Rwandan Coffee arabica has caffeine increasing with altitude, but undetectable phytomelatonin

Abstract

Altitude affects plants’ constituents. The presence of caffeine and melatonin in many plants, including C. arabica, has been widely reported. However, a possible variation of their quantity in Rwandan C. arabica samples across different altitudinal locations is not yet known. This study sought to provide this information. C. arabica samples from Kayonza, Ruhango, Gakenke, Gatsibo, Nyagatare, and Karongi districts, covering different altitude ranges in Rwanda, were obtained from the National Agriculture Export Development Board (NAEB). Analytical techniques like Thin-Layer Chromatography (TLC), High-Performance Liquid Chromatography (HPLC), and Gas Chromatography-Mass Spectrometry (GC–MS) were used. C. arabica samples from higher altitudes yielded higher caffeine content, while instant coffee samples showed a broad caffeine range. However, all the techniques detected no phytomelatonin in the C. arabica samples collected from different altitudinal locations in Rwanda following two extraction methods, even though melatonin supplements from pharmaceutical outlets manufactured in the USA (110 %), Canada (106 %), Denmark (102 %), and Belgium (2.8 %) had detectable melatonin. Rwandan C. arabica has no phytomelatonin but shows increased caffeine content with increasing locational altitude. Further studies to analyze the precursors and enzymes involved in the phytomelatonin biosynthetic pathways in plants are needed to unravel this mystery.

Highlights

Rwandan C. arabica at high altitude had more caffeine than at lower altitudes.

TLC, GC–MS, and HP-LC detected no melatonin in Rwandan C. arabica.

Melatonin products from Belgium failed the quality assessment test.

Background

Coffee arabica and Coffee robusta are the two coffee species that exist (López-Froilán et al., 2016), with the former being the most adored, accounting for over 70 % of the world’s coffee production and plantation (Ali et al., 2022). Its high consumption is due to many health benefits linked to its constituent phytochemicals, including amino acids, polyphenols, alkaloids, hormones, and sesquiterpenoids; while caffeine, quinic acid derivatives, caffeic acid, ferulic acid, p-coumaric acid, melatonin, and serotonin are reported as its most readily available components (Yamagata, 2018). Furthermore, the components of coffee include proanthocyanidins, cinnamaldehydes, and cinnamic acids, which have been shown to possess antibacterial, antioxidant, antidiabetic, anticancer, and cardio-protective qualities (Saeed et al., 2019). Because phenolic chemicals can scavenge free radicals in the biological system, they are primarily responsible for coffee’s antioxidant qualities (Komes et al., 2009). Apart from C. arabica, caffeine is also present in other plants like tea, cocoa, and cola nut (Alagbonsi et al., 2016a). Caffeine, for instance, is known to increase blood glucose (Patil, 2012; Alagbonsi et al., 2016a) while also stimulating the cardiac muscle, central nervous system, and respiratory system (Sati et al., 2023).

Melatonin, a metabolite of serotonin from the primary amino acid precursor tryptophan, is an environment-friendly bioactive molecule with little or no toxic effect on living things, and thus, it is a safe natural dietary supplement (Ruddick et al., 2006). It is a native neuro-hormone synthesized and released into the brain interstitial, cerebrospinal fluid (CSF), and circulation by the pineal gland (Geoffriau et al., 1998), though little is also secreted from the extra-pineal tissues (e,g. eye, intestine, skin, platelet, and bone marrow). It peaks at night under normal environmental conditions, transmits the information about “darkness”, and is suppressed by light (Cheng et al., 2021). Nevertheless, it can also be gotten from external sources as a supplement, either in the form of synthetic melatonin or phytomelatonin derived from vegetables, seeds, fruits, and nuts (Alagbonsi et al., 2016b). It was initially documented to modulate the biological clock and seasonal breeding in living organisms, but further studies have revealed its other pharmacological effects, including antioxidant (Olayaki et al., 2018; Omeiza et al., 2021; Maliki et al., 2021; Nopparat et al., 2017), anti-inflammatory, anxiolytic, anti-depressant, anti-convulsant, and anti-apoptotic activities (Vivien-Roels, 1993).

Melatonin has been identified in various animals and plants. For instance, it has been identified in phototrophic unicell (Gonyaulax polyedra) and many non-vertebrates like crustaceans, mollusks, planarians, cnidarians, and insects (Vivien-Roels, 1993). Its presence in many medicinal herbs and plants has been reported. For instance, it has been identified in C arabica’s bean (6,800 ng/g), C. robusta’s bean (5,800 ng/g), black pepper’s leaf (1,093 ng/g), Wolf berry’s fruit (530 ng/g), white radish’ bulb (485 ng/g), white mustard’s seed (189 ng/g), black mustard’s seed (129 ng/g), curcuma’s root (120 ng/g), almond’s seed (39 ng/g), sunflower’s seed (29 ng/g), cucumber’s seed (11–80 ng/g), strawberry’s fruit (11.3 ng/g), tomato’s fruit (2.5 ng/g), corn’s seed (1.4 ng/g), rice (1 ng/g), just to mention a few among so many plants (Salehi et al., 2019). In plants, it increases the capacity for stress tolerance, serves as a crop bio-stimulating agent and pathogen repeller, and stimulates growth (Salehi et al., 2019). Even though they both have the needed enzymatic systems to synthesize melatonin, its levels in plants are higher than those found in animals. Moreover, plants can synthesize tryptophan (the precursor of melatonin) while animals cannot, as they only rely on food to get this precursor. Thus, tryptophan from plant sources—including coffee—is necessary for the synthesis of melatonin in all animals, including humans. However, there is presently no study that has either confirmed the presence of melatonin in Rwandan coffee or reported its quantity therein.

There have been reports of how caffeine and melatonin differently affect the sleep-wake cycle in humans. For instance, agonists of adenosine receptors elicit an increase in melatonin secretion by causing accumulation of cyclic adenosine monophosphate via activation of the A2 receptor in the pineal gland, while caffeine, being an antagonist of the adenosine receptors, prevents melatonin rise in the pineal gland and reduces sleep quality (Shilo et al., 2002). As both compounds have been reported in coffee samples, it is important to know how altitude affects their concentrations. Moreover, the availability of substandard pharmaceutical products in the markets poses significant risks to public health, as such products often fail to meet required safety and efficacy standards, leading to ineffective treatment and prolonged illness. These substandard products may contain incorrect quantities of bioactive components, resulting in adverse health outcomes, including drug resistance and increased mortality (Haji et al., 2022). As melatonin products are available in the Rwandan market as dietary supplements, there is a need to conduct a quality assurance study to determine if they comply with the United States Pharmacopeia (USP). Presently, there is no clear information on whether the quantities of caffeine and melatonin differ in C. arabica samples sourced from different altitudinal locations, which would guide farmers and consumers about their choice and serve other quality assurance purposes. Thus, this study sought to identify and quantify caffeine and melatonin in C. arabica sourced from different altitudinal locations in Rwanda.

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