SpectroscopyNOW.com-Cooking up cocoa: Ammonia analysis

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Solid fermentation

The potent aroma precursors that give cocoa its distinctive smell and flavour are due to fermentation processes. As such quality control relies on the use of analytical techniques to monitor progress. Researchers in France have now developed a near infrared spectroscopic method that is fast and efficient at monitoring release of the ubiquitous ammonia by-product to displace the traditional and time-consuming Conway technique.

Clotilde Hue of Valrhona SA in Tain l'Hermitage, Ziya Gunata of the University of Montpellier, Audrey Bergounhou, Sophie Assemat, Renaud Boulanger and Fabrice  Davrieux of CIRAD in Montpellier and François Xavier Sauvage of INRA also in Montpellier, France, explain how cocoa beans (the fatty seeds of the South American evergreen Theobroma cacao L.) are the starting point for one of the most well-known confections, chocolate, they also represent the source for important favouring ingredients in beverages, confectionery, ice-cream, baked products and other foods. Originally, chocolate beverages were a bitter drink not dissimilar to coffee but to the Western World chocolate is a sweet, fatty product. Almost five million tonnes of cocoa "futures" is traded across the globe annually with Côte d’Ivoire, Ghana and Indonesia the major producing countries.

Purple and brown

The team explains that cocoa bean quality is linked to the cocoa variety, soil, climate, crop management and to post-harvest processing, which involves fermentation and drying. Post-harvest processing plays the biggest role in the development of cocoa flavour but is done almost entirely empirically despite efforts to rationalise the process using analytical tools.

After harvesting, farmers break open cocoa seed pods and pack the extracted seeds in wooden boxes or bags with the pulp from the pods. This mucous-like pulp is four-fifths water, about 11 to 13 percent carbohydrate (mostly glucose and fructose) and contains 0.3% citric acid. The packed material is left to ferment for several days, the pulp draining away leaving behind fermented seeds for further processing. With such a process there is plenty of scope for product inconsistency and no guarantees for any given batch.

The official quality control test simply involves cutting open a sample of 300 dried beans and counting the proportion of purple and brown beans. Some manufacturers use the Conway test. This test dates back to 1933 and apparently quantifies ammonia nitrogen content, which allegedly correlates with quality at the fermentation level. However, there is no evidence for the origins of ammonia and definitive information about the effects of different stages of processing is lacking. It seems clear that a more science-based approach to cocoa bean quality analysis is ripe for adoption by growers and manufacturers as well as food agencies and regulators.

So NIR, so far

The team points out that near-infrared spectroscopy (NIRS) is a now fairly well-established and efficient technique for high-throughput screening of agronomic and agrifood products, allowing chemical characteristics to be revealed objectively. NIRS is rapid, non-destructive and can produce a chemical "fingerprint" for a sample. The team has now tested the approach against a wide variety of samples and correlated this with the established Conway technique.

"We confirm that ammonia is produced during fermentation and the amount depends on the fermentation time, sum of temperatures and geographical origin," the team reports. "NIRS could be used by chocolate manufacturers as a routine method to sort cocoa samples according to their level of fermentation."

"The next step for us is to develop an easy tool (NIR) for the monitoring of fermentation batches available for producers and buyers," Fabrice told SpectroscopyNOW.