**3. Pectolytic enzymes**

202 Food Industrial Processes – Methods and Equipment

acetylated at the C-2 and C-3 positions, and side chains of residues of neutral sugars may be linked to the galacturonic acid or to the C-4 of the rhamnose residue in the main chain (Caffall & Mohnen, 2009; Mohnen, 2008; Pilnik & Voragen, 1970; Rombouts & Pilnik, 1980).

Fig. 1. Structure (main chain) of low (a) and high (b) methylated pectic substances and site of

The generic name of pectic substances is used for referring to four types of molecules: protopectin (pectic substance in intact tissue), pectinic acids (polygalacturonan containing >0-75% methylated galacturonate units), pectic acids (polygalacturonan that contains negligible amount of methoxyl groups), and pectins (pectinic acid with at least 75% methylated galacturonate units). Protopectines are insoluble in water, while the rest are

Pectic substances represent between 0.5-4% of fresh weight plant material (Jayani et al., 2005; Sakai et al., 1993). In addition to their role as cementing and lubricating agents in the cell walls of higher plants, they are responsible for the texture of fruits and vegetables during growth, maturation and their storage (Alkorta et al., 1998; Caffall & Mohnen, 2009). Furthermore, pectic substances are involved in the interaction between plant hosts and their

Pectins have numerous and important applications in the food and pharmaceutical industries. In the food sector, it is primarily used as a gelling agent, replacing sugars and/or fats in low-calorie food and as nutritional fiber (Panchev et al., 1988; Sakai et al., 1993; Thakur et al., 1997). The pharmaceutical industry offers them as preparations to reduce cholesterol or to act as a lubricant in the intestines thus promoting normal peristaltic movement without causing irritation. In addition, these polysaccharides are used as drug delivery systems, which can also reduce the toxicity of these and make their activity longer lasting without altering their therapeutic effects (Morris et al., 2010; Pilnik & Voragen, 1970;

wholly or partially soluble in water (Alkorta et al., 1998; Kertesz, 1951).

action of enzymes involved in their degradation

a

b

pathogens (Collmer & Keen, 1986; Prade et al., 1999).

Schols et al., 2009; Thakur et al., 1997).

The enzymes which hydrolyze pectic substances are known as pectic enzymes, pectinases or pectinolytic enzymes (Blanco et al., 1999). Based on its mode of action and substrate preference these enzymes are classified into three types:

I. Protopectinases, which solubilize protopectin forming soluble pectin

II. Esterases (pectin methyl esterases and pectin acetyl esterases), which eliminate methoxyl and acetyl residues from pectin giving rise to polygalacturonic acid

III. Depolymerases, which break the glycosidic α-(1- 4) bonds between galacturonic residues via:

1. Hydrolysis (polygalacturonases)

2. Transelimination (pectin lyases and pectate lyases)

Also, the latter enzymes are subdivided into endo- if its pattern of action is random or exoif its pattern of action is at the terminal end (Fogarty & Kelly, 1983; Rexova-Bencova & Markovie, 1976; Sakai, 1992; Whitaker, 1990). The detailed classification of these enzymes, their mode of action and final product are shown in Table 1 and in Fig. 1.


Table 1. Pectolytic enzymes classified according to its mode of action
