Interactions between EPS-producing Streptococcus thermophilus strains in mixed yoghurt cultures

Abstract

Mixed cultures of different EPS-producing Streptococcus thermophilus strains in combination with a Lactobacillus delbrueckii subsp. bulgaricus strain with negligible EPS-production were used for yoghurt production. The yoghurt texture was characterised with respect to sensory, rheological and microstructural properties and the EPS-concentrations were determined. The cultures resulted in yoghurts with highly different texture properties, and positive interactions between certain Streptococcus thermophilus strains were observed. The underlying properties of yoghurt texture are multidimensional, but a number of microstructural characteristics were apparent in the yoghurts with the highest mouth thickness, creaminess and viscosity. A strong protein network, not too dense and with medium size pores containing EPS, seems associated with these properties. The presence of capsular polysaccharides (CPS) also appeared to be beneficial as did a combination of EPS types, which were distributed differently in the protein network (in serum pores, respectively in association with protein). Obviously, a certain concentration of EPS must be present to provide for these effects on yoghurt texture, but other factors than concentration per se seem more important.

Use of Lactobacillus mucosae DPC 6426, an exopolysaccharide-producing strain, positively influences the techno-functional properties of yoghurt

“…Similar results have previously been reported in numerous studies when EPS-containing yoghurt was compared with control yoghurt (Amatayakul et al, 2006;De Vuyst & Degeest, 1999;Guler-Akin et al, 2009;Kearney et al, 2011;Purwandari et al, 2007). It has been shown that ropy EPS has a greater ability to retain serum, resulting in lower levels of syneresis (Folkenberg, Dejmek, Skriver, & Ipsen, 2006b). The increase in EPS concentration, which was inversely proportional to the decrease in syneresis found in our study, therefore suggests that L. mucosae DPC 6426 produced a ropy EPS.…”

Suitability of camel milk for making yogurt

“…Food additives, including gelatin and κ-carrageenan, have been used in yogurt manufacture (4,10,11). In fact, the yogurt starters Streptococcus thermophiles and Lactobacillus bulgaricus have been used to produce capsular polysaccharides (exo-polysaccharides) that have been shown to contribute to higher yogurt viscosity and thicker mouth feel (12,13). The objective of this study was preparation of yogurt from CAM and investigation of the properties of the resultant yogurt in comparison with yogurt made using bovine milk.…”

Binding Interactions Between α-glucans from Lactobacillus reuteri and Milk Proteins Characterised by Surface Plasmon Resonance

“…Interactions between glucans and milk proteins are reported to alter the microstructure of fermented milk products and to increase viscosity. 35 Thus, EPS-milk protein interactions, but also the intrinsic viscosity of the EPS itself, 36 are important for the texture. Intrinsic viscosity increases with increasing EPS molecular weight 34 and chain stiffness 36,37 .…”

“…High molecular weight EPS may thus increase the viscosity by interacting with κ-casein and by contributing with its high intrinsic viscosity, while EPS with rigid chains may not interact with milk proteins and only contribute to texture solely by increasing the viscosity of the serum phase. Hence a mixture of EPS that interact differently with milk proteins would be favourable in manufacture of fermented milk products with higher viscosities 35,38 . The correlation between molecular properties of EPS, their interactions with milk proteins and texture of fermented milk should be further elucidated to gain insight in the origins of EPS functionality.…”