peanut shells. The mature peanut shells had higher concentrations of luteolin; also
with maturation there was an increase in the flavonoid concentration in the hull
(Pendse et al. 1973). The effectiveness of flavonoids, eriodictyol,
5,7-dihydroxychromone, and luteolin isolated from peanuts, was later confirmed in
a separate study (Duh and Yen 1995, 1997; Duh et al. 1992). Peanut skins (testae), a
low-value by-product having dark pink color and tangy taste are obtained after
removal from the seed and are mostly used as a constituent of cattle feed (Stalker
et al. 2016). In the mid-1900s, they were considered poisonous; however research
into their constituents proved that it contained useful oligomer pro-anthocyanidins in
addition to flavanols (Yu et al. 2005). Furthermore, studies revealed that the skins of
mature peanuts contain up to six different types of pro-anthocyanidins and account
for 17% of the weight. Isolated pro-anthocyanidins include pro-cyanidins A1 and A2
and 3 epi-catechin oligomers. Furthermore, eight types of flavonoids; two types of
indole-based-alkaloids; pro-anthocyanidins, B2, B3, and B4; and epicatechin-4-β
were also isolated from the peanut skins (Lou et al. 2001). In another study, flavanols
known as catechins (type A and B procyanidin dimers, trimers, and tetramers) were
also detected in peanut skins (Yu et al. 2006). Flavanols and isoflavones, due to their
antioxidant potential, have been implicated in the prevention of cardiovascular
diseases and cancer (Fraser et al. 1992; Ros and Hu 2013; Ellsworth et al. 2001;
Pfeffer et al. 1995; Bao et al. 2016).
4.1.5.2 Phytosterols
Chemically, sterols are alcohols of steroids and are an important constituent of cell
membranes in eukaryotes. Phytosterols are specifically synthesized by plants which
include sterols and stanols. Their generic structure is the same as cholesterol with an
additional alcohol molecule as a side chain and can exist either as free molecules, as
steryl glycosides, or as esterified to fatty acids. The most commonly occurring
phytosterols include campesterol, β-sitosterol, and stigmasterol. Phytosterols can
impede the absorption of cholesterol from the gut and are also poorly absorbed
through the gut (Ostlund Jr 2004; Racette et al. 2015; Moreau et al. 2018; Gylling
and Simonen 2015).
Peanuts and peanut-derived products both contain phytosterols (Table 4.7). The
Valencia variety has the highest amount of phytosterols whether raw
(0.023–1.792 μg/g), roasted (dry and fried) (0.018–0.080 μg/g), and in the form of
peanut butter (0.148–0.504 μg/g) (Sobolev and Cole 1999). Aboriginal cultivars
from Bolivia, Peru, and South America have seven types of phytosterols
(4-desmethylsterols): campesterol, stigmasterol, Δ 7-stigmasterol, cholesterol,
β-sitosterol, Δ 4-avenasterol, and Δ 7-avenasterol. In commercial species
(A. hypogea L), the concentrations of stigmasterol and β-sitosterol increase as the
peanut matures, whereas the campesterol levels remain constant throughout the
ripening process (Shin et al. 2010; Mora-Escobedo et al. 2015; Li et al. 2009).
Peanut oil, however, has slightly lower concentration of phytosterols (2.7–9.6 ppm)
due to the steps involved in refining process (such as filtration, heating, and
4 Groundnut (Peanut) (Arachis hypogaea)
101
with maturation there was an increase in the flavonoid concentration in the hull
(Pendse et al. 1973). The effectiveness of flavonoids, eriodictyol,
5,7-dihydroxychromone, and luteolin isolated from peanuts, was later confirmed in
a separate study (Duh and Yen 1995, 1997; Duh et al. 1992). Peanut skins (testae), a
low-value by-product having dark pink color and tangy taste are obtained after
removal from the seed and are mostly used as a constituent of cattle feed (Stalker
et al. 2016). In the mid-1900s, they were considered poisonous; however research
into their constituents proved that it contained useful oligomer pro-anthocyanidins in
addition to flavanols (Yu et al. 2005). Furthermore, studies revealed that the skins of
mature peanuts contain up to six different types of pro-anthocyanidins and account
for 17% of the weight. Isolated pro-anthocyanidins include pro-cyanidins A1 and A2
and 3 epi-catechin oligomers. Furthermore, eight types of flavonoids; two types of
indole-based-alkaloids; pro-anthocyanidins, B2, B3, and B4; and epicatechin-4-β
were also isolated from the peanut skins (Lou et al. 2001). In another study, flavanols
known as catechins (type A and B procyanidin dimers, trimers, and tetramers) were
also detected in peanut skins (Yu et al. 2006). Flavanols and isoflavones, due to their
antioxidant potential, have been implicated in the prevention of cardiovascular
diseases and cancer (Fraser et al. 1992; Ros and Hu 2013; Ellsworth et al. 2001;
Pfeffer et al. 1995; Bao et al. 2016).
4.1.5.2 Phytosterols
Chemically, sterols are alcohols of steroids and are an important constituent of cell
membranes in eukaryotes. Phytosterols are specifically synthesized by plants which
include sterols and stanols. Their generic structure is the same as cholesterol with an
additional alcohol molecule as a side chain and can exist either as free molecules, as
steryl glycosides, or as esterified to fatty acids. The most commonly occurring
phytosterols include campesterol, β-sitosterol, and stigmasterol. Phytosterols can
impede the absorption of cholesterol from the gut and are also poorly absorbed
through the gut (Ostlund Jr 2004; Racette et al. 2015; Moreau et al. 2018; Gylling
and Simonen 2015).
Peanuts and peanut-derived products both contain phytosterols (Table 4.7). The
Valencia variety has the highest amount of phytosterols whether raw
(0.023–1.792 μg/g), roasted (dry and fried) (0.018–0.080 μg/g), and in the form of
peanut butter (0.148–0.504 μg/g) (Sobolev and Cole 1999). Aboriginal cultivars
from Bolivia, Peru, and South America have seven types of phytosterols
(4-desmethylsterols): campesterol, stigmasterol, Δ 7-stigmasterol, cholesterol,
β-sitosterol, Δ 4-avenasterol, and Δ 7-avenasterol. In commercial species
(A. hypogea L), the concentrations of stigmasterol and β-sitosterol increase as the
peanut matures, whereas the campesterol levels remain constant throughout the
ripening process (Shin et al. 2010; Mora-Escobedo et al. 2015; Li et al. 2009).
Peanut oil, however, has slightly lower concentration of phytosterols (2.7–9.6 ppm)
due to the steps involved in refining process (such as filtration, heating, and
4 Groundnut (Peanut) (Arachis hypogaea)
101