The Effects of the Alkalization Process on the Quality of Produced Cocoa Powder

Introduction: Cocoa is one of the most important agricultural and economic commodities in the world and that is one of the basic ingredients in the production of chocolate and cocoa powder. Cocoa powder is mainly used in the preparation of beverages and for the confectionary purposes (Aprotosoaie et al., 2016). Cacao beans are wealthy in polyphenols, forming 12-18% of the dry weight of the total bean. Cocoa polyphenols have been associated with flavor, color, and the nutritional value of cocoa products (Niemenak et al., 2006). The alkalization by complex polymerization of polyphenols reduces the astringent and bitterness and produces darker products (Giacometti et al., 2014). Alkalization is one of several routes that may be used by a manufacturer to modify the color of cocoa with different susceptibilities to development of o-quinones and Maillard reactions, especially non-enzymatic brown compounds (Bonvehí , 2005). Researchers reported that the percentage of aromatic and colure materials can be changed by changing the amount of sodium or potassium carbonate used during the alkalization process (Yue et al., 2012). Although polyphenols in cocoa powder develop the specific color of cocoa products through roasting and alkalization, few studies have focused on the relationships among the alkalizing conditions, the color of cocoa products, and the polyphenol content. The objectives of the present study were to determine the alkalization effects. Cocoa powder was treated under different concentrations and types of an alkali solution (sodium hydroxide, potassium carbonate, and ammonium bicarbonate). Then, the influences of performed alkalizing conditions on color, colorimetric fractions, the anthocyanin and polyphenol contents and selected physicochemical properties (such as moisture, ash content, acid-insoluble ash content and pH) of cocoa powder were investigated.
Material and methods: The Cameroon cacao beans (Forastero cultivar, Cameroon) were used in the current study. Drying and fermentation of cacao beans were accomplished in Cameroon conforming to the local practices. Therefore, there is no detailed data related to the quality of these steps. Then Cameroon cacao beans underwent cleaning, drying at 100 °C, shelling and crushing to convert to cocoa nibs and the nibs were alkalized with the solutions of NaOH, K2CO3, and NH4HCO3 at their different concentrations and combinations. The alkalized cocoa nibs were roasted at 130 °C for 20 min. Samples were pulverized in a laboratory mill to obtain the cocoa powders.
Results and discussion: The optimization of the alkalization parameters is commonly considered in the processing of cocoa powder to improve its color and flavor qualities. The pH values were augmented proportionally with increased concentration of alkali. As can be seen, ash and acid-insoluble ash contents increased as levels of alkali were augmented and changed as type of alkali were changed. Different types and concentrations of alkali showed a significant effect (p ≤ 0.01) on the moisture content of the samples. The analysis of variance (ANOVA) showed that the total polyphenol content of the cocoa powders changed significantly (p ≤ 0.01) with changing the type and concentration of alkali solution. The lowest total value of polyphenol of the alkalized samples was observed in the A9 samples with 3% K2CO3 solution. The analysis of variance (ANOVA) showed that the browning index of the cocoa powders was changed significantly (p ≤ 0.01) with the change of the alkali solution type and concentration. The highest value of the browning index was observed in the A7 samples with 1.5% K2CO3 and 0.5% NH4HCO3 solution; It increased from 1.158 for the un alkalized cocoa powder (the A0 sample) to 1.787 for the alkalized cocoa powder (the A7 sample). The lowest value of the browning index of the alkalized samples was observed in the A1 samples with 1% NaOH solution. Cocoa powder alkalized with a 3% (w/w) K2CO3 solution exhibited a darker color and had a higher OD460/OD525 value than that alkalized with a 3% (w/w) NaOH solution. All alkalized samples had lower ratios of monomer anthocyanins to yellow/brown polymer content than the sample without alkalization, suggesting that more anthocyanins changed into brown polymers, compared to the no alkalized cocoa powder. The OD460/OD525 values (the browning index) for the alkalized samples were higher than those for the non-alkalized samples. The values of the browning index (OD460/OD525) were negatively correlated with the total polyphenol content, indicating that a darker color was related to lower total polyphenol content. Thus, less astringent taste and darker cocoa powder were associated with a decreased polyphenol content. Cocoa powders displayed darker colors when a K2CO3 solution was used, while they exhibited very darker colors when an NH4HCO3 solution with other alkali solutions (such as K2CO3 and NaOH solutions) were used for alkalization. In this study, the range of F1/F3 values of the cocoa powders was lower at 0.33. The values of F1/F3 for cocoa powders were changed significantly (p ≤ 0.01) with changing the alkali solution type. All alkalized samples had lower ratios of monomer anthocyanins to yellow/brown polymer content than the sample without alkalization, suggesting that more anthocyanins were changed into brown polymers, compared to the no alkalized cocoa powder. Alkalization with a combination of NH4HCO3 solution and NaOH or K2CO3 solution produced lower F1/F3 values than other alkali solutions.
Conclusions: The formation of color compounds during the Maillard reaction depended on the time and temperature of the roasting stage and the pH of alkalization stage; therefore, the color properties of cocoa powder could be modified by improving alkalization parameters. The cocoa powder alkalized under different types and concentrations of alkali was studied for its color, color fractions, polyphenol content and qualities. Alkalization increased the browning index (OD460/OD525 value), while it decreased the value of F1/F3 of cocoa powder. The alkalized cocoa powders displayed darker color than the non-alkalized cocoa powders. The alkalization process affected the moisture, total polyphenol, ash, acid-insoluble ash contents and pH. It was also observed that the combination of alkali type and concentration affected the studied parameters. The A4 alkalized sample with combination of 1% NaOH solution and 1% K2CO3 solution had a high content of polyphenol and a low content of ash and moisture, which could be considered as a fine sample, compared to other alkalized powders. Furthermore, among the studied alkalized powders, A6 (alkalization with a combination of NaOH and NH4HCO3 solutions) and A7 (alkalization with a combination of K2CO3 and NH4HCO3 solutions) displayed better color property (high browning index and low value of F1/F3).