Comparison of Physicochemical Properties, Antioxidants, and Aroma Profiles of Water- and Sodium-Hydroxide-Treated Natural Cocoa Powder

Abstract

Cocoa powder alkalization is an essential process in chocolate manufacturing, and traditionally, this process involves the use of alkaline agents, such as sodium hydroxide (NaOH), potassium hydroxide (KOH), and potassium carbonate (K2CO3). However, these methods involve harsh chemicals and energy-intensive procedures, raising significant environmental concerns. Water (H2O) has emerged as a promising alternative due to its safety, minimally harmful byproducts, and accessibility. Green chemistry principles have gained importance across industries, especially in food production, where sustainable practices are highly valued. This study aimed to develop a greener process by investigating the alkalization potential of H2O and comparing the results with those of NaOH. The particle size distribution, pH, color, antioxidant capacity, phenolic composition, and aroma profile of cocoa powders treated with H2O and NaOH were evaluated. The alkalization temperature significantly affected the color of the cocoa powders, and the alkali solution ratio influenced the L* values of H2O-treated powders. In industrial and commercial specifications, an Delta E value below 3 is considered standard for color measurements. Both H2O-treated and NaOH-treated natural cocoa powders had Delta E values exceeding 3 compared to the untreated powder, indicating that H2O treatment darkens the color in a similar way to that of traditional methods. While NaOH produced a darker color, process optimization allowed both H2O and NaOH treatments to achieve similar color attributes (Delta E < 3). Significant differences were observed in the antioxidant capacity and total phenolic content (TPC) between the H2O-treated and NaOH-treated cocoa powders. H2O treatment positively impacted the antioxidative properties of the cocoa powder. The antioxidant capacity, measured by the DPPH and CUPRAC methods, was significantly higher in H2O-treated samples (295.5-317.7 TEAC mg/100 g and 835-1542 TEAC mg/100 g, respectively) compared to NaOH-treated samples (256.6-306.2 TEAC mg/100 g and 171-849 TEAC mg/100 g, respectively). Additionally, the TPC of H2O-treated cocoa powder [281.3-321.6 gallic acid equivalent (GAE) mg/100 g] was significantly higher than that of NaOH-treated powder (100.0-298.6 GAE mg/100 g). The significant differences in the phenolic profiles suggested that the alkalization process affects individual phenolic compounds differently. Moreover, H2O-treated cocoa powders had significantly higher trimethylpyrazine/tetramethylpyrazine (TrMP/TMP) ratios than those of NaOH-treated samples, indicating notable differences in aroma profiles. This study suggests that H2O can replace NaOH in the alkalization process of the cocoa industry, particularly for lightly treated alkalized cocoa powders that maintain high antioxidant activity and TrMP/TMP ratios. This offers a more environmentally friendly, easily manageable, and sustainable process for cocoa powder alkalization.