• Energy Research

Surfactants play major role in the delignification of lignocellulosic biomass. Surfactant-assisted hydrothermal pretreatment was evaluated for chili post-harvest residue. Maximum reducing sugar yield of 0.445 g per g of dry biomass (g/g) was obtained when surfactant PEG 6000 was used. Compositional analysis revealed an efficient removal of lignin and hemicelluloses from the pretreated biomass. Fermentation inhibitors such as furfural, 5-hydroxymethylfurfural and organic acids were absent in the hydrolyzate. After pretreatment, the biomass can be directly hydrolyzed without any neutralization, washing and drying, and the hydrolyzate is devoid of major fermentation inhibitors. Fermentation with Saccharomyces cerevisiae yielded 1.84% of ethanol with a fermentation efficiency of 63.88%.

The biorefinery approach for the production of fuels and chemicals is gaining more and more attraction in recent years. The major advantages of biorefineries are the generation of multiple products with complete utilization of biomass with zero waste generation. Moreover the process will be economically viable when it targets low volume high value products in addition to high volume low value products like bioethanol. The present review discuss about the potential of rice straw based biorefinery. Since rice is a major staple food for many Asian countries, the utilization of the rice straw residue for fuel and chemicals would be very economical. The review focuses the availability and the potential of this residue for the production of fuel and other high value chemicals.

Lignocellulosic materials are the favoured feedstock for biorefineries due to their abundant availability and non-completion with food. Biobased technologies for refining these materials are limited mainly by the cost of biomass hydrolyzing enzymes, typically sourced from filamentous fungi. Therefore, considerable efforts have been directed at improving the quantity and quality of secreted lignocellulose degrading enzymes from fungi in order to attain overall economic viability. Process improvements and media engineering probably have reached their thresholds and further production enhancements require modifying the fungal metabolism to improve production and secretion of these enzymes. This review focusses on the types and mechanisms of action of known fungal biomass degrading enzymes, our current understanding of the genetic control exerted on their expression, and possible routes for intervention, especially on modulating catabolite repression, transcriptional regulators, signal transduction, secretion pathways etc., in order to improve enzyme productivity, activity and stability.

Characterization of glucose tolerant beta glucosidase (GT-BGL) secreted by Aspergillus unguis NII 08123, determination of the gene and protein sequences of the enzyme and establishing its performance in blends for lignocellulose hydrolysis.Supplementation of A. unguis beta glucosidase (BGL) to cellulase released 1.6 times more sugar within 12 h during the hydrolysis of lignocellulosic biomass. The enzyme was determined to be similar to BGL-F from Emericella nidulans by MALDI-TOF analysis, and was found to be a GH3 family protein. Molecular Docking simulation studies showed that the enzyme has lesser affinity for glucose (- 5.7 kcal/mol) compared to its substrate cellobiose (- 7.5 kcal/mol). The residues present in the N-terminal domain are mostly involved in bond formation with both the substrate and the product, while the C-terminal domain contains the catalytic region. In-silico studies showed that its predicted structure is unlike that of previously reported BGLs, which might provide a clue to its exceptional catalytic activity.The GT-BGL from A. unguis NII 08123 was proven effective as a blend in for biomass hydrolyzing enzyme cocktails and the possible reasons for its glucose tolerance was determined through studies on its modeled structure.

The inclusion of a pretreatment step in anaerobic digestion processes increases the digestibility of lignocellulosic biomass and enhances biogas yields by promoting lignin removal and the destruction of complex biomass structures. The increase in surface area enables the efficient interaction of microbes or enzymes, and a reduction in cellulose crystallinity improves the digestion process under anaerobic conditions. The pretreatment methods may vary based on the type of the lignocellulosic biomass, the nature of the subsequent process and the overall economics of the process. An improved biogas production by 1200% had been reported when ionic liquid used as pretreatment strategy for anaerobic digestion. The different pretreatment techniques used for lignocellulosic biomasses are generally grouped into physical, chemical, physicochemical, and biological methods. These four modes of pretreatment on lignocellulosic biomass and their impact on biogas production process is the major focus of this review article.

A novel ultrasound-assisted alkali pretreatment strategy was developed which could effectively remove lignin and hemicelluloses and improve the sugar yield from chili post harvest residue. Operational parameters that affect the pretreatment efficiency were studied and optimized. Inhibitor analysis of the hydrolyzate revealed that major fermentation inhibitors like furfural, 5-hydroxymethyl furfural as well as organic acids like citric acid, succinic acid and propionic acid were absent. Hence fermentation can be carried out without detoxification of the hydrolyzate. Changes in structural properties of the biomass were studied in relation to the pretreatment process using Scanning Electron Microscopy (SEM) and the changes in chemical composition were also monitored. The biomass pretreated with the optimized novel method could yield 0.428g/g of reducing sugars upon enzymatic hydrolysis. The hydrolyzate obtained by this novel pretreatment strategy was found to be suitable for bioethanol and xylanase production.

Abstract BackgroundMajor cost of bioethanol is attributed to enzymes employed in biomass hydrolysis. Biomass hydrolyzing enzymes are predominantly produced from the hyper cellulolytic mutant filamentous fungus Trichoderma reesei RUT-C30. Several decades of research have failed to provide an industrial grade organism other than T. reesei, capable of producing higher titers of an effective synergistic biomass hydrolyzing enzyme cocktail. Penicillium janthinellum NCIM1366 was reported as a cellulase hyper producer and a potential alternative to T. reesei, but a comparison of their hydrolytic performance was seldom attempted. ResultsHydrolysis of acid or alkali pretreated rice straw using cellulase enzyme preparations from P. janthinellum and T. reesei indicated 37 and 43 % higher glucose release respectively with P. janthinellum enzymes. A comparison of these fungi with respect to their secreted enzymes indicated that the crude enzyme preparation from P. janthinellum showed 28 % higher overall cellulase activity. It also had an exceptional 10-fold higher beta-glucosidase activity compared to that of T. reesei, leading to a lower cellobiose accumulation and thus alleviating the feedback inhibition. P. janthinellum secreted more number of proteins to the extracellular medium whose total concentration was 1.8 fold higher than T. reesei. Secretome analyses of the two fungi revealed higher number of CAZymes and a higher relative abundance of cellulases upon cellulose induction in the fungus.ConclusionsThe results revealed the ability of P. janthinellum for efficient biomass degradation through hyper cellulase production, and it outperformed the established industrial cellulase producer T. reesei in the hydrolysis experiments. A higher level of induction, larger number of secreted CAZymes and a high relative proportion of BGL to cellulases indicate the possible reasons for its performance advantage in biomass hydrolysis.