Cell Immobilization Using Alginate-Based Beads as a Protective Technique against Stressful Conditions of Hydrolysates for 2G Ethanol Production

Alginate gels: Chemistry, gelation mechanisms, and therapeutic applications with a focus on GERD treatment

Alginate, a natural polysaccharide derived primarily from marine algae, has become popular in biomedical research due to its versatile gelation properties and biocompatibility. This review explores the chemistry, gelation mechanisms, and therapeutic applications of alginate gels, with a particular focus on their role in gastroesophageal reflux disease (GERD) management. Alginate's structure, comprised of guluronic and mannuronic acid blocks, allows for gel formation by ionic cross-linking with divalent cations like calcium ions, generating a stable "egg-box" structure. The effects of pH, temperature, and ion concentration on gelation are explored, as well as other gel forms such as in situ and heat-sensitive gels. Alginate is widely used in the medical and pharmaceutical areas to promote tissue engineering through cell encapsulation and scaffolding, as well as in drug delivery systems for controlled and targeted release. In GERD therapy, alginate produces a gel raft that inhibits acid reflux, providing an effective alternative to proton pump inhibitors. Alginate-based products have demonstrated clinical success, strengthening alginate's medicinal promise. The review also discusses alginate-related issues, such as source variability and stability, as well as innovative modifications to improve treatment effects. These improvements establish alginate as a potential material for customized medication and tailored delivery systems.

Role of non-genetically modified or native pentose fermenting microorganisms in establishing viable lignocellulosic biorefineries in the Brazilian context

Brazil can play a pivotal role in the development of a circular bioeconomy as the country ranks among the top five major agricultural countries in the world producing a foreseeable lignocellulosic biomass from crops, such as sugarcane, soybean, corn, rice, coffee, and eucalyptus. Considering that pentose sugars (C5 sugars) represent 20%-35% of the amount of lignocellulosic biomass components, these sugars have a great potential in the development of carbon neutral economy. From the biomass conversion economic point of view, the conversion of hemicellulose into renewable products with a satisfactory yield is the most needed. However, the biochemical conversion of pentose sugars is challenging due to the scarcity of native pentose sugars fermenting microorganisms. While recent advances in metabolic engineering have been effective in developing a strong molecular chassis for efficient pentose sugars conversion, the yields, productivities, and stability of the genetically modified organisms (GMOs) are major limiting factors for industrial-scale applications. Native lignocellulosic sugars fermenting microorganisms are competent, robust, and inhibitor-tolerant but their lower productivities continue to be a big concern. This article explains the inherent characteristics of native pentose fermenting microorganisms in establishing viable lignocellulosic biorefineries in the Brazilian context, with a special focus on their isolation from Brazilian biodiversity, along with the evaluation of nongenetic engineering techniques to improve strains for biorefinery application.

Removal of phenolic inhibitors from lignocellulose hydrolysates using laccases for the production of fuels and chemicals

Lignocellulose is the most abundant biopolymer in the biosphere. It is inexpensive and therefore considered an attractive feedstock to produce biofuels and other biochemicals. Thermochemical and/or enzymatic pretreatment is used to release fermentable monomeric sugars. However, a variety of inhibitory by-products such as weak acids, furans, and phenolics that inhibit cell growth and fermentation are also released. Phenolic compounds are among the most toxic components in lignocellulosic hydrolysates and slurries derived from lignin decomposition, affecting overall fermentation processes and production yields and productivity. Ligninolytic enzymes have been shown to lower inhibitor concentrations in these hydrolysates, thereby enhancing their fermentability into valuable products. Among them, laccases, which are capable of oxidizing lignin and a variety of phenolic compounds in an environmentally benign manner, have been used for biomass delignification and detoxification of lignocellulose hydrolysates with promising results. This review discusses the state of the art of different enzymatic approaches to hydrolysate detoxification. In particular, laccases are used in separate or in situ detoxification steps, namely in free enzyme processes or immobilized by cell surface display technology to improve the efficiency of the fermentative process and consequently the production of second-generation biofuels and bio-based chemicals.

Effective application of immobilized second generation industrial Saccharomyces cerevisiae strain on consolidated bioprocessing

Integrated bioprocessing strategies can facilitate ethanol production from both cellulose and hemicellulose fractions of lignocellulosic biomass. Consolidated bioprocessing (CBP) is an approach that combines enzyme production, biomass hydrolysis and sugar fermentation in a single step. However, technologies that propose the use of microorganisms together with solid biomass present the difficulty of the recovery and reuse of the biocatalyst, which can be overcome by cell immobilization. In this regard, this work applied immobilized cells of AC14 yeast, a recombinant yeast that secretes 7 hydrolytic enzymes, in the CBP process in a successful proof-of-concept for the enzyme access to the substrate polymers. The most appropriate cell load for CBP under the conditions studied with immobilized cells was selected among three optical densities (OD) 10, 55 and 100. These experiments were performed with free cells to ensure that the results were not biased by mass limitations effects. OD 10 achieved 100% of the sugar consumption and the higher specific production of enzymes, being selected for further studies. Diffusional effects were observed with immobilized cells under static conditions. However, mass transfer limitations were mitigated under agitation, with an 18.5% increase in substrate consumption rate (from 2.7 to 3.5 g/L/h), reaching the same substrate uptake rates as free cells. In addition, immobilized cells achieved 100% hydrolysis and consumption of all substrates offered within only 12 h. Overall, this is the first report of a successful application of immobilized yeast cells in CBP processes for bioethanol production, a promising technology that can be extended to other biorefinery bioproducts.

Production of the Polysaccharide Pullulan by Aureobasidium pullulans Cell Immobilization

This review examines the immobilization of A. pullulans cells for production of the fungal polysaccharide pullulan. Pullulan is a water-soluble gum that exists structurally as a glucan consisting primarily of maltotriose units, which has a variety of food, non-food and biomedical applications. Cells can be immobilized by carrier-binding or entrapment techniques. The number of studies utilizing carrier-binding as a method to immobilize A. pullulans cells appears to outnumber the investigations using cell entrapment. A variety of solid supports, including polyurethane foam, sponge, diatomaceous earth, ion-exchanger, zeolite and plastic composite, have been employed to immobilize pullulan-producing A. pullulans cells. The most effective solid support that was used to adsorb the fungal cells was polyurethane foam which produced polysaccharide after 18 cycles of use. To entrap pullulan-producing fungal cells, agents such as polyurethane foam, polyvinyl alcohol, calcium alginate, agar, agarose, carrageenan and chitosan were investigated. Polysaccharide production by cells entrapped in polyurethane foam, polyvinyl alcohol or calcium alginate was highest and the immobilized cells could be reutilized for several cycles. It was shown that the pullulan content of the polysaccharide synthesized by cells entrapped in calcium alginate beads was low, which limits the method’s usefulness for pullulan production. Further, many of the entrapped fungal cells synthesized polysaccharide with a low pullulan content. It was concluded that carrier-binding techniques may be more effective than entrapment techniques for A. pullulans cell immobilization, since carrier-binding is less likely to affect the pullulan content of the polysaccharide being synthesized.