrations of
flavonoids than the flavedo, the section membrane or the juice. Naringin, narirutin, hesperidin,
neohesperidin, and poncirin are present in all tissue parts of grapefruit, with the highest concentrations in
albedo. Naringin concentration in grapefruit decreases as the citrus season progresses. The largest decrease
of naringin occurs during the early part of grapefruit season.
Concentrations of individual flavonoids vary with grapefruit variety, fruit tissue, juice extraction method
and geographic location. Red and pink grapefruit tend to have relatively lower total flavanone content than
white grapefruit. Grapefruit juices obtained from commercial extractors normally contain higher amounts
of flavonoids compared to those obtained by hand-squeezing.
Naringin is the predominant flavonoid in grapefruit and a major bitter compound. Naringin is one of the
most important flavonoids in grapefruit and needs to be further explored to substantiate its medical
benefits. The possible health benefits of other grapefruit flavonoids, such as hesperidin, neohesperidin,
narirutin, poncerin and quercetin, should also be investigated.
Public interest in the possible health benefits of flavanoids has increased largely due to their antioxidant
and free-radical scavenging activities. Flavonoids have long been recognized to possess anti-inflammatory,
anti-allergic, hepatoprotective, anti-thrombotic, antiviral, and anti-carcinogenic activities. Flavonoids have
2
been linked to a reduced risk of certain cancers, inflammation, stroke, heart diseases, asthma, vision
disorders, and bone loss.
Studies on naringin have shown that naringin could (1) act as a free radical scavenger and antioxidant; (2)
reduce total cholesterol level and enhance lipid metabolism; (3) enhance ethanol metabolism; (4) reduce
the risk of atherosclerosis; (5) act as an anti-apoptotic agent; (6) protect plasma vitamin E levels; (7) reduce
radiation-induced chromosome damage in bone marrow and increase bone cell activity, and stimulate DNA
repair in prostate cancer cells; and (8) reduce oxidative stress and inflammatory response. However, so far
most of the data on the health benefits of naringin have mainly been obtained from in vitro or animal
research. Clinical studies are needed to corroborate in human the health properties of naringin.
For a more detailed and referenced review of this topic, please continued reading below
3
Flavonoids in Grapefruit and Grapefruit Juice:
Concentration, Distribution and Potential Health Benefits
Literature Review
John Zhang
INTRODUCTION
Florida is the main producer of grapefruit (Citrus paradisi Macf.) in the world. Florida
grapefruit accounts for about 48% of the world’s grapefruit production. During the 200304 crop year, about 41% and 59% of Florida’s grapefruit was marketed as fresh and juice
products, respectively, in both USA and foreign countries. Overseas shipments account
for approximately 54% of Florida=s fresh grapefruit shipments. Japan is the largest
importing country of Florida fresh grapefruit accounting for about 55.4% of all overseas
shipments during the 2003-04 season. Grapefruit consist of several varieties such as
Marsh, Flame and Ruby Red.
Citrus fruit and juice are among the most important nutrient-dense foods. Citrus fruit and
juice contain a range of key nutrients such as vitamin C, vitamin A, folate, and minerals
for human health. In addition, citrus fruit and juice contain many phytochemicals
including flavonoids, carotenoids, glucarates, coumarins, monoterpenes, limonoids,
triterpenes and phenolic acids. Unlike the traditional nutrients (protein, fat, vitamins,
minerals), phytochemicals are not essential for life, but they may provide many health
benefits such as anti-inflammatory and anti-tumor activity as well as inhibiting blood
clots (Baghurst, 2003; Manthey and Guthrie, 2002; Middleton et al., 2000). Bioactive
phytochemicals may also protect against some of common chronic diseases such as
cardiovascular diseases, degenerative eye and cognitive conditions and general damage
caused by aging.
4
There are at least three major groups (flavonoinds, carotenoids and limonoids) of
phytochemicals in citrus fruit and juice. This review primarily discusses the chemistry,
occurrence, concentration and distribution of flavonoids in grapefruit and grapefruit
juice.
FLAVONOIDS
Chemistry and classification of flavonoids:
Flavonoids are low molecular weight compounds composed of a three-ring structure with
various substitutes (Middleton et al., 2000). Flavonoids consist of 2 benzene rings (A and
B), which are connected by an oxygen-containing pyrone ring (C) (Fig. 1). Flavonoids
containing a hydroxyl group in position C-3 of the C ring are classified as 3hydroxyflavonoids (flavonols, anthocynidins, and cyanidins, and catechins), and those
lacking it as 3-desoxyflavonoids (flavanones and flavones) (Erlund, 2004). Classification
within the 2 families is based on whether and how additional hydroxyl or methyl groups
have been introduced to the different positions of the molecule. Isoflavonoids differ from
the other groups; the B ring is bound to C-3 of ring C instead of C-2. Anthocyanidins and
catechins, on the other hand, lack the carbonyl group on C-4.
When sugars are attached to the flavonoid nucleus, the compounds are called glycosides;
when the sugars have been removed or are not present, the term “aglycone” is applied.
Flavonoids are mainly present in plants as glycosides. Aglycones occur less
frequently. At least 8 different monosaccharides or combinations of these can bind to the
different hydroxyl groups of the flavonoid aglycone. The most common sugar moieties
include D-glucose and L-rhamnose. The glycosides are usually O-glycosides, with the
sugar moiety bound to the hydroxyl group at the C-3 or C-7 position (Fig. 1) (Erlund,
2004).
5
Fig. 1. Chemical structures of the flavane nucleus, quercetin, hesperetin and naringenin,
and some of their common glycosides.
6
More than 5,000 different flavonoid compounds have been identified (Holden et al.,
2005). Flavonoids are found in most edible fruits and vegetables, but the types of
flavonoids obtained from different dietary sources vary (Erlund, 2004). Citrus fruit are
rich source of health promoting flavonoids, especially flavanones (Vanamala et al., 2006,
Baghurst, 2003; Horowitz and Gentili, 1977). The principal citrus flavanones do not
occur as the free aglycones but are combined through the C-7 hydroxy group with either
β-neohesperidoside or β-rutinose (Horowitz and Gentili, 1977).
Flavonoids in grapefruit:
Based on the review in flavonoid constituents of citrus conducted by Horowitz and
Gentili (1977), the following flavanone and flavone glycosides have been detected in
grapefruit: Naringin, naringenin 7-β-rutinoside, naringin 4’-β-D-glucoside, naringenin 7β-rutinoside 4’-β-D-glucoside, poncirin, didymin, neohesperidin, hesperidin,
dihydrokaempferol glycoside, rhoifolin, apigenin 7-β-rutinoside, kaempferol glycoside,
tangeritin, nobeletin, 3,5,6,7,8,3’, 4’-heptamethoxyflavone. Later, additional flavonoids
were identified and reported by other researchers. They include: quercetin, diosmin,
ehoifolin, isorhoifolin, eriocitrin, neoeriocitrin, eriodictyol, naringin-6’-malonate,
narirutin, narirutin-4’-glucoside (Berhow et al., 1998; Vanamala et al., 2006; Ross et al.,
2000).
Taste of flavonones:
Some of flavonones are bitter compounds, which contribute the bitterness of grapefruit
and gapefruit juice. These bitter flavonones all have a chemical structure that
neohesperidoside (sugar moiety) bounds to C-7 position (Fig. 2). These compounds
include naringin, neohesperidin, neoeriocitrin and poncirin (Sinclair, 1972). Naringin is
by far the most dominant bitter flavonoid compound in grapefruit (Lee and Kim, 2003;
Hagen et al., 1966). Narirutin, hesperidin, eriocitrin and neoponcirin, which are the
isomers of naringin, neohesperidin, neoeriocitrin and poncirin, respectively, are tasteless,
and have a chemical structure that rutinoside (sugar moiety) bounds to C-7 position (Fig.
7
2). Thus, flavonone neohesperidosides can be distinguished from the flavonone
rutinosides by the taste. Neohesperidosides are bitter; the rutinosides are tasteless
(Horowitz and Gentili, 1977). Naringin and poncirin are the most bitter, followed by
neohesperidin and neoeriocitrin (Horowitz and Gentili, 1977). The bitterness of naringin
is so pronounced that it can be detected when 1 part is dissolved in 50,000 parts of water
(Braverman, 1949). Maurer et al., (1950) indicated that when the naringin in the juice
samples exceeded 0.07%, the juice was inferior and had a bitter taste, while fruit with
juice containing less than 0.05% naringin appeared to have superior flavor quality. In
most grapefruit-growing countries, the flavor of the juice is considered to be the best
when the naringin concentration is at the lowest level. However, other factors, such as
sugars, acids, total soluble solids, pH, and oil content, also affect the juice flavor
(Sinclair, 1972).
Among different citrus varieties, the analysis of neohesperidoside and rutinoside as
markers for the bitterness showed that sweet oranges and lemon yielded rutinose; bitter
oranges Ponderosa (a hybrid) yielded mainly neohesperidose together with a trace of a
second, unidentified glycoside; and grapefruit yielded both neohesperidose and rutinose
(Horowitz and Gentili, 1977). Although bitterness or lack of bitterness can sometimes be
a rough guide as to whether a fruit contains neohesperidosides or rutinosides, there are
doubtlessly many exceptions (Horowitz and Gentili, 1977).
8
Fig. 2: Flavanone glycosides in citrus
Data source: J. Sci. Food Agric., Robards et al., 1997.
9
Polymethoxylated flavones in grapefruit:
Citrus fruits contain a significant amount of a diverse array of polymethoxylated flavones
(PMFs) in both their peel and juice (Stremple, 1998). The PMF levels are significantly
higher in the peel oil than the juice, but they make no contribution to the bitter taste of
orange juice at their natural concentration (Stremple, 1998). The author reported that
grapefruit oil was found to produce tangeretin, nobiletin and heptamethoxyflavone in
much lower concentrations than found in either orange or tangerine oils; however, the
author did not show specific concentrations of these compounds in the report. Nogata et
al. (2006) detected nobiletin in both flavedo and albedo tissues of Marsh grapefruit. Only
heptamethoxyflavone was found in flavedo tissues of Marsh grapefruit.
Flavonoid compounds in grapefruit juice:
Belajova and Suhaj (2003) analyzed certain flavonoids in a fresh-pressed grapefruit juice
and a commercial grapefruit juice (no specific brands and cultivars) using a HPLC
method. The concentrations of naringin, hesperidin, neohesperidin, and quercetin are
presented in Table 1.
Table 1. The flavonoid content in filtered grapefruit juices
Grapefruit juice
Naringin
Hesperidin
Neohesperidin
Quercetin
(mg/100 ml)
Fresh-squeezed
21.1
1.5
11.1
0.7
100% commercial
11.6
1.5
2.0
1.2
Vanamala et al. (2006) tested five different brands of grapefruit juices for major
flavonoid compound concentrations and showed that naringin, narirutin and poncirin
were the major flavonoids in all 5 brands of grapefruit juices. Their results are presented
in Table 2. The average concentration of naringin, narirutin and poncirin was 30.4, 10.1
and 1.24 mg/100 ml of juice, respectively. There were significant differences in
concentrations of naringin and narirutin among 5 tested brands of grapefruit juices. Other
two flavonoids that were reported in this study were neohesperidin and quercetin with an
10
average concentration at 0.59 and 0.64 mg/100 ml of juice, respectively (Vanamala et al.,
2006).
Table 2: Major flavonoid content of not-from-concentrate (NFC) commercial grapefruit juices brandz
Brand name
z
Naringin
Narirutin Poncerin Neohesperidin Quercetin Total
(mg/100 ml)
Albertson's grapefruit juice
30.6
10.4
1.3
0.5
0.8
43.6
Florida natural original
31.5
10.2
1.3
0.7
0.7
44.7
Horizon
23.5
9.2
1.1
0.5
0.6
40.8
Kroger grapefruit juice
29.2
9.1
1.1
0.7
0.6
40.7
Tropicana grapefruit juice
plus calcium
37.2
11.7
1.4
0.6
0.5
52.2
Average
30.4
10.1
1.2
0.6
0.6
44.4
Data source: J. Food Comp. Anal., Vanamala et al., 2006.
Ross et al. (2000) tested variance of common flavonoids of 6 brands of grapefruit juices.
Their results are listed in Table 3. Seven flavonoids, naringin, narirutin, hesperidin,
neohesperidin, didymin, poncirin and quercetin, were identified and quantified.
Significant differences in total amount of flavonoids and the concentrations of individual
flavonoid compounds in tested brands of grapefruit juices were found. Naringin (14.56 to
63.8 mg/100 ml) was found to be the major flavonoid, followed by narirutin (2.6 to 12.2
mg/100 ml) and hesperidin (1.44 to 3.12 mg/100 ml).
11
Table 3: Major flavonoid content of some commercial grapefruit juices brandz
Brand name
Naringin
Narirutin Hesperidin
Neohesperidin Didymin Quercetin Poncirin
(mg/100 ml)
________________________________________________________________________________________________________________
Kroger (grapefruit juice from
ndy
concentrate unsweetened)
35.3
7.8
3.1
0.9
1.0
0.8
Kroger (unsweetened pink grapefruit
juice from concentrate)
38.5
8.6
2.2
1.1
0.0
0.9
1.0
Kroger (unsweetened grapefruit
from concentrate)
63.8
12.2
2.2
1.1
1.7
nd
2.4
Ocean Spray (Ruby Red grapefruit
juice from concentrate)
14.6
2.6
1.4
0.2
0.3
0.2
0.1
Ocean Spray (grapefruit juice from
concentrate)
51.2
11.4
1.6
1.0
1.4
nd
1.9
Texsun (pink grapefruit juice from
concentrate)
46.3
9.9
2.6
1.1
1.1
nd
0.6
Tropicana (Ruby Red grapefruit
51.2
10.5
1.6
1.1
1.1
nd
1.2
juice, not from concentrate)
________________________________________________________________________________________________________________
z
y
Data source: Fitoterapia 71:154-161, Ross et al., 2000.
Not detected under the test conditions.
12
The USDA’s Database for Flavonoid Content of Selected Food (2003) provided certain
data of individual flavonoid compounds that were detected in 5 different grapefruit juices
(Table 4). These flavonoid compounds included: naringenin, hesperetin, eriodictyol,
kaempferol, quercetin, and myricetin. Only naringenin was consistently detected from all
5 grapefruit juice products. Naringenin was presented at the highest concentration in all
juices tested, followed by hesperitin. Eriodictyol, kaemferol and quercetin were reported
at low concentrations, and were found in a few grapefruit juice products. It should be
noted that naringenin and hesperetin are flavanone aglycone forms which are normally
presented in citrus fruit and juices as forms of naringin and hesperedin (flavanone
glycoside forms). The forms of naringenin and hesperetin in the Table 4 appear to be
largely due to the analytical conversions of naringin and hesperedin, respectively.
13
Table 4. Concentrations of flavanoids in grapefruit and grapefruit juices from the USDA report, 2003.
(For mean, standard error, min and max units = mg/100 grams, edible portion)
NDB No.a
Description
9123
Grapefruit juice, canned,
unsweetened
9126
9404
9128
Nb
Max
CCc
0.5
26.3
C
B
30.5
31.9
C
24.0
24.0
24.0
0
0.4
9.7
0
1.4
62.6
B
B
B
Flavonoid
Mean
St. error
Flananones Hesperitin
Naringenin
0.5
18.1
0.01
Grapefruit juice, frozen
concentrate, unsweetened, Flavanones Naringenin
diluted with 3 volume water
31.2
0.5
2.0
Flavanones Eriodictyol
Hesperetin
Naringenin
0
0.5
14.2
0
0
0.2
Grapefruit juice, pink, raw
Subclass
1.0 0.52
526.0 13.96
Flavones
Apigenin
0
1.0
0
0
C
Flavonols
Quercetin
0
1.0
0
0
C
Grapefruit juice, white, raw Flavanones Eriodictyol
Hesperetin
Naringenin
99347 Grapefruit, raw
Min
0.7
3.4
20.1
0
0.1
0.2
29.0
29.0
32.0
0
0
0
11.4
34.9
58.0
B
B
B
0
18.0
1.0
0
0
0
0
C
B
1.0
1.0
9.0
0
0.1
0
0
0.1
0.5
B
B
C
Flavones
Apigenin
Luteolin
0
.
Flavonols
Kaempferol
Myricetin
Quercetin
0
0.1
0.1
Flavanones Hesperetin
Naringenin
1.5
53.0
0
0
2.0
2.0
0.5
53.0
0.5
53.0
C
C
Flavonols
0.4
0.5
0
0
2.0
2.0
0.4
0.5
0.4
0.5
C
C
Kaempferol
Quercetin
0.1
a
USDA nutrient data bank number.
Number of samples.
c
Confidence code (it is esignated as A, B. C, or D for a general indicator of the quality of the data,
and A is the best).
b
14
Naringin concenrstion in the juices of three Florida grapefruit cultivars:
Mansell et al. (1983) conducted an analysis of naringin content of 6,686 grapefruit juice
samples of three cultivars collected from three Florida State Test Houses. They reported
that an average naringin concentration of 41.2 mg/100 ml was detected and the range of
concentration was from 0.6 to 211.5 mg/100 ml. Juice samples from Duncan grapefruit
contained the lowest mean concentration of naringin (37.5 mg/100 ml). Pink seedless
samples contained an average naringin concentration of 41.2 mg/100 ml, and Marsh
White seedless contained the highest mean naringin concentration of 45.1 mg/100 ml.
Naringin concentration in grapefruit juices and its distribution in Ruby Red
grapefruit tissues:
Jourdan et al. (1983) in German developed a radioimmunoassay (RIA), rather than HPLC
methods, to quantify the naringin concentrations of grapefruit juices. Their assays
showed that the concentration of naringin in 15 commercial grapefruit juices, obtained
from German’s markets, ranged from 20 to 70 mg/100 ml with the average being 44.6 
13.5 mg/100 ml of juice. This range coincided with the “slightly bitter” to “bitter” taste
classification for naringin concentration.
In the same study, the authors (Jourdan et al., 1983) also examined the distributions of
naringin within different Ruby Red grapefruit tissues using the RIA method. Their
approach was that a 1-cm thick cross tissue section was cut from the middle of a Ruby
Red grapefruit, and the individual tissues were dissected, extracted, and analyzed for the
concentration of naringin. Fig. 3 shows the results of naringin concentrations within
different Ruby Red grapefruit tissues. It can be seen that the order of naringin
concentration of different tissues within a Ruby Red grapefruit is: core tissue (11.4 mg/g
fresh tissue) > sac membrane (9.4 mg/g fresh tissue) > albedo (6.2 mg/g fresh tissue) >
flavedo (3.5 mg/g fresh tissue) > seeds (1.4 mg/g fresh tissue) > juice (0.2 mg/g fresh
weight).
15
Fig. 3. Distribution of naringin in a 1-cm thick cross section of a Ruby Red grapefruit.
gfwt = gram fresh weight. Data source: J. Agric. Food Chem., Jourdan et al., 1983.
16
Variations of naringin concentrations among grapefruit varieties:
Maurer et al. (1950) analyzed naringin concentrations within different grapefruit tissues
among 6 grapefruit varieties. Their results are shown in Table 5. The pink and red
grapefruit varieties tended, on the whole, to have less naringin than the light-fleshed
Marsh and Duncan grapefruit varieties. In all varieties, the percentage of naringin in the
grapefruit decreased as the season progressed. The most significant decrease of naringin
during the harvest season in 1948 was between October 13 and November 17, when the
naringin content of the juice dropped, on the average, by 66%. The juice at all times with
the season contained less naringin than did the peel, membrane, or core tissues.
17
Table 5. Distribution of naringin in Texas grapefruit harvested in 1948
____________________________________________________________________________________
Section
Varieties
Dates picked Flavedo Albedo mambrane
Core
Juice
(mg/100 grams fresh tissue or 100 ml of juice)
____________________________________________________________________________________
Oct. 13
1730
4000
2920
3510
95
Duncan
Nov. 17
560
2520
890
1130
49
(white, seedy)
Dec. 23
570
2000
790
1200
35
Jan. 27
450
1490
690
1280
15
Marsh
Oct. 13
(white, seedless) Nov. 17
Dec. 23
Jan. 27
2380
610
670
670
5350
2040
2690
2370
2910
740
1350
1380
2420
970
1070
1670
130
43
54
19
Thompson
(pink)
Oct. 13
Nov. 17
Jan. 27
5450
770
570
4900
2430
2110
2050
680
900
1340
740
1000
95
35
13
Foster
(pink)
Oct. 13
Nov. 17
Dec. 23
Jan. 27
1400
670
1050
570
4120
2300
3320
2040
2100
930
1410
840
2600
920
1680
1170
133
35
31
19
Ruby Red
(Henninger)
Oct. 13
Nov. 17
Dec. 23
Jan. 27
1250
410
510
590
4020
2460
4100
2750
3070
1150
1160
1270
5420
1480
2240
1580
74
19
19
39
Webb
(Redblush)
Oct. 13
2430
4950
1700
2920
86
Nov. 17
550
2530
1260
2060
23
Dec. 23
710
3750
1560
1560
19
Jan. 27
540
1880
990
1190
16
____________________________________________________________________________________
Data were from Maurer et al. (1950)
18
Total concentrations of flavonone, flavone/flavonol in different fruit tissues of 9
grapefruit cultivars:
A survey of phenolic compounds in citrus was conducted by the USDA, and it provided
estimated amounts of flavanones, and flavones/flavonols in flavedo, albedo, and juice
vesicle tissues of 9 different grapefruit cultivars based on the identification by ultraviolet
spectra (Berhow et al., 1998). Their results are shown in Table 6. However, the Table 6
only shows the concentrations of two groups of flavonoids in different fruit tissues, and it
does not show the total concentrations of individual flavonoid compounds. It can be seen
that there are large differences in total concentrations of flavonones and flavone/flavonol
among 9 grapefruit cultivars. Within a grapefruit, albedo had the highest concentrations
of flavanones compared to flavedo and juice. But flavedo had the highest concentration
of flavones/flavonols compared to albedo and juice (Berhow et al., 1998).
19
z
Table 6. Total concentrations of flavone/flavonol and flavanone in Citrus paradisi (grapefruit)
C. paradisi cultivers
z
Fruit part
Flavone/Flavonol
(mg/100 g fresh tissue)
Flavanone
(mg/ 100 g fresh tissue)
Camulos
Flavedo
Albedo
Juice
51
5
2
116
769
128
CRC #343
Flavedo
Albedo
Juice
37
0
0
74
953
147
Duncan
Flavedo
Albedo
Juice
0
0
0
64
565
63
Hall
Juice
3
38
Jochimsen
Flavedo
Albedo
Juice
46
5
4
109
395
39
Reed Seedling Marsh
Juice
2
31
Star Ruby
Flavedo
Albedo
Juice
22
10
5
121
1503
139
Whitney Old Line Marsh
Juice
5
73
Yellow Rind Mandarin
Flavedo
Albedo
Juice
82
57
6
96
107
30
Data source: USDA Technical Bulletin Number 1856 (Berhow et al., 1998)
20
Flavonoid concentrations in different fruit tissues of 9 grapefruit cultivars:
The USDA’s survey of phenolic compounds produced in citrus quantitatively analyzed
individual flavonoid compounds in flavedo, albedo and juice of 9 grapefruit cultivars
using HPLC methods. Their results are presented in Table 7 (Berhow et al., 1998). This
survey demonstrated that a variety of flavanones (at least 12) were present in grapefruit
cultivars. The concentrations of individual flavanones in different grapefruit cultivars
varied largely. Of tested cultivars, Camulos, CRC #343, Duncan, Jochimsen, Star Ruby
and Whitney Old Line Marsh contained large percentages of naringin. However, Hall,
Reed Seedling Marsh and Yellow Rind Mandarin grapefruit cultivars contained only
flavonoid rutinosides and did not accumulate naringin, naringin-6”-malonate, naringin4’-glucoside or poncerin. Within a grapefruit, albedo tissue contained more naringin,
neohesperindin, narirutin than that of flavedo tissue or juice. Flavones, rhoifilin,
isorhoifolin and diosmin, were also detected from some grapefruit cultivars such as Star
Ruby (Berhow et al., 1998).
21
Table 7: Flavanone composition in Citrus paradisi (grapefruit)y
C. paradisi cultiver
Fruit
part
NTGz DID ERC HSP NRT NER NRG NGG NHP NMO PON NMC
(mg/ 100 gram fresh weight)
Camulos
Flavedo 0
Albedo 10
Juice
tr
0
10
tr
0
0
0
0
0
0
20
80
20
0
tr
0
80
580
90
0
20
tr
10
10
tr
0
20
tr
0
0
0
tr
40
10
CRC #343
Flavedo tr
Albedo 10
Juice
tr
0
0
0
0
50
10
0
40
10
10
40
10
20
90
10
10
270
40
0
20
tr
20
420
60
0
10
tr
0
0
0
0
10
0
Duncan
Flavedo
Albedo
Juice
0
0
0
0
0
0
0
0
0
0
0
0
10
40
10
0
0
0
50
490
50
0
tr
0
tr
0
0
tr
10
0
0
0
0
0
20
tr
Hall
Juice
0
0
0
40
tr
0
0
0
0
0
0
0
Jochimsen
Flavedo
Albedo
Juice
0
tr
0
0
0
0
0
0
0
10
0
10
20
40
10
0
0
0
70
320
20
0
10
0
10
0
0
30
10
0
0
0
0
0
10
0
Reed Seedling Marsh
Juice
0
0
0
30
tr
0
0
0
0
0
0
0
Star Ruby
Flavedo
Albedo
Juice
0
0
tr
0
10
0
0
0
0
0
0
0
10
140
20
0
10
0
100
1130
100
0
30
0
tr
20
tr
10
70
tr
0
0
0
0
70
tr
Whitney Old Line Marsh
Juice
tr
0
0
tr
30
0
40
0
0
0
0
tr
Yellow Rind Mandarin
Flavedo
Albedo
Juice
0
0
0
0
0
0
10
10
tr
80
90
30
tr
tr
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
y
Data source: USDA Technical Bulletin Number 1856 (Berhow et al., 1998)
z
Abbreviations: NTG, narirutin-4'-glucoside; DID, didymin; ERC, eriocitrin; HSP, hesperidin; NRT, narirutin;
NER, neoeriocitrin; NRG, naringin; NGG, naringin-4'-glucoside; NHP, neohesperidin; NMO, naringin-6'malonate (open form); PON, poncirin; NMC, naringin-6"-malonate (closed form); tr, trace. Concentrstions
are average of two to four runs, mg/g fresh weight).
22
Flavonoid compounds in different fruit tissues of Marsh grapefruit:
Nogata et al. (2006) analyzed certain flavanones, flavones and polymethoxylated
flavones in juice vesicle, flavedo, albedo and segment epidemis tissues of Marsh
grapefruit. The individual flavonoid compounds and their concentrations in different fruit
tissues from their study are listed in Table 8. Flavanones found in all fruit tissues of
Marsh grapefruit included eriocitrin, narirutin, naringin, neohesperidin, neoponcirin and
pocirin. Flavones found in all fruit tissues of Marsh grapefruit included rutin, rhoifolin
and neodiosmin. Polymethoxylated flavones nobiletin and heptamethoxyflavone were
found in flavedo tissues of Marsh gapefruit. Naringin occurred in the highest
concentration in Marsh grapefruit, followed by poncirin, narirutin, neohesperidin,
neodiosmin, eriocitrin, rhoifolin, neopocirin and rutin. Albedo tissue contained the
highest concentrations of naringin, pocirin, and narirutin compared to other fruit tissues.
Flavedo tissues contained the highest concentrations of rhoifolin and nobiletin, while
albedo tissues contained more neoponcirin and neodiosmin.
23
Table 8. Flavonoid concentrations in Marsh grapefruit tissues
______________________________________________________________________________________
Segment
Flavonoids
Whole fruit Juice vesicle
Peel
Flavedo
Albedo
epidemis
(mg/100 g fresh tissue)
______________________________________________________________________________________
Flavanones
Eriocitrin
Neoeriocitrin
Narirutin
Naringin
Hesperidin
Neohesperidin
Neoponcirin
Poncirin
18.3
0
170
1360
0
21.0
5.3
304
27.5
0
208
1270
0
45.7
4.1
256
9.2
0
190
2100
0
20.3
8.4
462
25.8
0
114
994
0
29.5
5.1
140
0.0
0
231
2700
0
15.2
10.2
638
13.6
0
118
1130
0
16.2
5.5
301
5.1
0
9.5
0
18.5
5.4
0
10.6
0
14.6
5.1
0
18.4
0
11.0
0
0
46.9
0
6.3
7.9
0
2.7
0
13.6
5.5
0
2.1
0
5.7
0
1.0
0
0.2
0
0
0
0
0
4.6
0
0
0
11.1
0
2.2
0
1.1
0
0
0
0
0
0
Flavone
Rutin
Isorhoifolin
Rhoifolin
Diosmin
Neodiosmin
Polymethoxylated
flavone
Sinensetin
Nobiletin
Tangeretin
Heptamethoxyflavone
______________________________________________________________________________________
24
Health benefits of flavonoids:
Flavonoids have long been recognized to possess anti-inflammatory, antioxidant,
antiallergic, hepatoprotective, and antithrombotic, antiviral, and anticarcinogenic
activities (Middleton, et al., 2000; Havsteen, 1984). Flavonoids are typical phenolic
compounds, and therefore, act as potent metal chelators and free redical scavengers
(Middleton, et al., 2000; Middleton and Kandaswami, 1992). Flavonoids are powerful
chain-breaking antioxidants (Middleton, et al., 2000). The detailed information on the
health benefits of flavonoids present in citrus fruit and citrus juice will be discussed in a
separate review.
Summary for flavonoids:
Grapefruit are rich in phytochemicals (phytonutrients) including flavonoids. Flavonoids
can be chemically divided into six subgroups, flavanones, flavonols, flavones, flavanols,
anthocyanidins and isoflavonoids. Based on the information obtained, flavonoids that
have been detected in grapefruit include flavonols, flavones and flavanones. Flavanones
are the dominant flavonoids in grapefruit. Flavonols include kaempferol, myricetin,
and quercetin. Flavones include apigenin 7-β-rutinoside, diosmin, ehoifolin, rhoifolin,
isorhoifolin, tangeritin, nobiletin, and 3,5,6,7,8,3’,4’-heptamethoxyflavone. Flavanones
include: didymin, eriocitrin, eriodictyol, hesperidin, hesperitin, naringin, naringenin,
naringin-4’-glucoside, naringin-6”-malonate, narirutin, narirutin-4’-glucoside,
neoeriocitrin, neohesperidin, poncirin, and dihydrokaempferol glycoside. Naringin
occurs in grapefruit at the highest concentration followed by narirutin, hesperidin,
poncirin, neohesperidin, didymin, and quercetin. The concentration ranges of
naringin, narirutin, hesperidin, poncerin, didymin, neohesperidin and quercetin in
commercial grapefruit juices are 14.6 – 63.8, 1.4 – 11.7, 1.4 – 3.1, 0.1 – 2.7, 0 – 2.0, 0.04
– 1.7, and 0 – 0.9 mg/100 ml, respectively.
Albedo tissues of grapefruit generally contain higher concentrations of flavonoids than
flavedo or juice. Based on the USDA’s report, the total concentration of flavonoids in
albedo, flavedo and juice of Duncan grapefruit was 5.65, 0.64 and 0.63 mg/gram fresh
tissue, respectively. For Star Ruby grapefruit, the total flavonoid concentration in albedo,
25
flavedo and juice was 15.13, 1.43 and 1.44 mg/gram fresh tissue, respectively. Naringin,
narirutin and hesperidin are present in all flavedo, albedo and juice of grapefruit, with the
highest concentrations in albedo tissues. Based on a report (Jourdan et al., 1983), within a
Ruby Red grapefruit, the order of naringin concentration in different tissues was
determined as: core tissue (11.4 mg/g fresh tissue) > juice sac membrance (9.4 mg/g fresh
tissue) > albedo (6.2 mg/g fresh tissue) > flavedo (3.5 mg/g fresh tissue) > seeds (1.4
mg/g fresh tissue) > juice (0.2 mg/g fresh weight). Naringin concentration in grapefruit
and juice basically decreases as citrus season progresses. The biggest concentration
decrease of naringin occurs between October and November.
The contents of individual flavonoid compounds can vary with the different grapefruit
cultivars. For example, Camulos, CRC #343, Duncan, Jochimsen, Star Ruby and
Whitney Old Line Marsh grapefruit cultivars contained large percentages of naringin.
However, Hall, Reed Seedling Marsh and Yellow Rind Mandarin grapefruit cultivars
contained only flavonoid rutinosides and did not accumulate naringin, naringin-6”malonate, naringin-4’-glucoside, or poncerin.
Naringin is the predominant flavonoid compound in grapefruit, and it is also the
predominant bitter compound. Naringin seems to be one of the most important
phytonutrients in grapefruit to be further explored for its medical benefits in order to
promote the marketing of Florida grapefruit and juices. However, other grapefruit
phytochemicals, such as hesperidin, neohesperidin, narirutin, poncerin and quercetin,
may also have important health benefits to humans.
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