Investigation of water kefir microbiota and antioxidative capacity

Abstract

The effects of a change of environment on water kefir’s microbial diversity was studied by splitting up two existing cultures (stem 1 and stem 2) among several households and culturing them for three weeks using the same method and ingredients. Next Generation Sequencing (NGS) was used on the 16S rRNA gene to identify bacterial families, genera and strains. Sphingomonadaceae, Lactobacillaceae, Acetobacteraceae, Leuconostocaceae and Carnobacteriaceae were identified in stem 1, Lactobacillaceae, Acetobacteraceae, Leuconostocaceae, Enterobacteriaceae and Bacillaceae were identified in stem 2. Lactobacillus zeae was the only strain identified in all samples. Stem 1 was minimally affected by the method and ingredients used whereas stem 2’s diversity was severely reduced by the method and ingredients. The effect of the change of environment was found to be minimal compared to the effect of the method and ingredients used in both cases. The antioxidative capacity of kefir grains and drink respectively was measured using an ascorbic acid standard. The average ascorbic acid equivalent concentration of the grain samples was found to be 0,190 ± 0,0849 mM, which is comparable to the amount contained in 100g of unpeeled apple. The average ascorbic acid equivalent concentration of the drink samples was not determined accurately as the values obtained were below the limit of detection at 0,05mM. These findings are very exciting as it opens up the door for more studies being done on how kefir’s microbiome reacts to specific ingredients and methods and how it affects the resulting drink and grains.

Popular Abstract

We are multitudes: water kefir’s surprising biodiversity

While most of us are familiar with the trendy milk kefir, often touted for its probiotic and health-promoting properties, fewer have heard of its cousin water kefir. Though they work using broadly the same principle (a symbiotic relationship between a variety of yeast and bacterial strains living together in a grain-structure) and look relatively similar, do not be fooled: there is more to water kefir than meets the eye!
For one, it is severely under-studied: while many studies have been published about milk kefir’s biodiversity, antioxidative capacity and probiotic qualities, there are few such publications to be found concerning water kefir leaving a gaping hole in the body of knowledge, waiting to be filled. We have attempted to answer some of these questions, and more, by setting up two different experiments: one where the antioxidative capacity of different kefir drink and grain samples was measured, and one where a technique called Next Generation Sequencing (NGS) was used to determine which bacterial populations are present within the samples. The aim of the study was to investigate three different questions:
- How much antioxidative capacity (meaning antioxidative strength) does water kefir have?
- How do the ingredients and method used to culture the kefir affect the kefir?
- How does the environment the kefir is cultured in affect it?
To answer these questions, kefir cultures from two different households were selected. Each original culture, or “stem” was then split up into several smaller cultures, or “populations”. Each population was then cultured for three weeks according to the same method, using the same ingredients. Two populations were kept in the original households to study the effect of method and ingredients only. After three weeks, grain and drink samples were collected from each population, and the experiments to determine antioxidative capacity and identify bacterial species were performed.
NGS revealed that the two kefir stems were very different from one another in terms of bacterial composition: one contained mostly Sphingomonodaceae, Carnobacteriaceae, Acetobacteraceae, Lactobacillales and Leuconostocaceae while the other contained mostly Acetobacteraceae, Lactobacillaceae, Enterobacteriaceae, Bacillaceae and Leuconostocaceae. Very few bacterial strains were common to all samples, which shows just how diverse water kefir cultures can be from household to household. Both stems were also affected differently by the method and ingredients used: one stem’s bacterial populations were essentially unaffected by the three-week culturing phase, keeping the relative amounts of the various bacterial populations stable. By contrast, the other stem changed drastically: originally containing a very large variety of different types of bacteria, it contained only a fraction after the culture phase. This shows that the method and ingredients all but decimated the diversity present originally, which may sounds like a bad thing at first but isn’t necessarily the case: indeed, only a few families of bacteria and yeasts are involved in the actual “kefir-making”, so the presence of undesired strains can actually be a health concern. In fact, the second stem did contain a non-negligible amount of Enterobacteriaceae, the family that contains such infamous members as E. coli, Salmonella and more.
There were very few differences in bacterial populations present in most cases when looking at the differences between the populations that stayed in the original households for the culturing period and those that were cultured in other households. The types of bacteria present were similar, and so were their relative amounts. The only population that had a significantly different composition to the stem population likely got contaminated by some outside source of bacteria.
When it comes to the antioxidative capacity, the results varied: kefir grain samples showed on average approximately the same amount of antioxidants as an unpeeled apple, which is nothing to be laughed at. The drink samples however did not give any conclusive results, probably due to a misjudgement in the method. We therefore still don’t know whether drink water kefir is beneficial from an antioxidant perspective, but it would seem that consuming the kefir grains may have positive effects, if you are willing to do that.
Although much remains to be discovered concerning water kefir’s antioxidative capacity and its biodiversity, this study shows that a water kefir culture doesn’t necessarily mean just one thing: in much the same way that each person’s gut flora is heavily influenced by what we eat and how, each kefir culture’s biodiversity is influenced by the method and ingredients used. This is very exciting as it opens up the door for more studies being done on how kefir reacts to specific ingredients and ways of preparing it and how it affects the resulting drink we consume.

• author: Sutton, Lola
• supervisor: Elisabeth Uhlig; Åsa Håkansson
• organization: Department of Chemistry
• course: KEMK10 20201
• year: 2020
• type: M2 - Bachelor Degree
• subject: Chemistry
• keywords: water kefir, microbiology, 16S, next generation sequencing, NGS, Illumina, bacteria, kefir, antioxidant, DPPH, biochemistry, biokemi
• language: English
• id: 9020268
• date added to LUP: 2020-06-25 13:34:54
• date last changed: 2020-06-25 13:34:54