Enhancement of the concentration of melatonin and its precursors in legume sprouts germinated under salinity stress and evaluation of the feasibility of using legume sprouts to develop melatonin-rich instant beverage

Melatonin is a bioactive indolamine possessing multifunctional properties in humans and plants. Germination conditions under salinity stress were optimized to maximize melatonin, serotonin, tryptophan and total phenolic content (TPC) levels of Vigna angularis to develop melatonin-rich instant beverage from legume sprouts. The effect of stress conditions on these compounds was also evaluated in soybean and chickpea. Optimum germination conditions of V. angularis were investigated using response surface methodology (RSM) under NaCl stress at 9.5–115.5 mmol/L and 14.1–81.9 h. V. angularis germinated under normal conditions (without NaCl) served as the control. Optimum germination conditions obtained were 68 mmol/L NaCl and germination time 72 h, resulting in increase of melatonin, serotonin and TPC in V. angularis sprouts of 47, 37 and 12%, respectively compared with normal condition. These conditions were successfully applied to germinate soybean and chickpea, while improving melatonin and bioactive compounds levels. The three legume sprouts showed high feasibility to formulate melatonin-rich instant beverages with acceptable sensory quality. These findings provide useful information as an alternative approach to enhance the level of health-beneficial compounds in legume sprouts, with potential use as natural sources of melatonin for functional food product development.