Valuable Source Of Phenolic Compounds Research Articles

Enhanced Preservation of Bioactives in Wild Garlic (Allium ursinum L.) through Advanced Primary Processing

Medicinal and aromatic plants, such as wild garlic (Allium ursinum), are valuable sources of bioactive compounds in traditional and modern medicine. However, the challenges in cultivating wild garlic and its seasonality limit its availability primarily to early spring. To maintain the quality of wild garlic, effective postharvest practices are essential, considering the delicate nature of its leaves and their susceptibility to rapid decay. This study focuses on implementing eco-friendly postharvest practices to address the seasonality and perishability of wild garlic. Optimizing storage conditions and drying processes is essential for extending its shelf life and preserving bioactive components. Two postharvest approaches were evaluated, with vacuum packaging at 4 °C demonstrating the most effective preservation of sensory attributes and bioactive composition over a 9-day period. Additionally, different drying methods, including convective and vacuum drying at various temperatures, were investigated. When the best drying temperature was selected, the results revealed that convective drying is more efficient at preserving phenolic compounds in wild garlic leaves at 60 °C. Conversely, vacuum drying shows superior preservation of alliinase activity and total thiosulfinate content at 70 °C. Furthermore, this study explores the utilization of unused wild garlic, which is typically discarded as waste during storage. By employing suitable drying methods, this material can be preserved and provide a valuable source of phenolic compounds (7.17–10.12 g GAE/100 g) and thiosulfinate (9.35–12.72 mg AC/110 g) compounds for various extraction processes. Accordingly, this research presents significant implications for the integration of wild garlic into diverse industries, particularly in the fields of food and pharmaceutical sectors. The findings offer opportunities for sustainable utilization, economic benefits, and a more environmentally friendly and economically viable approach to wild garlic production and processing.

Phenolic profile of unripe areca nuts cultivated in various districts of Karnataka, India

AbstractBackgroundAnnual production of areca nut in Karnataka state exceeds 1.08 million tonnes, contributing 80% and 49% to Indian and global production, respectively. Areca nut (pericarp of Areca catechu L.) is found to be a rich source of valuable phenolic compounds. Total phenolic content (TPC) and total flavonoid content (TFC) were estimated in 21 unripe areca nut samples collected from the major areca nut growing regions of Karnataka state. Arecoline, a prominent alkaloid present in areca nut was estimated and phenolic profile of one areca nut sample was generated using UHPLC–MS/MS studies.ResultsA significant variability was found in TPC, TFC and arecoline content among the samples, belongs to different agroclimatic zones. Flavonoids were found to be the major phenolic compounds present in these unripe areca nut samples. The median values of TPC, TFC and arecoline were found to be 99.609 ± 0.002 mg gallic acid equivalent, 78.86 ± 0.007 mg catechin equivalent and 2.17 ± 0.13 mg/g of the sample on fresh weight basis. A positive correlation was found to exist between TPC and arecoline content in the green unripe areca nuts of 6–7 months' maturity. Through UHPLC–MS/MS studies, 61 prominent compounds have been identified.ConclusionThe TPC and TFC of areca nuts collected from different districts of Karnataka falling in various agroclimatic zones varied significantly. In general, the arecoline content found in all these samples was less than that reported elsewhere, and the variability among the samples was also found to be minimal. A positive correlation was observed between TPC and arecoline. UHPLC–MS/MS studies showed the presence of about 52 unique phenolic compounds.

Development of Pegylated Nano-Phytosome Formulation with Oleuropein and Rutin to compare Anti-Colonic Cancer.

Olive leaf extract is a valuable source of phenolic compounds; primarily, oleuropein (major component) and rutin. This natural olive leaf extract has potential use as a therapeutic agent for cancer treatment. However, its clinical application is hindered by poor pharmacokinetics and low stability. To overcome these limitations, this study aimed to enhance the anticancer activity and stability of oleuropein and rutin by loading them into PEGylated Nano-phytosomes. The developed PEGylated Nano-phytosomes exhibited favorable characteristics in terms of size, charge, and stability. Notably, the anticolonic cancer activity of the Pegylated Nano-phytosomes loaded with oleuropein (IC50 = 0.14 µM) and rutin (IC50 = 0.44 µM) surpassed that of pure oleuropein and rutin alone. This outcome highlights the advantageous impact of Nano-phytosomes to augment the anticancer potential of oleuropein and rutin. These results present a promising pathway for the future development of oleuropein and rutin Nano-phytosomes as effective options for passive tumor-targeted therapy, given their improved stability and efficacy.

Solvent-resistant ultrafiltration to recover bioactive compounds from wet olive pomace extracts

To contribute to the circular economy in olive mills, wet olive pomace can be employed as a source of valuable phenolic compounds. These compounds are efficiently extracted with ethanol/water 50:50 (v/v), at 40 °C. Here, the ultrafiltration membranes UF010104, UF010801v3 (from SolSep BV), and UP005 (Microdyn Nadir) have been tested to purify the phenolic compounds present in the hydroalcoholic extracts of the pomace. Several membrane conditioning protocols were explored, being the most adequate a short pre-treatment consisting of soaking the membrane in the working solvent for 2 h. All the considered membranes permitted the recovery of the biophenols of interest in the permeate stream, being most of the organic matter retained. A powerful analytical methodology based on liquid chromatography coupled to mass spectrometry (LC-ESI-QToF-MS) allowed the evaluation of the individual rejection of 43 compounds. The UF010104 membrane displayed the highest permeate flux (15 L h−1·m−2, at 2.5 bar) and high rejection of the total solids (67 ± 3%, at 2.5 bar), thus achieving the purification of the phenolic compounds in the permeate stream. The cleaning of the membranes used in organic solvent media was also investigated.

Chokeberry Pomace Utilization for Improving Selected Quality Parameters of Green Tea Leaves or Hibiscus Flower Infusions

The utilization of food industrial by-products, especially pomace after juice processing, could be a big challenge. Chokeberry pomace is a valuable source of phenolic compounds, including procyanidins and anthocyanins. These compounds have, e.g., antioxidant, anticancer, hypoglycemic, hypotensive, hepatoprotective and cardioprotective effects. In this work, dried chokeberry pomace (2.0 g, 2.5 g and 3.0 g) was added to green tea leaves or white or red hibiscus flowers (0.5 g of each) to obtain mixtures for preparing infusions. Such products could be a valuable source of bioactive compounds. After brewing and cooling, selected quality parameters of the obtained infusions were tested: pH, total phenolic content (TPC), anthocyanin content and the instrumentally and sensorily determined color. The composition of the infusion had an impact on the color. Those from a mixture of chokeberry by-products and hibiscus possessed lower L* and higher a* and b* values than those composed of chokeberry and green tea leaves. Infusions prepared from the mixture containing dried chokeberry pomace (3.0 g) and green tea leaves (0.5 g) had a higher content of anthocyanins (17%) and phenols (48%), respectively, than other samples with the same proportions of ingredients. According to PCA analysis, the highest content of the tested bioactive compounds was obtained in infusions of green tea leaves with the addition of chokeberry pomace.

Fermentative extraction of phenolic compounds from unripe areca nuts by solid‐state fermentation using newly isolated Rhizopus orizaeMW538932

SummaryAreca nut (pericarp of Areca catechu L.) is a rich source of valuable phenolic compounds. Presence of a psychoactive agent, Arecoline, pose a challenge in the use of areca nut extracts. With an aim to maximise the extraction of phenolic compounds, a newly isolated Rhizopus orizae MW538932, was employed for the solid‐state fermentation of unripe areca nut (6–7 months' maturity) powder. Supplementary nutrients (carbon and nitrogen sources) for the media and the solvents for the extraction of phenolic compounds from the fermented medium were optimised. The optimised process could produce an extract having a total phenolic content of 186.03 ± 2.50 mg gallic acid equivalent and total flavonoid content of 139.70 ± 2.00 mg catechin equivalent per gram of the sample. UHPLC–MS/MS studies and HPLC analysis showed the presence of plethora of phenolic compounds and the absence of Arecoline and other alkaloids. This flavonoid‐rich extract can be a potential source of natural antioxidants for food and pharmaceutical industry.

Electrospun TiO2 Nanofibers in the Presence of Avocado Seed Extract

The electrospinning technique is particularly prominent in membrane production techniques due to its easy applicability and ability to obtain nanofibers in various diameters with high surface area. Titanium dioxide (TiO2) is often used in biomaterial technologies due to their high biocompatibility, high processability and their photocatalytic activities in waste water treatment. In this study, TTIP (Titanium tetra isopropoxide) was used as a TiO2 precursor and PVP polymer was used as a carrier polymer for electrospinning. Avocado seed extract (ASE) which is a new and valuable source of phenolic compounds was used for the coordination and reduction of TTIP. TiO2-PVP-Avocado seed extract (T/P/A) composite nanofibers were produced at different voltages, distances and polymer concentrations. Crystalline TiO2 formation was not observed in as-spun nanofibers, thus selected nanofibers were heat treated at 500oC for 3 h. Smooth and integrated TiO2 nanofibers prepared by using 5 w% PVP, at 15 kV and 15 cm distance with or without ASE were imaged by Scanning Electron Microscopy (SEM). X-ray Diffraction (XRD) patterns of heat-treated TiO2 nanofibers prepared in the presence of ASE were crystallized mainly in anatase form. However, both anatase and rutile phases were obtained in the crystalline structure of TiO2 nanofibers when ASE was not used. Specific IR vibrations of TiO2 were shown by Fourier Transform Infrared Spectroscopy (FTIR). These green synthesized electrospun TiO2 nanofibers may have potential to be used in biomaterial and engineering applications.

Enrichment of Starch Desserts with the Addition of Apple Juice and Buckwheat Fiber.

Buckwheat hulls which are rich in fiber are good ingredients to increase the nutritional value of food products. The aim of this study was to determine the effect of the applied additives in the form of fiber and apple juice on the properties of both potato and corn starch (normal and waxy). In order to characterize the rheological properties of kissel, the pasting characteristic was measured. In the obtained gels, the basic quality parameters were determined. The analysis of texture, color parameters, and also total polyphenol content were determined. Buckwheat hulls, in addition to their high fiber content, are a valuable source of phenolic compounds and can be a great additive in starch desserts. The addition of buckwheat hulls and apple juice improved the nutritional value of the final products but also caused changes in the technological qualities: it increased the initial temperature of potato starch mixtures (by approx. 9 °C); it decreased the viscosity of cold desserts (from 8 to 55%); and increased the hardness of the final product by more than 7 times. In the case of other starches, the recorded changes were much smaller than for potato starch-based products.

Applicability of an HPLC method for analysis of alcoholic and glycolic Brazilian green-propolis extracts

Brazilian green propolis has been widely used in food and pharmaceutical products due to its valuable source of phenolic compounds and versatile biological activities. The development and validation of analytical methods are extremely useful for the characterization and quality control of products containing propolis. Therefore, the aim of this study was to optimize, validate and investigate the applicability of a reversed-phase HPLC method for analysis of different types of Brazilian green propolis extracts (glycolic and ethanolic). The method showed to be selective for the propolis phenolic markers. The analysis of variance and residues demonstrated that the method had significant linear regression, without lack of fit. It was also a precise, accurate and robust method, which was of utmost importance to analyze both glycolic and ethanolic extracts and at different concentrations. Moreover, as these products can display most complex matrices to analyze, a valid HPLC method can also prove to be specific and versatile.

Tailor-made alkaliphilic and thermostable fungal laccases for industrial wood processing

BackgroundDuring the kraft process to obtain cellulosic pulp from wood, most of the lignin is removed by high-temperature alkaline cooking, released in the black liquors and usually incinerated for energy. However, kraft lignins are a valuable source of phenolic compounds that can be valorized in new bio-based products. The aim of this work is to develop laccases capable of working under the extreme conditions of high temperature and pH, typical of the industrial conversion of wood into kraft pulp and fibreboard, in order to provide extremophilic biocatalysts for depolymerising kraft lignin, and enzyme-assisted technologies for kraft pulp and fibreboard production.ResultsThrough systematic enzyme engineering, combining enzyme-directed evolution and rational design, we changed the optimal pH of the laccase for oxidation of lignin phenols from acidic to basic, enhanced the catalytic activity at alkaline pH and increased the thermal tolerance of the enzyme by accumulating up to eight mutations in the protein sequence. The extremophilic laccase variants show maximum activity at 70 °C and oxidize kraft lignin at pH 10. Their integration into industrial-type processes saves energy and chemicals. As a pre-bleaching stage, the enzymes promote kraft pulp bleachability and significantly reduce the need for chlorine dioxide compared to the industrial sequence. Their application in wood chips during fibreboard production, facilitates the defibering stage, with less energy required.ConclusionsA set of new alkaliphilic and thermophilic fungal laccases has been developed to operate under the extreme conditions of high temperature and pH typical of industrial wood conversion processes. For the first time basidiomycete laccases of high-redox potential show activity on lignin-derived phenols and polymeric lignin at pH 10. Considering the extreme conditions of current industrial processes for kraft pulp and fibreboard production, the new tailor-made laccases constitute a step forward towards turning kraft pulp mills into biorefineries. Their use as biocatalysts in the wood conversion sector is expected to support the development of more environmentally sound and efficient processes, and more sustainable products.

Microalgae as a Source of Valuable Phenolic Compounds and Carotenoids.

Microalgae are photosynthetic, eukaryotic organisms that are widely used in the industry as cell factories to produce valuable substances, such as fatty acids (polyunsaturated fatty acids (PUFAs) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)), sterols (sitosterol), recombinant therapeutic proteins, carbohydrates, vitamins, phenolic compounds (gallic acid, quercetin), and pigments (β-carotene, astaxanthin, lutein). Phenolic compounds and carotenoids, including those extracted from microalgae, possess beneficial bioactivities such as antioxidant capacity, antimicrobial and immunomodulatory activities, and direct health-promoting effects, which may alleviate oxidative stress and age-related diseases, including cardiovascular diseases or diabetes. The production of valuable microalgal metabolites can be modified by using abiotic stressors, such as light, salinity, nutrient availability, and xenobiotics (for instance, phytohormones).

Recovery of phenolic compounds from wine lees using green processing: Identifying target molecules and assessing membrane ultrafiltration performance

Winery wastes are rich in polyphenols with high added value to be used in cosmetics, pharmaceuticals, and food products. This work aims at recovering and purifying the polyphenolic fraction occurring in the malolactic fermentation lees generated during the production of Albariño wines. Phenolic acids, flavonoids, and related compounds were recovered from this oenological waste by green liquid extraction using water as the solvent. The resulting extract solution was microfiltered to remove microparticles and further treated by ultrafiltration (UF) using membranes of 30 kDa and 5 kDa molecular weight cut-offs (MWCOs). The feed sample and the filtrate and retentate solutions from each membrane system were analyzed by reversed-phase liquid chromatography (HPLC) with UV and mass spectrometric (MS) detection. The most abundant polyphenols in the extracts were identified and quantified, namely: caftaric acid with a concentration of 200 µg g−1 and trans-coutaric acid, cis-coutaric acid, gallic acid, and astilbin with concentrations between 15 and 40 µg g−1. Other minor phenolic acids and flavanols were also found. The UF process using the 30 kDa membrane did not modify the extract composition, but filtration through the 5 kDa poly-acrylonitrile membrane elicited a decrease in polyphenolic content. Hence, the 30 kDa membrane was recommended to further pre-process the extracts. The combined extraction and purification process presented here is environmentally friendly and demonstrates that malolactic fermentation lees of Albariño wines are a valuable source of phenolic compounds, especially phenolic acids.

HPLC Analysis, Acute toxicity and Assessment of Antioxidant and Anti-inflammatory Capacity of different Extracts of Equisetum arvense

Equisetum arvense, a medicinal plant belonging to the family of Equisetaceae, is used in the fight against infectious or inflammatory diseases. The aim of this research was to assess the acute oral toxicity, to identify some phenolic acids and flavonoids by HPLC analysis, and to evaluate the antioxidant and the anti-inflammatory activities of E. arvense methanol extract (EAME) and aqueous (EAQE) extracts. The acute toxicity study was carried out using Swiss albino mice. Animals were observed during 14 days and signs of toxicity were controlled, afterwards, mice were sacrificed for biochemical studies. HPLC method was used to analyze E. arvense extracts. Antioxidant activity was determined using DPPH, reducing power, free hydroxyl radicals assays and antihemolytic activity. Xylene-induced ear edema in mice and carrageenan-induced paw edema in rat were used to evaluate anti-inflammatory activity. Formaldehyde-induced paw edema was used to assess anti-arthritic effect of extracts. In the acute toxicity study, both extracts did not engender any mortality or changes in general behaviors of tested animals. The LD50 was found to be superior to 5000 mg/kg DW. Extracts, rich in polyphenols and/or flavonoids, showed high antioxidant activity. Both extracts showed significant anti-inflammatory and anti-arthritic effects on animal models. These results revealed that E. arvense extracts can be a valuable source of phenolic compounds and flavonoids with powerful antioxidant and anti-inflammatory properties.

Membrane diafiltration for enhanced purification of biologically active compounds from goji berries extracts

• The recovery of phenolic compounds from aqueous goji berries extract was investigated. • Three tight ultrafiltration membranes with different cut-off (1, 2.5 and 3.5 kDa) were studied. • Diafiltration was implemented to improve the separation of phenolic compounds from sugars. • Membrane performance was evaluated in terms of productivity and selectivity towards target compounds. • All selected membranes allowed high recovery of phenolic compounds into the retentate. Goji berries represent a valuable source of phenolic compounds with a strong antioxidant and free radical scavenging activity combined to huge quantities of small sugars. This study was aimed at evaluating the potential of three tight ultrafiltration (UF) membranes with molecular weight cut-off (MWCO) from 1.0 to 3.5 kDa in the fractionation of phenolic compounds from sugars in the aqueous extract of dried goji berries. The aqueous extract produced in optimized conditions of water-to-solid ratio and temperature (6.66 mL/g and 65 °C, respectively) was preliminarily clarified by UF in order to remove suspended solids and colloidal particles. A membrane diafiltration (DF) process was developed in order to fractionate phenolic compounds from sugars with selected UF membranes from the clarified extract. The membrane performance was evaluated in terms of productivity and selectivity towards target compounds. All selected membranes allowed high recovery (more than 80%) of phenolic compounds into the retentate. On the other hand, the yield of carbohydrates increased in the permeate by increasing the diafiltration volume. Among the selected membranes, the 2.5 kDa membrane allowed to reduce the concentration of total carbohydrates from 26.5 up to 2.2 g glucose/L (a reduction of 91.7%) in a diafiltration/batch concentration process producing a concentrated extract enriched in phenolic compounds of interest for pharmaceutical or nutraceutical applications.

Evaluation of different extraction methods on the polyphenols yield, flavonoids yield, and antioxidant activity of the pomelo flavedo extract from Da Xanh (Citrus maxima [burm] merr.) variety

Pomelo peels have been well known as a valuable source of phenolic compounds mainly flavonoids. In this study, the influences of extraction conditions of three extraction methods on the polyphenols yield, flavonoids yield, and antioxidant activity of resulting pomelo flavedo extract (PFE) were evaluated. As a result, the suitable process parameters for the ultrasound assisted extraction were selected at an applied power of 120 W, the temperature of 60 oC for 20 min. Meanwhile, the microwave assisted extraction was operated at an applied power of 150 W for 25 min and the Soxhlet extraction was carried out up to 4 reflux cycles (35 min per cycle) at 80 oC. Among three methods, the microwave assisted extraction was considered as the most efficient method to obtain the high yield of polyphenols (80.56%) and flavonoids (86.58%). Naringin and hesperidin determined by high-performance liquid chromatography showed the value of 64.42 ± 2.90 mg/g DW and 0.97 ± 0.02 mg/g DW, respectively. The PFE extracted by the microwave assisted extraction could be a potent nutraceutical in further application on food or pharmaceutical industries.

Chemical Characteristics and Antioxidant Activity of Arctostaphylos uva-ursi L. Spreng. at the Southern Border of the Geographical Range of the Species in Europe.

The bearberry (Arctostaphylos uva-ursi L. Spreng.) is a source of herbal material—bearberry leaf (Uvae ursi folium), which is highly valued and sought by pharmaceutical and cosmetic industries. For many years, leaves of this plant have been used in traditional medicine as a diuretic, antimicrobial, and anti-inflammatory agent for various diseases of the urogenital tract. The bearberry has also been proposed as a natural antioxidant additive due to the high contents of phenolic compounds in its leaves. The study was focused on characterization of the basic phytochemical composition and antioxidant activity of extracts derived from bearberry leaves collected from plants located at the southern border of the geographical range of the species in Europe. The investigated herbal material is characterized by a different chemical profile compared to the chemical profiles of bearberry found in other parts of the continent. Bearberry extracts from plants growing in two different habitat types—heathlands and pine forests showed a wide range of variation, especially in the concentration of hyperoside, corilagin, and methylartutin and the total flavonoid contents. In addition to arbutin, bearberry can be a valuable source of phenolic compounds, which are mainly responsible for the antioxidant properties of extracts. The high content of phenols and high values of antioxidant parameters indicate a high potential of bearberry leaves to be used as a powerful natural source of antioxidants in herbal preparations. Therefore, the A. uva-ursi populations can be a source of plant material for pharmaceutical, cosmetic, and food industries.

Morus alba L. and Morus nigra L. Leaves as a Promising Food Source of Phenolic Compounds with Antioxidant Activity

Bioactivity of mulberry has been widely described, but mostly related to its fruits, while studies with leaves are scarce. Herein, in this study leaves of two mulberry species (Morus alba L. and Morus nigra L.) were characterized, compared, and evaluated in terms of their phenolic composition and antioxidant activity. Aiming to valorize mulberry leaves extracts which can be included in modern diet four different extracts (infusions, decoctions, tinctures and hydromethanolic) were examined. The chemical characterization was done by quantifying total phenolics (TPC), flavonoids (TFC) and phenolic acids (TPAC) content, L( +)ascorbic acid (ASA) and individual phenolic compounds in the extracts by HPLC technique. Moreover, DPPH and FRAP assays were used to assess the antioxidant activity of white and black mulberry leaves. Findings of these studies revealed that black mulberry leaves were richer in TFC and TPAC, while white mulberry leaves contained higher levels of individual phenolic compounds in water extracts. Gallic acid was found in the highest concentrations in two mulberry leave extracts. Correlation analysis showed strong relationships between antioxidant activity and TPC and TFC. This fact suggests the crucial role of phenolic compounds as antioxidant agents in white and black mulberry leaves. The results obtained in this study demonstrate that leaves of both white and black mulberry can be used as a valuable source of phenolic compounds with bioactive potential, which can be applied in the food sector, as foods and as promising source of natural ingredients.

Enhanced separation of chlorogenic and gallic acids extracted from spent coffee grounds using a three‐zone simulated moving bed process with partial feed and partial collection strategies

AbstractBACKGROUNDSpent coffee grounds, a valuable source of phenolic compounds, are considered beneficial for human health because of their antioxidative properties. The liquid extract containing phenolic compounds (such as chlorogenic and gallic acids) can be obtained via extraction using environmentally friendly organic solvent. The separation of chlorogenic and gallic acids from the liquid extract was carried out using isocratic chromatography technique in a three‐zone simulated moving bed (SMB). However, due to the low selectivity of separation, the productivity of three‐zone SMB was sacrificed to meet the purity criteria. Hence this work aimed to enhance the productivity of three‐zone SMB for the separation of chlorogenic and gallic acids via model simulation using partial feed operation and to improve the concentration of extract and raffinate products using partial collection strategy.RESULTSThe full feed scenario was designed based on the triangle theory, and the partial feed patterns (initial feed, middle feed and late feed) were implemented for each operating point in the triangle diagram to investigate the possibility of increasing the feed flow rate. The maximum productivity was evaluated based on the purity criteria (≥98%) for both extract and raffinate products. Under optimal conditions, productivity was doubled to 0.24 mg min−1 L−1 for both middle feed and late feed patterns compared to that of the full feed scenario. The partial collection strategy applied to the optimal point for each operational mode significantly increased the raffinate concentration to approximately 0.02 g L−1 at the optimal time fraction for discarding the solvent.CONCLUSIONThis work could be a foundation for the valorization of spent coffee ground. © 2021 Society of Chemical Industry (SCI).

Assessment of the phenolic compounds of pearl and finger millets obtained from South Africa and Zimbabwe.

Millet grains are rich in phenolic compounds which have health benefits. This study aims to elucidate the phenolic properties of pearl and finger millet grown in South Africa and Zimbabwe. The milled samples were analyzed by Waters Synapt G2 Quadrupole time‐of‐flight (QTOF) mass spectrometer (MS). A total of eight phenolic compounds were detected and quantified in the millet varieties, which included derivatives of benzoic acid such as protocatechuic and p‐hydroxybenzoic acids. Flavonoids such as catechin, epicatechin, procyanidin B1, procyanidin B2, and kaempferol glycoside were also detected. Generally, catechin was the dominant phenolic compound, followed by epicatechin. The mean values for catechin ranged from 2.50 to 12.6 mg/kg for the pearl millet and 610.4 to 675.1 mg/kg for the finger millet. While the epicatechin mean values ranged between 1.2 to 1.8 for pearl millet and 99.1 to 139.5 for finger millet. Procyanidins B1 and B2 were only detected and quantified in the finger millet types, While Kaempferol glycoside was only recorded in the pearl millets with mean values of 196.0 mg/kg for pearl millet South Africa and 213.6 mg/kg for pearl millet Zimbabwe. There was a difference among the varieties for the content of kaempferol glycoside. Protocatechuic and p‐hydroxybenzoic acids were only present in the finger millet types, their mean values were (20.9, 23.7 mg/kg) and (16.8,13.5 mg/kg) respectively. It can be substantiated from the outcome of this study that millet can be used as a source of valuable phenolic compounds and that the variety of millet is the determining factor of the phenolic compound content.

Lignin from Tree Barks: Chemical Structure and Valorization.

Lignins from different tree barks, including Norway spruce (Picea abies), eucalyptus (Eucalyptus globulus), mimosa (Acacia dealbata) and blackwood acacia (A. melanoxylon), are thoroughly characterized. The lignin from E. globulus bark is found to be enriched in syringyl (S) units, with lower amounts of guaiacyl (G) and p‐hydroxyphenyl (H) units (H/G/S ratio of 1:26:73), which produces a lignin that is highly enriched in β‐ether linkages (83 %), whereas those from the two Acacia barks have similar compositions (H/G/S ratio of ≈5:50:45), with a predominance of β‐ethers (73–75 %) and lower amounts of condensed carbon–carbon linkages; the lignin from A. dealbata bark also includes some resorcinol‐related compounds, that appear to be incorporated or intimately associated to the polymer. The lignin from P. abies bark is enriched in G units, with lower amounts of H units (H/G ratio of 14:86); this lignin is thus depleted in β‐O‐4′ alkyl–aryl ether linkages (44 %) and enriched in condensed linkages. Interestingly, this lignin contains large amounts of hydroxystilbene glucosides that seem to be integrally incorporated into the lignin structure. This study indicates that lignins from tree barks can be seen as an interesting source of valuable phenolic compounds. Moreover, this study is useful for tailoring conversion technologies for bark deconstruction and valorization.