Influence of pH on the Formation of Glucan by Lactobacillus reuteri TMW 1.106 Exerting a Protective Function Against Extreme pH Values

Abstract

Lactobacillus reuteri TMW 1.106, a dominant type II sourdough bacterium, produces glucan from sucrose in vitro and in situ. Exopolysaccharides positively affect the texture and mouth feel of foods and their in situ production in fermented foods could be an alternative to the addition of hydrocolloids from plants or non-GRAS microorganisms. The aim of this study was to elucidate a probable function of the EPS for the bacterium. Lb. reuteri TMW 1.106 harbors two glucosyltransferases, Gtf106A and Gtf106B and produces a dextran. Gtf106B exhibited hydrolysis but no transferase activity. Enzymatic production of dextran with the heterologously expressed, N-terminally truncated ΔN Gtf106A was highest at a pH of 4.0, whereas dextran formation in pH static fermentations was optimal between pH 4.7 and 5.4. The dextran synthesised at these pH values had the highest molecular mass (1.2 × 10⁷) and 15% α–(1–4) linkages. A protective effect of this EPS on Lb. reuteri TMW 1.106 against low pH, explaining the low pH-production maximum, could be demonstrated through the delay of cell death.

Key Words:

• Lactobacillus reuteri
• pH value
• exopolysaccharides
• dextran
• protective function

ACKNOWLEDGMENT

Part of the work discussed in this study was supported by the FEI (Forschungskreis der Ernährungsindustrie e.V., Bonn, Germany), the AiF and the Ministry of Economics and Technology. Project No.: AiF-FV 14037 N. The authors acknowledge support during measurements and evaluation by Postnova Analytics GmbH, Landsberg/Lech, Germany (www.postnova.com). The authors are indebted to Nina Körber (Technische Universität München, Germany) for helping with the pH-static fermentations and Jens Walter (University of Nebraska, Lincoln, Nebraska, USA) for providing the dextran sucrase deletion mutant.