Kombucha has received significant attention over last few years and has become an increasingly popular beverage with purported health-promoting properties. Kombucha is a traditional fermented drink that can be simply made by adding specific strains of bacteria, yeast, and sugar to tea extract. Allowing the mixture to ferment for a week or more results in a mildly acidic and mildly sweet carbonated drink.

While several studies have investigated the health benefits, toxicity, and bacterial compositions of kombucha, the actual concentration of key components in such beverages is still obscure. Ethanol is one of the crucial components believed to be present in low concentrations in kombucha. Quality control and regulatory demands necessitate strict and precise monitoring of the alcohol content in commercial products. According to the U.S. Alcohol and Tobacco Tax and Trade Bureau (TTB), any beverage containing more than 0.5% alcohol by volume (ABV) is considered alcoholic and should be consumed only by adults 21 years or older. In recent years, certain kombucha products have been found to exceed this limit, which translates to a need for an efficient method to monitor the ethanol levels in kombucha beverages.

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Gas chromatography (GC) is a powerful technique for analysis of alcoholic beverages. GC is a separation technique which uses liquid coated on a solid support as stationary phase and gas as a mobile phase, and it is a universal technique for the analysis of volatile compounds. Coupling headspace sampling technique with GC facilitates extraction of volatile species from complex multicomponent samples such as kombucha. Separation of ethanol from other volatile components of kombucha was carried out on the recently developed ionic liquid-based WatercolTM 1910 column.

Figure 1. A chromatogram of a typical analysis of a commercial kombucha drink on WatercolTM 1910 column at 100 °C (left). Structure of ionic liquid-based WatercolTM 1910 column (right). Credit: the authors

Unlike conventional GC columns, the WatercolTM capillary columns are highly moisture-stable and their performance is not affected by the water present in kombucha samples. Analysis of kombucha products from five different brands revealed that these bottles contained 1.12-2% ABV, which was two-three times higher than the TTB regulatory limit for non-alcoholic beverages. Further, the ethanol content increased with time in these samples. Acetaldehyde and acetic acid were also identified in kombucha bottles.

Some kombucha manufacturers claim that store-bought kombucha products contain higher ethanol because the bottled product keeps fermenting while sitting on shelves. The effect of storage period on the ethanol concentration of kombucha products was examined under two different conditions; room temperature (22 °C) and refrigeration temperature (4 °C). A gradual increase in the ethanol concentration of kombucha drinks was observed for both batches. However, refrigeration helped in decreasing the rate at which ethanol accumulated in commercial bottled products. In both cases, the ethanol content seemed to maximize within ~14 days.

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Figure 2. Effect of storage period on the ethanol content of kombucha. Credit: the authors

Several factors may impact the amount of alcohol in kombucha beverages, including but not limited to the microbial composition of kombucha culture, the initial sugar content, the time course of fermentation, and incubation temperature.

These findings are described in the article entitled Examination of the Varied and Changing Ethanol Content of Commercial Kombucha Products, published in the journal Food Analytical Methods. This work was led by Daniel Armstrong from the University of Texas at Arlington.

About The Author

My research background at UTA lies at the intersection of organic synthesis and analytical chemistry, where innovative ionic liquid (IL) materials are synthesized using specific structural modifications. For those ILs with optimal properties, they are coated onto the fused silica capillaries and evaluated as extremely polar and thermally stable stationary phases for gas chromatography. The best of these columns are then utilized to resolve challenging separations that are useful industrially including petrochemical, environmental, clinical, and food areas.

Synthetic analytical chemist with substantial experience in organic synthesis, chromatography, and chiral separation science. Extensive research experience in synthesis, development, and applications of ionic liquid gas chromatography stationary phases. Two years’ experience of working in GLP regulated laboratories. Developed methods for the analysis of drug residues in biological matrices. Developed and validated methods for analysis of active pharmaceutical ingredients, petroleum samples, and food products.

Daniel W. Armstrong has over 700 publications, including 32 book chapters, one book (“Use of Ordered Media in Chemical Separations”) and 33 patents. He has been names by the Scientific Citation Index as one of the world’s most highly cited scientists, and he has given ~ 580 invited/keynote/plenary lectures and colloquia worldwide. His work has been cited over 41,000 times and his Hirsch index is ~ 103 (G.S.).

Daniel Armstrong is considered the “Father” of micelle and cyclodextrin-based separations, he elucidated the first chiral recognition mechanism by cyclodextrins, he was the first to develop macrocyclic antibiotics as chiral selectors, and he is one of the world’s leading authorities on the theory, mechanism, and use of enantioselective molecular interactions. Over 30 different LC and GC columns that were originally developed in his laboratories have been commercialized and/or copied worldwide. His work and columns were in part responsible for the chromatography and electrophoresis-led revolution in chiral separations over the last two and one half decades. Currently, the columns, chiral selectors and techniques he developed dominate the work of analytical enantiomeric separations.

He has developed the most effective way to characterize the solvent properties of room temperature ionic liquids (RTILs). This has proven to be an essential and effective way to explain the effect of RTILs on organic reactions, and in various analytical methodologies. Surfactant aggregation to form normal micelles in RTILs was demonstrated. The first MALDI-MS matrices and high stability GC stationary phases based on RTILs were developed in his laboratories and were recently commercialize by Supelco/Sigma/Aldrich. The new enhanced mass spectrometry technique of PIESI (Paired Ion Electrospray Ionization) was developed in his laboratory and is one of the most sensitive methods for ultra-trace anion analyses and speciation.He developed the first high efficiency CE separation approach for microorganisms (i.e., bacterial, viruses, fungi, etc.). This will extend the realm of separation science into the mainstream of biology and colloid science.

He founded or co-founded two separate companies focused on production of novel separation media and using them for difficult analyses.