ReviewMicrobial pectinolytic enzymes: A review
Introduction
In nature, microorganisms have been endowed with vast potentials. They produce an array of enzymes, which have been exploited commercially over the years. Pectinases are of great significance with tremendous potential to offer to industry [1]. They are one of the upcoming enzymes of the commercial sector, especially the juice and food industry [2] and in the paper and pulp industry [3], [4].
Pectinolytic enzymes or pectinases are a heterogeneous group of related enzymes that hydrolyze the pectic substances, present mostly in plants. Pectinolytic enzymes are widely distributed in higher plants and microorganisms [5]. They are of prime importance for plants as they help in cell wall extension [6] and softening of some plant tissues during maturation and storage [7], [8]. They also aid in maintaining ecological balance by causing decomposition and recycling of waste plant materials. Plant pathogenicity and spoilage of fruits and vegetables by rotting are some other major manifestations of pectinolytic enzymes [5], [9], [10], [11], [12], [13], [14].
It has been reported that microbial pectinases account for 25% of the global food enzymes sales. Almost all the commercial preparations of pectinases are produced from fungal sources [14]. Aspergillus niger is the most commonly used fungal species for industrial production of pectinolytic enzymes [15], [16], [17].
This review mainly concentrates on the types of pectinolytic enzymes, their classification, mode of action and the substrates on which they act. It also provides a bird's eye view of the possible applications of these enzymes in industrial sector.
Section snippets
Pectic substances
Pectic substance is the generic name used for the compounds that are acted upon by the pectinolytic enzymes. They are high molecular weight, negatively charged, acidic, complex glycosidic macromolecules (polysaccharides) that are present in the plant kingdom. They are present as the major components of middle lamella between the cells in the form of calcium pectate and magnesium pectate [18]. That the middle lamella is largely composed of pectic substances, has been confirmed by the comparable
The pectinolytic enzymes
The pectinolytic enzymes may be divided in three broader groups as follows [7], [10]:
- (I)
Protopectinases: degrade the insoluble protopectin and give rise to highly polymerized soluble pectin.
- (II)
Esterases: catalyze the de-esterification of pectin by the removal of methoxy esters.
- (III)
Depolymerases: catalyze the hydrolytic cleavage of the α-(1 → 4)-glycosidic bonds in the d-galacturonic acid moieties of the pectic substances.
Depolymerases act on pectic substances by two different mechanisms, hydrolysis, in
Biotechnological applications of microbial pectinases
Over the years, pectinases have been used in several conventional industrial processes, such as textile, plant fiber processing, tea, coffee, oil extraction, treatment of industrial wastewater, containing pectinacious material, etc. They have also been reported to work on purification of viruses [143] and in making of paper [144], [4]. They are yet to be commercialized.
Conclusion
Most of the studies performed so far have been concentrated with the screening, isolation, production, purification, characterization and applications of pectinolytic enzymes in increasing the fruit juice yield and its clarification. Some reports are available on the applications of pectinases in other industries. Study of the molecular aspects of pectinases and engineering of enzymes that are more robust with respect to their pH and temperature kinetics by the techniques of protein engineering
Acknowledgement
The financial support from the Department of Biotechnology, Ministry of Science and Technology, Government of India to Department of Biotechnology, Himachal Pradesh University, Shimla (India) is thankfully acknowledged.
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