Pectinase

Pectinases are a group of enzymes that breaks down pectin, a polysaccharide found in plant cell walls, through hydrolysis, transelimination and deesterification reactions. Commonly referred to as pectic enzymes, they include pectolyase, pectozyme, and polygalacturonase, one of the most studied and widely used commercial pectinases. It is useful because pectin is the jelly-like matrix which helps cement plant cells together and in which other cell wall components, such as cellulose fibrils, are embedded. Therefore, pectinase enzymes are commonly used in processes involving the degradation of plant materials, such as speeding up the extraction of fruit juice from fruit, including apples and sapota. Pectinases have also been used in wine production since the 1960s. The function of pectinase in brewing is twofold, first it helps break down the plant (typically fruit) material and so helps the extraction of flavors from the mash. Secondly the presence of pectin in finished wine causes a haze or slight cloudiness. Pectinase is used to break this down and so clear the wine.

Pectinases can be extracted from fungi such as Aspergillus niger. The fungus produces these enzymes to break down the middle lamella in plants so that it can extract nutrients from the plant tissues and insert fungal hyphae. If pectinase is boiled it is denatured (unfolded) making it harder to connect with the pectin at the active site, and produce as much juice.

Characterizations

Pectinase is a generic term used for a group of enzymes that catalyse the degradation of pectin by hydrolysis, trans-elimination, as well as de-esterification reactions. The degradation of pectic polymers is mainly caused by exo- and endo-polygalacturonases (exo- and endo-PGs), pectate and pectin lyases (PLs), pectin methylesterase (PME) and acetylesterase (PAE), β-galactosidase (β-Gal), and α-L-arabinofuranosidase (α-L-Af), among others.

• Endo-polygalacturonase (E.C. 3.2.1.15) is known to be the most important enzyme responsible for pectic depolymerization and solubilization. This enzyme hydrolyses the α-1 → 4 glycosidic bonds of the methyl de-esterified homogalacturonan backbone. The enzyme randomly attacks its substrate and produces a number of D-GalA oligosaccharides.
• Exo-polygalacturonase (E.C. 3.2.1.67 and E.C. 3.2.1.82) attacks the substrate from the non-reducing end and is able to remove terminally (1→)–linked D-GalA residues from homogalacturonan chains. The enzyme requires a non-esterified D-GalA unit at subsites −2, −1, and + 1 and is tolerant for xylose substitution (able to remove a D-GalA-Xyl dimer), hence XGA is also an exo-polygalacturonase substrate.
• PLs (pectate lyases, E.C. 4.2.2.2, and pectin lyases, E.C. 4.2.2.10) acts through the β-elimination of methyl esterified homogalacturonan in the presence of Ca²⁺, Mn²⁺, or Ni²⁺.

Optimum environment

As with all enzymes, pectinases have an optimum temperature and pH at which they are most active. For example, a commercial pectinase might typically be activated at 45 to 55 °C and work well at a pH of 3.0 to 6.5.

(1,4-alpha-D-galacturonosyl)_n+m + H₂O = (1,4-alpha-D-galacturonosyl)_n + (1,4-alpha-D-galacturonosyl)_m

Occurrence and Application

Pectinase in nature

Pectinase enzymes used today are naturally produced by fungi and yeasts (50%), insects, bacteria and microbes (35%) and various plants (15%), but cannot be synthesized by animal or human cells. In plants, pectinase enzymes hydrolyze pectin that is found in the cell wall, allowing for new growth and changes to be made. The chemical and structural properties of pectin is especially prone to changes in the fruit due to solubilization and enzymatic degradation which are considered to be the key processes responsible for the softening of fruit during ripening. Structural changes that occur in the middle lamella and primary cell wall during ripening result in cell separation and softening of the tissues. The molecular components of primary walls are modified during fruit ripening by the temporally and spatially regulated action of endogenous enzymes.

Similarly to their role in plants, pectinases break down pectin during the developmental stage of fungi.

Industrial uses

Pectinase enzymes play various roles in both the fruit juice and wine industries. They are used for clarification in fruit juices and also speed up fruit juice extraction through enzymatic liquefaction of fruit pulp. In addition, pectinase enzymes aid in formation of pulpy products in the fruit juice industry. Pectinase enzymes are used for extracting juice from purée. This is done when the enzyme pectinase breaks down the substrate pectin and the juice is extracted. The enzyme pectinase lowers the activation energy needed for the juice to be produced and catalyzes the reaction.

Pectinases are useful in the wine industry by extracting anthocyanin from the fruit, effectively intensifying the wine coloring. Pectinase can also be used to extract juices from cell walls of plants cells.

Pectinases are also used for retting in the textile industry. Addition of chelating agents or pretreatment of the plant material with acid enhance the effect of the enzyme.

References