Development and Multi-Level Characterization of Cocoa-Flavored Tiger Nut Beverages (Horchata): From Physicochemical and Sensory Properties to In Vivo Antioxidant Assessment

Horchata, the traditional tiger nut (Cyperus esculentus L.) beverage from Valencia (Spain), is nutritious and rich in antioxidants, yet its consumption remains largely local and tied to its original flavor. This work explored cocoa as a route to diversify horchata and enhance its functional value: natural and alkaline cocoa powders were added at 0.5–3% to obtain 20 formulations that were characterized in terms of their physicochemical, functional, and sensory properties. Cocoa contributed soluble solids and modified color and pH without altering the beverage’s Newtonian behavior and markedly increased its phenolic content (up to ca. 6-fold) and antioxidant capacity (up to ca. 9-fold) with 3% of natural cocoa. Following a sequential study design, biological activity was first evaluated using concentrations compatible with the C. elegans model and, for the first time, the antioxidant potential of cocoa-flavored horchata was validated in vivo under UV-induced oxidative stress. The cocoa-flavored beverage lowered nematode lethality to a level statistically indistinguishable from the unexposed control, indicating its capacity to alleviate oxidative stress and enhance resistance to an environmental challenge. Subsequently, consumer acceptance was evaluated, revealing high overall acceptance. The 3% natural cocoa beverages received the highest preference scores and exhibited the highest polyphenol contents and antioxidant capacities among the formulations evaluated. Overall, cocoa incorporation effectively modified the physicochemical, functional and sensory characteristics of tiger nut beverages, while selected natural cocoa formulations showed biological activity in the C. elegans model under the experimental conditions evaluated.