Table 2 Different types of pectic substances and pectinolytic enzymes responsible for its degradation

1.

Protopectin: Protopectin is present in the inner tissues of plant cell walls which is insoluble in water. Upon restricted hydrolysis yields pectin or pectic acids

2.

Pectic acid: Pectic acids are soluble pectic substances (galacturonans) with lesser number of methoxyl groups. Normal and pectic acid salts are called as pectates

3.

Pectinic acids: Are long polygalacturonans with < 75% methylated galacturonate units, salts of pectinic acids are called pectinates

4.

Pectin: (or) Polymethyl galacturonate is a polymeric material with 75% of the carboxyl groups are esterified with methanol. Pectin provides rigidity to the plant cell walls

Pectinolytic enzymes

1.

Pectin methyl esterases: These esterases catalyze the de-esterification pectin by releasing methoxy esters, resulting in pectic acids and methanol

2.

Pectin-depolymerizing enzymes

(a) Protopectins are enzymatically hydrolyzed by set of enzymes called as protopectinases (PPase). PPase are classified into two types (a) A-type PPase, which reacts with polygalacturonic acid regions and (b) B-type PPase reacts with the polysaccharide chains on outer region. (Protopectin_(insoluble) + H₂O–(PPase)– → Pectin_(soluble))

(b) The pectin-depolymerizing enzymes can be majorly classified as hydrolases divided into: Endo and Exo polygalacturonases such as (Exo-polygalacturonan-digalacturono hydrolase, Oligo galacturonate hydrolase, Delta 4:5 Unsaturated oligo galacturonate hydrolases, Endo-polymethyl-galacturonases, Endo-polymethyl-galacturonases). Lyases which majorly contains enzymes such as Endo and Exo polygalacturonase lyases