Some foods make us feel good, which is why we cannot stop eating when we have had enough.
Scientists call this hedonic hunger - the drive to eat for pleasure rather than to satisfy an actual biological need.
Researchers from the Friedrich-Alexander-Universitat Erlangen-Nurnberg (FAU) in Germany investigated whether there are special substances in foods that activate the dopamine D2 receptor in the same way as dopamine.
The team used a virtual screening approach - a process that analyses food components in a computer simulation rather than in the laboratory.
The scientists set up a database of 13,000 molecules which are present in foods to find those molecules that fit the dopamine D2 receptor.
The system was then used to identify which molecules could interact with the dopamine D2 receptor; these might be present in synthetic substances already known to interact with the receptor, such as medicines for treating Parkinson's and schizophrenia, or which might be candidates for interaction due to the three-dimensional structure of the receptor.
In the end, 17 of the original 13,000 options were selected and these were analysed in the laboratory.
The most promising results were obtained for hordenine, a substance present in malted barley and beer.
"It came as a bit of surprise that a substance in beer activates the dopamine D2 receptor, especially as we were not specifically looking at stimulant foodstuffs," said Monika Pischetsrieder, professor at FAU.
Just like dopamine, hordenine stimulates the dopamine D2 receptor, however it uses a different signalling pathway.
In contrast with dopamine, hordenine activates the receptor solely through G proteins, potentially leading to a more prolonged effect on the reward centre of the brain.
The team is now investigating whether hordenine levels in beer are sufficient to have a significant effect on the reward centre.
The results indicate that hordenine may well contribute to the mood-boosting effect of beer.