Enzymes in Degradation of the Lignocellulosic Wastes by Aparna B. Gunjal & Neha N. Patil & Sonali S. Shinde

Author:Aparna B. Gunjal & Neha N. Patil & Sonali S. Shinde
Language: eng
Format: epub
ISBN: 9783030446710
Publisher: Springer International Publishing

4.2 Lignin Occurrence, Biogenesis, and Biodegradation

Lignins are plant polymers derived from the hydroxycinnamyl alcohols or monolignols p-coumaryl, coniferyl, and sinapyl. It was a debatable question on what are lignins? Histochemical studies investigated on lignin as a plant polymer. Total lignin contents are determined by solvent extraction, alkali extraction, and more recent spectroscopic methods including NMR, infrared, and UV methods. Water-soluble and water-insoluble intermediate lignins degradation can be detected under solid-state and submerged fermentation. The intermediate can be extracted with polar solvent. Degradation of lignins to generate biofuels strongly depends on lignin’s chemical structure and fractionation process. These materials are decomposed in nature by several microorganisms like fungi and bacteria. Lignocellulosic biomass decomposition is carried out primarily by microbial involvement, utilizing it as carbon and nutrient/energy source for their growth. Lignocellulosic hydrolysis yield simple sugars that can be utilized for biofuel production. Microbes are known to break down the lignin and cellulose to utilize it as energy source. Few fungi and certain bacteria can also decolorize the cellulose.

Lignin is a complex molecule with a non-repeating phenylpropane backbone biosynthesized by random polymerization of phenylpropanoid precursor with irregular structure. The two-dimensional structure of lignin is represented in Fig. 4.1. The major building blocks are monolignols or hydroxycinnamyl alcohols (Vanholme et al. 2010). Polymerization can be carried out in vitro to produce synthetic lignin or dehydrogenate polymerizes (DHP). The non-repeating structure is an important feature for biological delignification. Diversity of lignins is observed in the interunits making it difficult to beak the interunit bonds, complicating its use as a carbon and energy source for biological degradation. Degradation of lignins is only possible with few organisms that harbor the pathway to degrade it. The derivatives of lignin are shown is Fig. 4.2.

Fig. 4.1Two-dimensional structure of lignin polymer molecule

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