Cocoa is alkalised during the manufacturing process to make it easier to mix and digest.
Alkalisation can also be applied to change the colour of the product.
The health benefits of antioxidant-rich chocolate such as improvements to cardiovascular health have received much recognition in recent years, with positive findings from a number of studies impacting on consumer awareness.
Chocolate manufacturers are using high cocoa content (over 70 per cent) as a means of differentiation, and cocoa has also received attention for its potential in functional food applications.
However, the cocoa content does not necessarily mean that the flavonol content is high, as new research published in the Journal of Agricultural and Food Chemistry found that alkalising has negative impacts on the flavonol levels.
"The large decrease found in the flavonoid content of natural cocoa powder, together with the observed change in the monomeric flavanol profile that results from the alkalisation treatment, could affect the antioxidant properties and the polyphenol bioavailability of cocoa powder products," said the study's authors.
The study Major brands of cocoa powder products present in the Spanish market were analysed for monomeric flavanols (epicatechin and catechin) and flavanols (quercetin and quercetin-3-glucuronide, -glucoside and -arabinoside).
Researchers found that epicatechin was in the range of 116-730 micrograms per gram and catechin was in the range of 81-447 micrograms per gram.
Among flavanols, quercetin-3-arabionside and isoquercitrin were the major flavanols in the cocoa powder (2-40 micrograms and 4-43 micrograms respectively).
The researchers said this was the first time quantitative data of individual flavanol derivatives in cocoa powder products.
They added: "This data is very useful for the calculation of daily flavanoid intake and its correlation with disease incidence or early markers in epidemiologic and clinical studies."
To measure the effect of the manufacturing process, 10 batches of natural cocoa powder were submitted to alkalisation up to pH 7.2.
The alkalisation treatment resulted in 60 per cent loss of the mean total flavanoid content.
Among flavanols, epicatechin presented a larger decline (67 per cent as a mean percentage difference) and in the case of flavanols, quercetin presented the highest loss (86 per cent).
"Considering that cocoa powder products have a lower level of saturated fats than chocolate bars, it seems necessary to establish a compromise between colour and phenolic content, especially for cocoa powder products derived from alkalised cocoa powder," said the study's authors.
Increasing flavanols in cocoa products Manufacturers wishing to tap in to the 'healthy' chocolate market are aware of the detrimental effects of processing on the final flavonol content of their products, and this has led to the development of new processing techniques.
Confectionary giant Mars, for example, has been pro-active in research into the potential health benefits of flavanols from cocoa and has been sponsoring researchers in Germany and the US for about 15 years.
Other companies targeting this market include Barry Callebaut, with its Acticoa range, which boasts high polyphenol content and are marketed as healthy options.
Spanish firm Natraceutical has also made inroads into the market, but has been the subject to legal challenges from Mars regarding alleged patent infringements.
Similarly, US chocolate manufacturer Hershey increased its health-boosting chocolate range last year with Antioxidant Milk Chocolate and Whole Bean Chocolate.
Hershey's goodness portfolio also consists of the Extra dark chocolate range - with a 60 per cent cacao content - and Hershey's Sticks which contain 60 calories per bar.
Sources Journal of Agricultural and Food Chemistry Published online ahead of print April 2008, doi: 10.1021/jf0728754 "Flavanol and Flavanol Contents of Cocoa Powder Products: Influence of the Manufacturing Process" Authors: C Andres-Lacueva, M Monagas, N Khan, M Izquierdo-Pulido, M Urpi-Sarda, J Permanyer and R M Lamuela-Raverntos