A Bibliometric Analysis and Review of Pullulan-Degrading Enzymes—Past and Current Trends

Kian Mau Goh,Syazwani Itri Amran,Nurriza Ab Latif,Ummirul Mukminin Kahar,Kok Jun Liew

doi:10.3390/catal12020143

Abstract

Starch and pullulan degrading enzymes are essential industrial biocatalysts. Pullulan-degrading enzymes are grouped into pullulanases (types I and type II) and pullulan hydrolase (types I, II and III). Generally, these enzymes hydrolyse the α-1,6 glucosidic bonds (and α-1,4 for certain enzyme groups) of substrates and form reducing sugars such as glucose, maltose, maltotriose, panose or isopanose. This review covers two main aspects: (i) bibliometric analysis of publications and patents related to pullulan-degrading enzymes and (ii) biological aspects of free and immobilised pullulan-degrading enzymes and protein engineering. The collective data suggest that most publications involved researchers within the same institution or country in the past and current practice. Multi-national interaction shall be improved, especially in tapping the enzymes from unculturable prokaryotes. While the understanding of pullulanases may reach a certain extend of saturation, the discovery of pullulan hydrolases is still limited. In this report, we suggest readers consider using the next-generation sequencing technique to fill the gaps of finding more new sequences encoding pullulan-degrading enzymes to expand the knowledge body of this topic.

Highlights

Pullulan is a biopolymer containing repeating units of maltotriose joined by α-1,6 glucosidic bonds and a small number of α-1,4 linked maltotetraose units
We believe that the understanding of type I and type II pullulanases is reaching saturation, since enzymology research on these groups of enzymes was initiated decades ago
The number of reported genes encoding pullulan hydrolases is more petite in total quantity, probably because microorganisms prefer to conserve the type I and type II pullulanases

Summary

Introduction

Pullulan is a biopolymer containing repeating units of maltotriose joined by α-1,6 glucosidic bonds and a small number of α-1,4 linked maltotetraose units. Pullulan-degrading enzymes can hydrolyse glucosidic bonds of polysaccharides (i.e., pullulan and starch), forming reducing sugars such as maltotriose, maltose, glucose, panose or isopanose [11]. The saccharification process is conducted by using several thermostable glycoside hydrolases (GH) enzymes (i.e., type I pullulanase, isoamylase, β-amylase and glucoamylase) under certain conditions (i.e., 60 ◦C and pH 4.5) to degrade the starch slurry in order to produce sugar syrups [13]. Apart from that, type II pullulanases are excellent biocatalysts in the starch processing industries This enzyme group exhibits hydrolytic activity on both α-1,4 and α-1,6 glucosidic bonds. None of the earlier reviews has covered bibliometric information on pullulan-degrading enzymes to the best of our knowledge. 66.68 48.50 10.36 23.00 47.54 53.80 11.94 48.93 128.38 a: Scopus data; b: data for citations and citation means were generated by Dimensions https://www.dimensions. ai/products/free/)

Patents Bibliometric Analysis

Single Immobilisation of Pullulan-Degrading Enzyme

Co-Immobilisation of Pullulan-Degrading Enzymes

Findings

Conclusions