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Special Issue "Plant Waste Management: Bioactive Compounds with Therapeutic Role in Disease Prevention"

A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Natural Products Chemistry".

Deadline for manuscript submissions: 30 November 2021.

Special Issue Editors

Dr. Ana Barros
E-Mail Website
Guest Editor
Centre for the Research and Technology of Agro-Environmental and Biological Sciences, (CITAB), University of Trás-os-Montes and Alto Douro (UTAD), Quinta de Prados, 5000-801 Vila Real, Portugal
Interests: vegetable foods; by-products; nutritional composition; amino acids; minerals; phenolic compounds; vitamin C; functional foods; bioactivity; circular economy; HPLC-PAD; HPLC-PAD-MS/MS; UPLC/MS/MS; UPLC/FL; FTIR
Special Issues and Collections in MDPI journals
Dr. Irene Gouvinhas
E-Mail Website
Guest Editor
Centre for the Research and Technology of Agro-Environmental and Biological Sciences, (CITAB), University of Trás-os-Montes and Alto Douro (UTAD), Quinta de Prados, 5000-801 Vila Real, Portugal
Interests: bioactivity and chemical characterization of natural products; identification, quantification, separation, and recovery of bioactive compounds from different food and agro-food byproducts; experimental design applied to extraction and process optimization of natural products

Special Issue Information

Dear Colleagues,

In the scientific community, it has been well established that some plants have an important role in the prevention of some degenerative or cardiovascular diseases, resulting from their content in bioactive phytochemicals with several biological properties. Furthermore, the agro-food industry involves the production of large quantities of waste, also characterized by a valuable composition in phytochemicals with putative health-promoting qualities. Due to increasing production, disposal represents a growing problem since plant material is usually prone to microbial spoilage, thus limiting further exploitation. On the other hand, costs of drying, storage, and shipment of these materials are economically limiting factors. Therefore, agro-industrial waste is often utilized as feed or fertilizer, or as combustion feedstock for biofuels. Additionally, in light of the biological properties recently revealed, the search for natural bioactive compounds has drawn attention to these materials, namely phenolic compounds that may have an added-value to be used as an alternative to synthetic substances employed in distinct industries, such as the food, cosmetic, or pharmaceutical sectors, giving rise to sustainable agro-industrial activities.

Due to contemporary lifestyle issues, research on secondary metabolites with health-promoting effects in countering or slowing-down chronic and degenerative diseases (e.g., cancer, cardiovascular, and neurodegenerative diseases) have recognized that phenols and polyphenols are beneficial for human health, and are widespread and copious in dietary plant sources.

Taking all this into account, and considering not only the increasing trend to reduce the costs of industrial activities, but also the growing interest in the major therapeutic role that bioactive compounds from plant waste can play in disease prevention in humans, the main goal is the valorization of less-characterized plant wastes, of low commercial value, as a source of bioactive compounds with the capacity to influence health-related conditions.

Contributions to this Special Issue may cover all research aspects related to plant wastes, characterized to be all those parts from plants discarded during the agricultural and industrial processing, distribution and consumption stages of the food supply chain, which could be either edible or inedible, and that can be further processed and valorized in several ways; plant food residues (fruit and vegetable waste); characterization of their biological properties, including (but not limited to) methods for their extraction, purification, comprehensive profiling characterization, and quantification, as well as new technologies explored for more efficient extraction; beneficial biological properties that could potentially contribute to functional food and nutraceutical development; functional properties such as antioxidant, antibacterial, anticancer, antidiabetic, anti-obesity, antitumor, antiviral, anti-inflammatory, and anticoagulant properties, among others; in vitro and in vivo model systems; clinical investigations; biotechnological applications of plant wastes, such as nutraceuticals, cosmeceuticals, and pharmaceuticals. Original research papers and review articles on these different areas are welcome.

Dr. Ana Barros
Dr. Irene Gouvinhas
Guest Editors

Manuscript Submission Information

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Molecules is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Plant waste
  • Phytochemicals
  • Bioactive compounds
  • Biological properties
  • Natural products
  • Nutraceuticals
  • Added-value products Disease prevention

Published Papers (8 papers)

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Research

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Article
Olive Pomace Phenolic Compounds Stability and Safety Evaluation: From Raw Material to Future Ophthalmic Applications
Molecules 2021, 26(19), 6002; https://doi.org/10.3390/molecules26196002 - 02 Oct 2021
Viewed by 597
Abstract
Nowadays, increasing interest in olive pomace (OP) valorization aims to improve olive’s industry sustainability. Interestingly, several studies propose a high-value application for OP extracts containing its main phenolic compounds, hydroxytyrosol and oleuropein, as therapy for ocular surface diseases. In this work, the stability [...] Read more.
Nowadays, increasing interest in olive pomace (OP) valorization aims to improve olive’s industry sustainability. Interestingly, several studies propose a high-value application for OP extracts containing its main phenolic compounds, hydroxytyrosol and oleuropein, as therapy for ocular surface diseases. In this work, the stability and accessibility of OP total phenolic and flavonoid content, main representative compounds, and antioxidant activity were assessed under different pretreatment conditions. Among them, lyophilization and supercritical CO2 extraction were found to increase significantly most responses measured in the produced extracts. Two selected extracts (CONV and OPT3) were obtained by different techniques (conventional and pressurized liquid extraction); Their aqueous solutions were characterized by HPLC-DAD-MS/MS. Additionally, their safety and stability were evaluated according to EMA requirements towards their approval as ophthalmic products: their genotoxic effect on ocular surface cells and their 6-months storage stability at 4 different temperature/moisture conditions (CPMP/ICH/2736/99), together with pure hydroxytyrosol and oleuropein solutions. The concentration of hydroxytyrosol and oleuropein in pure or extract solutions was tracked, and possible degradation products were putatively identified by HPLC-DAD-MS/MS. Hydroxytyrosol and oleuropein had different stability as standard or extract solutions, with oleuropein also showing different degradation profile. All compounds/extracts were safe for ophthalmic use at the concentrations tested. Full article
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Article
Formulation Effects in the Antioxidant Activity of Extract from the Leaves of Cymbopogon citratus (DC) Stapf
Molecules 2021, 26(15), 4518; https://doi.org/10.3390/molecules26154518 - 27 Jul 2021
Viewed by 382
Abstract
Cymbopogon citratus DC (Stapf.) is a perennial grass and it is distributed around the world. It is used as a condiment for food and beverage flavouring in the form of infusions and decoctions of its dried leaves. Our previous studies have shown antioxidant, [...] Read more.
Cymbopogon citratus DC (Stapf.) is a perennial grass and it is distributed around the world. It is used as a condiment for food and beverage flavouring in the form of infusions and decoctions of its dried leaves. Our previous studies have shown antioxidant, anti-inflammatory and gastroprotective activities for the infusion and its phenolic fractions. The aim of the present work was to develop oral dosage forms from a Cymbopogon citratus extract to be used as a functional food with antioxidant properties. Initially, an essential oil-free infusion was prepared, lyophilized and characterized by HPLC-PDA. Total phenols were quantified with the Folin–Ciocalteu method and the antioxidant activity was assessed by DPPH assay. Gelatine capsules containing the extract with different excipients, selected after DSC and IR trials, were prepared. A formulation exhibiting better antioxidant behaviour in a gastric environment was attained. These results suggest that the proposed formulation for this extract could be a valuable antioxidant product and, consequently, make an important contribution to “preventing” and minimizing diseases related to oxidative stress conditions. Full article
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Article
Invasive Plant Species Biomass—Evaluation of Functional Value
Molecules 2021, 26(13), 3814; https://doi.org/10.3390/molecules26133814 - 22 Jun 2021
Viewed by 385
Abstract
Invasive plant species (IAS), with their numerous negative ecological, health, and economic impacts, represent one of the greatest conservation challenges in the world. Reducing the negative impacts and potentially exploiting the biomass of these plant species can significantly contribute to sustainable management, protect [...] Read more.
Invasive plant species (IAS), with their numerous negative ecological, health, and economic impacts, represent one of the greatest conservation challenges in the world. Reducing the negative impacts and potentially exploiting the biomass of these plant species can significantly contribute to sustainable management, protect biodiversity, and create a healthy environment. Therefore, the main objective of this study was to evaluate the nutritional potential, phytochemical status, and antioxidant capacity of nine alien invasive plant species: Abutilon theophrasti, Amaranthus retroflexus, Ambrosia artemisiifolia, Datura stramonium, Erigeron annuus, Galinsoga ciliata, Reynoutria japonica, Solidago gigantea, and Sorghum halepense. Multivariate statistical methods such as cluster and PCA were performed to determine possible connections and correlations among selected IAS depending on the phytochemical content. According to the obtained results, R. japonica was notable with the highest content of vitamin C (38.46 mg/100 g FW); while E. annuus (1365.92 mg GAE/100 g FW) showed the highest values of total polyphenolic compounds. A. retroflexus was characterized by the highest content of total chlorophylls (0.26 mg/g) and antioxidant capacity (2221.97 µmol TE/kg). Therefore, it can be concluded that the selected IAS represent nutrient-rich plant material with significant potential for the recovering of bioactive compounds. Full article
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Article
An Insight into Kiwiberry Leaf Valorization: Phenolic Composition, Bioactivity and Health Benefits
Molecules 2021, 26(8), 2314; https://doi.org/10.3390/molecules26082314 - 16 Apr 2021
Cited by 2 | Viewed by 590
Abstract
During kiwiberry production, different by-products are generated, including leaves that are removed to increase the fruit’s solar exposure. The aim of this work was to extract bioactive compounds from kiwiberry leaf by employing microwave-assisted extraction (MAE). Compatible food solvents (water and ethanol) were [...] Read more.
During kiwiberry production, different by-products are generated, including leaves that are removed to increase the fruit’s solar exposure. The aim of this work was to extract bioactive compounds from kiwiberry leaf by employing microwave-assisted extraction (MAE). Compatible food solvents (water and ethanol) were employed. The alcoholic extract contained the highest phenolic and flavonoid contents (629.48 mg of gallic acid equivalents (GAE) per gram of plant material on dry weight (dw) (GAE/g dw) and 136.81 mg of catechin equivalents per gram of plant material on dw (CAE/g dw), respectively). Oppositely, the hydroalcoholic extract achieved the highest antioxidant activity and scavenging activity against reactive oxygen and nitrogen species (IC50 = 29.10 μg/mL for O2•−, IC50 = 1.87 μg/mL for HOCl and IC50 = 1.18 μg/mL for NO). The phenolic profile showed the presence of caffeoylquinic acids, proanthocyanidin, and quercetin in all samples. However, caffeoylquinic acids and quercetin were detected in higher amounts in the alcoholic extract, while proanthocyanidins were prevalent in the hydroalcoholic extract. No adverse effects were observed on Caco-2 viability, while the highest concentration (1000 µg/mL) of hydroalcoholic and alcoholic extracts conducted to a decrease of HT29-MTX viability. These results highlight the MAE potentialities to extract bioactive compounds from kiwiberry leaf. Full article
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Article
Olive Pâté by Multi-Phase Decanter as Potential Source of Bioactive Compounds of Both Nutraceutical and Anticancer Effects
Molecules 2020, 25(24), 5967; https://doi.org/10.3390/molecules25245967 - 16 Dec 2020
Cited by 1 | Viewed by 821
Abstract
In the oil sector, a novelty in the centrifugal extraction system is represented by the multi-phase decanters (DMF) that work without adding process water and with the advantage of recovering a dried pomace and a by-product, called “pâté”, consisting of the pulp and [...] Read more.
In the oil sector, a novelty in the centrifugal extraction system is represented by the multi-phase decanters (DMF) that work without adding process water and with the advantage of recovering a dried pomace and a by-product, called “pâté”, consisting of the pulp and its vegetation water, without traces of stone. The pâté has a high content of phenolic compounds, mainly represented by secoiridoids and verbascoside. The present work investigated the efficacy of two different ways of debittering (by sequential filtrations and spontaneous fermentation) of DMF pâté from three olive cultivars (Olea europaea L. “Leccino”, “Carboncella” and “Tortiglione”) to make the pâté edible, and, contemporary, investigated also the effect of its phenolic bioactive extracts on pathogenic bacteria and colon cancer cell model. Daily filtrations of pâté of the three cultivars have been shown to be more efficient in phenolic degradation. The activity of the indigenous microflora on the other hand takes a longer time to degrade the phenolic component and therefore to de-bitter it. None of pâté showed antibacterial activity. Colorimetric assay MTS for cell viability and metabolic activity tested on colon cancer cells Caco-2 and HCT116 suggest a potential beneficial effect of the dried extracts probably related to the modulation of gene expression under these treatments. Full article
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Article
Acorn Flour as a Source of Bioactive Compounds in Gluten-Free Bread
Molecules 2020, 25(16), 3568; https://doi.org/10.3390/molecules25163568 - 06 Aug 2020
Cited by 6 | Viewed by 1494
Abstract
Polyphenols are important bioactive compounds whose regular ingestion has shown different positive impacts in health. Celiac patients have nutritional deficiencies, bringing many problems to their health. Thus, it is important to develop gluten-free (GF) products, such as bread, with nutritional benefits. The acorn [...] Read more.
Polyphenols are important bioactive compounds whose regular ingestion has shown different positive impacts in health. Celiac patients have nutritional deficiencies, bringing many problems to their health. Thus, it is important to develop gluten-free (GF) products, such as bread, with nutritional benefits. The acorn is the fruit of holm oak and cork oak, being an underexploited resource nowadays. Its nutritional and functional characteristics are remarkable: rich in unsaturated fatty acids and fiber, vitamin E, chlorophylls, carotenoids, phenolic compounds, and antioxidant properties. The purpose of this study was to assess the use of acorn flour as a bioactive compounds source and natural GF ingredient for baking GF bread. Bread loaves were prepared with buckwheat, rice, acorn flour, and potato starch. Two levels of acorn flour (23% and 35% of the flour mixture) were tested. The physical, nutritional, and sensory characteristics of the bread were analysed, as well as the composition of phenolic compounds: total phenols, ortho-diphenols, and flavonoids. The phenolic profile was assessed by Reverse Phase–High-Performance Liquid Chromatography–Diode Array Detector (RP-HPLC-DAD). The antioxidant activity of the bread extracts was determined by 2,2-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) diammonium salt (ABTS), diphenyl-1-picrylhidrazyl radical (DPPH), and ferric reducing antioxidant power (FRAP) methodologies. Acorn flour can be considered a good source of bioactive compounds and antioxidants in GF bread. Acorn flour showed good technological properties in GF baking, improving bread nutritional and sensory characteristics. Full article
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Article
Identification of Polyphenols from Coniferous Shoots as Natural Antioxidants and Antimicrobial Compounds
Molecules 2020, 25(15), 3527; https://doi.org/10.3390/molecules25153527 - 01 Aug 2020
Cited by 7 | Viewed by 1235
Abstract
Currently, coniferous shoots are almost absent as a food ingredient despite their wide availability in many parts of the world. The aim of the study was to assess and compare the composition of selected plant metabolites, evaluate the antioxidant and antimicrobial properties of [...] Read more.
Currently, coniferous shoots are almost absent as a food ingredient despite their wide availability in many parts of the world. The aim of the study was to assess and compare the composition of selected plant metabolites, evaluate the antioxidant and antimicrobial properties of selected shoots collected in 2019 from the arboretum in Zielonka (Poland), including individual samples from Picea abies L. (PA), Larix decidua Mill (LD), Pinus sylvestris L. (PS), Pseudotsuga menziesii (PM) and Juniperus communis L. (JC). The present work has shown that aqueous extracts obtained from tested shoots are a rich source of phenols such as caffeic acid, ferulic acid, chlorogenic acid, 4-hydroxybenzoic acid and many others. Obtained extracts exhibit antioxidant and antimicrobial properties in vitro. The highest sum of the studied phenolic compounds was found in the PA sample (13,947.80 µg/g dw), while the lowest in PS (6123.57 µg/g dw). The samples were particularly rich in ferulic acid, chlorogenic acid and 4-hydroxybenzoic acid. The highest values regarding the Folin-Ciocâlteu reagent (FCR) and ferric reducing ability of plasma (FRAP) reducing ability tests, as well as the total flavonoid content assay, were obtained for the LD sample, although the LD (14.83 mg GAE/g dw) and PM (14.53 mg GAE/g dw) samples did not differ statistically in the FCR assay. With respect to free radical quenching measurements (DPPH), the PA (404.18-μM Trolox/g dw) and JC (384.30-μM Trolox/g dw) samples had the highest radical quenching ability and did not differ statistically. Generally, extracts obtained from PA and PS showed the highest antimicrobial activity against tested Gram-negative bacteria, Gram-positive bacteria and fungi. Full article
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Review

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Review
Processing Factors Affecting the Phytochemical and Nutritional Properties of Pomegranate (Punica granatum L.) Peel Waste: A Review
Molecules 2020, 25(20), 4690; https://doi.org/10.3390/molecules25204690 - 14 Oct 2020
Cited by 12 | Viewed by 1343
Abstract
Pomegranate peel has substantial amounts of phenolic compounds, such as hydrolysable tannins (punicalin, punicalagin, ellagic acid, and gallic acid), flavonoids (anthocyanins and catechins), and nutrients, which are responsible for its biological activity. However, during processing, the level of peel compounds can be significantly [...] Read more.
Pomegranate peel has substantial amounts of phenolic compounds, such as hydrolysable tannins (punicalin, punicalagin, ellagic acid, and gallic acid), flavonoids (anthocyanins and catechins), and nutrients, which are responsible for its biological activity. However, during processing, the level of peel compounds can be significantly altered depending on the peel processing technique used, for example, ranging from 38.6 to 50.3 mg/g for punicalagins. This review focuses on the influence of postharvest processing factors on the pharmacological, phytochemical, and nutritional properties of pomegranate (Punica granatum L.) peel. Various peel drying strategies (sun drying, microwave drying, vacuum drying, and oven drying) and different extraction protocols (solvent, super-critical fluid, ultrasound-assisted, microwave-assisted, and pressurized liquid extractions) that are used to recover phytochemical compounds of the pomegranate peel are described. A total phenolic content of 40.8 mg gallic acid equivalent (GAE)/g DM was recorded when sun drying was used, but the recovery of the total phenolic content was higher at 264.3 mg TAE/g when pressurised liquid extraction was performed. However, pressurised liquid extraction is costly due to the high initial investment costs and the limited possibility of carrying out selective extractions of organic compounds from complex peel samples. The effects of these methods on the phytochemical profiles of pomegranate peel extracts are also influenced by the cultivar and conditions used, making it difficult to determine best practice. For example, oven drying at 60 °C resulted in higher levels of punicalin of 888.04 mg CE/kg DM compared to those obtained 40 °C of 768.11 mg CE/kg DM for the Wonderful cultivar. Processes that are easy to set up, cost-effective, and do not compromise the quality and safety aspects of the peel are, thus, more desirable. From the literature survey, we identified a lack of studies testing pretreatment protocols that may result in a lower loss of the valuable biological compounds of pomegranate peels to allow for full exploitation of their health-promoting properties in potentially new value-added products. Full article
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