theobromine

Theobromine is a component belonging to the methylxanthines (a group of compounds related to caffeine), and it is abundant in cacao beans. Research on roasted cacao nibs has reported that, even after repeated quantitative reconstitution and omission trials—in which the amounts were standardized and reformulated or specific components were removed—theobromine remained a major bitter taste contributor.

However, when cacao liquor samples are compared with each other, the extent to which the amount of theobromine corresponds to the perceived bitterness differs among studies. In one study, a low correlation was observed between bitterness and theobromine and catechin, whereas in another study, theobromine, caffeine, and catechins were reported to correlate strongly with bitterness and astringency in cacao liquor from Mexico's Tabasco State. In research focused on polyphenols, it was polyphenol that showed positive correlation with bitterness; no statement is made regarding correlation or lack thereof with purine alkaloids. This is a discrepancy between studies using different samples and statistical methods, and it cannot be said that one is erroneous.

The link between bitterness and theobromine has also been reported in beverages other than cacao. In research comparing 3 white tea cultivars, integrated analysis of component analysis and taste data identified theobromine, together with a component group of high astringency, as a component showing positive association with bitterness and astringency strength. Additionally, in research comprehensively examining bitter taste receptors in mice, a receptor called Tas2r121 was reported to respond to theobromine at a threshold concentration of 0.03 mmol/L. This is a preliminary value based on a single study and is from a mouse receptor; therefore, the corresponding response in humans or the concentration at which theobromine elicits half of the response is not shown in this study.