Agriculture Reference
In-Depth Information
cellulose, lignin, and proteins through ester
bonds. Ferulic acid occurs primarily in the seeds
and leaves of plants, mainly covalently conjugated
to mono- and disaccharides, plant cell wall poly-
saccharides, glycoproteins, polyamines, lignin,
and insoluble carbohydrate biopolymers. Wheat
bran is a good source of ferulic acid, which is
esterifi ed to hemicellulose molecules in cell walls.
Food processing, such as thermal processing, pas-
teurization, fermentation, and freezing, contrib-
utes to the release of this bound phenolic acid
(Dewanto et al., 2002).
Ferulic, caffeic, p-coumaric, protocatechuic,
and vannilic acids are present in almost all plants.
Chlorogenic acids and curcumin are also major
derivatives of hydroxycinnamic acids present in
plants. Chlorogenic acids are the ester form of
caffeic acids and are the substrate for enzymatic
oxidation leading to browning. Curcumin is made
of two ferulic acid molecules linked by a methy-
lene in a diketone structure.
The common phenolic acids found in whole
grains such as wheat include ferulic acid, vanillic
acid, caffeic acid, syringic acid, and p-coumaric
acid (Sosulski et al., 1982). Ferulic acid (
trans
-4-
hydroxy-3-methoxycinnamic acid) is one of the
most common phenolic acids found in wheat
grains (Sosulski et al., 1982; Abdel-Aal et al.,
2001; Yang et al., 2001; Adom et al., 2003). It is
abundant in the aleurone, pericarp, and embryo
cell walls of various grains, but occurs only in
trace amounts in the endosperm (Smith and
Hartley 1983). Ferulic acid and other phenolic
acids protect whole grain kernels by providing
both physical and chemical barriers through
cross-linking carbohydrates, antioxidant activities
to combat destructive radicals, and astringency
that deters consumption by insects and animals
(Hahn et al., 1983; Arnason et al., 1992). Higher
concentrations of ferulic acid in grains increase
dimerization, which affects the physical and
chemical properties of grain structure. Caffeic
acid and other ortho-phenolic acids have been
linked to suppression of colon cancer in model
animal systems (Drankhan et al., 2003; Carter
et al., 2006).
Ferulic acid can exist in the free, soluble-
conjugated, and bound forms in wheat grains.
Bound ferulic acid was signifi cantly higher (>93%
of total) than free and soluble-conjugated ferulic
acid in maize, wheat, oat (
Avena sativa
L.), and
rice (
Oryza sativa
L.) (Adom and Liu 2002). The
ratio of free, soluble-conjugated, and bound
ferulic acid in maize and wheat was 0.1 : 1 : 100.
The order of total ferulic acid content among the
tested grains was maize > wheat > oat > rice
(Adom and Liu 2002).
Grain ferulic acid content differs among culti-
vars. For example, Adom et al. (2003) observed
signifi cant differences (up to twofold) among 11
wheat cultivars for total ferulic acid, which existed
mostly in the bound form (>97%) in all cultivars.
Similarly, signifi cant genetic variability in ferulic
acid content was reported in durum wheat (three-
fold) and common wheat (twofold) (Lempereur
et al., 1997). In another study, signifi cant differ-
ences among wheat cultivars in ferulic acid content
corresponded to levels of enzymes involved in
phenolic acid metabolism (Régnier and Macheix
1996). Ferulic acid content was similar among
cultivars during successive phases of grain devel-
opment, but fi nal concentrations in wheat were
different among cultivars. Ferulic acid content
also varied signifi cantly for some wheat cultivars
grown in different environments, with about a
13% difference in mean ferulic acid content
(Abdel-Aal et al., 2001).
Carotenoids
Carotenoids are nature's most widespread pig-
ments with yellow, orange, and red colors, and
they have received substantial attention for their
provitamin and antioxidant roles. Carotenoids are
classifi ed into hydrocarbons (carotenes) and their
oxygenated derivatives (xanthophylls). More than
600 carotenoids have been identifi ed in nature.
They occur widely in plants, microorganisms,
and animals. Carotenoids have a 40-carbon skel-
eton of isoprene units. The structure may be
cyclized at one or both ends, have various hydro-
genation levels, or possess oxygen-containing
functional groups. Lycopene and β-carotene are
examples of acyclized and cyclized carotenoids,
respectively. Carotenoid compounds most com-
monly occur in nature in the all-trans form. The
