Tastier and healthier chocolate has been created by scientists by modifying the cocoa bean roasting process. Presenting their findings at the 249th National Meeting & Exposition of the American Chemical Society (ACS), researchers highlighted the many health benefits of chocolate – previous studies have shown how it can lower blood pressure and reduce stroke risk.

However, harnessing the protective properties while retaining – and improving – the flavour has been a challenge.

There are several steps involved in making chocolate. Pods are cut down from cocoa trees then split open to remove the beans. They are fermented in baskets for a few days before being set out to dry in the sun. After this, the beans are roasted. It is at this point that the nutritional antioxidants (polyphenols) are lost.

Emmanuel Ohene Afoakwa, from the University of Ghana, and the team wanted to work out a way to retain both the polyphenols and flavour. To do this, they added a pod-storage step before the beans were fermented.

"This is not traditionally done, and this is what makes our research fundamentally different," he said. "It's also not known how roasting affects polyphenol content."

Three hundred pods were split into four groups. They were stored for different amounts of time (between three and 10 days) after which fermenting and drying were performed as normal. Pods stored for seven days retained the most antioxidant activity after roasting.

Researchers then took samples from each storage group and roasted them at the same temperature for different times. Findings showed a slower roasting at a lower temperature increased the antioxidant activity, compared with beans roasted in the traditional way.

Beans that were stored for seven days then roasted at the optimal temperature and length of time had more polyphenols and higher antioxidant activity than those that were not. Additionally, researchers believe the storage time allows the sweet pulp surrounding the beans inside the pod to alter the biochemical and physical properties, improving the flavour of the beans.

They now plan to study the effects of roasting further to see how different temperature, roasting time and storage periods affect antioxidants.