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

118 BARLEY PROCESSING: METHODS AND PRODUCT COMPOSITION
containing larger concentrations of bran. This presents a set of unique problems
to many food manufacturers, particularly in achieving palatability, texture, and
mouthfeel in products (Fulcher and Rooney-Duke 2002). Replacing some of the
starch in mixtures to be extruded by inclusion of fibrous ingredients alters the
plasticity of the mixture and shifts the balance between expandable and nonexpandable
material. The results of added fibrous material are products with lower
expansion and higher density. Production of such products requires modification
of extruder conditions to achieve consumer acceptable products (Fulger 1988).
As in other processing methods, barley presents a unique blend of components
that significantly influence extrusion processing characteristics and end products.
Primary factors are the β-glucan and TDF contents, but starch type (normal, waxy,
and high-amylose) can also require major procedural adjustments to apply extrusion
techniques successfully to barley. Although limited information is available
on extrusion processing of barley flour, a few reports appear in the scientific
literature. Østergård et al. (1989) reported that dietary fiber content of barley
flour increased with extrusion cooking, whereas starch content decreased. Heryford
(1987) extruded four barley cultivars using a laboratory-scale single-screw
extruder (Insta-Pro, Des Moines, Iowa) and reported increased viscosity in all
of the products extruded, although total and soluble β-glucans were decreased
by extrusion. This effect was probably due to molecular changes in the starch.
Berglund et al. (1994) studied the feasibility of producing RTE breakfast cereals
by extruding barley flour and blends of barley flour with rice or wheat flour using
a corotating twin-screw extruder. Cereals produced by extrusion of 100% barley
flour had limited expansion and high bulk density. Blending barley flour with 50%
rice flour reduced bulk density by 50%, producing a product similar in appearance
to 100% rice flour cereal. Extrusion increased β-glucan content and extract
viscosity measurements of the barley flour blends. These authors concluded that
extruding barley flour blends with rice flour produced RTE cereals comparable
in crispness, color, and flavor to that of extruded 100% rice flour products.
Huth et al. (2000) studied the effects of extrusion on the formation of resistant
starch in two barley cultivars differing in amylose content. The varieties
studied were Korna, containing 22.4% amylose starch and 2.4% total β-glucan,
and HiAmi Cheri having starch that contained 29.0% amylose and 6.1% total
β-glucan. After dehulling and pin-milling the barley, extrusion was accomplished
with a single-screw laboratory extruder (DN 20, Brabender, Duisburg, Germany).
The highest contents of resistant starch (6%) were generated by using a mass temperature
of about 150 ◦ C and about 20% moisture during extrusion followed by
storage at −18 ◦ C for 3 to 7 days. Under these conditions, the macromolecular
state of β-glucan was preserved. These authors concluded that barley cultivars
with high amylose and high β-glucan contents are preferred to produce extruded
barley foods with enhanced nutritional qualities.
The effects of extrusion cooking on properties of barley β-glucans in nonwaxy
and waxy barley cultivars were examined by Gaosong and Vasanthan
(2000). The barleys were pearled and pin-milled into flour prior to extrusion.
For both cultivars, β-glucan in the extruded flours had solubility values higher