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Spent coffee grounds (SCG) are an essential by-product of coffee beverage production. Containing low molecular weight bioactive compounds with potential health benefits when consumed regularly, SCG is one of the main byproducts of making coffee beverages.
SCG could help reduce the 6-8 million tonnes of coffee waste dumped annually into landfill sites, where they undergo slow anaerobic degradation and emit greenhouse gases [1]. SCG are also excellent fertilizers.
1. Caffeine
Caffeine is an alkaloid found in coffee beans (Coffea arabica). This alkaloid acts as an antagonist of adenosine receptors in the brain, stimulating cognitive abilities while decreasing fatigue and increasing alertness. Caffeine can be found anywhere between 0.25-1.4% caffeine per cup of brewed coffee consumed; additionally, it also contains rich amounts of phenolic acids, such as chlorogenic acids, that have been linked to reduced risk of heart disease and cancer.
The amount of coffee powder used when brewing determines its caffeine content, with a ratio of coffee to water also having an impact. Research that compares various brewing methods often reports caffeine concentration per gram of ground beans; instead, studies should consider volumetric calculations of prepared beverages.
Studies have demonstrated the effect of coffee grinding on caffeine content. Studies have shown that coarsely ground beans release more volatile compounds than finely ground ones, while grind sizes can have an enormous effect on extraction kinetics as they contain multiple particle sizes that differ – almost like concrete aggregate. When observed on a nanoscale level, they resemble this material – millimeter-sized particles embedded among smaller fragments, all packed closely together like concrete aggregate.
Studies that use different types of water can have significant impacts on the final caffeine concentration in their last brew. Distilled water without electrolytes tends to accentuate acidity, while soft water with alkaline ions can neutralize it.
Time of brewing is also crucial; longer brew times result in more excellent caffeine content in the final beverage, while shorter ones lower it due to more complete mass transfer steps occurring – studies that don’t account for this often produce inconsistent results.
2. Nutrients
Billions of coffee cups are consumed each day, producing millions of spent coffee grounds (SCG). SCG contains bioactive compounds with potential nutraceutical uses; polyphenols and melanoidins may help prevent metabolic disorders like NAFLD, type 2 diabetes, and cardiovascular disease, while cafestol and kahweol offer antioxidant protection and may protect against cancer [62]
SCG contains essential plant nutrients such as nitrogen, phosphorus, and potassium that provide natural fertilizer when mixed with soil. A 2019 study demonstrated how using coffee grounds improved the nutritional value of lettuce by increasing moisture retention within soil layers to prevent depletion and decreasing weed growth while improving drainage, resulting in healthier root development.
As well as nutrients, SCG also contains organic material, which aids pest control and soil structure, providing carbon-rich sources of matter that promote roots and stem growth. However, its benefits as a natural fertilizer depend on how it is utilized.
SCG should be evenly applied over a planting bed for optimal use. As SCG can alter soil pH levels and increase acidity levels, another source of nitrogen should also be considered when using it as fertilizer.
SCG can act as both a fungicide and improve root growth in coffee plants while suppressing the nematode population at the same time. Furthermore, it may assist with the prevention of diseases like leaf spots and rust on coffee crops.
3. Antioxidants
Not only are roasted coffee beans rich in caffeine, they’re also filled with antioxidants. Primary phenolic antioxidants include chlorogenic acid, caffeic acid, ferulic acid, and n-coumaric acid – three phenolic antioxidants commonly found in raw and various roasted coffee beans; their UV-vis and HPLC analyses revealed that microwave roasting maintained more antioxidant content than convection burning for antioxidant preservation; polyphenol and caffeine content was also measured during these analyses.
Antioxidants are essential because they help stop and slow oxidation reactions that lead to diseases such as cancer, cardiovascular disease, metabolic disorders, and liver problems. Furthermore, antioxidants reduce oxidative stress caused by aging, inflammation, smoking, or taking certain medications; one study from 2021 demonstrated this benefit with regards to coffee drinking; three cups per day decreased heart disease risk by 47% due to caffeine content, diterpene cafestol/kahweol diterpenes as well as polyphenols being key contributors.
Bioactive compounds in spent coffee grounds have been studied as functional food components. Their responses depend on both their dosage and frequency of intake as well as the source of these bioactives.
Spent coffee grounds contain high concentrations of antioxidants that may promote human health and sustainability, making them suitable for making functional drinks to benefit human well-being and the planet alike. Furthermore, their upcycling as feedstock for value-added food additive production reduces the environmental burden caused by coffee waste disposed in landfills.
SCG can be a valuable source of energy and is an ingredient in cosmetics and pharmaceuticals, including skin creams. Studies have demonstrated its antioxidative effects and improved skin elasticity properties, as well as the potential to treat metabolic disorders.
SCG is an organic waste stream with an immense value that can be leveraged into valuable products. Highly accessible, safe, and sustainable byproducts of SCG processing can be utilized in functional foods and beverages; however, further research must be conducted in order to elucidate how the compounds extracted from SCG contribute to health-related benefits; furthermore, it must address challenges posed by clinical studies using this waste stream such as limited industry funding, unsuitable placebos and maintaining food safety.
4. Fiber
Daily consumption of millions of cups of coffee results in an incredible volume of spent coffee grounds (SCG). SCG can serve as a promising natural source of nutraceuticals with potential benefits to human health, primarily related to gastrointestinal motility. The purpose of this research was to evaluate two SCG-derived by-products suggested as natural sources of dietary fiber on in vivo rat gastrointestinal motility using radiographic methods after intragastric administration of barium as a contrast agent.
Scientists have long recognized that coffee beans contain soluble fiber – the same kind found in oatmeal and apples that helps digestion while at the same time supporting body absorption of nutrients and keeping cholesterol at bay – but it remains unknown whether brewed coffee contains similar amounts. Now, researchers from Spain’s National Research Council have confirmed that coffee does contain some dietary fiber. Fulgencio Saura-Calixto and Elena Diaz-Rubio conducted three separate experiments to examine the amount of soluble fiber present in various coffee types, such as espresso, drip coffee, and freeze-dried. All three coffee types contained a significant amount of soluble fiber – with freeze-dried coffee having the highest content.
Researchers also assessed the effects of melanoidins, compounds produced during the roasting of coffee, on gastrointestinal motility. They discovered that these melanoidins behaved much like dietary fiber in terms of slowing down digestive tract activity and making digestion more straightforward while decreasing bowel movement. Melanoidins also prevent gastric acid secretion of g-amino butyric acid (GABA), which contributes to heartburn, one common side-effect of drinking too much coffee.
Researchers discovered that up to 4% of ground coffee could be added to solid foods like biscuits without adversely impacting quality or taste, according to findings published in Food Chemistry journal. Their sugar-free biscuit prototypes could even make nutritional claims such as “source of dietary fiber”, provided more than 3 grams were present per 100g final product – meeting EU requirements for such claims.
