Effect of Dendrobium officinale Leaf Extract on the Growth and Metabolism of Streptococcus thermophilus, a Most Commonly Used Bacterium in Yogurt Production

Abstract

Dendrobium officinale leaf contains a variety of bioactive compounds, and has the potential to be used for functional yogurt production. However, the compounds in D. officinale leaf may affect the growth and metabolism of lactic acid bacteria. In this work, extracts from different dosages of D. officinale leaves were added into the media of Streptococcus thermophilus (one of the most commonly used lactic acid bacteria in yogurt production), and the biomass, lactic acid content, glucose uptake capacity, and cellular metabolic/reducing activity were analyzed. Simultaneously, the changes in biomass, lactic acid production capacity, and key enzyme activities were determined during the 24 h fermentation. Furthermore, transcriptomics analysis was performed to explore the molecular mechanisms. Results showed that D. officinale leaf extract can promote the growth, cellular metabolic/reducing activity, glucose uptake, lactic acid production, and β-galactosidase, glucokinase, pyruvate decarboxylase and lactic dehydrogenase activities of S. thermophilus at the appropriate dosage, and the extract from 4% (w/v) leaves is optimal. Further transcriptomic analysis revealed that D. officinale leaf extract enhances the growth and metabolism of S. thermophilus by up-regulating the expression of genes related to amino acid metabolism, translation, membrane transport, carbohydrate metabolism, energy metabolism, and nucleotide metabolism. These findings will provide a theoretical basis for the utilization of D. officinale leaves to fortify the health function of yogurt.