# Optimized Isolation Procedure for the Extraction of Bioactive Compounds from Spent Coffee Grounds
## 1 Introduction  
One of the major global problems is food waste. Food waste currently totals 1.3 billion tons annually, and it is predicted that in less than 10 years it will increase to two billion tons annually. It is also important that huge amounts of water are consumed for the production of these foods. Given that in the European Union alone, 50% of irrigated water is used for food production, this ecological problem has also economic ramifications [1]. After the COVID-19 pandemic, consumers have acquired a completely different perspective on food choices, causing a total transformation in the food industry. More specifically, they have now turned their interest to organic products of local origin, while the bioavailability of bioactive compounds is also taken under consideration [2]. Due to the above reasons, more and more scientists are investigating food by-products to reuse them in the best possible way, ensuring a kind of circular economy. For instance, in this context, many researchers use various by-products for the re-production of food, in the pharmacological field, and in the livestock industry [3, 4]. [PERSON] et al. [5] reported that hydroxytyrosol, a polyphenol of high added value, can be isolated from olive mill wastewater and used as a functional ingredient in bread. Coffee is the food product that has the largest consumption worldwide and is the second largest commercial product after petroleum [6]. The global coffee consumption ranged between 9.1 and 9.4 million tons between 2015 and 2017. It may be made and served in a variety of ways, has an intense dark color, and is bitter and slightly acidic. All coffee plants belong to the _Rubiaceae_ family. Today, coffee plants are grown in more than70 countries, in America, Brazil, Southeast Asia, the Indian subcontinent, and Africa, with Brazil producing nearly 35% of the world production [7]. Today, the two most commercial species mainly cultivated are _Coffea canophora_ (mainly a form known as \"robusta\") and _C. arabica_, and the less popular species are _C. liberica_, _C. stenophylla_, _C. mauritiana_, and _C. racemosa_. Millions of tons of waste are produced and discarded annually, with the roasting process as well as the brewing process resulting in vast amounts of spent coffee grounds (SCGs) [8]. One of the existing uses of these by-products is the creation of poultry feed and the manufacture of paper and biocomposites, using it as a raw material [9], but [PERSON] et al. [10] argued that this coffee waste, due to its rich content of tannins and caffeine, could pose a potential environmental hazard if disposed of incorrectly. This means that the further study of coffee by-products is imperative to develop new, alternative uses, so as to avoid an improper disposal and enhance the circular economy. Coffee is widely consumed due to its cognitive effects, causing increased alertness and wakefulness among others [11]. This effect is caused by the caffeine present in the beverage. Due to its effects, caffeine-containing beverages and energy drinks are also widely consumed [12]. Such drinks contain plant extracts as a source of caffeine. However, in order to cover the increasing demand for caffeine, synthetic caffeine is being produced at an industrial scale and added to beverages. The synthesis of caffeine includes many laborious steps such as the methylation of theobromine under various conditions [13]. However, the cost of such synthesis may increase, and the extraction of caffeine from renewable plant sources could be a more economical option. SCGs are a good source of caffeine, as reported in previous studies [14; 15], and as such, have the potential to be used as a renewable source of caffeine. Aside from caffeine, SCGs contain also other bioactive compounds such as polyphenols, which are well known for their antioxidant properties [16; 17].