Serotonin content in fresh and processed tomatoes and its accumulation during fruit development

- Serotonin has anti-obesity effects in the peripheral system.
- Serotonin content was very low in processed tomato products.
- Serotonin accumulated in all fruit tissues during tomato fruit development.
- A tryptophan decarboxylase (SlTDC1) might play an important role in the accumulation.
- Fresh tomatoes are a promising serotonin source.

Serotonin is an aromatic amine neurotransmitter in the central nervous system; however, approximately 98% of serotonin is synthesized and stored in the peripheral system. We analyzed tomatoes (Solanum lycopersicum), which are relatively rich in serotonin, because serotonin has been found to have anti-obesity effects in the peripheral system. Serotonin content was very low in processed tomato products, whereas fresh tomatoes were much richer in serotonin. Serotonin content increased in all fruit tissues during tomato fruit development, reaching maximum levels at the ripe stage. Differences in serotonin content were relatively small among fruit tissues at the ripe stage. During storage, serotonin content did not decrease at either room temperature or at the lower temperature (4° C). Sequence and expression analyses were performed for tryptophan decarboxylase (TDC) and tryptamine 5-hydroxylase (T5H) genes, which could be related to the serotonin biosynthesis pathway from tryptophan. As a result, expression of SlTDC1, one of the tomato putative TDC family genes, and SlT5H, the tomato putative T5H homolog, likely corresponds to an increase in serotonin content during fruit development. The results suggest that fresh tomatoes are a promising source of serotonin, and SlTDC1 and SlT5H might be involved in physiological mechanisms of serotonin accumulation.