Transient in situ measurement of kombucha biofilm growth and mechanical properties.

Pascal Bertsch,Peter Fischer,Danai Etter

doi:10.1039/d1fo00630d

Abstract

Kombucha is a traditional beverage obtained by the fermentation of sugared tea by a symbiotic culture of bacteria and yeast which has recently re-emerged as a popular lifestyle product with potential health benefits. The characteristic feature of kombucha is the formation of a cellulosic biofilm due to the excretion of bacterial cellulose with high purity and crystallinity. Despite the growing industrial and technological interest in kombucha, current characterization techniques rely on the periodic sampling of tea broth or biofilm and ex situ analysis of its biochemical or microbial composition. Here, we use interfacial shear rheology (ISR) for the transient in situ determination of kombucha biofilm growth directly at the interface. ISR revealed that kombucha biofilm formation is a two step process with clearly distinguishable growth phases. The first phase can be attributed to the initial adsorption of bacteria at the air-water interface and shows great variability, probably due to varying bacteria content and composition. The second phase is initiated by bacterial cellulose excretion and shows astonishing reproducibility regarding onset and final mechanical properties. Hence, ISR qualifies as a new in situ characterization technique for kombucha biofilm growth and bacterial cellulose production.

Highlights

Kombucha is a mildly alcoholic and effervescent beverage obtained by the fermentation of sugared tea by a symbiotic culture of bacteria and yeast (SCOBY)
interfacial shear rheology (ISR) on the other hand allows the transient in situ determination of kombucha biofilm growth kinetics and mechanical properties
The formation kinetics and interfacial viscoelasticity of early kombucha biofilms are in good agreement with those reported for pure K. xylinus[24] and other bacteria biofilms investigated by ISR.[25,26,27,28,29,30,31,32,33]

Summary

Introduction

Kombucha is a mildly alcoholic and effervescent beverage obtained by the fermentation of sugared tea by a symbiotic culture of bacteria and yeast (SCOBY). The yeasts metabolize sucrose to ethanol and CO2. The yeast and bacteria composition of kombucha can differ significantly depending on the starter culture and growth conditions. The yeast ecology changes during the fermentation from osmotolerant species in early stages to acid tolerant species in later stages.[4] The majority of bacteria in kombucha are acetic acid bacteria, i.e. Acetobacter, Gluconobacter, and Komagataeibacter, which metabolize glucose or ethanol to acetic acid. We demonstrate that interfacial shear rheology (ISR) allows for the transient in situ measurement of kombucha biofilm growth, revealing new aspects of kombucha biofilm dynamics and mechanical properties

Experimental

Results and discussion

Conclusions