Glycerol and Glycerol-Based Deep Eutectic Mixtures as Emerging Green Solvents for Polyphenol Extraction: The Evidence So Far

Deep eutectic solvents for the extraction of polyphenols from food plants

Deep Eutectic Solvents (DESs) offer a promising, sustainable alternative for extracting polyphenols from food plants, known for their health benefits. Traditional extraction methods are often costly and involve toxic solvents. This review discusses the basic concepts, preparation techniques, and factors influencing the effective and safe use of DESs in polyphenol extraction. DESs' adaptability allows integration with other green extraction technologies, such as microwave- and ultrasound-assisted extractions, enhancing their efficiency. This adaptability demonstrates the potential of DESs in the sustainable extraction of bioactive compounds. Current research indicates that DESs could play a significant role in the sustainable procurement of these compounds, marking an important advancement in food science research and development. The review underscores DESs as a realistic, eco-friendly alternative in the realm of natural extraction technologies, offering a significant contribution to sustainable practices in food science.

Enhancing deep eutectic solvent systems for efficient fermentable sugar recovery from lignocellulosic fiber

Efficient conversion of sugars into fermentable sugars is a critical challenge in the cost-effective production of lignocellulosic biopolymers and biofuels. This study focuses on various sugar quantification techniques applied to Furcraea Foetida (Mauritius Hemp) samples, utilizing natural deep eutectic solvents (NADES) and deep eutectic solvents (DES) like urea, glycerol, citrates, pyrogallol (PY), and cetyltrimethylammonium bromide (CTAB). Employing a Taguchi-designed experiment, operational conditions were fine-tuned to evaluate the influence of time, concentration, and temperature on each deep eutectic solvent-based process. The emerging green solvent extraction approach demonstrated significant results, achieving notably high sugar yields compared to traditional techniques such as alkali, hot-water, and acid-mediated extraction. At a CTAB:PY molar ratio of 1:3, optimized for 60 min at 50 °C, the highest fermentable sugar (FS) yield of 0.6891 ± 0.0123 g FS/g LCB was attained-2 to 6 times higher than non-optimized values and 0.2 to 0.3 times higher than optimized traditional methods. In light of this, this research study emphasizes the pivotal significance of efficient sugar conversion through optimized deep eutectic solvent-based extraction methods, with a particular focus on Furcraea Foetida fibers, offering promising outcomes for the biofuel and biopolymer production industry.

Glycerol Extraction of Bioactive Compounds from Thanaka (Hesperethusa crenulata) Bark through LCMS Profiling and Their Antioxidant Properties

Organic solvents are hazardous to human and environmental health. The emergence of interest in finding greener solvents to replace organic solvents has sparked a series of studies in the use of glycerol for extracting bioactive compounds from natural products. In this study, we will first identify the bioactive compounds of glycerol- and nonglycerol-based Thanaka (Hesperethusa crenulata) bark extracts using liquid chromatography-mass spectrometry profiles; then, we will determine their antioxidant capacity, free radical scavenging activity, and total phenolic and flavonoid contents. Thanaka bark powder was extracted using solvents, namely, ethanol (TKE), water (TKW), glycerol (TKG), glycerol/water (1:1, v/v) (TKGW), and glycerol/ethanol (1:1, v/v) (TKGE). Among the five extracts, the extract of TKG has the highest number of bioactive compounds, as well as the highest total flavonoid content. TKGE possessed the highest total phenolic content and highest antioxidant activity shown in azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) and ferric-reducing antioxidant power assays among the five extracts. Overall, glycerol has better efficiency in extracting bioactive compounds from Thanaka bark as compared to ethanol and water. Hence, from the phytochemical content and antioxidant properties of Thanaka extracts, we conclude that glycerol is a good green solvent alternative to replace organic solvents.

Production and characterization of rhamnolipids by Pseudomonas aeruginosa isolated in the Amazon region, and potential antiviral, antitumor, and antimicrobial activity

Biosurfactants encompass structurally and chemically diverse molecules with surface active properties, and a broad industrial deployment, including pharmaceuticals. The interest is growing mainly for the low toxicity, biodegradability, and production from renewable sources. In this work, the optimized biosurfactant production by Pseudomonas aeruginosa BM02, isolated from the soil of a mining area in the Brazilian Amazon region was assessed, in addition to its antiviral, antitumor, and antimicrobial activities. The optimal conditions for biosurfactant production were determined using a factorial design, which showed the best yield (2.28 mg/mL) at 25 °C, pH 5, and 1% glycerol. The biosurfactant obtained was characterized as a mixture of rhamnolipids with virucidal properties against Herpes Simplex Virus, Coronavirus, and Respiratory Syncytial Virus, in addition to antimicrobial properties against Gram-positive bacteria (Staphylococcus aureus and Enterococcus faecium), at 50 µg/mL. The antitumor activity of BS (12.5 µg/mL) was also demonstrated, with potential selectivity in reducing the proliferation of breast tumor cells, after 1 min of exposure. These results demonstrate the importance of studying the interconnection between cultivation conditions and properties of industrially important compounds, such as rhamnolipid-type biosurfactant from P. aeruginosa BM02, a promising and sustainable alternative in the development of new antiviral, antitumor, and antimicrobial prototypes.

Optimizing the Solvent Selection of the Ultrasound-Assisted Extraction of Sea Buckthorn (Hippophae rhamnoides L.) Pomace: Phenolic Profiles and Antioxidant Activity

Sea buckthorn pomace (SBP) is a by-product of sea buckthorn processing that is rich in bioactive compounds. In this study, different active ingredients were extracted by using different solvents (water, methanol, ethanol, glycerol, ethyl acetate, and petroleum ether) combined with an ultrasonic assisted method. The correlation between the active ingredients and antioxidant properties of the extract was studied, which provided a research basis for the comprehensive utilization of SBP. This study revealed that the 75% ethanol extract had the highest total phenolic content (TPC) of 42.86 ± 0.73 mg GAE/g, while the 75% glycerol extract had the highest total flavonoid content (TFC) of 25.52 ± 1.35 mg RTE/g. The ethanol extract exhibited the strongest antioxidant activity at the same concentration compared with other solvents. The antioxidant activity of the ethanol, methanol, and glycerol extracts increased in a concentration-dependent manner. Thirteen phenolic compounds were detected in the SBP extracts using UPLC-MS/MS analysis. Notably, the 75% glycerol extract contained the highest concentration of all identified phenolic compounds, with rutin (192.21 ± 8.19 μg/g), epigallocatechin (105.49 ± 0.69 μg/g), and protocatechuic acid (27.9 ± 2.38 μg/g) being the most abundant. Flavonols were found to be the main phenolic substances in SBP. A strong correlation was observed between TPC and the antioxidant activities of SBP extracts. In conclusion, the choice of solvent significantly influences the active compounds and antioxidant activities of SBP extracts. SBP extracts are a valuable source of natural phenolics and antioxidants.

Organosolv Treatment of Red Grape Pomace for Effective Recovery of Antioxidant Polyphenols and Pigments Using a Ternary Glycerol/Ethanol/Water System under Mild Acidic Conditions

The purpose of this investigation was (i) the development of a novel, green tertiary solvent system, composed of water, ethanol and glycerol, and (ii) the implementation of an organosolv treatment of red grape pomace (RGP) for the efficient production of polyphenol-containing extracts with enhanced antioxidant properties. The treatment developed was performed under mild acidic conditions, imparted by the addition of citric acid, and it was first evaluated on the basis of severity, establishing linear models that described the correlation between treatment performance and combined severity factors. To solicit treatment optimization, response surface methodology was implemented, considering solvent acidity and residence time as the treatment variables. The optimized treatment afforded maximum total polyphenol (166 ± 6 mg GAE g-1 DM), total pigment (4.4 ± 0.2 mg MvE g-1 DM) and total flavanol (31.5 mg CtE g-1 DM) yields and extracts with particularly enhanced antioxidant activity. This might be attributed to specific constituents with high antioxidant potency, such as catechin, determined in the extract using high-performance liquid chromatography. Thus, the treatment developed is proposed as a highly efficient process to generate RGP extracts enriched in polyphenolic compounds, with enhanced antioxidant activity. Such extracts might then be valorized as food additives, to provide antioxidant protection and/or pigmentation.

Tuning the mechanical properties of pectin films with polyphenol-rich plant extracts

The mechanical properties of pectin films enhanced with polyphenol-rich fruit extracts were investigated. The scavenging and reducing activity of plant extracts incorporated into the pectin films were determined using bench assays, and their antioxidant activity was correlated with a high presence of polyphenols, which were predominantly comprised of flavonoids and anthocyanins. The pectin films generated from the extracts exhibited a range of mechanical properties; tensile strength (4.99 MPa - 6.91 MPa), elongation at break (45.8 % - 52.3 %), and stiffness (1835 g mm-1 - 2765 g mm-1). To investigate the underlying relationships between plant extract composition and mechanical properties, Projection to Latent Structures (PLS) models were developed. The PLS models revealed that extracts containing high sugar and polyphenol content increase the tensile strength and moisture content of films. The elongation at break of the films was improved or diminished depending on the profile of sugar, acids, and polyphenols in the fruit extracts. Furthermore, the structures and concentration of anthocyanins and flavonoids were identified to strongly influenced the elongation at break differences. By modifying the concentration of sugars, organic acids, and polyphenols, the mechanical properties of pectin-based films can be tuned for tailored applications as food packaging materials.

Phytochemical Characterization of Purple Coneflower Roots (Echinacea purpurea (L.) Moench.) and Their Extracts

Echinacea purpurea is a perennial plant that belongs to the Asteraceae family. It has a wide range of applications mainly in the treatment and prevention of inflammations in the respiratory system. The current study aimed to perform a phytochemical characterization of purple coneflower (Echinacea purpurea) roots and their extracts (water, 40%, 50%, 60% ethanol, and 60% glycerol). Phytochemical characterization was carried out by gravimetric, spectrophotometric, and chromatographic methods. Echinacea roots were characterized by a low lipid (0.8%) content. In contrast, carbohydrates (45%) and proteins (20%) occupied a large part of the dry matter. Amongst the extracts, the highest yield was obtained using water as a solvent (53%). Water extract was rich in protein and carbohydrates as fructans (inulin) were the most abundant carbohydrate constituent. The most exhaustive recovery of the phenolic components was conducted by extraction with 40% ethanol and 60% glycerol. It was found that water is the most suitable extractant for obtaining a polysaccharide-containing complex (PSC) (8.87%). PSC was composed mainly of fructans (inulin) and proteins with different molecular weight distributions. The yield of PSC decreased with an increasing ethanol concentration (40% > 50% > 60%) but the lowest yield was obtained from 60% glycerol extract. The obtained results showed that Echinacea roots contained a large amount of biologically active substances-phenolic components and polysaccharides and that glycerol was equally efficient to ethanol in extracting caffeic acid derivatives from purple coneflower roots. The data can be used for the preparation of extracts having different compositions and thus easily be incorporated into commercial products.

Green Extraction of Antioxidant Compounds from Olive Tree Leaves Based on Natural Deep Eutectic Solvents

Agri-food industries generate a large amount of waste that offers great revalorization opportunities within the circular economy framework. In recent years, new methodologies for the extraction of compounds with more eco-friendly solvents have been developed, such as the case of natural deep eutectic solvents (NADES). In this study, a methodology for extracting phenolic compounds from olive tree leaves using NADES has been optimized. The conditions established as the optimal rely on a solvent composed of choline chloride and glycerol at a molar ratio of 1:5 with 30% water. The extraction was carried out at 80 °C for 2 h with constant agitation. The extracts obtained have been analyzed by high-performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS) in MRM mode. The comparison with conventional ethanol/water extraction has shown that NADES, a more environmentally friendly alternative, has improved extraction efficiency. The main polyphenols identified in the NADES extract were Luteolin-7-O-glucoside, Oleuropein, 3-Hydroxytyrosol, Rutin, and Luteolin at the concentrations of 262, 173, 129, 34, and 29 mg kg^-1 fresh weight, respectively.

Qualitative Analysis of Polyphenols in Glycerol Plant Extracts Using Untargeted Metabolomics

Glycerol is a reliable solvent for extracting polyphenols from food and waste products. There has been an increase in the application of glycerol over benchmark alcoholic solvents such as ethanol and methanol for natural product generation because of its non-toxic nature and high extraction efficiency. However, plant extracts containing a high glycerol concentration are unsuitable for mass spectrometry-based investigation utilising electrospray ionization, inhibiting the ability to analyse compounds of interest. In this investigation, a solid phase extraction protocol is outlined for removing glycerol from plant extracts containing a high concentration of glycerol and their subsequent analysis of polyphenols using ultra-performance liquid chromatography coupled with quadrupole time of flight tandem mass spectrometry. Using this method, glycerol-based extracts of Queen Garnet Plum (Prunus salicina) were investigated and compared to ethanolic extracts. Anthocyanins and flavonoids in high abundance were found in both glycerol and ethanol extracts. The polyphenol metabolome of Queen Garnet Plum was 53% polyphenol glycoside derivatives and 47% polyphenols in their aglycone forms. Furthermore, 56% of the flavonoid derivates were found to be flavonoid glycosides, and 44% were flavonoid aglycones. In addition, two flavonoid glycosides not previously found in Queen Garnet Plum were putatively identified: Quercetin-3-O-xyloside and Quercetin-3-O-rhamnoside.

Food Industry Byproducts as Starting Material for Innovative, Green Feed Formulation: A Sustainable Alternative for Poultry Feeding

Rising global populations and enhanced standards of living in so-called developing countries have led to an increased demand of food, in particular meat, worldwide. While increasing the production of broiler meat could be a potential solution to this problem, broiler meat is plagued by health concerns, such as the development of antimicrobial resistance and lower meat quality. For this reason, the supplementation of poultry feed with vitamins and antioxidant compounds, such as polyphenols, has become an attractive prospect for research in this sector. Such supplements could be obtained by extraction of agricultural byproducts (in particular, grape pomaces and artichoke leaves and bracts), thus contributing to reductions in the total amount of waste biomass produced by the agricultural industry. In this review, the effects of poultry feed supplementation with bioactive extracts from grape pomace (skins and/or seeds), as well as extracts from artichoke leaves and bracts, were explored. Moreover, the various methods that have been employed to obtain extracts from these and other agricultural byproducts were listed and described, with a particular focus on novel, eco-friendly extraction methods (using, for example, innovative and biocompatible solvents like Deep Eutectic Solvents (DESs)) that could reduce the costs and energy consumption of these procedures, with similar or higher yields compared to standard methods.

Process Optimization and Stability of Waste Orange Peel Polyphenols in Extracts Obtained with Organosolv Thermal Treatment Using Glycerol-Based Solvents

This study was focused on the simultaneous organosolv treatment/extraction of waste orange peels (WOP) for the effective recovery of polyphenolic antioxidants. The treatments were performed with aqueous glycerol mixtures, which were acidified either with citric acid or hydrochloric acid (HCl). Process optimization was carried out using response surface methodology and comparative appraisal of the different processes tested, based on both the extraction efficiency factor (FEE), severity factor (SF) or combined severity factor (CSF). Metabolite stability was also of major concern, and it was examined by deploying liquid chromatography-mass spectrometry. The results drawn suggested 90% (w/w) glycerol to be the highest-performing system, providing a yield in total polyphenols of 44.09 ± 5.46 mg GAE g−1 DM at 140 °C for 50 min, with a FEE of 2.20 and an SF of 2.88. Acidification with 1% citric acid was proven less efficient and equally severe, whereas acidification with 1% HCl was less severe but also less efficient. The major disadvantage associated with the use of HCl was its detrimental impact on the polyphenolic composition of WOP since major metabolites, such as narirutin, hesperidin and didymin, did not survive the process. By contrast, the formation of lower molecular weight compounds was observed. With regard to antioxidant properties, the extract obtained with aqueous glycerol displayed significantly higher antiradical activity and reducing power, which was in line with its higher concentration in total polyphenols. It was concluded that organosolv treatment with aqueous glycerol under the conditions employed may boost polyphenol recovery from WOP, thus giving extracts with powerful antioxidant characteristics.

Influence of the extraction method on the recovery of bioactive phenolic compounds from food industry by-products

Agro-foodindustries generate colossal amounts of non-edible waste and by-products, easily accessible as raw materials for up-cycling active phytochemicals. Phenolic compounds are particularly relevant in this field given their abundance in plant residues and the market interest of their functionalities (e.g. natural antioxidant activity) as part of nutraceutical, cosmetological and biomedical formulations. In "bench-to-bedside" achievements, sample extraction is essential because valorization benefits from matrix desorption and solubilization of targeted phytocompounds. Specifically, the composition and polarity of the extractant, the optimal sample particle size and sample:solvent ratio, as well as pH, pressure and temperature are strategic for the release and stability of mobilized species. On the other hand, current green chemistry environmental rules require extraction approaches that eliminate polluting consumables and reduce energy needs. Thus, the following pages provide an update on advanced technologies for the sustainable and efficient recovery of phenolics from plant matrices.

Enhanced In Vitro Cascade Catalysis of Glycerol into Pyruvate and Acetoin by Integration with Dihydroxy Acid Dehydratase from Paralcaligenes ureilyticus

Recently, an in vitro enzymatic cascade was constructed to transform glycerol into the high-value platform chemical pyruvate. However, the low activity of dihydroxy acid dehydratase from Sulfolobus solfataricus (SsDHAD) limited the efficiency. In this study, the enzymatic reduction of pyruvate catalyzed by d-lactate dehydrogenase from Pseudomonas aeruginosa PAO1 was used to assay the activities of dihydroxy acid dehydratases. Dihydroxy acid dehydratase from Paralcaligenes ureilyticus (PuDHT) was identified as the most efficient candidate for glycerate dehydration. After the optimization of the catalytic temperature for the enzymatic cascade, comprising alditol oxidase from Streptomyces coelicolor A3, PuDHT, and catalase from Aspergillus niger, 20.50 ± 0.27 mM of glycerol was consumed in 4 h to produce 18.95 ± 0.97 mM of pyruvate with a productivity 12.15-fold higher than the previous report using SsDHAD. The enzymatic cascade was further coupled with the pyruvate decarboxylase from Zymomonas mobile for the production of another platform compound, acetoin. Acetoin at a concentration of 8.52 ± 0.12 mM was produced from 21.62 ± 0.19 mM of glycerol with a productivity of 1.42 ± 0.02 mM h−1.

Emerging Green Techniques for the Extraction of Antioxidants from Agri-Food By-Products as Promising Ingredients for the Food Industry

Nowadays, the food industry is heavily involved in searching for green sources of valuable compounds, to be employed as potential food ingredients, to cater to the evolving consumers’ requirements for health-beneficial food ingredients. In this frame, agri-food by-products represent a low-cost source of natural bioactive compounds, including antioxidants. However, to effectively recover these intracellular compounds, it is necessary to reduce the mass transfer resistances represented by the cellular envelope, within which they are localized, to enhance their extractability. To this purpose, emerging extraction technologies, have been proposed, including Supercritical Fluid Extraction, Microwave-Assisted Extraction, Ultrasound-Assisted Extraction, High-Pressure Homogenization, Pulsed Electric Fields, High Voltage Electrical Discharges. These technologies demonstrated to be a sustainable alternative to conventional extraction, showing the potential to increase the extraction yield, decrease the extraction time and solvent consumption. Additionally, in green extraction processes, also the contribution of solvent selection, as well as environmental and economic aspects, represent a key factor. Therefore, this review focused on critically analyzing the main findings on the synergistic effect of low environmental impact technologies and green solvents towards the green extraction of antioxidants from food by-products, by discussing the main associated advantages and drawbacks, and the criteria of selection for process sustainability.

Pressurized Hot Liquid Extraction with 15% v/v Glycerol-Water as An Effective Environment-Friendly Process to Obtain Durvillaea incurvata and Lessonia spicata Phlorotannin Extracts with Antioxidant and Antihyperglycemic Potential

Brown seaweed phlorotannins have shown the potential to promote several health benefits. Durvillaea incurvata and Lessonia spicata-species that are widely distributed in central and southern Chile-were investigated to obtain phlorotannin extracts with antioxidant and antihyperglycemic potential. The use of an environmentally friendly and food-grade glycerol-based pressurized hot liquid extraction (PHLE) process (15% v/v glycerol water) was assessed for the first time to obtain phlorotannins. Multiple effects were analyzed, including the effect of the species, harvesting area (Las Cruces and Niebla), and anatomical part (holdfast, stipe, and frond) on the extracts' polyphenol content (TPC), antioxidant capacity (AC), and carbohydrate-hydrolyzing enzyme-α-glucosidase and α-amylase-inhibitory activity. Contaminants, such as mannitol, heavy metals (As, Cd, Pb, Hg, and Sn), and 5-hydroxymethylfurfural (HMF), were also determined. The anatomical part used demonstrated a significant impact on the extracts' TPC and AC, with holdfasts showing the highest values (TPC: 95 ± 24 mg phloroglucinol equivalents/g dry extract; DPPH: 400 ± 140 μmol Trolox equivalents/g dry extract; ORAC: 560 ± 130 μmol TE/g dry extract). Accordingly, holdfast extracts presented the most potent α-glucosidase inhibition, with D. incurvata from Niebla showing an activity equivalent to fifteen times that of acarbose. Only one frond and stipe extract showed significant α-glucosidase inhibitory capacity. No α-amylase inhibition was found in any extract. Although no HMF was detected, potentially hazardous cadmium levels (over the French limit) and substantial mannitol concentrations-reaching up to 50% of the extract dry weight-were found in most seaweed samples and extracts. Therefore, further purification steps are suggested if food or pharmaceutical applications are intended for the seaweed PHLE extracts obtained in this study.