Subcritical Water Extraction Research Articles

Comparison of different green extraction methods used for the extraction of anthocyanin from red onion skin.

Green extraction primarily emphasizes developing new extraction techniques that consume less energy. It involves using safe, non-toxic alternative solvents and sustainable natural resources to ensure the production of safe and high-quality extracts. Red onion skin is an important source of anthocyanins, a subgroup of phenolic compounds. Anthocyanins are an important group of natural pigments that have attracted a lot of attention due to their health benefits. However, the instability and high sensitivity of these pigments have limited their use in food and cosmetics. Therefore, in this study, various modern green extraction methods were used, including solvent extraction, ultrasound-assisted extraction, subcritical water extraction, microwave-assisted extraction (MAE), pulsed electric field extraction, supercritical fluid extraction (SFE), and high hydrostatic pressure-assisted (HHPAE) extraction, to specifically extract and purify anthocyanins. The extraction efficiency, specifically targeting anthocyanins, showed the highest efficiency with HHPAE (81.84%) and the lowest with MAE (40.01%). Measurement of total anthocyanin content revealed that HHPAE and SFE methods yielded the highest anthocyanin concentrations, with 248.49 and 244.98 mg/L, respectively. Identification of anthocyanin by LC-MS revealed that the main anthocyanidins in red onion peel are pelargonidin, cyanidin, delphinidin, and petunidin. These results indicate that innovative green extraction methods, particularly HHPAE and SFE, can effectively replace conventional techniques due to their superior efficiency and enhanced preservation of anthocyanin compounds.

Predicting PAHs removal from contaminated soil via subcritical water extraction using support vector regression

Subcritical water extraction (SCWE) has been increasingly studied and applied in recent decades for the extraction of organic pollutants from contaminated soil. However, the efficacy of the SCWE technique for soil remediation depends not only on the operating parameters but also on the soil and pollutant properties. Models for predicting PAHs removal by the SCWE process are highly desirable for the process design and for facilitating a global understanding of the influence of each parameter for optimal remediation without numerous trials. In this study, a support vector regression (SVR) model was developed to predict PAHs removal from contaminated soil based on the SCWE operating parameters and soil and PAHs’ properties. Results revealed that the model exhibited a good predictability with the correlation coefficients of 0.99 and 0.93 for the training and testing datasets, respectively. The importance of input variables was in the following order: operating conditions > chemical properties > soil properties. The statistical analysis demonstrated the reliability and robustness of the developed model. Based on our findings, the SVR model is suitable for predicting the removal rate of PAHs by SCWE process.

Obtaining Cellulose Fibers from Almond Shell by Combining Subcritical Water Extraction and Bleaching with Hydrogen Peroxide.

Almond shell (AS) represents about 33% of the almond fruit, being a cellulose-rich by-product. The use of greener methods for separating cellulose would contribute to better exploitation of this biomass. Subcritical water extraction (SWE) at 160 and 180 °C has been used as a previous treatment to purify cellulose of AS, followed by a bleaching step with hydrogen peroxide (8%) at pH 12. For comparison purposes, bleaching with sodium chlorite of the extraction residues was also studied. The highest extraction temperature promoted the removal of hemicellulose and the subsequent delignification during the bleaching step. After bleaching with hydrogen peroxide, the AS particles had a cellulose content of 71 and 78%, with crystallinity index of 50 and 62%, respectively, for those treated at 160 and 180 °C. The use of sodium chlorite as bleaching agent improved the cellulose purification and crystallinity index. Nevertheless, cellulose obtained by both bleaching treatments could be useful for different applications. Therefore, SWE represents a promising green technique to improve the bleaching sensitivity of lignocellulosic residues, such as AS, allowing for a great reduction in chemicals in the cellulose purification processes.

Pectin extracted from red dragon fruit (Hylocereus polyrhizus) peel and its usage in edible film

Pectin was extracted from red dragon fruit (Hylocereus polyrhizus) peel using two different extraction methods: subcritical water extraction (SCWE) and conventional acid extraction (AE), from two different types of peels, fresh peel puree and dried peel powder. SCWE method on fresh peel puree showed an ∼18.88 % increase in pectin yield compared to AE. Extracted pectin is classified as low methoxyl pectin (DE: 8.51–50.64 %), with an average molecular weight ranging from 115.23 kDa to 577.84 kDa and a Gal-A content of 44.09 % - 53.90 %. The potential of pectin from fresh peel puree to be applied as a biodegradable film was further explored. Different pectin concentrations (3–5 % w/v) were used to prepare the films. Regarding the film performance, PF-S5, which was produced from SCWE with 5 % of pectin concentration, exhibits better thermal stability (Tdmax 250 °C, residue of 28.69 %) and higher moisture barrier (WVP 5.59 × 10−11 g.cm−1.s−1.Pa−1). In comparison, PF-A showed lower water solubility (45.14–69.15 %), higher water contact angle (33.01° - 44.35°), and better mechanical properties (TS: 2.12–4.11 MPa, EB: 48.72–61.39 %). Higher molecular weight accompanied by higher DE and Gal-A content contributes to better pectin film properties.

Optimization of subcritical water extraction, UPLC–triple–TOF–MS/MS analysis, antioxidant and α-glucosidase inhibitory activities of anthocyanins from Nitraria sibirica Pall. fruits

This study aimed to optimize subcritical water extraction process, characterize chemical composition and investigate the biological activities of Nitraria sibirica Pall. (NSP) anthocyanin. Overall, the optimization was achieved under following conditions: extraction temperature 140 °C, extraction time 45 min and flow rate 7 mL/min with the extraction yield of 1.075 mg/g. 3 cyanidin, 3 petunidin, 1 delphinidin and 1 pelargonidin compounds were identified in the anthocyanic extract from NSP via UPLC–Triple–TOF–MS/MS. NSP anthocyanin exhibited better DPPH free-radical scavenging activity than ascorbic acid. It displayed superior α-glucosidase inhibition activity, which was ∼14 times higher than that of acarbose. Moreover, enzyme kinetics results indicated that NSP anthocyanin behaved as a reversible, mixed-type inhibitor. Molecular docking and molecular dynamics simulation results revealed that NSP anthocyanin interacted with α-glucosidase mainly via van der Waals forces, hydrogen bond and possessed fairly stable configuration. Therefore, NSP anthocyanin is a promising α-glucosidase inhibitor for diabetes mellitus.

Optimization of subcritical water extraction for pectin extraction from cocoa pod husks using the response surface methodology

This study optimized subcritical water extraction (SWE) conditions to maximize pectin yield from cocoa pod husk (CPH) and compared the characteristics of CPH pectin extracted through SWE with those of CPH pectin obtained through conventional extraction (CE) with citric acid. The Box–Behnken experimental design was employed to optimize SWE and examine the influence of process parameters, including temperature (100 °C–120 °C), extraction time (10–30 min), and solid:liquid ratio (SLR) (1:30–2:30 g/mL), on pectin yield. The maximum pectin yield of 6.58% was obtained under the optimal extraction conditions of 120 °C for 10 min with 1:15 g/mL SLR and closely corresponded with the predicted value of 7.29%. Compared with CE, SWE generated a higher yield and resulted in a higher degree of esterification, methoxyl content, and anhydrouronic acid value but a lower equivalent weight. The extracted pectin was pure, had low-methoxyl content, and similar melting and degradation temperatures.

Enhanced process for efficient extraction of oxygenated monoterpenes from thyme (Thymus vulgaris L.) using subcritical water

Subcritical water extraction (SWE) is a highly effective technique for extracting monoterpenes at elevated pressures and temperatures using only water solvent. This study investigated SWE of monoterpenes, including γ-terpinene, p-cymene, thymol, carvacrol, and thymoquinone, under varying extraction conditions of temperature (110–200 ℃) and time (5–20 min). The extract was qualitatively and quantitatively analyzed by gas chromatography. The maximal extraction conditions of p-cymene (0.11 ± 0.03 mg/g), thymol (0.40 ± 0.02 mg/g), carvacrol (5.28 ± 0.19 mg/g), and thymoquinone (1.28 ± 0.11 mg/g) were obtained at temperature/time of 150 °C/5 min, 200 °C/5 min, 200 °C/5 min, and 110 °C/5 min, respectively. Non-oxygenated monoterpenes, such as γ-terpinene and p-cymene, were either undetected or extracted in small quantities using SWE and were found to be more suited for organic solvent extraction. Oxygenated monoterpenes, such as thymol, carvacrol, and thymoquinone, exhibited optimal extraction when using SWE. By identifying the optimal conditions, SWE can be an efficient technique for selectively extracting target compounds from thyme. The selectivity of SWE could have practical applications in extracting desired compounds from a variety of industrials. SWE technology can be easily implemented on an industrial scale.

Effects of Defatting Pretreatment on Polysaccharide Extraction from Rambutan Seeds Using Subcritical Water: Optimization Using the Desirability Approach.

Rambutan seeds are by-products generated from fruit-processing factories; the leftover seeds are buried in landfills, generating methane emissions. This work aimed to extract polysaccharides (POLS) from rambutan seeds by using subcritical water extraction (SWE). The effects of defatting pretreatment and operating parameters in SWE were investigated using a Box-Behnken design. The results show that defatting pretreatment significantly enriched the POLS yield, while it had no significant effect on the total sugar content. Using the desirability approach, the suitable feedstock for SWE was defatted rambutan seeds. The maximum desirability of 0.86 was found at a temperature range of 145-150 °C, an extraction time of 15 min, and a liquid-solid ratio of 10:1. The POLS yield and total sugar content were in the range of 52.33-55.63 g/100 g feedstock and 83.37-87.45 g/100 g POLS, respectively. The extracted POLS had an equivalent molecular weight of 413.70 kDa that could be used as an extender in plant-based products. In conclusion, the defatting pretreatment of rambutan seeds not only improved the POLS yield obtained via SWE but also generated additional lipids that could be utilized as an unconventional source of specialty fat.

Alkaline subcritical water extraction of bioactive compounds and antioxidants from beach-cast brown algae (Ascophyllum Nodosum)

Beach-cast brown algae Ascophyllum nodosum (rockweed) is a seasonal phenomenon where rockweed accumulates on beaches, resulting in environmental impacts. However, rockweed is a valuable source of bioactive compounds and nutrients for use in biomaterials, food, cosmetic, and pharmaceutical industries. This study explores the utilization of alkaline subcritical water extraction in an accelerated solvent extractor (ASE) for extracting valuable compounds from beach-cast rockweed. The bioactive compounds and nutrients (alginate, fucoidan, phenolics, minerals, and vitamins) were first characterized. The yields of major components (alginate, fucoidan, and phenolics) and antioxidant properties of crude extract were further optimized in the ASE system as a function of extraction conditions (temperature, extraction time, and solid mass). The maximum yields of crude extract (86.52 dry wt%), alginate (38.25 dry wt%), and fucoidan (39.38 dry wt%) were achieved at 160 °C, 18 min, and 0.1 g mass loading. A higher temperature of 200 °C increased phenolic yield and antioxidant activities (ABTS and FRAP assays) but led to alginate/fucoidan degradation. The extraction rates for extract, alginate, and fucoidan were modeled using Fick’s and Peleg’s models. Both models fit the experimental data well, but Fick’s model showed a better overall fit. The effective diffusion coefficients for the extract (7.82 × 10−12 m2/s), fucoidan (7.56 × 10−12 m2/s), and alginate (8.55 × 10−12 m2/s) were determined. Thus, the ASE using alkaline subcritical water can effectively be used to identify and quantify key value-added compounds by modifying process conditions while minimizing extraction time (maximizing rate) from beach-cast rockweed.

Exploring Phenolic Compounds Extraction from Saffron (C. sativus) Floral By-Products Using Ultrasound-Assisted Extraction, Deep Eutectic Solvent Extraction, and Subcritical Water Extraction.

Saffron (Crocus sativus) floral by-products are a source of phenolic compounds that can be recovered and used in the nutraceutical, pharmaceutical, or cosmetic industries. This study aimed to evaluate the phenolic compounds' extraction using green extraction techniques (GETs) in saffron floral by-products and to explore the influence of selected extraction techniques on the phytochemical composition of the extracts. Specifically, ultrasound-assisted extraction (UAE), subcritical water extraction (SWE), and deep eutectic solvents extraction (DESE) were used. Phenolic compounds were identified with (HR) LC-ESI-QTOF MS/MS analysis, and the quantitative analysis was performed with HPLC-PDA. Concerning the extraction techniques, UAE showed the highest amount for both anthocyanins and flavonoids with 50:50% v/v ethanol/water as solvent (93.43 ± 4.67 mg/g of dry plant, dp). Among SWE, extraction with 96% ethanol and t = 125 °C gave the best quantitative results. The 16 different solvent mixtures used for the DESE showed the highest amount of flavonoids (110.95 ± 5.55-73.25 ± 3.66 mg/g dp), while anthocyanins were better extracted with choline chloride:butane-1,4-diol (16.0 ± 0.80 mg/g dp). Consequently, GETs can be employed to extract the bioactive compounds from saffron floral by-products, implementing recycling and reduction of waste and fitting into the broader circular economy discussion.

An updated review of composition, health benefits, and applications of phenolic compounds in Ficus Carica L.

AbstractFicus carica L. (FC) is rich in phenolic compounds such as phenolic acids, flavonoids, and anthocyanins. Phenolic compounds in FC show remarkable health benefits and applications. The composition of phenolic compounds in FC can vary with some factors, such as variety, ripeness, geographical location, extraction methods and processing methods. New techniques such as supercritical fluid extraction, subcritical water extraction and ionic liquid extraction should be further developed and combined with traditional techniques to obtain higher quality sources of phenolic compounds. Numerous in vivo and in vitro studies reported healthy benefits of phenolic compounds in FC, such as anti‐oxidant, anti‐inflammatory, anti‐diabetic, anti‐obesity, anti‐cancer and anti‐Alzheimer's. Further works are required to reveal mechanisms and structure‐activity relationships, such as targeted metabolomics and pharmacological studies. In terms of applications, phenolic compounds in FC as prebiotics on the intestinal flora need to be further studied to expand their applicability in food fermentation. In a word, this review highlights the remarkable health benefits and application value of phenolic compounds in FC.

Phytochemical Screening, Antimicrobial and In-vitro Cytotoxic Activities of Several Extracts of Six Medicinal Plants (Crossopteryx febrifuga Benth, Khaya anthotheca, Gardenia ternifolia, and Terminalia glaucescens) from Central Africa Region

The qualitative study of secondary metabolites of the root and stem bark of Crossopteryx febrifuga Benth, Khaya anthotheca, Gardenia ternifolia, and Terminalia glaucescens obtained by maceration were estimated by tub reaction. Antimicrobial and cytotoxic activities of the root and stem bark of the same plants obtained by maceration and subcritical water extraction were respectively tested whit antibiogram disc test on Pseudomonas Aeruginosa (ATCC 27853), Enterobacter Hormaechei (ATCC700323), Bacillus Spizizenii (ATCC6633), Enterococcus Casseliflavus (ATCC700327), Staphylococcus aureus subsp. Rosenbach (ATCC 6538), and Salmonella Typhus (ATCC 6539). The Tetrazolium test (MTT test) was realized by using the mouse fibroblast cells (NIH3T3). Extracts based on the bark of Terminalia glaucescens and Crossopteryx febrifuga Benth induce sensitivity to 4/6 bacterial strains, in particular Enterobacter Hormaechei (ATCC700323): 3±2cm; Bacillus Spizizenii (ATCC6633): 5±2 cm; Staphylococcus aureus subsp. Rosenbach (ATCC 6538): 5±2; and Salmonella Typhus (ATCC 6539): 3±2cm. Extracts based on the bark of Khaya anthotheca and those of the bark of Gardenia ternifolia induce only the sensitivity on 2/6 bacterial strains specially Enterobacter Hormaechei (ATCC700323) and Bacillus Spizizenii (ATCC6633) respectively 4±2cm and 5±2cm. Extracts based on the barks and roots of Khaya anthotheca and those of the roots and barks of Gardenia ternifolia only induce sensitivity on 2/6 bacterial strains tested, in particular the strain of Enterobacter Hormaechei (ATCC700323) and Bacillus Spizizenii (ATCC6633). Only extracts based on the bark of Crossopteryx febrifuga Benth and Terminalia glaucescens show sensitivity against Salmonella Typhus (ATCC 6539). All the plant extracts tested show very low cytotoxic power. Plant extracts obtained by the maceration method (Hydro Methanol 90%) induce 19% inhibition of cell growth compared to extracts obtained by supercritical water 125°C 60ATM and 125°C80 ATM. The extracts obtained using the supercritical water 125°C 60ATM method are the least offensive on cell proliferation. The most concentrated extracts show the greatest inhibitions. The extracts of plant E show the greatest inhibition at a concentration of 1 g/ml.

Industrial byproduct pine nut skin factorial design optimization for production of subcritical water extracts rich in pectic polysaccharides, xyloglucans, and phenolic compounds by microwave extraction

Pine nut skin (Pinus pinea L.) is a poorly explored industrial byproduct with potential to be utilized as a food ingredient. Subcritical water extraction (SWE), an eco-friendly extraction technique with higher efficiency than hot-water extraction (HWE), was studied to evaluate its suitability in producing extracts rich in soluble fiber and phenolic compounds. For this, a factorial design was developed considering temperature (120–180 °C), time (2–10 min), and mass/volume ratio (1–3 g/60 mL) under microwave irradiation. This design aimed to maximize the extraction of carbohydrates, while achieving the highest content of phenolic compounds and antioxidant activity. SWE produced higher yields (2.6-fold in relation to HWE) of extracts rich in polysaccharides, determined by methylation analysis, oligosaccharides, determined by GC-qMS as alditol acetates, and phenolic compounds, determined by HPLC-ESI-MS. SWE increased the recovery of pectic oligosaccharides (10-fold) and xyloglucans (2-fold), and allowed to recover pectic polysaccharides, type II arabinogalactans and insoluble-bound phenolic compounds. Mono-, oligo- and polysaccharides were not hydrolyzed during in vitro gastrointestinal digestion, showing potential prebiotic functionality. Although phenolic compounds suffered a 23 % (gallic acid equivalents) decrease, phenolic acids and aldehydes were released or conserved upon intestinal phase. These results highlight the potential of PNS valorization as functional food ingredients through the subcritical water solubilization of polysaccharides and phenolic compounds.

Catalytic Conversion of Oil Shale over Fe or Ni Catalysts under Sub-Critical Water

Sub-critical water is an environment-friendly solvent. It is widely used for the extraction of various organic compounds. It can be used to dissolve and transport organic matter in oil shale. In this study, the conversion of oil shale was synergistically catalyzed by the addition of Fe or Ni to the Fe inherent in samples under sub-critical water conditions. Oil shale can be converted to gas, oil and residues of oil. Thermogravimetric (TG) analysis results presented that the weight loss of raw oil shale was up to 15.85%. After sub-critical water extraction, the weight loss rate of the residues was reduced to 8.41%. With the application of a metal catalyst, Fe or Ni, the weight loss of residues was further reduced to 7.43% and 6.57%, respectively. According to DTG curves, it was found that there were two weight-loss rate peaks. The decomposition process of kerogen in oil shale could be divided into two cracking processes. One is decomposed at a high velocity at around 420 °C, and another is decomposed at a low velocity at around 515 °C. Gas chromatography (GC) results of gas products indicated that Fe or Ni could contribute to producing normal alkanes, such as methane, ethane, propane, etc., which are produced by the hydrogenation of alkenes via hydrogen transfer during the conversion process of kerogen. Gas chromatography-mass spectrometry (GC–MS) was conducted to analyze the components of the liquid products. The results showed that n-alkanes, iso-alkane, oxygenated hydrocarbons and aromatic compounds were the major components of the kerogen cracking products. When Ni was introduced as a catalyst, the contents of aromatic compounds and oxygenated hydrocarbons in the liquid products were increased from 19.55% and 6.87% to 22.38% and 13.77%, respectively. This is due to the synergistic effect of the addition of Ni with the inherent Fe in oil shale under sub-critical water which ensures kerogen is more easily cracked to produce aromatic compounds and oxygenated hydrocarbons.

Antioxidant and antimicrobial extracts from grape stalks obtained with subcritical water. Potential use in active food packaging development

In order to valorise winemaking grape stalks, subcritical water extraction at 160 and 180 °C has been carried out to obtain phenolic-rich extracts useful for developing active food packaging materials. Red (R) and white (W) varieties (from Requena, Spain) were used, and thus, four kinds of extracts were obtained. These were characterised as to their composition, thermal stability and antioxidant and antibacterial activity. The extracts were incorporated at 6 wt% into polylactic acid (PLA) films and their effect on the optical and barrier properties of the films and their protective effect against sunflower oil oxidation was analysed. Carbohydrates were the major compounds (25–38%) in the extracts that contained 3.5–6.6% of phenolic compounds, the R extracts being the richest, with higher radical scavenging capacity. Every extract exhibited antibacterial effect against Escherichia coli and Listeria innocua, while PLA films with extracts preserved sunflower oil against oxidation.

Unveiling the multifaceted world of anthocyanins: Biosynthesis pathway, natural sources, extraction methods, copigmentation, encapsulation techniques, and future food applications

Numerous datasets regarding anthocyanins have been noted elsewhere. These previous studies emphasized that all processes must be carried out meticulously from the source used to obtain anthocyanins to their inclusion in relevant applications. However, today, full standardization has not yet been achieved for these processes. For this, presenting the latest developments regarding anthocyanins under one roof would be a useful approach to guide the scientific literature. The current review was designed to serve the stated points. In this context, their biosynthesis pathway was elaborated. Superior potential of fruits and certain by-products in obtaining anthocyanins was revealed compared to their other counterparts. Health-promoting benefits of anthocyanins were detailed. Also, the situation of innovative techniques (ultrasound-assisted extraction, subcritical water extraction, pulse electrical field extraction, and so on) in the anthocyanin extraction was explained. The stability issues, which is one of the most important problems limiting the use of anthocyanins in applications were discussed. The role of copigmentation and various encapsulation techniques in solving these stability problems was summarized. This critical review is a map that provides detailed information about the processes from obtaining anthocyanins, which stand out with their functional properties, to their incorporation into various systems.

Enhanced recovery of rare ginsenosides and bioactive compounds from red ginseng marc using CO2-Assisted subcritical water

Subcritical water extraction (SWE) is a high-efficiency and environmentally sustainable technique for extracting bioactive compounds from red ginseng marc (RGM). In this study, CO2 was introduced into the SWE system as a green catalyst to enhance the extraction efficiency of biologically active compounds from RGM. A wide range of parameters, such as temperature (140–180 °C), pressure (10–20 MPa), and time (10–60 min), were optimized using response surface methodology to maximize the recovery of highly valuable bioactive components, including rare ginsenosides (RGs), total phenolic contents (TPCs), and Maillard reaction products (MRPs), as well as the antioxidant activity of the RGM extract. The extract obtained using CO2-assisted SWE (CO2-SWE) under the optimal conditions (172 °C, 10 MPa, and 10 min) was enriched in RGs (1.02–2.16 times), TPCs (0.98–4.68 times), and MRPs (1.08–2.20 times) and exhibited enhanced antioxidant activities (1.07–3.50 times) compared with the extracts produced by conventional SWE (N2 environment) and Soxhlet extraction with H2O or 80 vol% ethanol. Thus, CO2-SWE is an environmentally friendly and nontoxic technique with considerable potential for use in the pharmaceutical, cosmeceutical, and functional food sectors.

Using Subcritical Water to Obtain Polyphenol-Rich Extracts with Antimicrobial Properties.

The use of green extraction methods that meet the criteria of sustainable and environmentally friendly technologies has been increasing in recent decades due to their many benefits. In this respect, extracts obtained using subcritical water are also gaining increased attention because of their potential antioxidant and antimicrobial properties. Their antimicrobial activity is mainly due to the presence of various polyphenolic compounds. Although the exact mechanism of the antibacterial action of polyphenolic compounds has not yet been fully investigated and described, polyphenols are known to affect the bacterial cell at several cellular levels; among other things, they cause changes and ruptures in the cell membranes of the bacterial cell, affect the inactivation of bacterial enzymes and damage bacterial DNA. The difference in the strength of the antimicrobial activity of the extracts is most likely a result of differences in their lipophilicity and in the number and position of hydroxyl groups and double bonds in the chemical structure of polyphenols. By changing the extraction conditions, especially the temperature, during subcritical water extraction, we affect the solubility of the compounds we want to extract. In general, as the temperature increases, the solubility of polyphenolic compounds also increases, and the reduction of the surface tension of subcritical water at higher temperatures also enables faster dissolution of polyphenolic compounds. Different bacterial strains have different sensitivity to different extracts. However, extracts obtained with subcritical water extraction demonstrate strong antimicrobial activity compared to extracts obtained with conventional methods.

Combining subcritical water extraction and bleaching with hydrogen peroxide to obtain cellulose fibres from rice straw

Cellulose fibres from rice straw (RS) were obtained by applying a combined and green process consisting of subcritical water extraction (SWE) (at 160 and 180 °C), followed by bleaching with hydrogen peroxide (H2O2). The bleaching variables were optimised for both extraction residues (R160 and R180), obtaining optimum conditions for 4 % H2O2 at pH 12 for 1 h of reaction. Under these conditions, four successive bleaching cycles were applied to promote cellulose purification in both R160 and R180 lignocellulosic samples, which were characterised as to their yield, whiteness index (WI), chemical composition, microstructural characteristics, degree of crystallinity, and thermal stability. The samples pre-extracted with SWE at 180 °C were more susceptible to bleaching than those pre-treated at 160 °C, being richer in cellulose (86.2 vs. 72.4 %), with higher WI (80.1 vs. 78) and yield (46.2 vs. 36.7 %) after the four bleaching cycles. Likewise, the R180 bleached fractions had higher crystallinity (67 vs. 63%) and were more thermostable than the R160 bleached fibres. Therefore, the SWE at 180 °C, followed by four bleaching cycles with H2O2 (4 %, at pH 12, for 1 h), can be considered a green and more sustainable alternative for obtaining cellulose fibres from RS with high cellulose purity.

The Effect of Green Extraction Technologies on the Chemical Composition of Medicinal Chaga Mushroom Extracts.

The mushroom industry should implement green extraction technologies; however, there is not enough information on the differences between these techniques expressed as the chemical composition of the resulting extract. In this study, selected types of green extraction techniques (GETs) were used on Chaga (Inonotus obliquus) (Fr.) Pilát from Serbia (IS) and Mongolia (IM) to examine the differences that would enable the composition-based technology choices in the mushroom supplement industry. Subcritical water extraction (SWE), microwave-assisted (MW) extraction, and ultrasonic-assisted extraction (VAE) were used to prepare the extracts. SWE was performed at two different temperatures (120 and 200 °C), while 96% ethanol, 50% ethanol, and water were used for MW and VAE. The yield, the content of total phenols, total proteins, and carbohydrates, qualitative and quantitative analysis of phenolic compounds, carbohydrates, including α- and β- and total glucans, and fatty acids, were determined in the obtained extracts. SWE resulted in a significantly higher yield, total polysaccharide, and glucan content than any other technique. Glucose was the most dominant monosaccharide in the SWE samples, especially those extracted at 200 °C. The MW 50% EtOH extracts showed the highest yield of total phenols. Among the tested phenolic compounds, chlorogenic acid was the most dominant. SWE can be recommended as the most efficient method for extracting commercially important compounds, especially glucans and phenols.