## 3 Biorefinery Strategies for Upcycling Coffee By-Products
### Biorefinery and Coffee By-Products for Bioactive Food Ingredients Production
#### 3.2.3. Parchment  
Studies exploring coffee parchment's use as a food ingredient are recent. However, the product's significant health-promoting and technologically appealing features are opening its potential use as an ingredient in the food industry. The optimal conditions yielded high phytochemicals as reported by [PERSON] et al. [14], who found a 2.3% yield and an extract containing high caffeine levels (1.3 mg/g) and a lower concentration of chlorogenic acid (0.14 mg/g). The main phenolic compounds in the coffee parchment are hydroxybenzoic and hydroxycinamic acids (chlorogenic, vanillic, protocatechuic, and \(p\)-cumaric acids) [58]. These compounds are associated with the coffee parchment's in vitro antioxidant and antifungal properties [36; 58]. In addition, the coffee parchment is also a potential source of dietary fiber. The coffee parchment is rich in insoluble dietary fiber (89%), mostly lignin (~30%), xylans (~28%), and cellulose (~10%). In previous studies, the presence of xylans [129], cellulose, and lignin [14] was similarly confirmed. The antioxidant capacity of the dietary fiber compared to the antioxidant potential associated with phenolic compounds was also studied, showing higher dietary fiber antioxidant potential than that of associated phenolic compounds, indicating that cell wall components (mainly lignin and xylans) may also be contributing to the antioxidant properties [19]. The coffee parchment's technological features (water holding capacity, water absorption, swelling capacities, oil holding capacity, and gelation capacities) open the potential for food applications both as physiological and technological ingredients. The main factors influencing hydration properties are the polysaccharide composition and their organization within the cell walls. In general, coffee parchment showed good hydration properties, suggesting that this by-product could be used as a functional ingredient to reduce calories or modify the viscosity and texture of formulated foods. Moreover, hydration properties are also related to some physiological effects such as hypoglycemic and hypolipidemic, exhibiting a potential for glucose adsorption, retarded diffusion, and inhibited \(\alpha\)-amylase, which led to lower starch digestibility. Similarly, the coffee parchment exhibited in vitro hypolipidemic properties, including pancreatic lipase inhibition and cholesterol and bile salts binding [34]. Recent investigations also explored the synthesis of xylo-oligosaccharides from coffee parchment [129]. Xylo-oligosaccharides could be a valuable product since they possess prebiotic features as functional food ingredients with tremendous potential [130]. The aqueous extracts could also be produced if the extracted phytochemicals are economically profitable (nutraceuticaltical or pharmaceutical purposes). Following a biorefinery approach, the water-insoluble residue could also be revalorized as a dietary fiber source exhibiting properties similar to the non-extracted coffee parchment [34]. The main use of the parchment is addressed as a source of antioxidant dietary fiber. Coffee parchment has been added to gluten-free bread (2-4%) [35]. The addition led to increases in dietary fiber, phenolic compounds, and antioxidant capacity without modifying the appearance of the bread and its texture properties. Consumer acceptance studies found that a 4% replacement gave the final product a distinct bitter taste due to the presence of caffeine [35]. The work suggested that a debittering step should be considered to increase the coffee parchment quantity in gluten-free bread in order to enhance its sensory and nutritional properties [35]. Therefore, using the water-insoluble residue from the coffee parchment would allow for producing bread with higher dietary fiber content and maintain its health-promoting properties. Similarly, cookies with 1-5% coffee parchment flour were developed by [PERSON] et al. as a strategy to increase the dietary fiber content and enhance cookies' antioxidant capacity [56].