Cocoa By-Products as Functional Ingredients in Food: Composition, Emerging Extraction Technologies, Food Applications and Challenges of the Circular Economy

Cocoa processing generates large amounts of agro-industrial by-products, mainly cocoa bean shells (CBS), cocoa pod husks (CPH), and cocoa mucilage, which remain underutilized despite their nutritional and bioactive potential. This narrative review critically analyzes the composition of cocoa by-products and emerging technologies for bioactive compound recovery. Results show that CBS and CPH are rich sources of dietary fiber (13.8–65.6%), phenolic compounds (up to 100 mg GAE/g), and methylxanthines (theobromine up to 11.6 mg/g in CBS). Emerging extraction technologies, ultrasound-assisted extraction, pressurized liquid extraction, microwave-assisted extraction, pulsed electric fields, and cold atmospheric plasma, improve extraction yield (20–150%), reduce processing time (from hours to minutes), and decrease solvent consumption compared to conventional methods. Regarding food applications, moderate CBS inclusion levels (10–20% in cookies, 2–8% in bread, 0.75–1.0% in sausages) improve dietary fiber and antioxidant capacity without compromising sensory acceptability, whereas higher levels (>20–30%) increase hardness, bitterness, and astringency. It is concluded that cocoa by-products are promising resources for sustainable functional food ingredients. However, industrial implementation remains limited by raw material variability, lack of standardized extraction protocols, sensory constraints, and insufficient biological validation of recovered compounds. Future research should focus on standardizing extraction protocols, validating bioaccessibility and bioactivity through in vivo studies, optimizing food formulations for sensory balance, assessing contaminants (heavy metals, mycotoxins), and evaluating techno-economic feasibility and life-cycle sustainability at industrial scale.