Degradation of lignin in birch sawdust treated by a novel Myrothecium verrucaria coupled with ultrasound assistance

Recent advances on physical technologies for the pretreatment of food waste and lignocellulosic residues

The complete deployment of a bio-based economy is essential to meet the United Nations' Sustainable Development Goals from the 2030 Agenda. In this context, food waste and lignocellulosic residues are considered low-cost feedstocks for obtaining industrially attractive products through biological processes. The effective conversion of these raw materials is, however, still challenging, since they are recalcitrant to bioprocessing and must be first treated to alter their physicochemical properties and ease the accessibility to their structural components. Among the full pallet of pretreatments, physical methods are recognised to have a high potential to transform food waste and lignocellulosic residues. This review provides a critical discussion about the recent advances on milling, extrusion, ultrasound, and microwave pretreatments. Their mechanisms and modes of application are analysed and the main drawbacks and limitations for their use at an industrial scale are discussed.

Ultrasonic Irradiation Enables Facile Production of Lovastatin from Sugar Cane Bagasse

This study investigated the effect of ultrasound-assisted hydrogen peroxide (H₂O₂) pretreatment on sugar cane bagasse (SCB) followed by Monascus purpureus TISTR 3003 cultivation for lovastatin production under solid-state fermentation (SSF). Optimization of the pretreatment conditions was investigated using a response surface methodology (RSM). Within the range of the selected operating conditions, the optimized values of H₂O₂ concentration, amplitude, SCB dosage, and sonication time were found to be 2.74%, 83.22 μm, 2.84% and 52.29 min, respectively. The R ² value of 0.9749 indicated that the fitted model is in good agreement with the predicted and actual lovastatin production. On the basis of the optimum conditions, the lovastatin production was 2347.10 ± 17.19 μg/g, which is 2.4 times higher than that under untreated conditions. Scanning electron microscopy (SEM) analysis explored the surface structure of the untreated SCB, which showed a compact rigid structure. In contrast, treated SCB had a rough surface structure and cracks as a result of the pretreatment.

The Fractionation of Corn Stalk Components by Hydrothermal Treatment Followed by Ultrasonic Ethanol Extraction

The fractionation of components of lignocellulosic biomass is important to be able to take advantage of biomass resources. The hydrothermal–ethanol method has significant advantages for fraction separation. The first step of hydrothermal treatment can separate hemicellulose efficiently, but hydrothermal treatment affects the efficiency of ethanol treatment to delignify lignin. In this study, the efficiency of lignin removal was improved by an ultrasonic-assisted second-step ethanol treatment. The effects of ultrasonic time, ultrasonic temperature, and ultrasonic power on the ultrasonic ethanol treatment of hydrothermal straw were investigated. The separated lignin was characterized by solid product composition analysis, FT-IR, and XRD. The hydrolysate was characterized by GC-MS to investigate the advantage on the products obtained by ethanol treatment. The results showed that an appropriate sonication time (15 min) could improve the delignification efficiency. A proper sonication temperature (180 °C) can improve the lignin removal efficiency with a better retention of cellulose. However, a high sonication power 70% (840 W) favored the retention of cellulose and lignin removal.

Ultrasound-assisted biomass valorization to industrial interesting products: state-of-the-art, perspectives and challenges

Nowadays, the application of ultrasound (US) energy for assisting the lignocellulosic biomass and waste materials conversion into value-added products has dramatically increased. In this sense, this review covers theoretical aspects, promising applications, challenges and perspectives about US and its use for biomass treatment. The combination of US energy with a suitable reaction time, temperature and solvent contributes to the destruction of recalcitrant lignin structure, allowing the products to be used in thermochemical and biological process. The main mechanisms related to US propagation and impact on the fragmentation of lignocellulosic materials, selectivity, and yield of conversion treatments are discussed. Moreover, the synergistic effects between US and alternative green solvents with the perspective of industrial applications are investigated. The present survey analysed the last ten years of literature, studying challenges and perspectives of US application in biorefinery. We were aiming to highlight value-added products and some new areas of research.

Recent advances in removal of lignin from paper industry wastewater and its industrial applications - A review

Pulp and paper mill wastewater contains lignin related synthetic, aromatic and chlorinated chemical compounds. Extracting lignin from pulp and paper mill wastewater is one way of recovering valuable organic material. Due to its complex structure, lignin is difficult to break and provides economical and technical provocations in biomass recovery. The conventional wastewater treatment processes are seldom efficacious for the complete removal of lignin from paper mill effluents. A wide range of thermal, mechanical and physico-chemical methods have been reported for the removal of lignin. Moreover, biological method of lignin removal employed microorganisms including bacteria and fungi as a one-step treatment and/or amalgamation of various physico-chemical techniques. Compared with other methods, biological process for degradation of lignin is regarded as eco-friendly, cost-effective and sustainable. Therefore, this review will provide insight into the recent breakthroughs and future trends in lignin removal with special emphasis on biological treatment and scope of lignin utilization.

Ultrasound enhanced biosynthesis of L-theanine from L-glutamine and ethylamine by recombinant γ-glutamyltranspeptidase

A mutant library of the key amino acid residue site E387 in γ-glutamyltranspeptidase was constructed to screen the mutant enzymes with significantly improved thermal stability (E387Q). The reaction temperature of the mutant enzyme (E387Q) was 10℃ higher than that of the parent enzyme. Ultrasound-assisted synthesis of L-theanine by γ-glutamyltranspeptidase was investigated. The effects of ultrasonic power, reaction pH and substrate concentration on the enzymatic synthesis of L-theanine were studied by the response surface method. The results showed that the optimal process conditions are ultrasonic power of 100 W, reaction pH of 9, substrate L-glutamine concentration of 120 mmol/L, reaction temperature of 45℃, and L-theanine yield of 89.1%. The yield of L-theanine is 2.61 times higher than that obtained without ultrasound. Ultrasound can significantly promote the synthesis of L-theanine by γ-glutamyltranspeptidase.

Increase in Cell Wall Thickening and Biomass Production by Overexpression of PmCesA2 in Poplar

Cellulose, the most abundant constituent material of the plant cell walls, is a major structural component of plant biomass. Manipulating cellulose synthesis (CesA) genes by genetic engineering technology, to increase cellulose production may thus offer novel opportunities for plant growth and development. To investigate this, here we produced transgenic "Populus 895 plants" overexpressing the cellulose synthase (CesA2) gene derived from Pinus massoniana under the control of constitutive 35S promoter, via Agrobacterium-mediated transformation. Relative expression levels of PmCesA2 were functionally characterized in poplar hybrid clone "Nanlin895" (Populus deltoides × Populus euramericana). The results demonstrated the transgenic lines showed enhanced growth performance with increased biomass production than did the untransformed controls. It is noteworthy that the overexpression of PmCesA2 in poplar led to an altered cell wall polysaccharide composition, which resulted in the thickening of the secondary cell wall and xylem width under scanning electron microscopy. Consequently, the cellulose and lignin content were increased. Hence, this study suggests that overexpression of PmCesA2 could be used as a potential candidate gene to enhance cellulose synthesis and biomass accumulation in genetically engineered trees.