Clustering of Streptococcus thermophilus Strains to Establish a Relation between Exopolysaccharide Characteristics and Gel Properties of Acidified Milk.

Georg Surber,Doris Jaros,Harald Rohm,Susann Mende

doi:10.3390/foods8050146

Abstract

In situ produced extracellular polysaccharides (EPS) from lactic acid bacteria are generally known to affect the texture of fermented dairy products; however, the interplay between EPS and product properties is still poorly understood. The aim of this study was to establish a relationship between concentration and properties of EPS, and gel formation of milk analysed by noninvasive Multispeckle Diffusing Wave Spectroscopy. Twenty Streptococcus thermophilus strains were classified with respect to EPS concentration (8–126 mg GE/kg) and ropiness (thread length: 15–80 mm). Five groups identified by cluster analysis demonstrate the high strain-to-strain variability even within one species of lactic acid bacteria. Results from acidification and gelation experiments averaged per cluster indicate that fermentation time and gel stiffness is higher for strains that produce ropy EPS. A further increase in gel stiffness was detected for strains that also produced cell-bound EPS, which underlines the importance of both ropy and cell-bound EPS for improving acid gel properties. The results may be helpful for a proper selection of EPS-producing starter cultures.

Highlights

IntroductionIn situ produced extracellular polysaccharides (EPS) from lactic acid bacteria (LAB) are generally known to have an impact on the texture and, on sensory properties of fermented foods
In situ produced extracellular polysaccharides (EPS) from lactic acid bacteria (LAB) are generally known to have an impact on the texture and, on sensory properties of fermented foods.Bacteria strains with the ability of synthesising EPS are utilised in the manufacture of a broad range of products, especially in the cereal [1] and dairy sector [2]
EPS from LAB are often distinguished by the degree of ropiness they induce in the product, and by their location: whereas free EPS are released into the surrounding medium, cell-bound EPS remain attached to the bacteria cells

Summary

Introduction

In situ produced extracellular polysaccharides (EPS) from lactic acid bacteria (LAB) are generally known to have an impact on the texture and, on sensory properties of fermented foods. Bacteria strains with the ability of synthesising EPS are utilised in the manufacture of a broad range of products, especially in the cereal [1] and dairy sector [2]. For the latter, positive effects were observed for viscosity, thickness and creaminess of yoghurt [3,4], and EPS reduce the protein particle growth during fresh cheese manufacture [5]. EPS from LAB are often distinguished by the degree of ropiness they induce in the product, and by their location: whereas free EPS (fEPS) are released into the surrounding medium, cell-bound EPS (cEPS) remain attached to the bacteria cells

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