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Coffee, alongside cocoa and tea, is one of three most popular beverages. Since the 1600s, coffee has steadily become one of the most consumed drinks globally, second only to oil as a traded commodity [1]. With its immense global production and sales volume, the increasing demand for raw coffee materials has consequently led to a substantial accumulation of coffee grounds as waste. As the global coffee market continues to rapidly expand, the annual production of coffee grounds has now reached millions of tons.
Unfortunately, most coffee grounds ultimately end up in landfills, where they are decomposed by soil microorganisms, which generates methane, a greenhouse gas 25 times more potent than carbon dioxide [2]. Additionally, coffee grounds contain large amounts of organic compounds, such as caffeine, cellulose, and other polysaccharides, which can be converted by soil microorganisms into toxic substances, causing significant environmental risks [3]. Therefore, optimizing the recycling pathways for coffee grounds is a critical step to prevent environmental pollution.
In this context, we aim to develop a novel approach to treat coffee grounds. Through extensive research, we identified a strain of Pseudomonas putida that naturally utilizes caffeine as a carbon and nitrogen source, converting it into a high-value methylxanthine compound: 7-methylxanthine (7-MX). In recent years, 7-MX has gained increasing attention for its potential to effectively prevent and treat myopia. It is one of the few myopia treatment drugs without adverse side effects.
Inspired by this, we seek to use synthetic biology to convert the caffeine in coffee grounds into the valuable compound 7-MX, to achieve an innovative form of coffee ground recycling. This approach not only addresses environmental concerns but also fills a gap in the production of a myopia treatment drug.
Whether it's to shake off afternoon fatigue, stay alert during late-night study sessions, or wake up for an early morning, coffee has become a favored beverage for many of us. Today, it ranks among the top three beverages globally and is a daily staple for numerous people. According to the International Coffee Organization (ICO), global coffee consumption in 2022 reached an astonishing 170.3 million bags, each weighing 60 kilograms [4].
The enormous demand for coffee has driven an increase in the production of its raw materials, resulting in a substantial accumulation of coffee grounds. Current studies estimate that global coffee ground production reaches millions of tons annually [5], a volume equivalent to filling 2 to 3 Bird’s Nest National Stadium in Beijing, which has hosted the Olympic Games in 2008. According to ICO statistics, every ton of processed coffee beans generates about 650 kilograms of coffee grounds, leading to a significant amount of waste each year [6].
Figure 1 Statistics of global coffee bean and coffee ground production from 2014 to 2022
Despite the massive volume of coffee ground waste, its effective recycling and utilization remain limited. Currently, coffee grounds are primarily disposed through incineration, landfill, or repurposing as animal feed and fertilizer.
Here are some of the existing methods for recycling and utilizing coffee grounds [6]:
It is evident that, despite the rapid growth of coffee processing industry, the disposal of coffee grounds remains largely limited to low-tech landfill methods. Coffee grounds contain a high content of organic compounds, such as caffeine, cellulose, and many other polysaccharides. When these compounds are extensively buried in the soil, they can be converted by soil microorganisms into toxic substances, causing significant environmental pollution [3]. Moreover, studies have indicated that when large quantities of coffee grounds are directly landfilled, they can decompose and produce tons of methane, which is a greenhouse gas approximately 25 times more potent than carbon dioxide [7]. In recent years, research into the utilization of coffee grounds has increased alongside technological advances, with the exploration ofvarious applications, such as biocomposting [8] and bioenergy production [9]. However, these studies have largely remained theoretical without practical implementation. Therefore, with millions of tons of coffee grounds being produced annually, developing feasible and practical methods for recycling and reusing this waste is a critical step toward preventing environmental pollution, unlocking the value of waste, and improving resource efficiency.
To address the challenge of coffee ground recycling, we explored the literature and discovered that caffeine, a major component of coffee grounds, can be converted into various methylxanthine compounds. Among them, 7-methylxanthine (7-MX) attracted our attention.
7-MX is a natural metabolite produced by Pseudomonas putida CBB5 during caffeine degradation and has emerged as a novel and promising treatment agent for myopia. It is suitable for all age groups and can be administered orally over a long term to slow down the progression of myopia. As a non-selective adenosine antagonist, 7-MX works by increasing scleral collagen fiber synthesis, thereby thickening the sclera. This process prevents the elongation of the eyeball, and thus effectively prevents and alleviates myopia [10].
Furthermore, 7-MX has negligible toxicity, causes no allergic reactions, possesses good blood-brain barrier permeability, and manifests notable therapeutic efficacy. When administered orally, 7-MX meets nearly all the criteria for an optimal therapeutic agent.
As a key component of emerging health supplements, 7-MX's safety and effectiveness have gained widespread attention. Existing animal studies, toxicological research, and clinical trials have demonstrated its lack of toxicity and side effects, indicating its status as an excellent health supplement with significant benefits for myopia treatment. Patients can use it safely and confidently [10][11].
Current methods for disposing of coffee grounds, whether through landfilling or as animal feed, offer a limited economic value. In contrast, the market price for chemically synthesized pure 7-MX is as high as $525 per gram. Given a daily dosage requirement of 400 mg for optimal myopia treatment, the daily cost per person would be around $210. By using low-cost coffee grounds as a substrate for large-scale production of 7-MX, we aim to significantly reduce the market price through using these lower cost raw materials, thereby making the myopia treatment more affordable.
Moreover, due to its non-toxic nature and notable efficacy, 7-MX is well-suited for the use as a food additive in the health and wellness market. Its primary drawbacks—difficulty in synthesis and high cost—currently limit its wider applications. However, if synthetic biology can solve these challenges, the market potential for 7-MX would expand significantly and can create many economic opportunities.
Thus, our vision is to utilize synthetic biology to convert caffeine in coffee grounds into the valuable compound 7-MX can greatly increase the economic value of coffee by-products.
The improper disposal of coffee grounds not only leads to the emission of greenhouse gases such as methane, which can increase the risk of global warming, but also result in the transformation of organic compounds into toxic substances during the landfill process, causing further environmental pollution. In response to this challenge, we propose an innovative solution: utilizing synthetic biology techniques to convert caffeine in coffee grounds into 7-methylxanthine (7-MX), a compound that has a medicinal value in the prevention and treatment of myopia.
As a non-toxic treatment for myopia, 7-MX presents substantial market potential. We aspire to fill the existing market gap through this innovative technology, offering new hope to worldwide people with myopia. Our vision extends beyond healthcare; we aim to integrate environmental sustainability with health benefits by recycling coffee grounds and transforming them into beneficial compounds. This approach not only reduces environmental pollution but also addresses the market void in the production of drugs for myopia treatment, contributing to sustainable development and improving human health.
This initiative represents not just a commitment to environmental responsibility but also an advancement in human welfare. We believe that through the power of technology, we can transform a seemingly useless byproduct into a high-value resource, making a significant progression in the fields of environmental protection and human health.
We envision a bright future where coffee grounds are no longer an environmental burden but are valuable resources that benefit both the society and environment. We are confident that, through technological innovation, we can realize this vision and contribute to creating a better world.
[1] Murthy, P. S., & Madhava Naidu, M. (2012). Sustainable management of coffee industry by-products and value addition—A review. Resources, Conservation and Recycling, 66, 45–58. https://doi.org/10.1016/j.resconrec.2012.06.005
[2] Kemfert, C., & Schill, W.-P. (2009). Methane: A Neglected Greenhouse Gas. Weekly Report, 5(32), 218–223. https://econpapers.repec.org/article/diwdiwwrp/wr5-32.htm
[3] Dafouz, R., Cáceres, N., Rodríguez-Gil, J. L., Mastroianni, N., López de Alda, M., Barceló, D., de Miguel, Á. G., & Valcárcel, Y. (2018). Does the presence of caffeine in the marine environment represent an environmental risk? A regional and global study. Science of the Total Environment, 615, 632–642. https://doi.org/10.1016/j.scitotenv.2017.09.155
[4] International Coffee Organization |. (2023). Icocoffee.org. https://icocoffee.org
[5] Mussatto, S. I., Carneiro, L. M., Silva, J. P. A., Roberto, I. C., & Teixeira, J. A. (2011). A study on chemical constituents and sugars extraction from spent coffee grounds. Carbohydrate Polymers, 83(2), 368–374. https://doi.org/10.1016/j.carbpol.2010.07.063
[6] McKenna, J. (2018, November 19). Here’s 5 innovative ways your coffee grounds can be recycled. World Economic Forum. https://www.weforum.org/agenda/2018/11/5-surprising-ways-coffee-grounds-can-be-reused/
[7] Kemfert, C., & Schill, W.-P. (2009). Methane: A Neglected Greenhouse Gas. Weekly Report, 5(32), 218–223. https://econpapers.repec.org/article/diwdiwwrp/wr5-32.htm
[8] Sarra Hechmi, Mokhtar Guizani, Amjad Kallel, Rahma Inès Zoghlami, Emna Ben Zrig, Zeineb Louati, Naceur Jedidi, & Ismail Trabelsi. (2023). Impact of raw and pre-treated spent coffee grounds on soil properties and plant growth: a mini-review. 25, 2831–2843, https://doi.org/10.1007/s10098-023-02544-w
[9] Kim, Y., Park, T., & Hong, D. (2021b). Heating and emission characteristics of briquettes developed from spent coffee grounds. Environmental Engineering Research. https://doi.org/10.4491/eer.2021.063
[10] Trier, K., Cui, D., Ribel-Madsen, S., & Guggenheim, J. (2022). Oral administration of caffeine metabolite 7-methylxanthine is associated with slowed myopia progression in Danish children. 27(4): 210063. The British Journal of Ophthalmology, bjophthalmol–2021-320920. https://doi.org/10.1136/bjo-2021-320920
[11] Singh, H., Singh, H., Sahajpal, N. S., Paul, S., Kaur, I., & Jain, S. K. (2020). Sub-chronic and chronic toxicity evaluation of 7-methylxanthine: a new molecule for the treatment of myopia. Drug and Chemical Toxicology, 45, 1383-1394 ,1–12. https://doi.org/10.1080/01480545.2020.1833904
