2009_Book_FoodChemistry

4.4 Polysaccharides 315
Table 4.22. Gelling time of pectins with differing degrees of esterification
Pectin type Esterification degree Gelling time a
(%) (s)
Fast gelling 72–75 20–70
Normal 68–71 100–135
Slow gelling 62–66 180–250
a Difference between the time when all the prerequisites for gelling are
fulfilled and the time of actual gel setting.
4.4.4.13.3 Utilization
Since pectin can set into a gel, it is widely used in
marmalade and jelly production. Standard conditions
to form a stable gel are, for instance: pectin
content <1%, sucrose 58–75% and pH 2.8–3.5.
In low-sugar products, low-ester pectin is used in
the presence of Ca 2+ ions. Pectin is also used to
stabilize soured milk beverages, yoghurts and ice
creams.
4.4.4.14 Starch
4.4.4.14.1 Occurrence, Isolation
Starch is widely distributed in various plant organs
as a storage carbohydrate. As an ingredient
of many foods, it is also the most important carbohydrate
source in human nutrition. In addition,
starch and its derivatives are important industrially,
for example, in the paper and textile industries.
Starch is isolated mainly from the sources listed
in Table 4.23. Starch obtained from corn, potatoes,
cassava, and wheat in the native and modified
form accounted for 99% of the world production
in 1980. Some other starches are also available
commercially. Recently, starches obtained
from legumes (peas, lentils) have become more
interesting because they have properties which
appear to make them a suitable substitute for
chemically modified starches in a series of products.
Starches of various origin have individual,
characteristic properties which go back to the
shape, size, size distribution, composition,
and crystallinity of the granules. The existing
connections are not yet completely understood
on a molecular basis.
Table 4.23. Raw materials for starch
Raw material
Starch production 1980 a
Raw materials of industrial
importance
Corn 77
Waxy corn
Potato 10
Cassava 8
Wheat 4
Rice
Waxy rice
Other raw materials
Sago palm
Kouzu
Sweet potato
Water chestnut
Arrowroot
Edible canna
Negro corn
Mungo bean
Lotus root
Taro
Lentil
a % of the world production.
In some cases, e. g., potato tubers, starch granules
occur free, deposited in cell vacuoles; hence,
their isolation is relatively simple. The plant
material is disintegrated, the starch granules are
washed out with water, and then sedimented from
the “starch milk” suspension and dried. In other
cases, such as cereals, the starch is embedded
in the endosperm protein matrix, hence granule
isolation is a more demanding process. Thus,
a counter-current process with water at 50 ◦ C
for 36–48 h is required to soften corn (steeping
step of processing). The steeping water contains
0.2% SO 2 in order to loosen the protein matrix
and, thereby, to accelerate the granule release
and increase the starch yield. The corn grain is
then disintegrated. The germ, due to its high oil
content, has a low density and is readily separated
by flotation. It is the source for corn oil isolation
(cf. 14.3.2.2.4). The protein and starch are then