Agriculture Reference
In-Depth Information
interior appearance of loaves of high-amylose and
waxy forms were inferior to that of the wild type.
However, high-amylose maize starch and fl our
have been the preferred starting material for pro-
ducing ingredients with highly resistant starch
content and/or total dietary fi ber content
(Thompson 2000; Shi and Liu 2002; Okoniewska
et al., 2006). Large-bowel function was improved
in rats fed a diet including high-amylose starch,
suggesting this approach has potential to improve
human health as well.
tocopherols, and oryzanols (Thompson 1994;
Lloyd et al., 2000). These phytochemicals play
important structural and defensive roles in grains.
The cereal species (or grain type) and cultivar
infl uence the concentration of whole-grain phy-
tochemicals (Adom et al., 2003). The most impor-
tant groups of phytochemicals found in whole
grains can be classifi ed as phenolics, carotenoids,
vitamin E compounds, lignans, β-glucan, inulin,
and betaine.
Phenolics
Phenolics are compounds possessing one or more
aromatic rings with one or more hydroxyl groups,
and generally are categorized as phenolic acids,
fl avonoids, stilbenes, coumarins, and tannins (Liu
2004). Phenolics are the products of secondary
metabolism in plants, providing essential func-
tions in the reproduction and growth of the plants,
acting as defense mechanisms against pathogens,
parasites, and predators, as well as contributing
to the color of plants. Phenolic compounds in our
diet may provide health benefi ts associated with
reduced risk of chronic diseases.
The concentration of phenolic compounds in
whole-wheat grains is infl uenced by grain type,
cultivar, and the part of the grain sampled (Adom
and Liu 2002; Adom et al., 2003, 2005). These
compounds usually exist as glycosides linked to
various sugar moieties or as other complexes
linked to organic acids, amines, lipids, carbohy-
drates, and other phenols. The most common
phenolic compounds found in whole grains are
phenolic acids and fl avonoids.
Phenolic acids can be subdivided into two
major groups, hydroxybenzoic acid and hydroxy-
cinnamic acid derivatives. The former include
p-hydroxybenzoic, protocatechuic, vannilic,
syringic, and gallic acids. They are commonly
present in the bound form and are typically com-
ponents of a complex structure like lignins and
hydrolyzable tannins. They can also be found in
the form of sugar derivatives and organic acids in
plant foods. Hydroxycinnamic acid derivatives
include p-coumaric, caffeic, ferulic, and sinapic
acids. They are mainly present in the bound form,
linked to cell wall structural components such as
WHEAT PHYTOCHEMICALS
Wheat is one of the major grains in the human
diet accounting for one-third of the total world-
wide grain production. Whole wheat grains are
composed of endosperm, germ, and bran. The
endosperm makes up about 75%-80% of the
grain weight, whereas the germ and bran weights
may vary among different wheat cultivars. Whole
grains are important components of the human
diet as evidenced by their inclusion in the Food
Guide Pyramid and US Dietary Guidelines
(National Research Council 1989). However,
emphasis on whole-grain consumption has been
less than on fruits and vegetables. Previous nutri-
tional guidelines placed grains and grain products
at the base of the food guide pyramid to empha-
size grains or grain product consumption as the
foundation for a healthy diet (USDA 2000,
2005).
The health benefi t of whole-grain consumption
is partly derived from unique phytochemicals in
whole grains which complement those in fruits
and vegetables when consumed together. For
example, various classes of phenolic compounds
in grains include phenolic acids, anthocyanidins,
quinones, fl avonols, chalcones, fl avones, fl ava-
nones, and amino phenolic compounds (Thomp-
son 1994; Maillard and Berset 1995; Shahidi and
Naczk 1995; Lloyd et al., 2000). Some of these
phytochemicals, such as ferulic acid and diferu-
lates, are predominantly found in grains but are
not present in signifi cant quantities in some fruits
and vegetables (Shahidi and Naczk 1995; Bunzel
et al., 2001). Grains also contain tocotrienols,
