*1.1.2 Classification of pectin*

The pectin polymer is divided into protopectin, pectic acid, pectinic acid and pectin because of variation in backbone chain of galacturonic acid residues [15].

#### *1.1.2.1 Protopectin*

Protopectin term is used to illustrate the insoluble pectin. It is parent pectin and yield pectin or pectinic acid on restricted hydrolysis.

#### *1.1.2.2 Pectic acid*

Pectic acid contains insignificant amounts of methoxy groups. It is soluble form of pectin.

#### *1.1.2.3 Pectinic acid*

Pectinic acid is the polygalacturonan that contains various amounts of methoxy groups having the property to form gel with sugar and acid.

#### *1.1.2.4 Pectin (Polymethylgalacturonate)*

Pectin is the polygalacturonic acid in which the galacturonic acid residues are 75% methylated.

#### *1.1.3 Distribution of pectin in nature*

Pectin is widely disturbed in nature and mostly found in angiosperms and gymnosperms plants along with pteridophytes, bryophytes, lycophytes and carophytes [16]. The pectin represents 35% of total plant biomass and among the high percentage containing biomolecules in plants [17]. The concentration of pectin in plants varied according to the plant types, maturation time and its environmental conditions (**Table 1**). The 100 grams of citrus peels and apple pomaces contained 20 grams of pectin and have been used for commercial extraction of pectin [21].

#### *1.1.4 Commercial utilization of pectin*

Pectin has been used in various industrial processes and applications due to its biocompatibility, cost-effective, easily available and among the most abundant natural compounds on earth. The food additive, thickening agent, gelling agent, cosmetic texturizing agent, a good source of dietary fiber and also components of biodegradable films, adhesives, paper and antimicrobial food packaging are the major applications of


#### **Table 1.**

*Pectin content in various fruits.*

pectin in industries [22]. The mechanism of enzymatic modification of pectin polymer needs to be understood to further increase the industrial scope of pectin polymer.
