Characterization of an exopolysaccharide produced by Streptococcus thermophilus ZJUIDS-2-01 isolated from traditional yak yogurt

Authors: CAO, FEIWEI - Zhejiang University; LIANG, MINGMING - Zhejiang University; LIU, JIANXIN - Zhejiang University; LIU, YU - Zhejiang University; Renye, John; Qi, Phoebe; REN, DAXI - Zhejiang University

Submitted to: International Journal of Biological Macromolecules
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/8/2021
Publication Date: 10/19/2021
Citation: Cao, F., Liang, M., Liu, J., Liu, Y., Renye Jr, J.A., Qi, P.X., Ren, D. 2021. Characterization of an exopolysaccharide produced by Streptococcus thermophilus ZJUIDS-2-01 isolated from traditional yak yogurt. International Journal of Biological Macromolecules. https://doi.org/10.1016/j.ijbiomac.2021.10.055.
DOI: https://doi.org/10.1016/j.ijbiomac.2021.10.055

Interpretive Summary: Known for its unique sour taste and creamy texture, yak yogurt is one of the traditionally fermented dairy products prepared by local herdsmen in the Qinghai-Tibet Autonomous region in southwest China. However, the diverse array of natural microorganisms involved in the yogurt remains mostly unknown. This work reports the discovery and identification of a novel bacterial strain, Streptococcus thermophilus ZJUIDS-2-01, from the yak yogurt, and the extracellular polymers secreted by this bacterium. We focused on one of these polymers, named EPS-3A, a high molecular weight polysaccharide responsible for the yogurt's smooth mouth-feel. We determined the sugar compositions and the molecular structure of EPS-3A and studied its heat stability, functional properties, and in vitro activities. We found that EPS-3A performed slightly better as an emulsifier in cooking oil and water systems than xanthan gum, the most commonly used commercial food additive. It also has antioxidative and antibacterial activities comparable to that of xanthan gum. These results suggested that EPS-3A has potential in a wide range of applications, such as in improving texture, preserving food products, and supporting oil/water emulsion systems.

Technical Abstract: Yak yogurt is one of the naturally fermented dairy products prepared by local herdsmen in the Qinghai-Tibet Plateau and contains diverse microorganisms. A novel strain, S. thermophilus ZJUIDS-2-01, was isolated and identified from the yak yogurt in this work. An exopolysaccharide (EPS-3A) produced by S. thermophilus ZJUIDS-2-01 was also isolated and purified. EPS-3A was determined to be mainly composed of glucose, galactose, and rhamnose in a ratio of 2.7:1.4:1.0 with an estimated weight-average molecular weight (Mw) of 1.38×106 Da. The structure of EPS-3A was characterized by FT-IR and NMR spectroscopic techniques. The zeta-potential studies revealed that the pKa of EPS-3A was 4.40. It exhibited noticeably greater stability in O/W emulsion systems and higher flocculating capability than xanthan gum (XG). It also presented slightly better antioxidant activity than XG and promising in vitro antibacterial properties. These results demonstrated that S. thermophilus ZJUIDS-2-01-derived EPS-3A holds the potentials for food and industrial applications.