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Commercial kefir products assessed for label accuracy of microbial composition and density

https://doi.org/10.3168/jdsc.2020-0056Get rights and content
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Highlights

  • Using 16S rRNA gene sequencing combined with traditional plating techniques offers greater label accuracy testing of commercial fermented foods than plating alone.

  • The Loop sequencing method allows for high-throughput identification of species-level bacterial taxa present in fermented foods.

  • Although a moderate level of label accuracy was observed, some bacterial species, including Streptococcus salivarius and Lactobacillus paracasei, were detected in 4 of 5 products yet not claimed on labels.

Abstract

Kefirs are fermented beverages containing yeast and bacteria produced by the fermentation of water or milk with kefir grains. Because microorganism density may influence a product's health benefits, label accuracy regarding viable bacterial density and taxonomy of fermented foods is important. In this study, the microbiota of 5 commercial kefir products were measured quantitatively using standard plating techniques and characterized using high-resolution, long-read 16S rRNA gene amplicon sequencing. To enumerate viable lactic acid bacteria, 2 lots of each product were plated on de Man, Rogosa and Sharpe agar upon opening and following 14 d and incubated under anaerobic and aerobic conditions. Results revealed that 66% of products with a guaranteed count of colony-forming units per gram overstated microorganism density by at least 1 log, with only product E exceeding 1 × 109 cfu/g. Sequencing results demonstrated moderate product label accuracy in regard to taxonomy, yet several products contained bacterial species above the minimum detectable threshold (0.001% relative abundance) that were not included on the labels (e.g., Streptococcus salivarius, Lactobacillus paracasei). Our results demonstrate a moderate level of labeling accuracy for commercial kefir products intended for human consumption. Regulatory agencies and consumers must continue to scrutinize these products and demand a higher level of accuracy and quality.

Graphical Abstract

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Summary: In this study, label claims of commercial kefir products were subjected to bacterial enumeration and taxa integrity. Previous research suggests that claims of colony-forming units per gram and bacterial taxa on product labels are inaccurate and may be misleading to consumers. This project analyzed 5 commercial kefir products and revealed inaccuracies of label claims that are of great importance to everyday consumers.

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