## 3 Biorefinery Strategies for Upcycling Coffee By-Products
### Biorefinery and Coffee By-Products for Bioactive Food Ingredients Production
#### 3.2.2 Mucilage  
The coffee mucilage, a by-product of coffee processing, holds promise for various applications in the food industry. It contains valuable nutrients, including protein, carbohydrates, fiber, fat, and potassium, which can be utilized in flour, baking mixes, nutritional supplements, and nutraceuticalals [121]. The fermentation of the coffee mucilage involves microorganisms such as yeasts and lactic acid bacteria, which contribute to the breakdown of mucilage and the creation of flavor-active components. These components find use in food additives, flavorings, and extracts [53]. Additionally, the extraction of simple sugars from the coffee mucilage can serve as a substrate for anaerobic digestion, enabling the production of methane and bioethanol [122; 123]. Fermentation of coffee mucilage can also yield ethanol, which finds application as a biofuel or in beverage production [123; 124]. The microbial community involved in coffee mucilage fermentation significantly influences the process and impacts the final product quality [125]. The introduction of yeasts in the fermentation process has been found to enhance coffee quality [54]. Furthermore, coffee mucilage fermentation involves microorganisms that play a crucial role in mucilage degradation and the generation of flavor-active components [52]. Research has investigated the fate of nucilge cell wall polysaccharides during coffee fermentation, revealing high levels of uronic acids in crude pectic substances [126]. The microbial utilization of the nucilge as a growth substrate results in the production of secondary metabolites, including organic acids, alcohols, esters, ketones, and aldehydes, which can affect the fermentation's impact on the final product quality [31]. Moreover, the coffee nucilge exhibits functional and technological properties suitable for producing bioplastics in the food industry [127]. However, it is important to note that the substantial waste generated by the coffee industry can pose environmental risks [123].  
In addition to its potential environmental impact, the coffee nucilge presents an opportunity for extracting bioactive compounds for use in food applications. The nucilge extract and flour derived from coffee fruits contain phenolic compounds, antioxidants, caffeine, lipidic compounds, dietary fiber, proteins, and peptides, as well as aromatic and volatile compounds [24]. By utilizing waste products like the coffee nucilage, bioactive molecules can be produced for pharmaceutical, cosmetic, food, and non-food applications [24]. Furthermore, coffee nucilage exhibits industrial potential, with studies highlighting its value as a source of raw pectins, antioxidants, and flavonoids [24]. Recent findings have demonstrated the inhibitory effect of coffee nucilage extracts on certain Gram-positive bacteria, although the specific compounds responsible for this activity remain unknown. The chemical composition of the nucilge and its potential as a prebiotic that impacts gut microbiota are areas that require further exploration [25]. Additionally, the potential of the total nucilage, including cellulose, as a thickener or in other applications warrants further investigation [128].