Food Chemistry

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4.4 Polysaccharides 315

Table 4.22.Gelling time of pectins with differing degrees of esterification


Pectin type Esterification degree Gelling timea
(%) (s)


Fast gelling 72–75 20–70
Normal 68–71 100–135
Slow gelling 62–66 180–250


aDifference 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 condi-
tions 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 or-
gans as a storage carbohydrate. As an ingredient
of many foods, it is also the most important carbo-
hydrate source in human nutrition. In addition,
starch and its derivatives are important industri-
ally, for example, in the paper and textile indus-
tries.
Starch is isolated mainly from the sources listed
in Table 4.23. Starch obtained from corn, pota-
toes, cassava, and wheat in the native and modi-
fied form accounted for 99% of the world produc-
tion in 1980. Some other starches are also avail-
able 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 prod-
ucts.
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 1980a

Raw materials of indus-
trial 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
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