Lignocellulosic biorefineries as a platform for the production of high-value yeast derived pigments - A review.

Lignocellulosic byproducts, mainly generated by the agro-industrial sector, have great potential as cost-effective feedstocks for bioprocesses because of their abundant availability and high content of sugar-rich and nutrient-rich elements. This biomass can be employed as a carbon source to produce various molecules using several microorganisms. Yeast strains have shown their capability to metabolize diverse C5 and C6 carbon sources, thereby facilitating their use in the bioprocessing of lignocellulosic biomass. Furthermore, yeasts can produce a wide range of valuable products, including biofuels, enzymes, proteins, and pigments, making them attractive for use in integrated biorefineries. Yeast-derived pigments have versatile applications and are environmentally friendly alternatives to their synthetic counterparts. This review emphasizes the potential of lignocellulosic biomass as a feedstock for producing yeast-derived products with a focus on pigments as valuable molecules. It also proposes a yeast-derived pigment platform utilizing lignocellulosic byproducts and explores its potential integration in biorefineries.

Surfactants in biorefineries: Role, challenges & perspectives.

The use of lignocellulosic biomass (LCB) as feedstock has received increasing attention as an alternative to fossil-based refineries. Initial steps such as pretreatment and enzymatic hydrolysis are essential to breakdown the complex structure of LCB to make the sugar molecules available to obtain bioproducts by fermentation. However, these steps increase the cost of the bioproduct and often reduces its competitiveness against synthetic products. Currently, the use of surfactants has shown considerable potential to enhance lignocellulosic biomass processing. This review addresses the main mechanisms and role of surfactants as key molecules in various steps of biorefinery processes, viz., increasing the removal of lignin and hemicellulose during the pretreatments, increasing enzymatic stability and enhancing the accessibility of enzymes to the polymeric fractions, and improving the downstream process during fermentation. Further, technical advances, challenges in application of surfactants, and future perspectives to augment the production of several high value-added bioproducts have been discussed.

Catalytic hydrolysis of cellobiose using different acid-functionalised Fe3O4 magnetic nanoparticles.

The present study demonstrated the preparation of three different acid-functionalised magnetic nanoparticles (MNPs) and evaluation for their catalytic efficacy in hydrolysis of cellobiose. Initially, iron oxide (Fe3O4)MNPs were synthesised, which further modified by applying silica coating (Fe3O4-MNPs@Si) and functionalised with alkylsulfonic acid (Fe3O4-MNPs@Si@AS), butylcarboxylic acid (Fe3O4-MNPs@Si@BCOOH) and sulphonic acid (Fe3O4-MNPs@Si@SO3H) groups. The Fourier transform infrared analysis confirmed the presence of above-mentioned acid functional groups on MNPs. Similarly, X-ray diffraction pattern and energy dispersive X-ray spectroscopy analysis confirmed the crystalline nature and elemental composition of MNPs, respectively. TEM micrographs showed the synthesis of spherical and polydispersed nanoparticles having diameter size in the range of 20-80 nm. Cellobiose hydrolysis was used as a model reaction to evaluate the catalytic efficacy of acid-functionalised nanoparticles. A maximum 74.8% cellobiose conversion was reported in case of Fe3O4-MNPs@Si@SO3H in first cycle of hydrolysis. Moreover, thus used acid-functionalised MNPs were magnetically separated and reused. In second cycle of hydrolysis, Fe3O4-MNPs@Si@SO3H showed 49.8% cellobiose conversion followed by Fe3O4-MNPs@Si@AS (45%) and Fe3O4-MNPs@Si@BCOOH (18.3%). However, similar pattern was reported in case of third cycle of hydrolysis. The proposed approach is considered as rapid and convenient. Moreover, reuse of acid-functionalised MNPs makes the process economically viable.

The realm of cellulases in biorefinery development.

Geopolitical concerns (unstable supply of gasoline, environmental pollution, and regular price hikes), economic, and employment concerns have been prompting researchers, entrepreneurs, and policy makers to focus on harnessing the potential of lignocellulosic feedstock for fuel ethanol production and its commercialization. The carbohydrate skeleton of plant cell walls needs to be depolymerised into simpler sugars for their application in fermentation reactions as a chief carbon source of suitable ethnologic strains for ethanol production. The role of cellulolytic enzymes in the degradation of structural carbohydrates of the plant cell wall into ready-to-fermentable sugar stream is inevitable. Cellulase synergistically acts upon plant cell wall polysaccharides to release glucose into the liquid media. Cellulase predominantly dominates all the plant cell wall degrading enzymes due to their vast and diverse range of applications. Apart from the major applications of cellulases such as in detergent formulations, textile desizing, and development of monogastric feed for ruminants, their role in biorefinery is truly remarkable. This is a major area where new research tools based upon fermentation based formulations, biochemistry, and system biology to expedite the structure-function relationships of cellulases including cellulosomes and new designer enzymatic cocktails are required. In the last two decades, a considerable amount of research work has been performed on cellulases and their application in biomass saccharification. However, there are still technical and economic impediments to the development of an inexpensive commercial cellulase production process. Advancements in biotechnology such as screening of microorganisms, manipulation of novel cellulase encoding traits, site-specific mutagenesis, and modifications to the fermentation process could enhance the production of cellulases. Commercially, cheaper sources of carbohydrates and modified fermentation conditions could lead to more cost-effective production of cellulases with the goal to reduce the cost of ethanol production from lignocellulosics. Implementation of integrated steps like cellulase production and cellulase mediated saccharification of biomass in conjunction with the fermentation of released sugars in ethanol in a single step so called consolidated bio-processing (CBP) is very important to reduce the cost of bioethanol. This paper aims to explore and review the important findings in cellulase biotechnology and the forward path for new cutting edge opportunities in the success of biorefineries.

Biotechnological production of xylitol in a three-phase fluidized bed bioreactor with immobilized yeast cells in Ca-alginate beads.

Cells of Candida guilliermondii entrapped in Ca-alginate beads were used for xylitol production, from concentrated hemicellulose hydrolyzate of sugarcane bagasse, in a fluidized bed bioreactor (FBR). The maximum xylitol concentration 28.9 g xylitol/L was obtained at a high aeration rate of 600 mL/min after 70 h of fermentation, indicating that the use of high aeration rate in this system is favored for better oxygen transfer into the immobilized cells. The specific xylitol productivity and the xylitol yield were of 0.4 g xylitol/L.h and 0.58 g xylitol/g xylose respectively. The immobilization efficiency at the end of the fermentation was of 65 %. After 90 h of fermentation xylitol productivity and yield decreased to 0.25 g xylitol/L.h and 0.47 g xylitol/g xylose respectively, indicating the beginning of xylitol consumption by the yeast. The use of FBR system with immobilized cells presented high xylitol yield and productivity.