Food Chemistry

334 4 Carbohydrates

4.4.5.1.4 α-Dextrin Endo-1,6-α-glucosidase(Pullulanase).............

This enzyme hydrolyzes 1,6-α-D-glucosidic
bonds in polysaccharides, e. g., in amylopectin,
glycogen, and pullulan. Linear amylose frag-
ments are formed from amylopectin.

4.4.5.2 PectinolyticEnzymes....................................

Pectins (cf. 4.4.4.13) in plant foods are attacked

by a series of enzymes. A distinction is made be-
tween:

• Pectin esterases which occur widely in plants
  and microorganisms and demethylate pectin to
  pectic acid (Formula 4.166).


• Enzymes which attack the glycosidic
  bond in polygalacturonides (Table 4.28).
  These include hydrolases and lyases which
  catalyze a transelimination reaction (see
  Formula 4.167). The double bond formed in
  the product of the last mentioned reaction
  results in an increase in the absorption at
  235 nm.

The second group can be further subdivided ac-
cording to the substrate (pectin or pectic acid)
and to the site of attack (endo-/exo-enzyme), as
shown in Table 4.28. The endo-enzymes strongly
depolymerize and rapidly reduce the viscosity of
a pectin solution.

(4.166)

(4.167)

Table 4.28.Enzymes that cleave pectin and pectic acid

Enzyme EC No. Substrate

Polygalacturonase 3.2.1.15

Endo-polymethyl Pectin

galacturonase

Endo-polygalacturonase Pectic acid

Exo-polygalacturonase 3.2.1.67

Exo-polymethyl Pectin

galacturonase

Exo-polygalacturonase Pectic acid

Pectin lyase 4.2.2.10

Endo-polymethyl Pectin

galacturonlyase

Pectate lyase 4.2.2.2

Endo-polygalacturonate Pectic acid

lyase

Exo-polygalacturonate 4.2.2.9 Pectic acid

lyase

Polygalacturonases occur in plants and microor-

ganisms. They are activated by NaCl and some

by Ca^2 +ions as well.

Pectin and pectate lyases are only produced by

microorganisms. They are activated by Ca^2 +ions

and differ in the pH optimum (pH 8.5–9.5) from

the polygalacturonases (pH 5–6.5).