25 Rye Constituents and Their Impact on Rye Processing 569age. The chains of amylopectin can be classified into
three types: A-, B-, and C-chains. The A-chains are
unbranched outer chains and are attached to the
inner B-chains through their potential reducing end.
In their turn, the B-chains are attached to other B-
chains or to the single C-chain through their poten-
tial reducing end. The C-chain is the only chain car-
rying a reducing end group. Lii and Lineback (1977)
reported an A-chain to B-chain ratio of 1.71–1.81
and an average unit chain length of 26 for rye amy-
lopectin.
Minor components of starch granules are lipids,
proteins, phosphorus, and ash.
Starch Structure
Rye starch has a bimodal particle size distribution
comprising a major population of large, lenticular
A-type granules ( 10 m, 85%), and a minor pop-
ulation of small, spherical B-type granules ( 10
m, 15%) (Schierbaum et al. 1991, Verwimp et al.
2004). Rye A-type starch granules have larger aver-
age particle sizes and broader particle size distribu-
tion profiles than their wheat counterparts (Fred-
riksson et al. 1998, Verwimp et al. 2004).
In starch granules, the amylose and amylopectin
molecules are radially ordered, with their single
reducing end groups towards the center, or hilum.
Ordering of crystallites within the starch granule
causes optical birefringence, and a Maltese cross
can be observed under polarized light. Starch gran-
ules are made up of alternating semicrystalline and
amorphous growth rings, arranged concentrically
around the hilum. The amorphous growth ring con-
tains amylose and probably less-ordered amylop-
ectin (Morrison 1995). The semicrystalline growth
ring consists of alternating crystalline and amor-
phous lamellae. The crystalline lamellae are built
from amylopectin double helices, whereas the amor-
phous lamellae contain the branch points of the
amylopectin side chains (Andreev et al. 1999, Gal-
lant et al. 1997). Evidence has been provided that
the crystalline and amorphous lamellae of the amy-
lopectin are organized into larger, more or less
spherical blocklets (Gallant et al. 1997).
The structure of starch can be studied at different
levels by several techniques such as optical micro-
scopy, scanning electron microscopy, transmission
electron microscopy, and X-ray diffraction. X-ray
diffraction provides information about the crystal
structure of the starch polymers, but also about the
relative amounts of the crystalline and amorphous
phases. Cereal starches have an A-type X-ray diffrac-
tion pattern, while B-type and C-type X-ray diffrac-
tion patterns are characteristic for tuber and root
starches and for legume starches, respectively. C-type
starches are considered to be mixtures of A-type and
B-type starches. In general, rye starches show A-type
X-ray diffraction patterns, but some researchers
(Gernat et al. 1993, Schierbaum et al. 1991) also
reported a significant B-type portion.Starch Physicochemical PropertiesThe physicochemical gelatinization, pasting, gela-
tion, and retrogradation properties of starches are
important parameters in determining the behavior of
cereals in food systems.
When a starch suspension is heated above a char-
acteristic temperature (the gelatinization tempera-
ture) in the presence of a sufficient amount of water,
the starch granules undergo an order-disorder transi-
tion known as gelatinization. The phenomenon is
accompanied by melting of the crystallites (loss of
X-ray pattern), irreversible swelling of the granules,
and solubilization of the amylose. Gelatinization
can be studied by measuring the loss of birefrin-
gence of the starch granules when observed under
polarized light. The end point and the range of tem-
peratures at which gelatinization occurs can be
determined. For rye starch, birefringence end point
temperatures of 59.6°C (Klassen and Hill 1971) and
58.0°C (Lii and Lineback 1977) were reported.
These birefringence end point temperatures were
somewhat lower than those observed for wheat
starches by the same authors. Another technique
often used to study gelatinization-associated phe-
nomena is differential scanning calorimetry (DSC).
DSC enables determination of onset, peak, and con-
clusion gelatinization temperatures, gelatinization
temperature ranges, and gelatinization enthalpy. The
gelatinization temperature is a qualitative index of
crystal structure, whereas gelatinization enthalpy is
a quantitative measure of order. The DSC technique
also measures the temperature and enthalpy of the
dissociation of the amylose-lipid complexes. Rye
starches show an onset of gelatinization at rather low
temperatures. Gudmundsson and Eliasson (1991) re-
ported onset gelatinization temperatures of 54.8–
60.3°C, Radosta et al. (1992) of 53.5°C, and Verwimp