Chemical and Functional Properties of Food Saccharides

© 2004 by CRC Press LLC
OSO 2H, OSO 2R, ONO groups. R represents an organic moiety providing the chemical
activity of the X substituents. It is usually an aliphatic carbon chain carrying
additionally a Y substituent. Many Ys, from the hydrogen atom to complex groups,
have been tested. For instance, when Y = COOH, carboxylalkyl starches are formed.
Etherification with compounds carrying amino, alkyl amino, and dialkylamino as
well as quaternized dialkylamino groups leads to cationic starches, which are interesting
additives to cellulose pulp and sizes. Etherification can be performed with
ethylene oxide and aziridine and their derivatives too. When both X and Y functional
groups are capable of nucleophilic substitution or esterification, cross-linking of
starch is possible.
9.2.5 ACETALATION
The hydroxyl groups of starch glucose units are capable of forming hemiacetals
with aldehydes. Cross-linking of starch occurs with dialdehydes. 2 Starch acetals are
formed in reversible reactions. Hence, acetals are fairly unstable during storage and
liberate acetalating aldehyde, which is usually unacceptable in food technology.
However, acetals with such aldehydes as vanillin, eugenol, and other food-aromatizing
aldehydes might have certain applications in food technology as semimicrocapsules.
9.2.6 HALOGENATION
Chlorination of cereals is sometimes used to improve functional properties of flours.
Bleaching is a frequently used process but saccharides are not chlorinated in this
manner. Chlorination can be achieved by reacting starch with such common chlorinating
agents as PCl 3, PCl 5, POCl 3, or SOCl 2, by which the hydroxyl groups of
glucose units are substituted with chlorine.
9.2.7 AMINATION AND CARBAMOYLATION
Amino starches are available by etherification of starch with compounds carrying
amino groups. Treatment of starch with ammonia modifies starch and cereals, particularly,
on thermolysis of starch under ammonia. There is no addition of nitrogencontaining
functional groups to starch. 2 Reaction of starch with amides, particularly
urea, produces carbamoylated starches, which as specific urea-enriched products are
frequently used as a fodder for ruminants.
9.2.8 GRAFT POLYMERIZATION
Reaction of starch with vinyl monomers, that is, compounds with the general structure
of CH 2=CH-X, where X = H, Cl, COOH, CONH 2, COOCH 3, OCOCH 3, and so
on, results in formation of graft starch polymers. These reactions require initiation.
Depending on initiators used, process follows a free radical or an ionic mechanism.
The initiator used influences structure and properties of final products by either
promoting grafting of starch with monomers over polymerization of vinyl monomers