Trends in bioconversion of lignocellulose: Biofuels, platform chemicals & biorefinery concept

Despite an increased knowledge of microbial xylanolytic systems in the past few years, further studies are required to achieve a complete understanding of the mechanism of xylan degradation by microorganisms and their enzymes. The enzyme system used by microbes for the metabolism of xylan is the most important tool for investigating the use of the second most abundant polysaccharide (xylan) in nature. Recent studies on microbial xylanolytic systems have generally focussed on induction of enzyme production under different conditions, purification, characterization, molecular cloning and expression, and use of enzyme predominantly for pulp bleaching. Rationale approaches to achieve these goals require a detailed knowledge of the regulatory mechanism governing enzyme production. This review will focus on complex xylan structure and the microbial enzyme complex involved in its complete breakdown, studies on xylanase regulation and production and their potential industrial applications, with special reference to biobleaching.

Microbial xylanases and their industrial applications: a review.

Xylan is the principal type of hemicellulose. It is a linear polymer of beta-D-xylopyranosyl units linked by (1-4) glycosidic bonds. In nature, the polysaccharide backbone may be added to 4-O-methyl-alpha-D-glucuronopyranosyl units, acetyl groups, alpha-L-arabinofuranosyl, etc., in variable proportions. An enzymatic complex is responsible for the hydrolysis of xylan, but the main enzymes involved are endo-1,4-beta-xylanase and beta-xylosidase. These enzymes are produced by fungi, bacteria, yeast, marine algae, protozoans, snails, crustaceans, insect, seeds, etc., but the principal commercial source is filamentous fungi. Recently, there has been much industrial interest in xylan and its hydrolytic enzymatic complex, as a supplement in animal feed, for the manufacture of bread, food and drinks, textiles, bleaching of cellulose pulp, ethanol and xylitol production. This review describes some properties of xylan and its metabolism, as well as the biochemical properties of xylanases and their commercial applications.

Xylanases from fungi: properties and industrial applications

Developments in industrially important thermostable enzymes: a review.

Enhancement of biogas production from solid substrates using different techniques--a review.

Anaerobic digestion of fruit and vegetable processing wastes for biogas production

Ensilage of pineapple processing waste for methane generation.

Nineteen strains of lactic
acid producing bacteria of the genera Lactobacillus and Streptococcus collected
from different culture collections were screened for the production of extracellular
phytase. A number of them exhibited the enzyme activity in the fermentation
medium but Lactobacillus amylovorus B4552 produced the maximum amounts of phytase
ranging from 125 to 146 units ml-' extracellularly under the submerged cultivation
conditions. The optimum glucose and inorganic phosphate levels for highest phytase
production were found to be 1% and 24% mg, respectively. Lactobacillus
amylovorus has potential in improving nutritional qualities of cereal and pulse-based
food fermentations.

Lactobacillus amylovorus as a phytase producer in submerged culture

Investigations have been carried out on the production of fungal rennet using a thermophilic strain ofMucor miehei under solid state fermentation conditions. A high milk clotting enzyme activity (58000 Soxhlet units/g) was achieved when optimum conditions were used. Further, a high ratio of 6.6:1 between milk clotting and proteolytic activities for this enzyme was obtained. Cheese prepared using this enzyme was also found to be acceptable in organoleptic quality. Large scale production of the enzyme in trays using the optimum conditions gave milk-clotting enzyme activities comparable to those in flask experiments.

Krishna Nand

Papers

Anaerobic digestion of fruit and vegetable processing wastes for biogas production

Ensilage of pineapple processing waste for methane generation.

Lactobacillus amylovorus as a phytase producer in submerged culture

Production of fungal rennet by Mucor miehei using solid state fermentation

Production of thermostable cellulase-free xylanase by Clostridium absonum CFR-702