Food Chemistry

4.4 Polysaccharides 327

adipic or citric acids, are obtained in reactions
with the reactive derivatives (e. g., vinyl acetate)
or by heating the starch with free acids or their
salts. The thickening and paste clarity properties
of the esterified starch are better than in the cor-
responding native starch.
In addition, esterified starch has an improved
freeze–thaw stability. These starches are utilized
as thickeners and stabilizers in bakery products,
soup powders, sauces, puddings, refrigerated
food, heat-sterilized canned food and in mar-
garines. The starch esters are also suitable as
protective coatings, e. g., for dehydrated fruits
or for aroma trapping or encapsulation (cf.
Table 4.26).

4.4.4.15.8 Cross-LinkedStarches

Cross-linked starches are obtained by the reac-
tion of starch (R OH) with bi- or polyfunctional
reagents, such as sodium trimetaphosphate, phos-
phorus oxychloride, epichlorohydrin or mixed an-
hydrides of acetic and dicarboxylic acids (e. g.,
adipic acid):

(4.154)

(4.155)

(4.156)

The starch granule gelatinization temperature
increases in proportion to the extent of cross-
linking, while the swelling power decreases
(Fig. 4.38). Starch stability remains high at
extreme pH values (as in the presence of food
acids) and under conditions of shear force.
Cross-linked starch derivatives are generally used
when high starch stability is demanded.

Fig. 4.38.Corn starch viscosity curves as affected

by crosslinking degree. Instruments: Brabender amy-

lograph;acontrol,bcrosslinked with 0.05%,c 0 .10%,

d 0 .15% epichlorohydrin (according toPigman, 1970)

4.4.4.15.9 OxidizedStarches.......................................

Starch hydrolysis and oxidation occur when aque-

ous starch suspensions are treated with sodium

hypochlorite at a temperature below the starch

gelatinization temperature range. The products

obtained have an average of one carboxyl group

per 25–50 glucose residues:

(4.157)

Oxidized starch is used as a lower-viscosity filler

for salad dressings and mayonnaise. Unlike thin-

boiling starch, oxidized starch does not retrograde

nor does it set to an opaque gel.

4.4.4.16 Cellulose

4.4.4.16.1 Occurrence,Isolation

Cellulose is the main constituent of plant cell

walls, where it usually occurs together with hemi-

celluloses, pectin and lignin. Since cellulase en-

zymes are absent in the human digestive tract, cel-

lulose, together with some other inert polysaccha-

rides, constitute the indigestible carbohydrate of

plant food (vegetables, fruits or cereals), referred

to as dietary fiber. Cellulases are also absent in

the digestive tract of animals, but herbivorous an-