Barley for Food and Health: Science, Technology, and Products

80 BARLEY: GENETICS AND NUTRIENT COMPOSITION
phytonutrients, and when extracted and purified, they are often called nutraceuticals.
Grains in general contain different types of phytochemicals, and in barley
the most researched compounds are sterols, tocotrienols, flavonols, and phenolic
compounds (Groupy et al. 1999). Much of the antioxidant activity in grains,
including barley, comes from insoluble phenolic compounds such as ferulic acid,
which are esterified to cell wall polysaccharides (arabinoxlans) and lignin (Bunzel
et al. 2004).
The greatest concentrations of phytosterol compounds are located in the outer
layers of the kernel (Lampi et al. 2004). These authors reported 797 and
1738 mg/kg in whole hulless barley (cv. Doyce) and pearling fines, respectively.
In a follow-up study in the same laboratory using a seed scarifier, Moreau et al.
(2007) removed approximately the same amount of pearling fines (about 11 to
15%) from two hulled (cv. Throughbred and cv. Nomini) and two hulless (cv.
Doyce and Merlin) barleys. Total kernel phytosterols averaged 818 and 2349
mg/kg (fresh weight), respectively.
Zupfer et al. (1998) determined the concentrations of ferulic acid in 18 cultivars
of two- and six-rowed barleys grown at two locations in Minnesota. The
ferulic acid concentrations ranged from 365 to 605 mg/kg of dry weight. The concentration
of ferulic acid varied significantly among the cultivars. These authors
inferred a genetic basis for ferulic acid concentration due to the similar ranking
of the cultivars at the two locations. In a study reported by Holtekjølen et al.
(2006), ferulic acid was the most abundant phenolic acid, accounting for 52 to
69% of the total, ranging from 403 to 723 mg/kg in 16 different barley cultivars,
including hulled, hulless, waxy, and nonwaxy types. Higher levels of ferulic acids
were observed in hulled varieties than in the hulless cultivars. These results were
similar to those reported by Hernanz et al. (2001) and Moreau et al. (2007).
Holtekjølen et al. (2006) also reported on the concentration of proanthocyanidins
(flavonols). The main flavonols found were the catechins, procyanidin B 3 ,
and prodelphinidin B 3 . A waxy hulless Canadian barley, CDC Alamo, contained
the highest catechin content, almost three times the levels in the cultivars with
the lowest levels. Total flavonol content ranged from a low of 325 to a high of
527 mg/kg. The cultivars with the highest total flavonols were a hulled six-rowed
Norwegian barley, Thule, followed by CDC Alamo. Ragaee et al. (2006) reported
that barley contains more total phenols (as gallic acid equivalent) than hard and
soft wheat, but less than millet, rye, and sorghum.
Certain of the phytochemicals found in barley are pigments that produce kernels
of many different colors, including white, blue, black, purple, and red;
however, only varieties with blue or white kernels are grown extensively, and
the white varieties dominate. Black pigmentations of various parts of the barley
plant is generally due to the presence of melanins. Red or purple colors are
due primarily to anthocyanins (Takahashi 1955). The purple and blue colors in
barley kernels are usually the results of a phenolic compound on the surface of
the grains, particularly the anthocyanins. Many shades of the basic colors are
possible, due to combinations of anthocyanins and their interactions with other
phenolic compounds (Mazza and Miniati 1993). Mazza and Gao (2005) cited