Description
Author: Alan McClure
University of Missouri
PMCA Grant In Aid Recipient 2018-2019
Chocolate is made from the fermented, dried, and roasted seeds of the Theobroma cacao tree, an important agricultural food crop which contains bioactive flavonoid polyphenols with beneficial health effects. These include improvement of antioxidant status, positive impacts on cardiovascular health and endocrine system function, association with cancer prevention, LDL cholesterol reduction, and correlation with reduction of obesity and related conditions. However, products which have the highest levels of cacao flavonoids of all eating-chocolate, such as high-cacao-percentage dark chocolate, are known to be quite bitter, a taste modality that is not readily appreciated by consumers. Though the complex causes of bitterness in cacao are still not completely understood, it has long been known that the methylxanthines theobromine and caffeine impart bitterness, as do certain flavan-3-ols, sometimes called catechins, which are a class of the aforementioned healthy bioactive polyphenolic flavonoids, also found in tea. Yet, what else is known of bitterness in cacao is sparse and even contradictory. Work on cacao bitterness has described the importance of cyclic dipeptides called 2,5-diketopiperazines (DKPs), while suggesting some form of interaction between theobromine and DKPs as well. Yet these earlier assertions have only been confirmed with mixed results by others, in part due to the incredible complexity of bitterness in general and in roasted cacao specifically, which has been said to require further sensory evaluation. More recent work on bitterness in cacao suggested for the first time that a DKP called cyclo(Pro-Val) is the most important bitter compound. However, even while seeming to confirm the importance of previously known important bitter compound classes, this research was based upon only a single cacao sample from a single origin of cacao, and with an undefined roasting treatment, even though previous work had noted that differences in DKP formation are dependent upon roast profile. Additionally, sensory work was based in part on recombinants of bitter compounds in aqueous solution, allowing for potentially biased estimation of the contribution of the different compounds to finished chocolate bitterness, since the varying kinetics of dissolution of the diverse bitter
