You walk into the grocery store, head to the baking aisle, and grab a tin of cocoa off the shelf. But before you toss the container into your grocery cart, do you check to see what kind of cocoa it is? To the average home baker, one cocoa powder may seem the same as the next. But in reality, differences among cocoa powders exist and they have important implications, both to the characteristics of the chocolate-flavored products they are used to create and to the health of the individuals that eat those products.
One cause for differentiation among cocoa powders is the presence or absence of an alkalization step during the manufacture of cocoa powder. The optional alkalization step involves exposing the cocoa mixture to a high-pH substance to take away the natural acidity of the cocoa (Gu and others 2006). Cocoa powders that have undergone this process are referred to as alkalized or Dutch-processed cocoas and are the most common type found on Canadian grocery store shelves.
The alkali treatment is used to modify the cocoa powder's color and flavor (Zoumas and others 2002). The characteristic color of cocoa powder is primarily caused by the action of an enzyme present in the cocoa called polyphenol oxidase, which facilitates the reaction of polyphenols in cocoa powder to produce pigment precursors (Parkin 2008; Rodriguez and others 2009). These precursors then react to form larger, brown pigment molecules (Parkin 2008). As the pH increases as a result of the alkalization process, polyphenol oxidase is able to act more effectively, causing light brown cocoa powder to darken and turn a reddish-brown color (Rodriguez and others 2009). At even higher pHs, the cocoa powder becomes black, taking on the distinctive color of Oreo cookies (Rodriguez and others 2009). Certain attributes of the flavor and mouthfeel of cocoa powder are also related to the cocoa's polyphenol content, particularly the properties of bitterness and astringency (Misnawi and others 2004). Because polyphenols are unstable under neutral and alkaline conditions, a reduction in these sensory properties is noted when the cocoa is processed with alkali (Noor-Soffalina and others 2009; Rodriguez and others 2009). As would be expected, a reduction in the acidic flavor note also occurs with alkalization (Afoakwa 2010).
Several functional aspects of the cocoa are also affected by alkalization. The dispersability of the cocoa powder is increased, such that it is easier to mix it into a liquid (Tannenbaum 2004). This may be due to an increase in the porosity of the cocoa that occurs as an indirect effect of the alkalization process (Belitz and others 2009). The change in the pH of the cocoa powder can also have a direct effect on baked goods. Since natural cocoa is acidic, it can be used in combination with baking soda, which is alkaline, to produce carbon dioxide gas in order to cause baked goods to rise. However, if alkalized cocoa is substituted for natural cocoa in a recipe, another source of acid would have to be added in order to produce this effect.
Consumption of cocoa has been found to have a beneficial effect on human health (Gu and others 2006). Flavanoids, a type of polyphenols found in the cocoa, have been associated with cardioprotective effects, and these effects have primarily been attributed to the antioxidant capacity of these compounds (Gu and others 2006; Jalil and Ismail 2008). Antioxidants are substances that help prevent unstable molecules called free radicals from damaging cells in the body (U.S. Dept. of Health and Human Services 2004; Gu and others 2006). For example, consumption of cocoa flavanoids may decrease the risk of atherosclerosis by reacting with free radicals, thereby eliminating the opportunity for the free radicals to modify low-density lipoproteins (LDL) (the “bad” cholesterol) in a way that would promote the formation of atherosclerotic build-ups on artery walls (Ariefdjohan and Savaiano 2005). The potential health benefits of cocoa flavanoids can, however, only be seen if these compounds are present in the diet in sufficient amounts (Keen and others 2002). The alkalization step that is used in the processing of some cocoa powders has been found to greatly decrease the amount of flavanoids in the cocoa, with a reported loss as high as 60% (Gu and others 2006; Andres-Lacueva and others 2008). Thus if an equal amount of alkalized and natural cocoa powders were to be consumed, greater health benefit would be exerted by the natural cocoa.
Before reaching for a tin of cocoa of the grocery store shelf, think about why you want cocoa. If you are looking for a mild flavor and deep rich color, choose an alkalized cocoa powder. But if you are picking up the cocoa because you heard that it is good for you and may help prevent cardiovascular disease, look for natural cocoa powders. They can be more difficult to find, but are worth the search.