Extraction, Isolation, and TEMPO-NaBr Oxidation Modification of Cellulose from Coffee Grounds

Coffee is one of the most widely consumed beverages in the world. It is grown in more than 70 countries, with Brazil and Colombia being the two leading global producers. The average coffee consumer drinks three cups per day. Contrary to common belief, coffee contains vitamins and minerals, as well as antioxidant compounds such as caffeic acid, chlorogenic acid, and other phenolic acids, including lignans, which are converted into enterolignans by intestinal bacteria before entering the bloodstream. Lignans act as antioxidants and are thought to be associated with a reduced risk of cardiovascular diseases and certain cancers in humans. Coffee also contains diterpenoid alcohols, such as cafestol and kahweol, carbohydrates, including approximately 30% polysaccharides (both soluble and insoluble), and sugars like arabinose, fructose, glucose, and sucrose. It also contains proteins (around 10%), water, and cellulose, which is its most abundant structural component. Cellulose is the most abundant material on Earth, and its interest and applications in various fields drive its extraction. These include native cellulose (cotton), the transformation of cellulose into sheets (paper and filter paper), cupric cellulose, zinc cellulose (industrial applications), and the functionalization of cellulosic materials in the fields of printed electronics, textiles, processing, medicine, and the food industry. The objective of this study is the extraction of cellulose in multiple stages from coffee grounds and its valorization through oxidation using the TEMPO oxidant. The oxidation targets the alcohol groups in the cellulose contained within the carbohydrates. The main goal is to convert the hy-droxyl groups into carboxyl groups (-COOH) or to introduce other oxygenated functionalities onto the cellulose chain. This approach has attracted considerable interest in recent years, partly due to the interesting characteristics of these oxidized polysaccharides, as well as the potential to further chemically modify the oxidized polysaccharide substrate using a wide range of products, including esterifications and amidations. The aim is to chemically modify cellulose, starting with oxidation and followed by amidation of the carboxyl groups thus formed.