The presence of melatonin in grapevine (Vitis vinifera L.) berry tissues

Recent Advances in Postharvest Application of Exogenous Phytohormones for Quality Preservation of Fruits and Vegetables

The increasing global population has heightened the demand for food, leading to escalated food production and, consequently, the generation of significant food waste. Factors such as rapid ripening, susceptibility to physiological disorders, and vulnerability to microbial attacks have been implicated as contributing to the accelerated senescence associated with food waste generation. Fruits and vegetables, characterized by their high perishability, account for approximately half of all food waste produced, rendering them a major area of concern. Various postharvest technologies have thus been employed, including the application of phytohormone treatments, to safeguard and extend the storability of highly perishable food products. This review, therefore, explores the physicochemical properties and biological aspects of phytohormones that render them suitable for food preservation. Furthermore, this review examines the effects of externally applied phytohormones on the postharvest physiology and quality attributes of fresh produce. Finally, the review investigates the mechanisms by which exogenous phytohormones preserve food quality and discusses the associated limitations and safety considerations related to the use of these compounds in food applications.

Presence of melatonin in foods of daily consumption: The benefit of this hormone for health

Melatonin (MLT) is a hormone that exists in all living organisms, including bacteria, yeast, fungi, animals, and plants, many of which are ingested daily in the diet. However, the exact concentrations of melatonin in each of the foods and the effect on health of the intake of foods rich in MLT are not known. Therefore, the aim of this review was to gather the available information on the melatonin content of different foods and to evaluate the effect that this hormone has on different pathologies. The amount of MLT may vary depending on the variety, origin, heat treatment, processing, and analysis technique, among other factors. Dietary interventions with foods rich in MLT report health benefits, but there is no evidence that hormone is partially responsible for the clinical improvement. Therefore, it is necessary to evaluate the MLT content in more foods, as well as the effect that cooking/processing has on the amount of MLT, to estimate its total intake in a typical diet and better explore its potential impact on the health.

Ascorbate peroxidase in fruits and modulation of its activity by reactive species

Ascorbate peroxidase (APX) is one of the enzymes of the ascorbate-glutathione cycle and is the key enzyme that breaks down H2O2 with the aid of ascorbate as an electron source. APX is present in all photosynthetic eukaryotes from algae to higher plants and, at the cellular level, it is localized in all subcellular compartments where H2O2 is generated, including the apoplast, cytosol, plastids, mitochondria, and peroxisomes, either in soluble form or attached to the organelle membranes. APX activity can be modulated by various post-translational modifications including tyrosine nitration, S-nitrosation, persulfidation, and S-sulfenylation. This allows the connection of H2O2 metabolism with other relevant signaling molecules such as NO and H2S, thus building a complex coordination system. In both climacteric and non-climacteric fruits, APX plays a key role during the ripening process and during post-harvest, since it participates in the regulation of both H2O2 and ascorbate levels affecting fruit quality. Currently, the exogenous application of molecules such as NO, H2S, H2O2, and, more recently, melatonin is seen as a new alternative to maintain and extend the shelf life and quality of fruits because they can modulate APX activity as well as other antioxidant systems. Therefore, these molecules are being considered as new biotechnological tools to improve crop quality in the horticultural industry.

Melatonin - This is important to know

MEL (N-acetyl-5-methoxytryptamine) is a well-known natural compound that controls cellular processes in both plants and animals and is primarily found in plants as a neurohormone. Its roles have been described very broadly, from its antioxidant function related to the photoperiod and determination of seasonal rhythms to its role as a signalling molecule, imitating the action of plant hormones (or even being classified as a prohormone). MEL positively affects the yield and survival of plants by increasing their tolerance to unfavourable biotic and abiotic conditions, which makes MEL widely applicable in ecological farming as a stimulant of growth and development. Thus, it is called a phytobiostimulator. In this review, we discuss the genesis of MEL functions, the presence of MEL at the cellular level and its effects on gene expression and plant development, which can ensure the survival of plants under the conditions they encounter. Moreover, we consider the future application possibilities of MEL in agriculture.

Mediterranean Diet and Melatonin: A Systematic Review

The Mediterranean diet (MD) has beneficial effects on human health, which is evidenced by the observation of lower incidence rates of chronic diseases in Mediterranean countries. The MD dietary pattern is rich in antioxidants, such as melatonin, which is a hormone produced mainly by the pineal gland and controls several circadian rhythms. Additionally, melatonin is found in foods, such as fruit and vegetables. The purpose of this systematic review was to assess the melatonin content in Mediterranean foods and to evaluate the influence of the MD on melatonin levels in both humans and model organisms. A comprehensive search was conducted in four databases (PubMed, Scopus, Cochrane Library and Web of Science) and data were extracted. A total of 31 records were chosen. MD-related foods, such as tomatoes, olive oil, red wine, beer, nuts, and vegetables, showed high melatonin contents. The consumption of specific MD foods increases melatonin levels and improves the antioxidant status in plasma.

Melatonin in different food samples: Recent update on distribution, bioactivities, pretreatment and analysis techniques

Melatonin (MLT) plays a significant role on maintaining the basic physiological functions and regulating various metabolic processes in plentiful organisms. Recent years have witnessed an increase in MLT's share in global market with its affluent functions. However, the worrisome quality issues and inappropriate or excessive application of MLT take place inevitably. In addition, its photosensitive properties, oxidation, complex substrate concentration and trace levels leave exact detection of MLT doubly difficult. Therefore, it is essential to exploit precise, sensitive and stable extraction and detection methods to resolve above questions. In this study, we reviewed the distribution and bioactivities of MLT and conducted a comprehensive overview of the developments of pretreatment and analysis methods for MLT in food samples since 2010. Commonly used pretreatment methods for MLT include not only traditional techniques, but also novel ones, such as solid-phase extraction, QuEChERS, microextraction by packed sorbent, solid phase microextraction, liquid phase microextraction, and so on. Analysis methods include liquid chromatography coupled with different detectors, GC methods, capillary electrophoresis, sensors, and so on. The advantages and disadvantages of different techniques have been compared and the development tendency was prospected.

Exploring the Role of Antioxidants to Combat Oxidative Stress in Malaria Parasites

BACKGROUND

Malaria, a global challenge, is a parasitic disease caused by Plasmodium species. Approximately 229 million cases of malaria were reported in 2019. Major incidences occur in various continents, including African and Eastern Mediterranean Continents and South-East Asia.

INTRODUCTION

Despite the overall decline in global incidence from 2010 to 2018, the rate of decline has been almost constant since 2014. The morbidity and mortality have been accelerated due to reactive oxygen species (ROS) caused by oxidative stress generated by the parasite responsible for the destruction of host metabolism and cell nutrients.

METHODS

The excessive release of free radicals is associated with the infection in the animal or human body by the parasites. This may be related to a reduction in nutrients required for the generation of antioxidants and the destruction of cells by parasite activity. Therefore, an intensive literature search has been carried out to find the natural antioxidants used to neutralize the free radicals generated during malarial infection.

RESULTS

The natural antioxidants may be useful as an adjuvant treatment along with the antimalarial chemotherapeutics to reduce the death rate and enhance the success rate of malaria treatment.

CONCLUSION

In this manuscript, an attempt has been made to provide significant insight into the antioxidant activities of herbal extracts against malaria parasites.

Long-term effects of melatonin and resveratrol on aging rats: A multi-biomarker approach

Aging-related impaired body structure and functions may be, at least partially, caused by elevated oxidative stress. Melatonin (MEL) and resveratrol (RSV) may act as antioxidant and anti-aging compounds, but these actions in experimental animals and humans are controversial. Herein, a rat model of aging was used to study the long-term sex-related effects of MEL and RSV treatment on body mass and blood/plasma parameters of DNA damage, oxidative status (glutathione and malondialdehyde levels), and concentrations of sex hormones. Starting from the age of 3mo, for the next 9mo or 21mo male and female Wistar rats (n = 4-7 per group) were given water to drink (controls) or 0.1 % ethanol in water (vehicle), or MEL or RSV (each 10 mg/L vehicle). DNA damage in whole blood cells was tested by comet assay, whereas in plasma, glutathione, malondialdehyde, and sex hormones were determined by established methods. Using statistical analysis of data by ANOVA/Scheffe post hoc, we observed a similar sex- and aging-dependent rise of body mass in both sexes and drop of plasma testosterone in control and vehicle-treated male rats, whose pattern remained unaffected by MEL and RSV treatment. Compared with controls, all other parameters remained largely unchanged in aging and differently treated male and female rats. We concluded that the sex- and aging-related pattern of growth and various blood parameters in rats were not affected by the long-term treatment with MEL and RSV at the estimated daily doses (300-400 μg/kg b.m.) that exceed usual moderate consumption in humans.

Detection of Volatiles by HS-SPME-GC/MS and Biological Effect Evaluation of Buddha's Hand Fruit

The present work aimed to chemically characterize and evaluate the antiradical power and biological effects of Citrus medica var. sarcodactylus essential oil (EO) and hydrolate (Hy) from exocarp as well as methanol extracts, from both exocarp and mesocarp (EEX and MEX). The whole fresh fruit was also investigated by SPME-GC/MS to describe its volatile composition. EO and Hy were analyzed by GC/MS and HS-GC/MS techniques, respectively. Limonene and γ-terpinene were found to be the most abundant compounds both in the fresh parts of the fruit and in the EO, while α-terpineol and terpinen-4-ol were in the Hy. The extracts were also rich in furan and coumarin derivatives. A good antiradical activity of all samples except Hy was detected both against ABTS·+ than DPPH·, removed up to about 50%. The antibacterial activity against Bacillus cereus and Escherichia coli was evaluated by microwell dilution method to determine MIC and MBC values. EEX and MEX showed efficacy at very high concentrations against both tested bacteria. The MIC value of EO against B. cereus was 0.5% v/v, while Hy was not able to inhibit the bacterial growth at the tested concentrations. Cytotoxicity investigated on the HL60 leukemia cell line by MTT assay provided an EC₅₀ of 1.24% v/v for EO. Interesting activity of Hy was also observed.

Role of Melatonin in Apple Fruit during Growth and Ripening: Possible Interaction with Ethylene

The role of melatonin during the growth and ripening of apple fruit was studied using local varieties. The evolution of the growth and ripening parameters, including fruit size and weight, firmness, color change, sugar content, and ethylene production, was different in the five varieties studied, with yellow apples (Reineta and Golden) initiating the ripening process earlier than reddish ones (Teórica, Sanroqueña, and Caguleira). Changes in the melatonin and melatonin isomer 2 contents during growth and ripening were studied in Golden apples, as was the effect of the melatonin treatment (500 µM, day 124 post-anthesis) on the apple tree. Melatonin content varied greatly, with higher value in the skin than in the flesh. In the skin, melatonin increased at day 132 post-anthesis, when ethylene synthesis started. In the flesh, melatonin levels were high at the beginning of the growth phase and at the end of ripening. Melatonin isomer 2 was also higher once the ripening started and when ethylene began to increase. The melatonin treatment significantly advanced the ethylene production and increased the fruit size, weight, sugar content, and firmness. The data suggest that melatonin stimulates fruit ripening through the induction of ethylene synthesis, while melatonin treatments before ripening improve the final fruit quality.

Grapevine Wastes: A Rich Source of Antioxidants and Other Biologically Active Compounds

Wine production is one of the most critical agro-industrial sectors worldwide, generating large amounts of waste with negative environmental impacts, but also with high economic value and several potential applications. From wine shoots to grape pomace or seeds, all of the wastes are rich sources of bioactive compounds with beneficial effects for human health, with these compounds being raw materials for other industries such as the pharmaceutical, cosmetic or food industries. Furthermore, these compounds present health benefits such as being antioxidants, supporting the immune system, anti-tumoral, or preventing cardiovascular and neural diseases. The present work aims to be a critical discussion of the extraction methods used for bioactive compounds from grapevine waste and their beneficial effects on human health.

Melatonin and Phytomelatonin: Chemistry, Biosynthesis, Metabolism, Distribution and Bioactivity in Plants and Animals-An Overview

Melatonin is a ubiquitous indolamine, largely investigated for its key role in the regulation of several physiological processes in both animals and plants. In the last century, it was reported that this molecule may be produced in high concentrations by several species belonging to the plant kingdom and stored in specialized tissues. In this review, the main information related to the chemistry of melatonin and its metabolism has been summarized. Furthermore, the biosynthetic pathway characteristics of animal and plant cells have been compared, and the main differences between the two systems highlighted. Additionally, in order to investigate the distribution of this indolamine in the plant kingdom, distribution cluster analysis was performed using a database composed by 47 previously published articles reporting the content of melatonin in different plant families, species and tissues. Finally, the potential pharmacological and biostimulant benefits derived from the administration of exogenous melatonin on animals or plants via the intake of dietary supplements or the application of biostimulant formulation have been largely discussed.

Plant-derived melatonin from food: a gift of nature

In recent years, people have become increasingly interested in bioactive ingredients from plants, especially antioxidant molecules such as melatonin, which are beneficial to human health. The purpose of this article is to provide new information on plant-derived foods with a high content of melatonin. We comprehensively summarize the content of melatonin in plant-derived foods and discuss the factors that influence melatonin levels to provide new ideas on enhancement. Additionally, we describe the biosynthetic pathway of melatonin and identify its major functions. Medicinal herbs are often rich in melatonin while many vegetables and fruits exhibit somewhat lower levels with wide variations among species. The genetic traits of plants, the phenological stage of the cultivar, the photoperiod, the level of stress to which the plants are exposed at the time of harvest, exposure to agrochemicals and determination methods are the main factors affecting the melatonin content. To date, standardization of uniform sampling times and the use of suitable pretreatments as well as determination methods have not been achieved. The results of the studies reviewed highlight the potentially important role of plant melatonin in influencing the progression of human diseases. Based on the health promotional aspects of melatonin, consuming foods containing higher concentrations of tryptophan and melatonin is suggested.

Melatonin alters the secondary metabolite profile of grape berry skin by promoting VvMYB14-mediated ethylene biosynthesis

The interplay between melatonin and ethylene in the regulation of fruit metabolism and the underlying molecular mechanism of this interplay remain largely unclear. Here, widely targeted metabolomics analysis revealed a total of 464 metabolites present in berry skin. Among them, 27 significantly differentially accumulated metabolites (DAMs) were produced in response to melatonin treatment in the presence or absence of 1-MCP. Most of the DAMs were secondary metabolites, including flavonoids, phenolic acids, stilbenes, and flavonols. Additionally, the accumulation of 25 DAMs was regulated by melatonin via ethylene. RNA-seq analysis indicated that melatonin primarily regulated the pathways of plant hormone signal transduction and secondary metabolite biosynthesis via ethylene. Gene-metabolite association analysis showed that melatonin regulated the expression of the VvSTS1, VvF3H, VvLAR2, and VvDFR genes, suggesting that these genes may play key roles in regulating secondary metabolites in the skin; additionally, VvMYB14 and VvACS1 were suggested to be involved in the regulation of secondary metabolites. Further experiments revealed that melatonin induced the expression of VvMYB14 and that VvMYB14 increased ethylene production by transcriptionally activating VvACS1, thereby affecting the accumulation of secondary metabolites. Collectively, melatonin promotes ethylene biosynthesis and alters secondary metabolite accumulation through the regulation of VvACS1 by VvMYB14.

Naturally occurring melatonin: Sources and possible ways of its biosynthesis

According to recent reports, the global market for melatonin is worth 700 million USD in 2018 and would reach 2,790 million USD by 2025, growing at a CAGR of 18.9% during 2019 to 2025. Having regard to the prevalence of sleep and circadian rhythm disorders and a clear tendency to increase the demand for melatonin, and the current lack of alternative green and cost-efficient technologies of its synthesis, the supply of this remedy will not be enough to guarantee melatonin supply and affordability on a global scale. The emergence of naturally occurring melatonin and its isomers in fermented foods has opened an exciting new research area; there are still, however, some obscure points in the efficient microbiological biosynthesis of melatonin. This review summarizes the research progress and recent evidence related to melatonin and its isomers in various foodstuffs. Additionally, one possible way to synthesize melatonin is also discussed. The evidence pointed out that the presence of melatonin and its isomers is not exclusive for grapes and grape-derived products, because it can be also found in sweet and sour cherries. However, different species of both Saccharomyces and non-Saccharomyces yeasts could be used to obtain melatonin and melatonin isomers in the process of alcoholic fermentation biotechnologically. The availability of L-tryptophan has been a key factor in determining the concentration of indolic compounds produced, and the utilization of probiotic lactic acid bacteria could help in the formation of melatonin isomers during malolactic fermentation. These approaches are environmentally friendly alternatives with a safer profile than conventional ones and could represent the future for sustainable industrial-scale melatonin production.

Melatonin rich foods in our diet: food for thought or wishful thinking?

Melatonin continues to generate interest in the scientific community and the general public. In recent years, there has been growing interest in the possibility that melatonin present in human foods may have physiological effects. This has led to the promotion of "melatonin-rich" foods and "phyto-melatonin". The night time secretion of endogenous melatonin from the pineal gland provides a daily circadian signal which is detected by receptors in various tissues. In animals the changing circadian pattern of melatonin secretion across seasons is important to them to program their reproductive behaviours to ensure optimal reproductive success, while in humans it probably plays a prominent role in anchoring sleep to the night period. When melatonin is administered in non-physiological, milligram amounts to humans, the onset of sleep can be manipulated and in larger doses anti-oxidant properties may emerge. Melatonin-rich foods are considered in this context too, but the question remains whether the amounts of melatonin in the food can be expected to be high enough to realistically change sleep or have antioxidant properties. In this review, papers reporting the effects of ingestion of melatonin-rich food on plasma or saliva melatonin or its urinary metabolite are critically evaluated. Unfortunately many of the papers are compromised by poor experimental design and assay methodologies and uncritical evaluation of results. The conclusion drawn from this review is that it is wishful thinking to expect that the amount of melatonin in "melatonin-rich" foods will impact on sleep or have any other physiological impact.

Melatonin Accumulation in Sweet Cherry and Its Influence on Fruit Quality and Antioxidant Properties

Although the effects of melatonin on plant abiotic and biotic stress resistance have been explored in recent decades, the accumulation of endogenous melatonin in plants and its influence on fruit quality remains unclear. In the present study, melatonin accumulation levels and the expression profiles of five synthesis genes were investigated during fruit and leaf development in sweet cherry (Prunus avium L.). Melatonin was strongly accumulated in young fruits and leaves, then decreased steadily with maturation. Transcript levels of PacTDC and PacSNAT were highly correlated with melatonin content in both fruit and leaves, indicating their importance in melatonin accumulation. Furthermore, application of 50 and 100 μmol·L^-1 of melatonin to leaves had a greater influence on fruit quality than treatments applied to fruits, by significantly improving fruit weight, soluble solids content, and phenolic content including total phenols, flavanols, total anthocyanins, and ascorbic acid. Meanwhile, melatonin application promoted the antioxidant capacity of fruit assayed by 2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2'-azinobis (3-ethylben zothiazoline-6-sulfonic acid) (ABTS), and ferric reducing antioxidant power (FRAP). These results provide insights into the physiological and molecular mechanisms underlying melatonin metabolism of sweet cherry.

Molecular cloning and characterization of a grapevine (Vitis vinifera L.) serotonin N-acetyltransferase (VvSNAT2) gene involved in plant defense

Background

Melatonin is a ubiquitous molecule and exists across kingdoms. Studies on melatonin in plants have mainly focused on its physiological influence on growth and development, and on its biosynthesis. A number of studies have been conducted on the melatonin content and exogenous melatonin treatment of grapevine (Vitis vinifera L.). However, key genes or enzymes of the melatonin biosynthetic pathway remain unclear.

Results

In this study, we cloned and identified the gene encoding serotonin N-acetyltransferase (SNAT) in grapevine (VvSNAT2). The VvSNAT2 protein was identified from a collection of 30 members of the grapevine GCN5-related N-acetyltransferase (GNAT) superfamily. Phylogenetic and protein sublocalization analyses showed that the candidate gene VvGNAT16 is VvSNAT2. Characterization of VvSNAT2 showed that its enzymatic activity is highest at a pH of 8.8 and a temperature of 45 °C. Analysis of enzyme kinetics showed the values of K_m and V_max of VvSNAT2 using serotonin were 392.5 μM and 836 pmol/min/mg protein, respectively. The expression of VvSNAT2 was induced by melatonin treatment and pathogen inoculation. Overexpression of VvSNAT2 in Arabidopsis resulted in greater accumulation of melatonin and chlorophyll and enhanced resistance to powdery mildew in the transgenic plants compared with the wild type (WT). Additionally, our data showed that the marker genes in the salicylic acid (SA) signaling pathway were expressed to higher levels in the transgenic plants compared with the WT.

Conclusions

The VvSNAT2 gene was cloned and identified in grapevine for the first time. Our results indicate that VvSNAT2 overexpression activates the SA and JA signaling pathways; however, the SA pathway plays a central role in VvSNAT2-mediated plant defense.

Exogenous Melatonin Delays Dark-Induced Grape Leaf Senescence by Regulation of Antioxidant System and Senescence Associated Genes (SAGs)

Leaf senescence is a developmentally programmed and degenerative process which comprises the last stage of the life cycle of leaves. In order to understand the melatonin effect on grapevine leaf senescence, the dark treatment on detached leaves of Vitis vinifera L. cv. Red Globe was performed to induce leaf senescence at short period of time. Then, a series of physiological and molecular changes in response to exogenous melatonin were measured. Results showed that 100 μM of melatonin treatment could significantly delay the dark induced leaf senescence, which is accompanied by the decreased production of reactive oxygen species (ROS). Meanwhile, melatonin treatment could increase the scavenging activity of antioxidant enzymes, such as peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT). Simultaneously, ascorbate (AsA) and glutathione (GSH) contents, the activities of ascorbate peroxidase (APX), and glutathione reductase (GR) were significantly higher than control treatment in samples treated with melatonin. Furthermore, melatonin treatment showed to suppress the expression of leaf senescence-associated genes (SAGs). All these results demonstrated that melatonin could activate the antioxidant and Ascorbate-Glutathione (AsA-GSH) cycle system and repress the expression of SAGs that lead to delay the dark induced grape leaf senescence.

Cluster bagging promotes melatonin biosynthesis in the berry skins of Vitis vinifera cv. Cabernet Sauvignon and Carignan during development and ripening

Melatonin, a tryptophan derivative, is an important functional component in grape berries. We investigated the effect of cluster bagging on melatonin biosynthesis in the berries of two wine grape cultivars, Cabernet Sauvignon and Carignan, during fruit development and ripening. Cluster bagging delayed fruit coloring and ripening, and bag-treated berries of both grape cultivars synthesized more melatonin and most of the precursor compounds including L-tryptophan, N-acetylserotonin, tryptamine, and serotonin compared to those exposed to light (control) conditions. Interestingly, 5-methoxytryptamine was only detected in the berries of Carignan and not of Cabernet Sauvignon, both in the cluster bagging and control groups. In addition, melatonin and most of its precursors, decreased after veraison. VvSNAT1 and VvT5H expression levels were positively correlated with melatonin content. Our findings suggested that melatonin synthesis pathways differ among grape cultivars, and that VvSNAT1 and VvT5H may show key regulatory roles in the melatonin synthesis of grape berries.

Melatonin in Medicinal and Food Plants: Occurrence, Bioavailability, and Health Potential for Humans

Melatonin is a widespread molecule among living organisms involved in multiple biological, hormonal, and physiological processes at cellular, tissue, and organic levels. It is well-known for its ability to cross the blood–brain barrier, and renowned antioxidant effects, acting as a free radical scavenger, up-regulating antioxidant enzymes, reducing mitochondrial electron leakage, and interfering with proinflammatory signaling pathways. Detected in various medicinal and food plants, its concentration is widely variable. Plant generative organs (e.g., flowers, fruits), and especially seeds, have been proposed as having the highest melatonin concentrations, markedly higher than those found in vertebrate tissues. In addition, seeds are also rich in other substances (lipids, sugars, and proteins), constituting the energetic reserve for a potentially growing seedling and beneficial for the human diet. Thus, given that dietary melatonin is absorbed in the gastrointestinal tract and transported into the bloodstream, the ingestion of medicinal and plant foods by mammals as a source of melatonin may be conceived as a key step in serum melatonin modulation and, consequently, health promotion.

The Importance of Yeasts on Fermentation Quality and Human Health-Promoting Compounds

Non-Saccharomyces are important during wine fermentation once they influence wine composition. In the early stages of wine fermentation, and together with indigenous or commercial strains of Saccharomyces cerevisiae, non-Saccharomyces are able to transform grape-must sugars into ethanol, CO2, and other important secondary metabolites. A better understanding of yeast biochemistry will allow the selection of yeast strains that have defined specific influences on fermentation efficiency, wine quality, and the production of human health-promoting compounds. Yeast metabolism produces compounds derived from tryptophan, melatonin, and serotonin, which are found in fermented beverages, such as wine and beer. Melatonin is a neurohormone secreted from the pineal gland and has a wide-ranging regulatory and neuroprotective role, while serotonin, as well as being a precursor of melatonin synthesis, is also a neurotransmitter. This review summarizes the importance of some conventional and nonconventional yeast strains’ alcoholic fermentations, especially in the production of metabolites that promote human health and thus, attract consumers attention towards fermented beverages. A brief reference is also made on fermented beverages containing probiotics, namely kombucha, also known as kombucha tea, and its interesting microorganism’s symbiotic relationships named SCOBY.

Melatonin Is a Potential Target for Improving Post-Harvest Preservation of Fruits and Vegetables

Melatonin is a ubiquitous molecule distributed in nature and not only plays an important role in animals and humans but also has extensive functions in plants, such as delaying senescence, exerting antioxidant effects, regulating growth and development, and facilitating plant adaption to stress conditions. Endogenous melatonin is widespread in fruits and vegetables and plays prominent roles in the ripening and post-harvest process of fruits and vegetables. Exogenous application of melatonin removes excess reactive oxygen species from post-harvest fruits and vegetables by increasing antioxidant enzymes, non-enzymatic antioxidants, and enzymes related to oxidized protein repair. Moreover, exogenous application of melatonin can increase endogenous melatonin to augment its effects on various physiological processes. Many previous reports have demonstrated that application of exogenous melatonin improves the post-harvest preservation of fruits and vegetables. Although overproduction of melatonin in plants via transgenic approaches could be a potential means for improving the post-harvest preservation of fruits and vegetables, efforts to increase endogenous melatonin in plants are limited. In this review, we summarize the recent progress revealing the role and action mechanisms of melatonin in post-harvest fruits and vegetables and provide future directions for the utilization of melatonin to improve the post-harvest preservation of fruits and vegetables.

Melatonin promotes ripening of grape berry via increasing the levels of ABA, H2O2, and particularly ethylene

The role of melatonin in the regulation of fruit ripening and the mechanism involved remain largely unknown. In "Moldova" grape berries, melatonin accumulated rapidly from onset of veraison, reached the maximum at 94 days after bloom (DAB) and then exhibited low levels at late stages of berry ripening. By contrast, abscisic acid (ABA) and hydrogen peroxide (H2O2) exhibited different accumulation patterns, and ethylene was primarily produced immediately before veraison. Further experiments demonstrated that 10 and particularly 100 µM melatonin treatments increased the levels of ABA, H2O2, and ethylene production and promoted berry ripening compared with the control treatment, whereas 0.1 and 1.0 µM melatonin did not lead to clear effects. Additionally, the application of inhibitors indicated that ABA, H2O2, and ethylene participated in the regulation of berry ripening induced by melatonin, and the suppression of ethylene biosynthesis produced the greatest inhibitory effects on melatonin-induced berry ripening compared with those of ABA and H2O2. Melatonin also promoted ethylene production via ABA. In summary, 10 and particularly 100 µM melatonin treatments promoted berry ripening, which was accomplished, at least partially, via the other signaling molecules of ABA, H2O2, and particularly ethylene. This research provides insight into melatonin signaling during berry ripening and may advance the application of melatonin to accelerate berry ripening.

The Potential of Phytomelatonin as a Nutraceutical

Phytomelatonin (plant melatonin) is chemically related to the amino acid tryptophan and has many diverse properties. Phytomelatonin is an interesting compound due to its outstanding actions at the cellular and physiological level, especially its protective effect in plants exposed to diverse stress situations, while its vegetable origin offers many opportunities because it is a natural compound. We present an overview of its origin, its action in plants in general (particularly in plant species with high levels of phytomelatonin), and its possibilities for use as a nutraceutical with particular attention paid to the beneficial effects that it may have in human health. The differences between synthetic melatonin and phytomelatonin, according to its origin and purity, are presented. Finally, the current market for phytomelatonin and its limits and potentials are discussed.

Dietary Sources and Bioactivities of Melatonin

Insomnia is a serious worldwide health threat, affecting nearly one third of the general population. Melatonin has been reported to improve sleep efficiency and it was found that eating melatonin-rich foods could assist sleep. During the last decades, melatonin has been widely identified and qualified in various foods from fungi to animals and plants. Eggs and fish are higher melatonin-containing food groups in animal foods, whereas in plant foods, nuts are with the highest content of melatonin. Some kinds of mushrooms, cereals and germinated legumes or seeds are also good dietary sources of melatonin. It has been proved that the melatonin concentration in human serum could significantly increase after the consumption of melatonin containing food. Furthermore, studies show that melatonin exhibits many bioactivities, such as antioxidant activity, anti-inflammatory characteristics, boosting immunity, anticancer activity, cardiovascular protection, anti-diabetic, anti-obese, neuroprotective and anti-aging activity. This review summaries the dietary sources and bioactivities of melatonin, with special attention paid to the mechanisms of action.

Melatonin protects against uric acid-induced mitochondrial dysfunction, oxidative stress, and triglyceride accumulation in C2C12myotubes

Excess uric acid has been shown to induce oxidative stress, triglyceride accumulation, and mitochondrial dysfunction in the liver and is an independent predictor of type-2 diabetes. Skeletal muscle plays a dominant role in type 2 diabetes and presents a large surface area to plasma uric acid. However, the effects of uric acid on skeletal muscle are underinvestigated. Our aim was therefore to characterize the effects of excessive uric acid on oxidative stress, triglyceride content, and mitochondrial function in skeletal muscle C2C12myotubes and assess how these are modulated by the antioxidant molecule melatonin. Differentiated C2C12myotubes were exposed to 750 µM uric acid or uric acid + 10 nM melatonin for 72 h. Compared with control, uric acid increased triglyceride content by ~237%, oxidative stress by 32%, and antioxidant capacity by 135%. Uric acid also reduced endogenous ROUTINE respiration, complex II-linked oxidative phosphorylation, and electron transfer system capacities. Melatonin counteracted the effects of uric acid without further altering antioxidant capacity. Our data demonstrate that excess uric acid has adverse effects on skeletal muscle similar to those previously reported in hepatocytes and suggest that melatonin at a low physiological concentration of 10 nM may be a possible therapy against some adverse effects of excess uric acid.

NEW & NOTEWORTHY Few studies have investigated the effects of uric acid on skeletal muscle. This study shows that hyperuricemia induces mitochondrial dysfunction and triglyceride accumulation in skeletal muscle. The findings may explain why hyperuricemia is an independent predictor of diabetes.

Melatonin in grapes and grape-related foodstuffs: A review

A decade has passed since melatonin was first reported in grapes in 2006. During this time, melatonin has not only been found in the berries of most wine grape (Vitis vinifera L.) cultivars, but also in most grape-related foodstuffs, e.g. wine, grape juice and grape vinegar. In this review, we discuss the melatonin content in grapes and grape-related foodstuffs (especially wine) from previous studies, the physiological function of melatonin in grapes, and the factors contributing to the production of melatonin in grapes and wines. In addition, we identify future research needed to clarify the mechanisms of grape melatonin biosynthesis and regulation, and establish more accurate analysis methods for melatonin in grapes and wines.

Ultrahigh-Performance Liquid Chromatography (UHPLC)-Tandem Mass Spectrometry (MS/MS) Quantification of Nine Target Indoles in Sparkling Wines

An ultrahigh-performance liquid chromatography (UHPLC)-tandem mass spectrometry (MS/MS) method was developed for the simultaneous determination of nine target indoles in sparkling wines. The proposed method requires minimal sample pretreatment, and its performance parameters (accuracy, repeatability, LOD, and matrix effect) indicate that it is suitable for routine analysis. Four indoles were found at detectable levels in commercial Cava samples: 5-methoxytryptophol (5MTL), tryptophan (TRP), tryptophan ethyl ester (TEE), and N-acetylserotonin (NSER). Two of them, NSER and 5MTL, are reported here for the first time in sparkling wines, with values of 0.3-2 and 0.29-29.2 μg/L, respectively. In the same samples, the contents of melatonin (MEL), serotonin (SER), 5-hydroxytryptophan (5-OHTRP), 5-hydroxyindole-3-acetic acid (5OHIA), and 5-methoxy-3-indoleacetic acid (5MIA) were all below the corresponding limits of detection.

Melatonin in Mediterranean diet, a new perspective

The health-promoting properties of the Mediterranean diet have been attributed, at least in part, to the chemical diversity of plant foods. Among phytochemicals, polyphenols represent the paradigm of the relationship between healthy foods and reduced risk of chronic-degenerative diseases, although, in the past few years, a new element has enriched this scenario. Melatonin, and possibly other indoleamines recently discovered in some relevant Mediterranean foods, may represent a new factor contributing to the elucidation of the protective effects of diets rich in plant products. Therefore, in synergy with polyphenols and other bioactive phytochemicals (e.g. carotenoids and glucosinolates), melatonin may contribute to maximizing the benefits of healthy dietary styles. This brief survey deals with the occurrence of melatonin in the Mediterranean diet, with an emphasis on grape products, and focuses on the biological significance of dietary melatonin, an emerging and exciting topic in the field of nutritional sciences.

Safety assessment of Vitis vinifera (grape)-derived ingredients as used in cosmetics

The Cosmetic Ingredient Review Expert Panel (Panel) assessed the safety of 24 Vitis vinifera (grape)-derived ingredients and found them safe in the present practices of use and concentration in cosmetics. These ingredients function in cosmetics mostly as skin-conditioning agents, but some function as antioxidants, flavoring agents, and/or colorants. The Panel reviewed the available animal and clinical data to determine the safety of these ingredients. Additionally, some constituents of grapes have been assessed previously for safety as cosmetic ingredients by the Panel, and others are compounds that have been discussed in previous Panel safety assessments.

Yeast contribution to melatonin, melatonin isomers and tryptophan ethyl ester during alcoholic fermentation of grape musts

Melatonin (MEL) has been found in some medicinal and food plants, including grapevine, a commodity of particular interest for the production of wine, a beverage of economic relevance. It has also been suggested that MEL in wine may, at least in part, contribute to the health-promoting properties attributed to this beverage and, possibly, to other traditional Mediterranean foodstuffs. After a preliminary screening of 9 yeast strains in laboratory medium, three selected strains (Saccharomyces cerevisiae EC1118, Torulaspora delbrueckii CBS1146(T) and Zygosaccharomyces bailii ATCC36947(T) ) were inoculated in experimental musts obtained from 2 white (Moscato and Chardonnay) and 2 red (Croatina and Merlot) grape varieties. The production of MEL, melatonin isomers (MIs) and tryptophan ethyl ester (TEE) was monitored during the alcoholic fermentation. The screening showed that the three investigated strains produced the highest concentrations of MEL and two MIs in optimal growth conditions. However, MEL and MIs were not produced in oenological conditions, but the three strains synthesized high concentrations of a new MI and TEE in musts.

Tryptophan-ethylester, the false (unveiled) melatonin isomer in red wine

Among the food plants, the presence of melatonin in grapes (Vitis vinifera L.) deserves particular attention because of the production of wine, an alcoholic beverage of economic relevance and with putative healthy effects. Furthermore, melatonin isomers have been detected in wine too. Recently, one of these isomers has been identified as tryptophan-ethylester, a compound with the same molecular weight of melatonin. In this Commentary, we briefly comment the source(s) of tryptophan-ethylester in wine and the putative nutritional role(s).

Melatonin in plants and other phototrophs: advances and gaps concerning the diversity of functions

Melatonin is synthesized in Alphaproteobacteria, Cyanobacteria, Dinoflagellata, Euglenoidea, Rhodophyta, Phae ophyta, and Viridiplantae. The biosynthetic pathways have been identified in dinoflagellates and plants. Other than in dinoflagellates and animals, tryptophan is not 5-hydroxylated in plants but is first decarboxylated. Serotonin is formed by 5-hydroxylation of tryptamine. Serotonin N-acetyltransferase is localized in plastids and lacks homology to the vertebrate aralkylamine N-acetyltransferase. Melatonin content varies considerably among species, from a few picograms to several micrograms per gram, a strong hint for different actions of this indoleamine. At elevated levels, the common and presumably ancient property as an antioxidant may prevail. Although melatonin exhibits nocturnal maxima in some phototrophs, it is not generally a mediator of the signal 'darkness'. In various plants, its formation is upregulated by visible and/or UV light. Increases are often induced by high or low temperature and several other stressors including drought, salinity, and chemical toxins. In Arabidopsis, melatonin induces cold- and stress-responsive genes. It has been shown to support cold resistance and to delay experimental leaf senescence. Transcriptome data from Arabidopsis indicate upregulation of genes related to ethylene, abscisic acid, jasmonic acid, and salicylic acid. Auxin-like actions have been reported concerning root growth and inhibition, and hypocotyl or coleoptile lengthening, but effects caused by melatonin and auxins can be dissected. Assumptions on roles in flower morphogenesis and fruit ripening are based mainly on concentration changes. Whether or not melatonin will find a place in the phytohormone network depends especially on the identification of molecular signals regulating its synthesis, high-affinity binding sites, and signal transduction pathways.

Phytomelatonin: Discovery, Content, and Role in Plants

Melatonin (N-acetyl-5-methoxytryptamine) is an indolic compound derived from tryptophan. Usually identified as a neurotransmitter or animal hormone, this compound was detected in plants in 1995. Interest in knowing the melatonin content of plants and its possible role therein is growing, as indicated by the increasing number of related publications. Melatonin is present in all plant species studied, with large variations in its level depending on the plant organ or tissue. It seems to be more abundant in aromatic plants and in leaves than in seeds. Regarding its physiological function in plants, melatonin shows auxin activity and is an excellent antioxidant, regulating the growth of roots, shoots, and explants, activating seed germination and rhizogenesis (lateral- and adventitious-roots), and delaying induced leaf senescence. Its ability to strengthen plants subjected to abiotic stress such as drought, cold, heat, salinity, chemical pollutants, herbicides, and UV radiation makes melatonin an interesting candidate for use as a natural biostimulating substance for treating field crops.

Melatonin synthesis in rice seedlings in vivo is enhanced at high temperatures and under dark conditions due to increased serotonin N-acetyltransferase and N-acetylserotonin methyltransferase activities

Temperature and light are important environmental factors for plant growth and development. The final two enzymes in the melatonin synthesis pathway in plants are serotonin N-acetyltransferase (SNAT) and N-acetylserotonin methyltransferase (ASMT), which have thermophilic characteristics. Thus, the effects of temperature and light on melatonin synthesis in rice seedlings were investigated. Here, we demonstrated that melatonin levels increased as temperature increased when rice seedlings were exposed to various temperatures for 1 hr. Moreover, the relative melatonin levels were higher in the dark. For example, exposure of rice seedlings to 1-hr darkness at 55°C resulted in a melatonin yield of 4.9 ng/g fresh weight (fw), compared with 2.95 ng/g fw under light conditions. Temperature-dependent melatonin synthesis was closely associated with an increase in both SNAT and ASMT activities, but not with transcript levels of melatonin biosynthetic genes. The daily melatonin levels in field-grown rice plants were unaffected as the positive effect of the relatively high temperature during the day was counteracted by the negative effect of the high light. The opposite effect occurred during the night, in which the positive effect of darkness on melatonin synthesis was counteracted by the negative effect of a low temperature.

Identification of genes for melatonin synthetic enzymes in 'Red Fuji' apple (Malus domestica Borkh.cv.Red) and their expression and melatonin production during fruit development

Melatonin is present in many edible fruits; however, the presence of melatonin in apple has not previously been reported. In this study, the genes for melatonin synthetic enzymes including tryptophan decarboxylase, tryptamine 5-hydroxylase (T5H), arylalkylamine N-acetyltransferase, and N-acetylserotonin methyltransferase were identified in 'Red Fuji' apple. Each gene has several homologous genes. Sequence analysis shows that these genes have little homology with those of animals and they only have limited homology with known genes of rice melatonin synthetic enzymes. Multiple origins of melatonin synthetic genes during the evolution are expected. The expression of these genes is fully coordinated with melatonin production in apple development. Melatonin levels in apple exhibit an inverse relationship with the content of malondialdehyde, a product of lipid peroxidation. Two major melatonin synthetic peaks appeared on July 17 and on October 8 in both unbagged and bagged apple samples. At the periods mentioned above, apples experienced rapid expansion and increased respiration. These episodes significantly elevate reactive oxygen species production in the apple. Current data further confirmed that melatonin produced in apple was used to neutralize the toxic oxidants and protect the developing apple against oxidative stress.

Transient induction of melatonin biosynthesis in rice (Oryza sativa L.) during the reproductive stage

The regulation of reproduction-stage inducible melatonin biosynthesis in rice (Oryza sativa cv. Dongjin) was investigated. The flag leaf and panicle (flower) were collected from field-grown rice at three different reproductive stages: the preflowering stage, flowering stage, and postflowering stage. Melatonin synthesis was induced in the panicle, whereas no induction was observed in the flag leaf during the reproductive stages. The panicle displayed a peak melatonin level of 0.4 ng/g fresh weight (fw), which was six times that found in the flag leaf. The induction of melatonin biosynthesis was paralleled by the induction of corresponding genes and proteins such as tryptophan decarboxylase, tryptamine 5-hydroxylase, and N-acetylserotonin methyltransferase. In addition, melatonin induction was preceded by the accumulation of its precursor, tryptophan, in the panicle. These results suggest that the induction of melatonin during flower development is regulated by the transcriptional control of its biosynthesis genes and that melatonin may participate in flower development.