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CHAPTER 104
Antioxidants in Pecan
Nut Cultivars [Carya
illinoinensis (Wangenh.)
K. Koch]
Ana G. Ortiz-Quezada, Leonardo Lombardini, Luis Cisneros-Zevallos
Department of Horticultural Sciences, Fruit and Vegetable Improvement Center,
Texas A&M University, College Station, Texas, USA
CHAPTER OUTLINE
Introduction 881
Botanical Description 882
Historical Cultivation and
Usage 882
Present-Day Cultivation and
Usage 883
Applications to Health Promotion
and Disease Prevention 883
Adverse Effects and Reactions
(Allergies and Toxicity) 887
Summary Points 888
References 889
LIST OF ABBREVIATIONS
AC, antioxidant capacity
CAE, chlorogenic acid equivalents
CE, catechin equivalents
CT, condensed tannins
DPPH, 2, 2-diphenyl-1-picrylhydrazyl
GAE, gallic acid equivalents
HPLC-MS, high performance liquid chromatography-mass spectrometry
ORAC, oxygen radical absorbance capacity assay
PDA, photodiode array
TE, Trolox equivalents
TP, total phenolics
INTRODUCTION
Pecan [Carya illinoinensis (Wangenh.) K. Koch] is the most valuable nut tree native to North
America. Over 1000 different pecan varieties have been described, although 90% of cultivated
acreage is represented by only a few dozen varieties. Pecan kernels contain about 70% lipids,
881
Nuts & Seeds in Health and Disease Prevention. DOI: 10.1016/B978-0-12-375688-6.10104-5
Copyright Ó2011 Elsevier Inc. All rights reserved.
namely oleic (over 60%), linoleic, palmitic, stearic, and linolenic acids. Pecans’ antioxidant
capacity, considered one of the highest among nut crops, comes from the non-lipid portion,
and is cultivar-dependent. Defatted pecan kernels contain mainly condensed and hydrolyzable
tannins. After a consecutive base/acid hydrolysis, phenolics released are mainly gallic acid,
catechin, epicatechin, ellagic acid, and ellagic acid derivatives.
BOTANICAL DESCRIPTION
Pecan has been known for centuries for its edible nuts. The species is distributed over a broad
geographic area, encompassing tremendous climatic variation. The native range of pecan
extends for about 26in latitude, from northern Iowa (lat. 42200N) to Oaxaca in Mexico (lat.
16300N) (Figure 104.1)(Thompson & Grauke, 1991). Pecan trees grow abundantly along
the Mississippi River, the rivers of central and eastern Oklahoma, and on the Edwards plateau
of Texas. The long tap roots and the frequent presence of shallow water tables allow
native trees to survive the severe hot and dry summers that characterize the area of native
distribution. However, the deeper the water source, the greater is the energy expended to
obtain it, which leads to diversion of valuable energy from the developing leaves and nuts.
HISTORICAL CULTIVATION AND USAGE
The pecan is the only nut crop native to the North American continent that has significant
commercial importance. All other major nut crops have been imported from other areas of the
world. The term “pecan” derives from the word pacane, which is the Algonquin word for “nut
that must be cracked with a stone” (Brison, 1974). Spanish explorers in the 16th century came
to refer to them as “pacanos,” or sometime simply nueces (nuts) or nogales, due to their
resemblance to the fruit of the Persian walnut, Juglans regia L. The botanical name of the
species was chosen because Carya is the ancient Greek name for walnut, and because one of the
earliest indications of pecan use by Native Americans goes back to archaeological evidence
found in present-day Illinois, dating from 9000 years ago. The archeological findings,
combined with the descriptions made by the first Europeans during the 16th century, show
that pecans were an essential ingredient for most Native American tribes of the southern part of
what is now the United States. There is also evidence that some migration patterns traced the
FIGURE 104.1
Native distribution of pecan. Native distribution of pecans includes south central states of the United States and different
regions of Mexico (from Thompson & Grauke, 1991).
882
PART 2
Effects of Specific Nuts and Seeds
pecan season along alluvial plains and other fertile areas of modern Mexico and the United
States. Pecan trees were revered by Native Americans not only as a food source. Members of the
Ojibwa tribe utilized the wood of pecan and other hickories to make bows and finish off
baskets. Additionally, pecan paste and oil, as well as leaf or bark infusions, were used by other
tribes as abatement for several illnesses, such as intestinal worms, constipation, skin eruptions,
rheumatism, gastrointestinal problems, and colds, or as facilitator in abortions. Despite the
importance of pecans for Native Americans, it is almost certain that the Natives only relied on
large groves of uncultivated or wild pecan trees, without making use of any widespread
horticulture techniques to propagate and cultivate these trees. It was not until the mid-1800s
that farmers began to realize the commercial value, plus the culinary importance, of pecans,
and started developing horticultural techniques to maximize production. In 1847, it took
a slave gardener (remembered only by his first name of Antoine) at the Oak Alley Plantation,
Louisiana, to develop a technique to graft an improved variety (“scion”) onto a different tree
(“rootstock”). This episode marked the beginning of the modern pecan industry, because it
allowed mass propagation of those trees which showed desirable characteristics, such as high
kernel percentage (high meat content), resistance to diseases and insects, and reduced alternate
bearing characteristics (Worley, 1994).
PRESENT-DAY CULTIVATION AND USAGE
A little bit more than a century and a half after Antoine’s breakthrough discovery, pecan is
today an economically important tree-nut crop for the United States and Mexico, with an
annual economic value of about $300 million for the United States alone. There are over 1000
different pecan varieties that have been described, classified as either native or improved
varieties.
Native trees or seedlings are those that have not been grafted with improved varieties. The
latter are those that have been genetically altered through selection, and controlled, and are
usually associated with more intensive horticultural practices, but sell at a premium price
compared with native varieties because they usually produce larger kernels and are perceived as
higher quality products. The majority of the improved acreage in the United States comprises
only four varieties (Stuart, Western Schley, Desirable, and Wichita), and about 90% of the
acreage comprises 33 varieties. In recent years, other varieties, such as Pawnee, have been
extensively planted in newly established orchards; however, official data are not available
(T.E. Thompson, personal communication).
A survey conducted recently in Texas reported that most pecan consumers prefer to purchase
shelled pecans to use them as ingredient in food dishes (Figure 104.2)(Lombardini et al.,
2008). The United States and Mexico are the greatest producers of this nut. In the United
States, Georgia, New Mexico, and Texas are the major producers for improved varieties,
whereas fruits from native and seedlings trees are mainly from Oklahoma and Texas
(Table 104.1).
APPLICATIONS TO HEALTH PROMOTION AND
DISEASE PREVENTION
Pecan kernels are sources of protein, dietary fiber, vitamins, minerals, and many other
bioactive substances, also called phytochemicals, which are known to provide health benefits.
According to the US Department of Agriculture Nutrient Database (USDA, 2009), pecan
kernels contain 72% lipids, 14% carbohydrates, 9% protein, 3.5% water, and 1.5% ash.
Regarding the vitamins and minerals, pecan kernels are a good source of vitamins A and E, the
B vitamins, folic acid, calcium, magnesium, potassium, and zinc.
Clinical studies with human subjects have shown that consuming pecans and other tree nuts
may play an important role in reducing the risk of heart disease by improving the serum lipid
CHAPTER 104
Pecan Nut Cultivars and Antioxidants
883
profile. These benefits are mainly due to their high unsaturated fatty acid content (Rajaram
et al., 2001). Little information is available about the phytochemicals contained in the non-
fatty portion of pecan kernels, which is believed to protect the oil. Around 97% of the total
antioxidant capacity of pecans, measured by oxygen radical absorbance capacity assay
(ORAC), comes from the hydrophilic portion. Wu et al. (2004) screened pecan kernels from
unidentified cultivar(s), and nine other tree nuts, and found that pecans had the highest
antioxidant capacity by ORAC (179.40 mmol TE/g) and total content of phenolics (20.16 mg
of GAE/g). In another study, 98 common foods were screened for their proanthocyanidin
content, or condensed tannin. It was found that within the nut group, pecans from uniden-
tified cultivar(s) had the second highest content (494 mg/100 g fresh weight), after hazelnuts
(500 mg/100 g fresh weight) (Gu et al., 2004).
Recently, the phytochemical constituents in defatted pecan kernels were investigated (Villar-
real-Lozoya et al., 2007) in six cultivars (Desirable, Kanza, Kiowa, Nacono, Pawnee, and
Shawnee) chosen for their commercial relevance. Results showed significant differences due to
cultivar and, to a lesser extent, to orchard location. The study also revealed that a large portion
of the antioxidant capacity was attributable to the total phenolics (TP), and especially to the
condensed tannins (CT), by a ratio ranging from 0.31 to 0.56 CT/TP (Figure 104.3). Total
phenolics measured by Folin-Ciocalteau spectrophotometric assay as chlorogenic acid
equivalents ranged from 62 to 102 mg CAE/g defatted pecan. Condensed tannins were
measured with the vanillin assay as catechin equivalents per gram defatted pecan, and their
values were between 25 and 47 mg CE/g defatted pecan. After base and acid hydrolysis of an
aqueous acetone extract of the defatted matrix, catechin, epicatechin, gallic acid, ellagic acid,
0 102030405060708090100
Frequency (% respondents)
0 102030405060708090100
Frequency (% respondents)
Ingredients in food dishes
Raw snack
Semiprepared snack (roasted, salted, spiced)
Other
Other
I do not use pecans
I do not buy pecans
Meal
Shelled (halves)
Pieces
In-shell
Cracked shell
Prepared (chocolate-covered, roasted, spiced)
FIGURE 104.2
Purchasing behavior (top) and consuming
preference (bottom) in regards to pecan, as
emerged from a survey conducted in Texas.
Pecan halves and pieces are preferentially
purchased by consumers and used mainly as
ingredients in food dishes and snacks (from
Lombardini et al., 2008).
PART 2
Effects of Specific Nuts and Seeds
884
and an ellagic acid derivative were identified (Villarreal-Lozoya et al., 2007). The compounds
found in greater concentrations were gallic acid (651e1300 mg/g defatted pecan) and ellagic
acid (2505e4732 mg/g defatted pecan), but no significant differences were detected among
cultivars. ORAC values ranged from 373 to 817 mmol TE/g defatted pecan, and strong corre-
lations were found between antioxidant capacity and TP, as well as with condensed tannins
(Villarreal-Lozoya et al., 2007). The range values obtained for CT/TP and AC
ORAC
/TP imply
that proportions of condensed and hydrolyzable tannins differ for each cultivar, and this
proportion determines the specific antioxidant activity of the phenolics present in each cultivar
(Villarreal-Lozoya et al., 2007).
The main fatty acids found in the lipid fraction of pecan kernels were oleic (over 60%), linoleic,
palmitic, stearic, and linolenic. Pecans are considered to have high amounts of g-tocopherol,
along with walnuts, while almonds and hazelnuts are rich in a-tocopherol. Tocopherol content
in pecans varies by cultivar, and other factors such as genetics, environment, maturity, and
storage conditions. Tocopherols (vitamin E) are fat-soluble antioxidants naturally present in
vegetable oils, such as those extracted from olive, almond, and hazelnut. Gamma-tocopherol
values for the six pecan cultivars ranged from 72 to 135 mgg-tocopherol/g oil.
TABLE 104.1 Utilized Pecan Production (31000 lb) in the United States by Variety
and State, 2004e2008
Utilized Production (In-Shell Basis)
Improved Varieties 2004 2005 2006 2007 2008
AL 1,000 3,200 5,400 10,000 7,400
AZ 14,000 22,000 14,000 23,000 17,500
AR 1,000 1,100 1,150 1,500 1,000
CA 3,500 3,900 3,400 4,400 3,750
FL 400 300 200 1,700 1,400
GA 42,000 72,000 36,000 135,000 66,000
LA 2,500 1,000 3,500 3,000 1,000
MS 700 800 2,000 2,200 900
MO 200 160 2 110
NM 39,000 65,000 47,000 74,000 43,000
NC 70 1,650 420 160 600
OK 6,000 6,000 5,000 3,000 1,000
SC 800 1,500 900 1,500 3,000
TX 28,000 50,000 33,000 44,000 20,000
US 138,970 228,650 152,130 303,462 166,660
Native and Seedlings 2004 2005 2006 2007 2008
AL 100 800 600 2,000 600
AR 700 1,200 1,050 800 500
FL 100 700 300 200 300
GA 3,000 8,000 6,000 15,000 4,000
KS 1,800 3,200 2,000 500 1,900
LA 6,500 4,000 17,500 11,000 4,000
MS 300 200 500 800 600
MO 2,400 940 3 830
NC 30 350 80 40 100
OK 22,000 15,000 12,000 27,000 4,000
SC 300 700 200 500 400
TX 12,000 15,000 14,000 26,000 10,000
US 46,830 51,550 55,170 83,843 27,230
Georgia, New Mexico, and Texas are the leading states in pecan production for improved varieties, whereas Texas, Oklahoma,
Louisiana, and Georgia lead native and seedling production.
Source: USDA Economics, Statistics and Market Information System (http://usda.mannlib.cornell.edu).
CHAPTER 104
Pecan Nut Cultivars and Antioxidants
885
Nut shells were also analyzed for total phenolic content and condensed tannins for the six
cultivars. Interestingly, their TP and CT values were 6 and 18 times higher than the ones found
in the defatted kernels. It was concluded that phenolics from shells are mainly formed by
condensed tannins (TP zCT), and their presence may affect the content of kernel phenolics.
It has been suggested that tannins leach from shells to kernels during soaking and precon-
ditioning during commercial processing. Another possible source of leaching could be
cold-room storage prior to cracking and shelling, due to water condensation inside the nuts as
a result of small temperature fluctuations. Shells represent a large by-product of the pecan
industry, with the shell percentage in pecan nuts varying from 40% to 50% (Worley, 1994).
Processing plants have found only a limited market for pecan shells, with minimal profit.
Thus, the high antioxidant capacity observed shows a potential alternative use of pecan shells
as a novel source of antioxidants.
The presence of high contents of phenolic compounds, tocopherol, and mononounsaturated
fatty acid suggest several health benefits. Phenolic compounds have been reported to protect
against atherosclerosis, hypertension, cardiovascular diseases, cancer, and viral infections, and
to act as general antioxidants. Tannins are water-soluble phenolic compounds of high
molecular weight, and are classified as condensed (proanthocyanidins) or hydrolyzable
(gallotannins or ellagitannins). The prevention of several chronic diseases, including cancer,
cardiovascular and neurological diseases, and inflammation, have been associated with the
intake of tannins. In general, tannins are known to have certain health benefits, such as
antioxidant, anti-allergy, antihypertensive, and antitumor, as well as antimicrobial activities
(Okuda, 2005). Condensed tannins are associated with foods of high antioxidant capacity,
such as wine, cocoa, and grape seed (Gu et al., 2004). Hydrolyzable tannins have been iden-
tified in several fruits and nuts, such as pomegranate juice (Seeram et al., 2007) and walnuts
(Fukuda et al., 2003). Ellagitannins have recently attracted attention because of their antioxi-
dant capacity and their antiproliferative activity, which inhibit prostate cancer growth (Seeram
et al., 2007). Upon hydrolysis, ellagitannins release ellagic acid, which is also of particular
interest, as it reportedly has antiviral properties (Corthourt et al., 1991) and provides protection
against cancers of the colon, lung, and esophagus (Rao et al., 1991; Stoner & Morse, 1997).
A study was conducted to evaluate the differences in phenolic compounds between
organically and conventionally grown pecan cultivars, and it concluded that the effects on
cultivation method vary by cultivar (Malik et al., 2009). Three pecan cultivars were analyzed:
Cheyenne, Desirable, and Wichita. Nine free phenolic compounds were identified: gallic
acid, catechol, m-coumaric acid, catechin, caffeic acid, epicatechin, chlorogenic acid, ellagic
FIGURE 104.3
Positive correlation between total phenolic content and
condensed tannins from defatted pecan kernels. Condensed
tannins are the major components of the total phenolics present
in defatted pecan kernels.
PART 2
Effects of Specific Nuts and Seeds
886
acid, and an ellagic acid derivative. Only catechin, gallic acid, and ellagic acid were present
in sufficient amounts to be quantified. Results showed that organically grown Desirable had
a higher concentration of catechin and ellagic acid (86% and 311%, respectively) than the
conventionally grown; however, there were no significant differences in the levels of gallic
acid. In the other two organically grown varieties, Cheyenne and Wichita, the differences
were smaller, but followed the same trend. It was concluded that growing organic pecans
could increase the phenolic content in the kernel, but that results may depend on the
cultivar investigated.
In another study, the condensed and hydrolyzable tannins present in kernels from four
cultivars (Choctaw, Desirable, GraCross, and Kiowa) were identified (Ortiz-Quezada et al.,
unpublished data) (Figure 104.4). Extracts of defatted pecan powder were obtained to
measure total phenolics (TP) and antioxidant activities, using 2, 2-diphenyl-1-picrylhydrazyl
(DPPH) and the ORAC assay. GraCross and Desirable had a significantly higher TP content,
but only GraCross showed a high CT content and antioxidant capacity by DPPH and ORAC
(Figure 104.5). Nonetheless, the ellagitannin content, as measured after a 2-M HCl hydro-
lysis by HPLC, showed inverse results, as Desirable and Kiowa had the highest ET value,
followed by Choctaw, and lastly by GraCross. Extracts were analyzed by HPLC-MS, and
tannins were identified in the negative ion mode according to their retention times, PDA
and mass spectra, daughter ions, and fragmentation patterns. Thirteen ellagitannins were
identified, but three other ellagitannins have not yet been characterized (599, 951 and
1085 m/z); free ellagic acid was also found. The masses of these ellagitannins ranged from
433 to 1207 m/z. Now that the chemistry of defatted pecan has been characterized, health
benefit assays can be performed in order to find alternative uses for pecan and understand
their mechanisms of action.
A study in progress will explore the effects of pecan metabolites on adipogenesis, as an anti-
obesity assay at the molecular level.
ADVERSE EFFECTS AND REACTIONS (ALLERGIES AND TOXICITY)
Pecan kernels can be allergenic for sensitive population. A 2S albumin, Car i 1, has been
characterized as the allergen contained in pecan protein. Another group of allergens
FIGURE 104.4
HPLC chromatogram of the main hydrolyzable
tannins from defatted Choctaw pecan kernels at
280 and 360 nm. Peaks were defined by mass
spectrometry, including (1) 2, 3 HHDP-glucose
(RT, 2.96 min; l
max
247; 481 m/z); (2)
Pedunculagin isomer (RT, 7.81 min; l
max
247;
783 m/z); (3) Galloyl pedunculagin (RT, 11.68 min;
l
max
248; 951 m/z); (4) Glausrin C (RT, 15.54 min;
l
max
270; 933 m/z); (5) Ellagic acid pentose
conjugate (RT, 19.35 min; l
max
249, 360; 433 m/z);
(6) Ellagic acid (RT, 20.42 min; l
max
246, 271,
365; 301 m/z); (7) Ellagic acid galloyl pentose
conjugate (RT, 22.24 min; l
max
247, 359; 585 m/z);
(8) Ellagic acid galloyl pentose conjugate (RT,
23.5 min; l
max
246, 360; 585 m/z).
CHAPTER 104
Pecan Nut Cultivars and Antioxidants
887
(neoallergens), characterized by the same molecular weight as the original allergen, can
develop during storage or after a thermal treatment, such as baking or roasting (Malanin et al.,
1995). These neoallergens can derive from protein degradation due to autolysis that involves
the interaction with hydrolyzed sugars (Maillard or browning reaction) (Berrens, 1996).
Consequently, several individuals that are not allergic to raw or fresh pecans may develop
symptoms in response to heated or stored pecan kernels. Another study found no toxicity for
pecan color after feeding at a concentration of 5% to female rats for 90 days (Sekita et al.,
1998).
Indirect toxicity caused by ingestion of pecan kernels may be also caused by mold developing
during storage at relatively high humidity. Even without apparent shell damage, spores of
Aspergillus spp. and Penicillium spp. may be present in the kernel (Doupnik & Bell, 1971).
Aspergillus is of special concern, since it produces aflatoxins, which are toxic and carcinogenic,
especially to the liver. If pecans are moldy, aflatoxins may be present above safe levels
of <20 ppb.
SUMMARY POINTS
lPecan is the most valuable nut tree native to North America.
lPecan use by Native Americans goes back to archaeological evidence found in present-day
Illinois, dating from 9000 years ago.
lOver 1000 different pecan varieties have been described.
lThe United States and Mexico are the greatest producers of this nut.
lPecan’s high antioxidant capacity comes from the non-lipid portion.
FIGURE 104.5
(A) Total phenolic content; (B) condensed tannin content; (C) antioxidant capacity by DPPH; (D) antioxidant capacity by
ORAC of four pecan cultivars. The effects of pecan variety on phenolic content and the corresponding antioxidant activity.
GraCross variety showed the overall highest phenolic and antioxidant activity.
PART 2
Effects of Specific Nuts and Seeds
888
lDefatted pecan kernels contain phenolic compounds; the main ones are gallic acid,
catechin, epicatechin, ellagic acid, and ellagic acid derivatives.
lThese individual phenolics are arranged in polymers as condensed and hydrolyzable
tannins.
lPecan nut shells contain mainly condensed tannins.
lThese phenolic compounds have been proven to be beneficial against several cancers and
inflammation, and to have antiviral and antihypertensive activity, among others.
lThe identified allergen is a 2S albumin called Car i 1.
lPecans can become toxic when they get moldy.
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