https://doi.org/10.17113/ftb.63.03.25.8819

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Co-Culturing Yogurt Bacteria with Probiotics Increased Melatonin Content and Enhanced the Antioxidant Activity of Soy Milk Yogurt

Treechada Utaida¹, Anuchita Moongngarm^1* and Pariyaporn Itsaranuwat²

¹Department of Food Technology and Nutrition, Faculty of Technology, Mahasarakham University, Kuntarawichai, Maha Sarakham, 44150, Thailand

²Department of Biotechnology, Faculty of Technology, Mahasarakham University, Kuntarawichai, Maha Sarakham, 44150, Thailand

Copyright © 2024 This is a Diamond Open Access article published under CC-BY licence. Copyright remains with the authors, who grant third parties the unrestricted right to use, copy, distribute and reproduce the article as long as the original author(s) and source are acknowledged.

Article history:

Received: 9 August 2024

Accepted: 4 April 2025

Keywords:

bifidobacteria; L. acidophilus; plant-based milk; prebiotic; serotonin

Summary:

Research background. Functional foods that improve sleep quality are attracting increasing attention. Melatonin is a key component that regulates circadian rhythms in humans. Soy milk yogurt contains melatonin and antioxidants and has beneficial health properties. Many previous authors have investigated soy milk yogurt produced by probiotic bacteria. This is the first study to explore the effect of using yogurt bacteria co-cultured with probiotics to improve melatonin content and antioxidant activity. This research investigated the melatonin, serotonin, and tryptophan contents, antioxidant activity, physical characteristics, and sensory properties of soy milk yogurt bacteria co‐cultured with different probiotics.

Experimental approach. Soy milk was fermented using four combinations of yogurt bacteria and probiotics including Lactobacillus bulgaricus and Streptococcus thermophilus (control, SB-YC), Bifidobacterium lactis, Lactobacillus acidophilus, L. bulgaricus and S. thermophilus (SB-BY), B. lactis, L. acidophilus and S. thermophilus (SB-BT), and L. acidophilus, L. bulgaricus and S. thermophilus (SB-LA). The yogurt samples were determined for melatonin, serotonin, and tryptophan content using LC-MS/MS, antioxidant activity, and quality characteristics including syneresis, texture profile analysis, color, and sensory evaluation.

Results and conclusions. The highest melatonin levels were detected in soy milk yogurt fermented with SB-BY (21.20 ng/g) and SB-YC (23.51 ng/g), while the highest tryptophan content was found in SB-LA (397.18 ng/g). Fermentation using different bacterial culture combinations resulted in varied antioxidant activities. The SB-LA yogurt exhibited the strongest antioxidant activity, as indicated by DPPH IC50 (10.69 mg/mL), ABTS IC50 (0.51 mg/mL), and FRAP (2577.86 μg FeSO4/g) assays. Incorporating a mixture of yogurt bacteria and probiotics enhanced the color values (L*, a*, b*), syneresis, and texture profiles of the soy milk yogurt. Sensory evaluation demonstrated that yogurt fermented with S. thermophilus, L. acidophilus, and B. lactis received a favorable overall liking score. The successful co-culture of probiotics (B. lactis and L. acidophilus) with yogurt bacteria produced soy milk yogurt enriched with melatonin, tryptophan, and antioxidants while maintaining acceptable quality characteristics.

Novelty and scientific contribution. Co-culturing yogurt bacteria and probiotics (Bifidobacterium lactis, Lactobacillus acidophilus; SB-BY) or L. acidophilus (SB-LA) improved melatonin production, antioxidant activity, and overall yogurt quality, providing valuable insights for developing functional foods to promote sleep and health.