Utilisation of yoghurt bacteria and probiotic combination enhanced melatonin content and antioxidant activity of yoghurt

Melatonin and its derivatives positively influence human circadian rhythms. Yoghurt is often suggested as a bedtime food because it contains tryptophan which can be converted to melatonin. However, the impact of yoghurt bacteria (YC) and probiotics on producing melatonin and its derivative content in yoghurt during fermentation has not yet been reported. Therefore, the present work investigated the effect of YC and probiotics on enhancing tryptophan, serotonin, and melatonin during yoghurt fermentation. Cow milk yoghurt was prepared using different combinations of YC (Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus, MP-YC, control); YC and Lactobacillus acidophilus and Bifidobacterium animalis subsp. lactis (MP-BY); S. thermophiles, L. acidophilus, and B. animalis subsp. lactis (MP-BT); and YC with L. acidophilus (MP-LA). Combining YC and probiotic mixtures had no impact on pH and total acidity after fermentation for 8 h. Yoghurt containing probiotics and YC had higher melatonin content ranging from 3.54 to 6.67 ng/g dry weight than the control, whereas serotonin was not detected. Tryptophan content significantly improved in all yoghurt samples ranging between 8.52 and 10.17 µg/g. The antioxidant activity of MP-BY and MP-BT was significantly enhanced compared with the control. The findings suggested a synergistic effect between YC and probiotics, highlighting the potential of probiotic yoghurt as a functional food rich in melatonin, tryptophan, and antioxidants, which could benefit and support human circadian rhythms and overall health.