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

Deadline for manuscript submissions: closed (30 June 2020) | Viewed by 64339

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Prof. Dr. Jesus Simal-Gandara

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Department of Analytical and Food Chemistry, Food Science and Technology Faculty, University of Vigo, 32004 Ourense, Spain
Interests: agro-environmental; food chemistry; sustainable primary production; food quality and safety
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Secondary metabolites in plants are not directly involved in the normal growth, development, and reproduction of the organism. They contribute to sustaining the overall functional status of the cells within organ systems. Though the production of metabolites is a natural chemical and bioenzymatic reaction that occurs during metabolism in all organisms, metabolites may also be produced as by-products of the plant’s reaction to exogenous/external substances or stimuli. The network of metabolites, working with enzyme reactions during the entire process of metabolism, is called the metabolome. The metabolome involves/implicates all the series of combinations of cascading reactions between enzymes and substrates in the steps of metabolism, and ending in the production of all metabolites. Plants are an important source for the discovery of new products of medicinal value for drug development and plants’ secondary metabolites are unique sources for pharmaceuticals, food additives, flavors, supplements, cosmetics, and other industrial values. The commercial importance of these secondary metabolites has resulted in a great interest in their production and in exploring the possibilities of enhancing their production. This Special Issue aims to identify and review the latest bioactive compounds that have been demonstrated to have beneficial effects for consumers.

Prof. Dr. Jesus Simal-Gandara
Guest Editor

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Keywords

Pharmacology
Biological assays
Extraction
Analysis
Medicinal chemistry
Plant foods
Secondary metabolites
Functional capacity

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Published Papers (10 papers)

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Research

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14 pages, 3312 KiB

Open AccessArticle

Silage Fermentation: A Potential Biological Approach for the Long-Term Preservation and Recycling of Polyphenols and Terpenes in Globe Artichoke (Cynara scolymus L.) By-Products

by Zhuoyan Fan, Kai Chen, Lingyin Ban, Yu Mao, Caiyun Hou and Jingming Li

Molecules 2020, 25(14), 3302; https://doi.org/10.3390/molecules25143302 - 21 Jul 2020

Cited by 11 | Viewed by 3529

Abstract

An economic and effective method for storage is necessary to make full use of the nature of active components in artichoke by-products and ease environmental pressure. In this paper, the potential of silage fermentation for the preservation and recycling of polyphenols and terpenes in artichoke by-products is evaluated. The silage of artichoke by-products is characterized by lactic acid bacteria fermentation. Silage distinctly increases the abundance of lactic acid bacteria in artichoke by-products, such as Lactobacillus, Lactococcus, Serratia, and Weissella, and greatly increases the abundance of Firmicutes. The improvement of the microorgan structure and composition is of great significance for the quality of artichoke by-products. Polyphenols in the stems and leaves of artichokes are preserved well in silage. Among the 18 polyphenol compounds detected by high performance liquid chromatography coupled with triple quadrupole tandem mass spectrometry (HPLC-QqQ-MS/MS), the contents of 11 phenolic acids and four flavonoids increased significantly. For terpenes detected by gas chromatography-mass spectrometry (GC-MS), the contents of four pentacyclic triterpenoids increased significantly, while two sterols were kept stable in the silage process. Silage is a potential biotechnology for the long-term preservation of bioactive components, such as polyphenols and terpenes in artichoke by-products, and the results provide a scientific basis for the efficient utilization of by-products. Full article

(This article belongs to the Special Issue Secondary Metabolites in Plant Foods)

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13 pages, 310 KiB

Open AccessArticle

Insights on the Extraction Performance of Alkanediols and Glycerol: Using Juglans regia L. Leaves as a Source of Bioactive Compounds

by Vanessa Vieira, Ricardo C. Calhelha, Lillian Barros, João A. P. Coutinho, Isabel C. F. R. Ferreira and Olga Ferreira

Molecules 2020, 25(11), 2497; https://doi.org/10.3390/molecules25112497 - 27 May 2020

Cited by 20 | Viewed by 3813

Abstract

Glycerol and alkanediols are being studied as alternative solvents to extract phytochemicals from plant material, often as hydrogen bond donors in deep eutectic solvents (DESs). Many of those alcohols are liquid at room temperature, yet studies of their use as extraction solvents are scarce. In this work, glycerol and a series of alkanediols (1,2-ethanediol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,2-pentanediol, 1,5-pentanediol, and 1,2-hexanediol) were studied for the extraction of phenolic compounds from Juglans regia L. leaves, a rich source of this class of bioactive compounds. The extraction yield was quantified, and the bioactivity of both extracts and pure solvents was evaluated by measuring the anti-inflammatory and cytotoxic activities. The solvents showing the best combined results were 1,2 and 1,3-propanediol, as their extracts presented a high amount of phenolic compounds, close to the results of ethanol, and similar cytotoxicity against cervical carcinoma cells, with no impact on non-tumor porcine liver cells in the studied concentration range. On the other hand, none of the extracts (and solvents) presented anti-inflammatory activity. Overall, the results obtained in this work contribute to the study of alternative solvents that could potentially be used also as formulation media, highlighting the importance of walnut leaves as a source of bioactive compounds. Full article

(This article belongs to the Special Issue Secondary Metabolites in Plant Foods)

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15 pages, 2430 KiB

Open AccessArticle

Exogenous Melatonin and Abscisic Acid Expedite the Flavonoids Biosynthesis in Grape Berry of Vitis vinifera cv. Kyoho

by Mingyi Yang, Lei Wang, Tarun Belwal, Xiaocheng Zhang, Hongyan Lu, Cunkun Chen and Li Li

Molecules 2020, 25(1), 12; https://doi.org/10.3390/molecules25010012 - 18 Dec 2019

Cited by 37 | Viewed by 4530

Abstract

Grape polyphenols contributing to more than half of the global polyphenol market were well studied; however, how melatonin (MLT), a potential plant hormone, and abscisic acid (ABA) affects polyphenols profile is still poorly understood. To explore whether these hormones are involved in polyphenolic biosynthesis, grape (Vitis vinifera cv. Kyoho) was exposed to MLT, ABA, and NDGA (nordihydroguaiaretic acid, an ABA biosynthesis inhibitor) treatments, and 16 polyphenols were identified from grape extracts by high performance liquid chromatography quadrupole time of flight mass spectrometry (HPLC-Q-TOF-MS). Both exogenous MLT and ABA significantly enhanced the biosynthesis of each flavonol and flavanol component, especially catechin, which was almost increased double by 200 µM of MLT treatment. Furthermore, the expression of genes involved in flavonoid biosynthesis, including 4-coumaroyl-CoA synthase, chalcone synthase, flavonoid 3′-hydroxylase, anthocyanin 3′-methyltransferase, flavonol synthase, flavonoid-3-O-glucosyltransferase, and flavonoid 3′,5′-methyltransferase were highly up-regulated as well but were down-regulated by NDGA. The present study provided new insights for improving flavonoids accumulation in agricultural production and its underlying mechanism. Full article

(This article belongs to the Special Issue Secondary Metabolites in Plant Foods)

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21 pages, 2105 KiB

Open AccessArticle

Phenolic Profile of Grape Canes: Novel Compounds Identified by LC-ESI-LTQ-Orbitrap-MS

by Danilo Escobar-Avello, Julián Lozano-Castellón, Claudia Mardones, Andy J. Pérez, Vania Saéz, Sebastián Riquelme, Dietrich von Baer and Anna Vallverdú-Queralt

Molecules 2019, 24(20), 3763; https://doi.org/10.3390/molecules24203763 - 18 Oct 2019

Cited by 83 | Viewed by 7982

Abstract

Grape canes (Vitis vinifera L.) are a viticulture industry by-product with an important content of secondary metabolites, mainly polyphenols with a broad spectrum of demonstrated health benefits. Grape canes, therefore, have considerable economic potential as a source of high-value phytochemicals. In this work, liquid chromatography coupled with electrospray ionization hybrid linear trap quadrupole-Orbitrap mass spectrometry (LC–LTQ-Orbitrap) was used for the comprehensive identification of polyphenolic compounds in grape canes. Identification of polyphenols was performed by comparing their retention times, accurate mass measured, and mass fragmentation patterns with those of reference substances or available data in the literature. A total of 75 compounds were identified, including phenolic acids, flavanols, flavonols, flavanonols, flavanones, and stilbenoids. The most abundant polyphenols were proanthocyanidins and stilbenoids and their oligomers. Moreover, the high-resolution mass spectrometry analysis revealed the occurrence of 17 polyphenols never described before in grape canes, thereby providing a more complete polyphenolic profile of this potentially valuable by-product. Full article

(This article belongs to the Special Issue Secondary Metabolites in Plant Foods)

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21 pages, 4407 KiB

Open AccessArticle

Transcriptome and Metabolite Profiling Reveal Novel Insights into Volatile Heterosis in the Tea Plant (Camellia Sinensis)

by Yucheng Zheng, Pengjie Wang, Xuejin Chen, Yun Sun, Chuan Yue and Naixing Ye

Molecules 2019, 24(18), 3380; https://doi.org/10.3390/molecules24183380 - 17 Sep 2019

Cited by 40 | Viewed by 5064

Abstract

Tea aroma is a key indicator for evaluating tea quality. Although notable success in tea aroma improvement has been achieved with heterosis breeding technology, the molecular basis underlying heterosis remains largely unexplored. Thus, the present report studies the tea plant volatile heterosis using a high-throughput next-generation RNA-seq strategy and gas chromatography–mass spectrometry. Phenotypically, we found higher terpenoid volatile and green leaf volatile contents by gas chromatography–mass spectrometry in the F1 hybrids than in their parental lines. Volatile heterosis was obvious in both F1 hybrids. At the molecular level, the comparative transcriptomics analysis revealed that approximately 41% (9027 of 21,995) of the genes showed non-additive expression, whereas only 7.83% (1723 of 21,995) showed additive expression. Among the non-additive genes, 42.1% showed high parental dominance and 17.6% showed over-dominance. Among different expression genes with high parental dominance and over-dominance expression patterns, KEGG and GO analyses found that plant hormone signal transduction, tea plant physiological process related pathways and most pathways associated with tea tree volatiles were enriched. In addition, we identified multiple genes (CsDXS, CsAATC2, CsSPLA2, etc.) and transcription factors (CsMYB1, CsbHLH79, CsWRKY40, etc.) that played important roles in tea volatile heterosis. Based on transcriptome and metabolite profiling, we conclude that non-additive action plays a major role in tea volatile heterosis. Genes and transcription factors involved in tea volatiles showing over-dominance expression patterns can be considered candidate genes and provide novel clues for breeding high-volatile tea varieties. Full article

(This article belongs to the Special Issue Secondary Metabolites in Plant Foods)

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22 pages, 597 KiB

Open AccessArticle

The Profile of Secondary Metabolites and Other Bioactive Compounds in Cucurbita pepo L. and Cucurbita moschata Pumpkin Cultivars

by Bartosz Kulczyński and Anna Gramza-Michałowska

Molecules 2019, 24(16), 2945; https://doi.org/10.3390/molecules24162945 - 14 Aug 2019

Cited by 90 | Viewed by 8700

Abstract

Plants and animals are sources of various bioactive compounds that exhibit a broad spectrum of health-promoting effects. Scientists continue studies on the chemical composition of many products in search of foods with high nutritional value. The pumpkin (Cucurbita sp.) is unquestionably a source of valuable nutrients. This vegetable is well-known all over the world and it is appreciated due to its high content of carotenoids, but it is still not much used in the processing industry. The aim of present study was to compare the flesh of 15 pumpkin varieties belonging to the Cucurbita pepo and C. moschata species in terms of the bioactive compound content (carotenoids, phenolic acids, flavonols, minerals and vitamins) and to demonstrate whether the variety has an effect on the chemical composition. To date, no such extensive research has been carried out in this area. The research revealed that the pumpkin pulp had high content of carotenoids. In nearly all cases lutein was the most abundant carotenoid. Numerous phenolic acids and flavonols were also identified. All the cultivars contained gallic acid, protocatechuic acid, 4-hydroxybenzoic acid, vanillic acid, chlorogenic acid, caffeic acid, and rutin. The pumpkin pulp also contained alpha- and gamma-tocopherol. No beta- or delta-tocopherol was found. Potassium, calcium, and sodium were the most abundant minerals. The research also proved that the profile of bioactive compounds in the pumpkin pulp was considerably diversified and depended on the species and cultivar Full article

(This article belongs to the Special Issue Secondary Metabolites in Plant Foods)

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19 pages, 3658 KiB

Open AccessArticle

Rubus ulmifolius Schott as a Novel Source of Food Colorant: Extraction Optimization of Coloring Pigments and Incorporation in a Bakery Product

by Liliana Primo da Silva, Eliana Pereira, Miguel A. Prieto, Jesus Simal-Gandara, Tânia C.S.P. Pires, Maria José Alves, Ricardo Calhelha, Lillian Barros and Isabel C.F.R. Ferreira

Molecules 2019, 24(11), 2181; https://doi.org/10.3390/molecules24112181 - 10 Jun 2019

Cited by 24 | Viewed by 5054

Abstract

(1) Background: Color has been considered to be the flashiest attribute of foodstuffs and researchers have shown a great interest in the extraction of pigmented compounds from vegetal products, with the purpose to provide alternative counterparts to the food industry; (2) Methods: This study aimed to explore Rubus ulmifolius Schott fruits as a potential source of anthocyanins, optimizing the extraction method, evaluating the bioactivity and incorporating the rich extract into a bakery food product; (3) Results: After the extraction optimization, results showed R. ulmifolius fruits to be a great source of anthocyanins, obtaining an amount of 33.58 mg AT/g E, with an extraction yield of 62.08%. The rich anthocyanin extract showed antitumor and antimicrobial potential in some tumor cell lines and strains, respectively, as well as the absence of toxicity; (4) Conclusions: The extract when incorporated in a bakery product showed a good coloring capacity, maintaining the nutritional value, revealing its use to be a great approach for replacing artificial colorants. Full article

(This article belongs to the Special Issue Secondary Metabolites in Plant Foods)

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10 pages, 2476 KiB

Open AccessArticle

Interaction of Caffeic Acid with SDS Micellar Aggregates

by Antonio Cid, Oscar A. Moldes, Juan C. Mejuto and Jesus Simal-Gandara

Molecules 2019, 24(7), 1204; https://doi.org/10.3390/molecules24071204 - 27 Mar 2019

Cited by 9 | Viewed by 4007

Abstract

Micellar systems consisting of a surfactant and an additive such as an organic salt or an acid usually self-organize as a series of worm-like micelles that ultimately form a micellar network. The nature of the additive influences micellar structure and properties such as aggregate lifetime. For ionic surfactants such as sodium dodecyl sulfate (SDS), CMC decreases with increasing temperature to a minimum in the low-temperature region beyond which it exhibits the opposite trend. The presence of additives in a surfactant micellar system also modifies monomer interactions in aggregates, thereby altering CMC and conductance. Because the standard deviation of β was always lower than 10%, its slight decrease with increasing temperature was not significant. However, the absolute value of Gibbs free enthalpy, a thermodynamic potential that can be used to calculate the maximum of reversible work, increased with increasing temperature and caffeic acid concentration. Micellization in the presence of caffeic acid was an endothermic process, which was entropically controlled. The enthalpy and enthropy positive values resulted from melting of “icebergs” or “flickering clusters” around the surfactant, leading to increased packing of hydrocarbon chains within the micellar core in a non-random manner. This can be possibly explained by caffeic acid governing the 3D matrix structure of water around the micellar aggregates. The fact that both enthalpy and entropy were positive testifies to the importance of hydrophobic interactions as a major driving force for micellization. Micellar systems allow the service life of some products to be extended without the need to increase the amounts of post-harvest storage preservatives used. If a surfactant is not an allowed ingredient or food additive, carefully washing it off before the product is consumed can avoid any associated risks. In this work, we examined the influence of temperature and SDS concentration on the properties of SDS–caffeic acid micellar systems. Micellar properties can be modified with various additives to develop new uses for micelles. This allows smaller amounts of additives to be used without detracting from their benefits. Full article

(This article belongs to the Special Issue Secondary Metabolites in Plant Foods)

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21 pages, 1365 KiB

Open AccessArticle

Profiling Metabolites and Biological Activities of Sugarcane (Saccharum officinarum Linn.) Juice and its Product Molasses via a Multiplex Metabolomics Approach

by Sara E. Ali, Rania A. El Gedaily, Andrei Mocan, Mohamed A. Farag and Hesham R. El-Seedi

Molecules 2019, 24(5), 934; https://doi.org/10.3390/molecules24050934 - 7 Mar 2019

Cited by 56 | Viewed by 11988

Abstract

Sugarcane (Saccharum officinarum L.) is an important perennial grass in the Poaceae family cultivated worldwide due to its economical and medicinal value. In this study, a combined approach using mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy was employed for the large-scale metabolite profiling of sugarcane juice and its by-product molasses. The polyphenols were analysed via UPLC-UV-ESI-MS, whereas the primary metabolites such as sugars and organic and amino acids were profiled using NMR spectroscopy and gas chromatography/mass spectrometry (GC/MS). UPLC/MS was more effective than NMR spectroscopy or GC/MS for determining differences among the metabolite compositions of the products. Under the optimized conditions, UPLC/MS led to the identification of 42 metabolites, including nine flavonoids, nine fatty acids, and two sterols. C/O Flavone glycosides were the main subclass detected, with tricin-7-O-deoxyhexosyl glucuronide being detected in sugarcane and molasses for the first time. Based on GC/MS analysis, disaccharides were the predominant species in the sugarcane juice and molasses, with sucrose accounting for 66% and 59%, respectively, by mass of all identified metabolites. The phenolic profiles of sugarcane and molasses were further investigated in relation to their in vitro antioxidant activities using free radical scavenging assays such as 2,2-Diphenyl-1-picrylhydrazyl free radical-scavenging ability (DPPH), Trolox equivalent antioxidant capacity (TEAC) and ferric reducing antioxidant power (FRAP). In view of its higher total phenolic content (TPC) (196 ± 2.1 mg GAE/100 g extract) compared to that of sugarcane juice (93 ± 2.9 mg GAE/100 g extract), molasses exhibited a substantially higher antioxidant effect. Interestingly, both extracts were also found to inhibit α-glucosidase and α-amylase enzymes, suggesting a possible antihyperglycaemic effect. These findings suggest molasses may be a new source of natural antioxidants for functional foods. Full article

(This article belongs to the Special Issue Secondary Metabolites in Plant Foods)

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32 pages, 879 KiB

Open AccessReview

Human, Animal and Plant Health Benefits of Glucosinolates and Strategies for Enhanced Bioactivity: A Systematic Review

by Sylvia Maina, Gerald Misinzo, Gaymary Bakari and Ho-Youn Kim

Molecules 2020, 25(16), 3682; https://doi.org/10.3390/molecules25163682 - 12 Aug 2020

Cited by 58 | Viewed by 8055

Abstract

Glucosinolates (GSs) are common anionic plant secondary metabolites in the order Brassicales. Together with glucosinolate hydrolysis products (GSHPs), they have recently gained much attention due to their biological activities and mechanisms of action. We review herein the health benefits of GSs/GSHPs, approaches to improve the plant contents, their bioavailability and bioactivity. In this review, only literature published between 2010 and March 2020 was retrieved from various scientific databases. Findings indicate that these compounds (natural, pure, synthetic, and derivatives) play an important role in human/animal health (disease therapy and prevention), plant health (defense chemicals, biofumigants/biocides), and food industries (preservatives). Overall, much interest is focused on in vitro studies as anti-cancer and antimicrobial agents. GS/GSHP levels improvement in plants utilizes mostly biotic/abiotic stresses and short periods of phytohormone application. Their availability and bioactivity are directly proportional to their contents at the source, which is affected by methods of food preparation, processing, and extraction. This review concludes that, to a greater extent, there is a need to explore and improve GS-rich sources, which should be emphasized to obtain natural bioactive compounds/active ingredients that can be included among synthetic and commercial products for use in maintaining and promoting health. Furthermore, the development of advanced research on compounds pharmacokinetics, their molecular mode of action, genetics based on biosynthesis, their uses in promoting the health of living organisms is highlighted. Full article

(This article belongs to the Special Issue Secondary Metabolites in Plant Foods)

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