Impact of Alkalization on the Antioxidant and Flavanol Content of Commercial Cocoa Powders
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J. Agric. Food Chem. 2008, 56, 8527–8533 8527 Impact of Alkalization on the Antioxidant and Flavanol Content of Commercial Cocoa Powders ,† † † KENNETH B. MILLER,* WILLIAM JEFFERY HURST, MARK J. PAYNE, † † † § DAVID A. STUART, JOAN APGAR, DANIEL S. SWEIGART, AND BOXIN OU Hershey Center for Health and Nutrition, The Hershey Company, 1025 Reese Avenue, Hershey, Pennsylvania 17033, and Brunswick Laboratories, 50 Commerce Way, Norton, Massachusetts 02766 Cocoa is a food ingredient that is important for the contribution of flavor to foods but is also associated with potential health benefits. The chemistry thought to be responsible for its cardiovascular health benefits is the flavanol (flavan-3-ol) antioxidants. Evidence from the literature indicates that natural cocoas are high in flavanols, but when the cocoa is processed with alkali, also known as Dutch processing or Dutching, the flavanols are substantially reduced. This paper provides a survey of the physical and chemical composition of representative natural cocoas and lightly, medium, and heavily alkalized cocoas. As part of the survey, both brown/black and red/brown alkali-processed cocoas were measured. Natural cocoa powders have an extractable pH of 5.3-5.8. Alkalized cocoa powders were grouped into lightly treated (pH 6.50-7.20), medium-treated (pH 7.21-7.60), and heavily treated (pH 7.61 and higher). The natural, nonalkalized powders had the highest ORAC and total polyphenols and flavanols (including procyanidins). These chemical measurements showed a linear decrease as the extractable pH of the cocoa powder increased. Likewise, the flavanol monomers, oligomers, and polymers all showed a linear decrease with increasing pH of the final cocoa powder. When brown/ black cocoa powders were compared to red cocoa powders, similar decreases in flavanols were observed with increased alkalization. The average total flavanol contents were 34.6 ( 6.8 mg/g for the natural cocoas, 13.8 ( 7.3 mg/g for the lightly processed cocoas, 7.8 ( 4.0 mg/g for the medium processed cocoas, and 3.9 ( 1.8 mg/g for the heavily processed cocoa powders. The observed linear and predictable impact of alkalization on flavanol content is discussed with respect to other reports in the literature as well as what implications it may have on diet and food manufacturing. KEYWORDS: Alkalization; Dutching; flavanols; flavan-3-ols; procyanidins; antioxidants; cocoa powder; cacao INTRODUCTION seed is borne in a fleshy, berry-like fruit, also known as the cacao pod (5). Cacao seeds are removed and typically fermented Cocoa powder is an important ingredient in the manufacture - of numerous foods and beverages. Significant quantities of cocoa in heaps or boxes for 4 5 days, dried, and transported to processing facilities, where they are deshelled and roasted at powder are used in the manufacture of chocolate syrups and - ° coatings as well as other nonconfectionery food applications 100 150 C. The roasted cocoa beans are then usually ground such as baking, flavorings in ice cream, icings, and beverages. into a suspension, called cocoa liquor or chocolate liquor, which Cocoa powder represents about 37% of the total U.S. imports contains cocoa butter and nonfat fine, brown particles. Cocoa of cocoa bean-related ingredients that include chocolate liquor, powder is usually made by mechanically pressing the liquor to cocoa butter, chocolate paste, and cocoa powder (1). More than expel most of the cocoa butter, leaving a solid cake, which is 130 million pounds of cocoa powder were consumed in the then ground into the product that most people know as cocoa powder. Typical cocoa powders contain 10-12% residual cocoa United States in 2004 (2). The remaining cocoa bean-derived s ingredients, mainly chocolate liquor and cocoa butter, go into butter, with the remainder being nonfat cocoa solids the brown the manufacture of chocolate candy (3, 4). These ingredients particulate matter of the seed (3, 4). The cocoa powder is where the vast majority of the chocolate flavor and the polyphenol are all products of the cocoa bean, which is botanically the seed - of the fruit of the cacao tree, Theobroma cacao L. The cacao antioxidants reside (6 8). Cocoa nibs, chocolate liquor, and cocoa powder can be modified by a 180-year-old process of treatment with alkali, * Corresponding author [e-mail [email protected]; telephone (717) 534-5233; fax (717) 534-5076]. also known as Dutching (3, 4). This process darkens the cocoa † The Hershey Co. ingredients, changes the taste by reducing bitterness, and § Brunswick Laboratories. increases the dispersability of cocoa powder for various 10.1021/jf801670p CCC: $40.75 2008 American Chemical Society Published on Web 08/19/2008 8528 J. Agric. Food Chem., Vol. 56, No. 18, 2008 Miller et al. applications such as beverages. By far most of the alkali- Table 1. Sources of the Cocoa Powders Used in This Survey treated powders are used in nonconfectionery applications. Alkalized cocoa powder and alkalized liquor are not com- manufacturer product code product name category monly used as major ingredients in the manufacture of Blommer 7-15-06 Natural natural chocolate confectionery (3, 9, 10), although there are several Blommer 7-15-06 Navajo alkalized ECOM-AMSA AMSA-201005 AMSA Natural natural large brands of dark chocolate in the United States that use DeZaan 7-15-06 D-11-R alkalized these ingredients (11). DeZaan 7-15-06 D-11-B alkalized Cocoa and dark chocolate increasingly have been associated Gerkens-Brazil NA-54 Bamboo natural with cardiovascular health benefits. These include increasing Gerkens-Brazil AL-70 Impact alkalized 12 13 Gerkens-Brazil RA-74 Bronze alkalized vasodilation ( ) and coronary arterial output ( ) as well as Gerkens-Brazil RE-78 Marquise alkalized decreasing blood pressure (14, 15) and platelet aggregation (16). Gerkens-Brazil BL-80 Midnight alkalized These combined effects, along with epidemiological studies that Gerkens-Holland DP-70 Russet alkalized show lowering of blood pressure (17) and decreases in mortality Hershey 2006 Hershey Regular natural due to cardiovascular disease (17, 18), suggest that cocoa powder Hershey 2006 Hershey Special Dark alkalized J. B. Cocoa ZMC-100 Zamacon Natural natural and dark chocolate are associated with heart and circulatory J. B. Cocoa ZMC-250 Zamacon Brown alkalized benefits. These benefits are thought to be conferred, in part, by J. B. Cocoa ZMC-360 Zamacon Red/Brown alkalized the flavanol antioxidants found in cocoa (19, 20). J. B. Cocoa ZMC-530 Zamacon Dark Red alkalized The central issue with the use of alkalinized or Dutch J. B. Cocoa ZMC-800 Zamacon Dark Brown alkalized processed ingredients is that phytonutrients, in particular J. B. Cocoa ZMC-550 Zamacon Dark Red alkalized J. B. Cocoa ZMC-900 Zamacon Black alkalized polyphenol and flavanols, may be modified or destroyed at alkaline pH. In 1961, Robinson et al. (21) reported that alkalizing cocoa caused a shift in the ultraviolet spectrum of the sample the set of alkalized cocoa powders was purposely chosen to contain not seen when a similar cocoa sample was roasted without examples of both brown/black and red cocoa powders to assess the alkalization. A U.S. patent (22) showed that an alkali-treated impact of these different processing steps on the antioxidant chemistries cocoa powder lost 81% of the amount of total procyanidins measured. All powders were analyzed for percent fat, color, pH, total compared to a cocoa powder that had not been alkali treated. polyphenols, antioxidant capacity (ORAC), flavanol monomers (cat- In 2006, Gu et al. (7) compared three commercially available echin and epicatechin), and flavanol polymers (procyanidins). The natural cocoa powders to two commercially available alkalized measured pH of the cocoa powders was used as a guide for the degree cocoa powders, which had 78% less flavanols. A recent Spanish of alkalization. paper (23) describes decreases in epicatechin and catechin of Fat, Color, and pH Analyses. Total fat of the cocoa powders was 67 and 38%, respectively, as a result of the alkalization of cocoa determined by Soxhlet extraction (25). The color of the cocoa powder powders. Finally, in a study simulating the alkaline conditions samples was determined using a Hunter Tristimulus Colorimeter, model of the lower gut, Zhu et al. (24) showed that catechin, D25L DP-9000 unit (Reston, VA), equipped with a standard area 3.5 in. diameter viewing port. Fifteen grams of cocoa powder were placed epicatechin, or procyanidin dimers were degraded by 85% at in a glass sample cup for color measurement. Color was measured on pH 7.4 after 24 h and by 100% at pH 9.0 after 4 h. Despite three scales: the Hunter L scale measures degree of lightness (100 ) these reports that alkali processing destroys flavanols, very few light to 0 ) black), the Hunter a scale measures red to green with true data exist on the detailed flavanol content of commercial cocoa red equal to +100 and true green equal to -100, and the Hunter b powders. scale measures yellow to blue with true yellow equal to +100 and true The objective of this study is to determine the effect of blue equal to -100. The extractable pH of the cocoa powders was varying degrees of alkali processing on the physical and determined by suspending 1 part powder in 9 parts deionized water at chemical characteristics of commercially available cocoa pow- room temperature and measuring with an Orion pH (Orion Research, ders. Color and extractable pH are measured as well as Inc., Cambridge, MA) calibrated at pH 4 and 10 on the day of use. antioxidant, polyphenol, and flavanol contents, including the Antioxidant Capacity Analysis. Cocoa powder samples were flavanol polymers (i.e., procyanidins). Total polyphenols refer analyzed in duplicate for antioxidant activity using oxygen radical absorbance capacity (ORAC), a widely used fluorescent method for to a very broad class of compounds found in all plants, assessing antioxidant capacity in biological samples.