Integrated analysis of phytomelatonin and related indoleamine accumulation in germinated rice: Effects of cultivar, germination stage, and grain fraction

Phytomelatonin is widely used for sleep regulation and antioxidant applications; however, its commercial production relies mainly on chemical synthesis, raising sustainability concerns. This study evaluated germination as a cost-effective bioprocess to enhance phytomelatonin and related indoleamines in rice. Five cultivars were germinated for up to four days, and phytomelatonin, serotonin, and free tryptophan were quantified by LC–MS/MS across grain fractions. Germination significantly increased phytomelatonin in all cultivars, with the highest levels observed in pigmented rice, particularly red rice and black glutinous rice (up to 676.9–681.8 ng/g). Serotonin increased during early germination, while free tryptophan markedly increased, indicating enhanced proteolysis and precursor availability. The germ and bran fractions were identified as major phytomelatonin reservoirs. In red rice, germination also increased α-amylase activity and induced structural changes in starch. Overall, germination enhances indoleamine accumulation and functional properties, supporting the development of phytomelatonin-enriched rice for sustainable functional food applications. • Germination significantly increases phytomelatonin, serotonin, and tryptophan in rice. • LC–MS/MS reveals cultivar-dependent induction of indoleamine biosynthesis. • Bran and germ are the primary reservoirs of melatonin and its precursors. • Pigmented rice, especially red rice, shows superior phytomelatonin enrichment. • Short-term germination offers a scalable strategy for functional rice products.