Food Biochemistry and Food Processing

568 Part V: Fruits, Vegetables, and Cereals

as its relatively good overwintering ability guarantee
continuing interest in the cereal, as it can be cultivat-
ed in areas generally not suited for other cereal
crops. In 2003, high amounts of rye were produced
by Russia (4.1 million tons), Poland (3.2 million
tons), Germany (2.3 million tons), and Belarus (1.4
million tons) (FAO 2004), making this cereal crop of
major importance in parts of Europe and Asia, but
of less importance in America. Production has re-
mained fairly constant, but with a downward trend,
during the past 10 years.

THE RYE KERNEL

The main components of the rye kernel are, from the
outside to the inside, the hull, pericarp, testa, nucel-
lar epidermis, aleurone and starchy endosperm, and
the germ. As the hull threshes free, the pericarp is
the actual outer part of the grain, surrounding the
seed and consisting of different layers, ranging from
the epidermis, hypodermis, and cross cells to tube
cells. The latter adhere to the testa or seed coat,
which is in turn lined with the nucellar epidermis.
The aleurone cells are located beneath the nucellar
epidermis, forming the outermost layer of the en-
dosperm tissue, and merge with the scutellum of the
germ. The starchy endosperm is composed of three
main cell types, that is, the subaleurone or peripheral
cells, the prismatic cells, and the central endosperm
cells, and contains two major storage reserves. The
subaleurone cells contain high levels of storage pro-
tein, while the prismatic cells contain high levels of
starch granules (Shewry and Bechtel 2001). The
pericarp, testa, and nucellar epidermis form the
botanical bran and are separated from the starchy

endosperm together with the aleurone layer and the

germ in the milling process, forming the technical or

miller’s bran.

RYE CONSTITUENTS

The major rye constituents are starch and nonstarch

polysaccharides and protein. Its lipids, vitamins, and

minerals are minor constituents (Table 25.1).

STARCH

Starch Composition

Starch granules are mainly composed of two types

of polymers, amylose and amylopectin. In general,

amylose is an essentially linear polymer consisting

of 
-D-glucopyranose residues linked by 
-1,4

bonds with few (
1%; Ball et al. 1996) 
-1,6

bonds. Amylose occurs in both free and lipid-

complexed forms. Lipid-complexed amylose may be

present in native starch, but is possibly also formed

during gelatinization of starch (Andreev et al. 1999,

Morrison 1995). Amylose contents in rye starch

vary from 12 to 30% (Andreev et al. 1999, Fred-

riksson et al. 1998, Mohammadkhani et al. 1998,

Wasserman et al. 2001). Berry et al. (1971) reported

the rye amylose fraction to have a molecular weight

of about 220 k.

Amylopectin is a highly branched polymer con-

sisting of 
-D-glucopyranose residues linked by 
-

1,4 linkages with 4–5% (according to Keetels et al.

1996) 
-1,6 linkages. Berry et al. (1971) showed

that rye amylopectin has 4.8% branching, with

branch points about every 21 glucose units on aver-

Table 25.1.Composition of the Rye Kernel

Constituent Content (%) References

Starch 57.0–65.6 Aman et al. 1997, Hansen et al. 2004

Nonstarch polysaccharide 13.0–15.0 Härkönen et al. 1997

Arabinoxylan 6.5–12.2 Aman et al. 1997; Hansen et al. 2003, 2004;

Henry 1987; Vinkx and Delcour 1996

Mixed-linkage -glucan 1.5–2.6 Aman et al. 1997, Hansen et al. 2003, Henry 1987

Cellulose 2.1–2.6 Aman et al. 1997, Vinkx and Delcour 1996

Arabinogalactan peptide 0.2 Van den Bulck et al. 2004

Fructan 4.6–6.6 Hansen et al. 2003, Karpinnen et al. 2003

Protein 8.0–17.7 Fowler et al. 1990, Hansen et al. 2004

Lipid 2.0–2.5 Härkönen et al. 1997, Vinkx and Delcour 1996

Mineral 1.7–2.2 Aman et al. 1997, Hansen et al. 2004