Microwave-assisted extraction of hemicellulosic oligosaccharides and phenolics from Robinia pseudoacacia wood.

Microwave-assisted autohydrolysis is an environmentally friendly intensification technology that permits the selective solubilization of hemicelluloses in form of oligosaccharides in a short time and with low energy consumption. The purpose of this work was to evaluate the suitability of microwave-assisted autohydrolysis to produce oligosaccharides and phenolics with potential prebiotic and antioxidant activities from Robinia pseudoacacia wood. The influence of treatment time (0-30 min) and temperature (200-230 °C) on oligosaccharide production was studied and conditions of 230 °C and 0.25 min resulted in maximum content of xylooligosaccharides (7.69 g XO/L) and more efficient energy consumption. Furthermore, under those conditions, liquors showed high contents of phenols (80.28 mg GAE/g of RW) and flavonoids (44.51 RE/g) with significant antioxidant activities (112.07 and 102.30 mg TE/g, measured by ABTS and FRAP tests, respectively). Additionally, the solubilized hemicelluloses were structurally characterized by HPAEC-PAD, MALDI-TOF-MS, FTIR and TGA/DSC, and HPLC-ESI-MS analysis allowed the tentative identification of 17 phytochemicals.

Recent advances in biorefineries based on lignin extraction using deep eutectic solvents: A review.

Considering the urgent need for alternative biorefinery schemes based on sustainable development, this review aims to summarize the state-of-the-art in the use of deep eutectic solvent pretreatment to fractionate lignocellulose, with a focus on lignin recovery. For that, the key parameters influencing the process are discussed, as well as various strategies to enhance this pretreatment efficiency are explored. Moreover, this review describes the challenges and opportunities associated with the valorization of extraction-derived streams and highlights recent advancements in solvent recovery techniques. Furthermore, the utilization of computational models for process design and optimization is introduced, as the initial attempts at the economic and environmental assessment of this lignocellulosic bioprocess based on deep eutectic solvents. Overall, this review offers a comprehensive perspective on the recent advances in this emerging field and serves as a foundation for further research on the potential integration of deep eutectic pretreatment in sustainable multi-product biorefinery schemes.

Microwave-assisted autohydrolysis of avocado seed for the recovery of antioxidant phenolics and glucose.

This study describes the valorization of avocado seed (AS) within a green biorefinery concept using microwave-assisted autohydrolysis. After the treatment at temperatures of 150-230 °C for 5 min, the resulting solid and liquor were characterized. The temperature of 220 °C led to the simultaneous optimal values of antioxidant phenolics/flavonoids (42.15 mg GAE/g AS, 31.89 RE/g AS, respectively) and glucose + glucooligosaccharides (38.82 g/L) in the liquor. Extraction with ethyl acetate allowed the recovery of the bioactive compounds while maintaining the polysaccharides in the liquor. The extract was rich in vanillin (99.02 mg/g AS) and contained several phenolic acids and flavonoids. The solid phase and the phenolic-free liquor were subjected to enzymatic hydrolysis to produce glucose, reaching values of 9.93 and 105 g glucose/L, respectively. This work demonstrates that microwave-assisted autohydrolysis is a promising technology to obtain fermentable sugars and antioxidant phenolic compounds from avocado seeds following a biorefinery scheme.

Valorization of Avocado Seed Wastes for Antioxidant Phenolics and Carbohydrates Recovery Using Deep Eutectic Solvents (DES).

Avocado seeds represent the chief waste produced in avocado processing, leading not only to environmental problems regarding its elimination but to a loss of economic profitability. In fact, avocado seeds are known as interesting sources of bioactive compounds and carbohydrates, so their utilization may reduce the negative effect produced during the industrial manufacture of avocado-related products. In this sense, deep eutectic solvents (DES) are a novel greener alternative than organic solvents to extract bioactive polyphenols and carbohydrates. The study was based on a Box-Behnken experimental design to study the effect of three factors, temperature (40, 50, 60 °C), time (60, 120, 180 min) and water content (10, 30, 50% v/v) on the responses of total phenolic (TPC) and flavonoid content (TFC), antioxidant capacity (measured as ABTS and FRAP) and xylose content in the extract. The DES Choline chloride:glycerol (1:1) was used as solvent on avocado seed. Under optimal conditions, TPC: 19.71 mg GAE/g, TFC: 33.41 mg RE/g, ABTS: 20.91 mg TE/g, FRAP: 15.59 mg TE/g and xylose: 5.47 g/L were obtained. The tentative identification of eight phenolic compounds was assayed via HPLC-ESI. The carbohydrate content of the solid residue was also evaluated, and that solid was subjected to two different processing (delignification with DES and microwave-assisted autohydrolysis) to increase the glucan susceptibility to enzymes, and was also assayed reaching almost quantitative glucose yields. These results, added to the non-toxic, eco-friendly, and economic nature of DES, demonstrate that these solvents are an efficient alternative to organic solvents to recover phenolics and carbohydrates from food wastes.

Current breakthroughs in the hardwood biorefineries: Hydrothermal processing for the co-production of xylooligosaccharides and bioethanol.

The development of lignocellulosic biorefineries requires a first stage of pretreatment which enables the efficient valorization of all fractions present in this renewable material. In this sense, this review aims to show the main advantages of hydrothermal treatment as a first step of a biorefinery infrastructure using hardwood as raw material, as well as, main drawback to overcome. Hydrothermal treatment of hardwood highlights for its high selectivity for hemicelluloses solubilization as xylooligosaccharides (XOS). Nevertheless, the suitable conditions for XOS production are inadequate to achieve an elevate cellulose to glucose conversion. Hence, several strategies namely the combination of hydrothermal treatment with delignification process, in situ modification of lignin and the mixture with another renewable resources (concretely, seaweeds, and by-products generated in the food industry with high sugar content) were pinpointed as promising alternative to increase the final ethanol concentration coupled with XOS recovery in the hydrolysate.

Potential and prospects for utilization of avocado by-products in integrated biorefineries.

The industrial processing of avocado to extract oil, and produce guacamole or sauces generates enormous quantities of peels and seeds (around 2 million tons worldwide in 2019) without commercially valuable applications. However, various studies have suggested the presence of a wide range of interesting compounds in the composition of these by-products. This review depicts a thorough outline of the capacity of avocado residues to be converted into a portfolio of commodities that can be employed in sectors such as the food, cosmetics, pharmaceuticals, environment, and energy industries. Therefore, a novel biorefinery strategy to valorize avocado-processing residues to obtain a polyphenolic extract, pectooligosaccharides, and succinic acid was presented. Additionally, the prospects and challenges facing a biorefinery based on the valorization of avocado residues are presented, particularly its techno-economic feasibility on an industrial scale, aiming for a resource-efficient circular bio-economy.

The Chemical, Microbiological and Volatile Composition of Kefir-like Beverages Produced from Red Table Grape Juice in Repeated 24-h Fed-Batch Subcultures.

The aim of this work was to study the production of kefir-like beverages via the fed-batch fermentation of red table grape juice at initial pHs of 3.99 (fermentation A) and 5.99 (fermentation B) with kefir grains during 4 repeated 24-h fed-batch subcultures. All kefir-like beverages (KLB) were characterized by low alcoholic grade (≤3.6%, v/v) and lactic and acetic acid concentrations. The beverages obtained from fermentation B had lower concentrations of sugars and higher microbial counts than the KLB obtained in fermentation A. Additionally, the KLB samples from fermentation B were the most aromatic and had the highest contents of alcohols, esters, aldehydes and organic acids, in contrast with the nonfermented juice and KLB from fermentation A. These results indicate the possibility of obtaining red table grape KLB with their own distinctive aromatic characteristics and high content in probiotic viable cells, contributing to the valorization of this fruit.

Fast-growing Paulownia wood fractionation by microwave-assisted hydrothermal treatment: A kinetic assessment.

Microwave hydrothermal treatment (MHT), a novel advanced technology, was proposed for the fractionation of Paulownia wood (PW) at temperatures ranging 200-230 °C and residence times of 0-50 min, corresponding to severities of 2.93-4.70. This procedure allowed 80% of xylan recovery as xylooligosaccharides and an average of 95% cellulose recovery in the pretreated PW biomass, showing the selectivity of the treatment, that was also compared to conduction-convection heating autohydrolysis. Finally, a kinetic model was proposed for the prediction of PW fractionation using MHT, with the ultimate goal of being applied to a wide range of feedstocks and minimizing the number of parameters used. For that, two strategies were approached, allowing the reduction of 80 to 34 parameters, without significant influence in the kinetic fitting. To the best of our knowledge, this is the first kinetic modelization of MHT of PW, taking into account all the lignocellulosic fractions.

Microwave hydrothermal processing of the invasive macroalgae Sargassum muticum within a green biorefinery scheme.

This study deals with the multiproduct valorization of the invasive macroalgae Sargassum muticum within a green biorefinery concept using microwave hydrothermal treatment. Temperatures of 160 and 180 °C for 0-60 min (severities 1.62-3.54) were evaluated, allowing a recovery of a liquid phase rich in fucoidan-derived compounds (up to 4.81 g/L), oligomers and phenolics with antioxidant capacity (up to 2.85 g TE/L by ABTS assay), and a high-enzymatically susceptible solid (glucan to glucose conversion 76-100% in 9 h) suitable for bioethanol production (20.5 g/L in 18 h, corresponding to 96% ethanol yield). Moreover, energy consumption of the pretreatments' temperature-time binomial was evaluated showing significant differences, demonstrating the advantages of microwave as alternative heating pretreatment.

Hydrothermal treatment of avocado peel waste for the simultaneous recovery of oligosaccharides and antioxidant phenolics.

Avocado industrial processing generates huge quantities of residues that are currently wasted without any valuable commercial application. This work deals with autohydrolysis of Avocado peel (AP) for the concomitant recovery of oligosaccharides and polyphenolics. Temperature of 150 °C allowed the highest recovery of oligosaccharides (14.3 g oligosaccharides/100 g AP) and high recovery of antioxidant phenolics (3.48 g gallic acid equivalents/100 g AP and 10.80 g Trolox equivalents/100 g AP measured with ABTS●+ assay). The liquor obtained at this temperature was characterized by TGA and FTIR to study its thermal stability and functional groups. UHPLC-TOF MS analysis of an ethyl acetate extract of AP liquor enabled the tentative identification of 43 compounds, belonging to various metabolite families, including flavonoids, phenolic acids, organic acids, lignans and fatty acids. These findings demonstrated that autohydrolysis of AP is a suitable technology to obtain bioactive agents with potential uses in food and cosmetic industries.

Comparative study of biorefinery processes for the valorization of fast-growing Paulownia wood.

In this work, valorization of Paulownia wood (PW) was proposed following several process configurations for biofuels and value-added compounds production. Firstly, autohydrolysis and ethanol-organosolv strategies were assessed separately for the fractionation of PW to enhance the enzymatic digestibility of cellulose. A third strategy focused on a sequential process (autohydrolysis and organosolv) was explored. Two temperatures were selected for the first stage of the combined process. High concentration of oligosaccharides (26.29 g/L) and high concentration of degradation products (17.21 g/L) were obtained at 210 and 230 °C, respectively. The solids obtained from both pretreatments were subjected to organosolv delignification (200 °C, 3 h and 50% ethanol) achieving delignification of 58 and 30% for the autohydrolyzed biomass at 210 °C and 230 °C, respectively. The combined process resulted in susceptible biomass able to produce 64 g/L of ethanol. Therefore, the strategies explored in this work open the possibility to build a refinery around Paulownia wood.

Recent trends on seaweed fractionation for liquid biofuels production.

Concerns about fossil fuels depletion has led to seek for new sources of energy. The use of marine biomass (seaweed) to produce biofuels presents widely recognized advantages over terrestrial biomasses such as higher production ratio, higher photosynthetic efficiency or carbon-neutral emissions. In here, interesting seaweed sources as a whole or as a residue from seaweed processing industries for biofuel production were identified and their diverse composition and availability compiled. In addition, the pretreatments used for seaweed fractionation were thoroughly revised as this step is pivotal in a seaweed biorefinery for integral biomass valorization and for enabling biomass-to-biofuel economic feasibility processes. Traditional and emerging technologies were revised, with particular emphasis on green technologies, relating pretreatment not only with the type of biomass but also with the final target product(s) and yields. Current hurdles of marine biomass-to-biofuel processes were pinpointed and discussed and future perspectives on the development of these processes given.