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

WHOLE-GRAIN PROCESSING 99
increased in the pearlings up to about 30% pearling and then remained stable,
while the starch level showed a continued increase with pearling up to 80%. In
a pearling study reported by Pedersen et al. (1989), the hull and seed coat were
in the first pearling fraction (11% of the total), the germ and aleurone made up
the second pearling fraction (11 to 25% of the total), and the remaining 75%
found in the third pearling fraction was composed primarily of the endosperm.
Nutrient composition of the pearling fractions represented the component parts
of the kernel from which the fractions originated. Sumner et al. (1985) compared
the pearling characteristics of waxy and nonwaxy hulled and hulless barley at
three extraction rates—high, medium, and low—resulting in yields of 84, 7l, and
56% pearl barley, respectively. Protein percentages were decreased in the pearl
barley and increased in the pearlings at each successive extraction level, with
opposite effects on the percentage of starch. Percentages of ash and fat were also
decreased in the pearled barley with concomitant increases in the pearlings, and
were highest in pearlings obtained from 71% extraction. This was indicative of the
mineral and oil contents of the outer layers of the kernel and germ, respectively.
Bhatty and Rossnagel (1998) compared the composition of 12 Canadian and
seven Japanese barleys pearled to 55% extraction in a Satake mill. The Canadian
barleys were hulless, whereas only two of the Japanese barleys were hulless.
Both groups of cultivars responded to pearling in a similar manner, although
differences were found in the ratio of protein and starch between the Canadian
and Japanese barleys. Fiber type and level differed due to the presence of hull in
some of the Japanese barleys. Protein, ash, and total dietary fiber (TDF) decreased
in the pearled barley kernel compared to the whole-grain kernels, whereas starch
level and extract viscosity increased. Soluble dietary fiber (SDF) and β-glucan
levels were essentially the same in whole and pearl barley. The data of Bhatty
and Rossnagel (1998) shown in Table 5.1 are representative of those reported
in most pearling studies (Norman et al. 1965; Bach Knudsen and Eggum 1984;
Sumner et al. 1985; Pedersen et al. 1989). In this study, three of the 12 Canadian
barleys were waxy, which had the highest levels of SDF and β-glucans in the
pearled kernels of all barleys, including the Japanese cultivars.
Zheng et al. (2000) and Yeung and Vasanthan (2001) compared pearling characteristics
of nonwaxy and waxy hulless barleys. In both of these studies, β-glucan
levels in the pearled kernels of nonwaxy barley showed a sharp increase up to
about 25% pearling, followed by a gradual decrease toward the center of the
kernel. These data suggested highest concentrations of β-glucan in aleurone, subaleurone,
and outer starchy endosperm of nonwaxy barley. In contrast, a gradual
increase in β-glucans in the pearled kernels of waxy barley indicated a positive
concentration gradient of these compounds toward the center of the kernel. These
data and those of others confirm earlier reports, such as those of Ullrich et al.
(1986) and Xue et al. (1997), concerning the positive relationship between the
waxy gene and β-glucan levels in barley.
Pearled barley and pearling by-products were obtained from two commercial
stocks of hulled nonwaxy barley of English and Italian origin (Marconi et al.
2000). The barleys were pearled using an industrial process in five consecutive