DNA barcoding a tool of ‘promise’ in authenticating supplements, review finds

Led by a team from Portugal, the review identifies this technique of promise, although researchers make clear they have not been able to find a universal barcode for all plant groups.

“The advent of DNA barcoding to detect species in herbal products has been widely exploited, showing promising results,”​ the team says led by Liliana Grazina, researcher at the University of Porto’s department of chemical sciences.

“DNA barcoding is a highly reliable tool for the identification of species in a wide range of botanicals, with potential of being routinely applied to their authentication. ​

“However, when analysing complex and highly processed herbal products, containing mixed botanicals and/or degraded DNA, the application of DNA barcoding might be limited because of relying on relatively long amplicons and Sanger sequencing.”​

Herbal products including dietary supplements, are of increasing global importance due to their health benefits and economic considerations. However, they are also vulnerable for adulteration practices.

Such incidences reported include the illegal spiking of pharmaceutical drugs into dietary supplements to boost their effect and increase sales.

Herbal dietary supplements are also vulnerable to the intentional replacement of plant material, including the addition of cheap plant fillers to increase product bulk and the substitution of high‐priced medicinal plants by other closely related/similar species.

Additionally, cases of misidentification of plant species, particularly when they are collected in the wild, can also occur.

To combat these growing practices, current tools at authorities’ disposal include thin‐layer chromatography and phytochemical analysis using high‐performance liquid chromatography–mass spectrometry.

Less than 1,000 Base Pairs​

Along with other DNA‐based techniques such as High‐Resolution Melting (HRM) analysis, and metabarcoding, DNA barcoding has emerged as a technique suited to identifying an unknown adulterant that may be present.

The technique relies on the use of short sequence regions, generally with less than 1,000 Base Pairs (BP) in order to discriminate animal, plant, fungal, and bacterial species.

These sequences can in theory be isolated and characterised for plant species by combining the strengths of molecular genetics, sequencing technologies, and bioinformatics.

DNA barcodes offer a quick and accurate means to recognise previously known, described, and named species and to retrieving information about them.

While mitochondrial genes were proposed as a barcode for species identification in animals, they have proved unsuitable as barcodes in plants lowering their effectiveness in plant species identification.

Researchers have gone on to propose genome regions with larger evolving rates than mitochondrial genes, such as nuclear and plastid, as alternative barcodes for plants.

The review​​ also discusses applications of DNA barcoding including an authenticity blind test for 44 herbal products (41 capsules, two powders, one tablet) representing 30 different plant species, and 50 leaf samples from 42 plant species.

DNA barcodes were recovered from 91% of the herbal products and 100% from all leaf samples. The results showed that most of the herbal products tested had a considerable rate of product substitution, contamination, and use of fillers, lowering their effectiveness.

The authors suggested that DNA barcoding should be applied for testing raw materials used in the manufacture of herbal products.

Ginseng and roseroot​

Another application of the technique was in a study​​ that tested 25 Siberian ginseng (Eleutherococcus senticosus​) and 14 roseroot (Rhodiola rosea​) herbal supplements, widely available in the UK market.

The results showed that all the Siberian ginseng supplements contained E. senticosus​. However, 36% also contained Eleutherococcus​ species other than E. senticosus​. From 13 roseroot products, three produced amplifiable DNA with sequences matching alfalfa (declared on the product label) and fenugreek (not declared).

Rhodiola was detected in the other 10 supplements, but only five matched the target species R. rosea.​

Nevertheless, as DNA was severely degraded during the manufacturing process, the study authors could not consider the absence of Rhodiola DNA as proof for a compromised product.

The authors suggested the substitution or mix of the target medicinal ingredient with other species seemed to be common in these two types of supplements.

Source: Comprehensive Reviews in Food Science and Food Safety​

Published online ahead of print: doi.org/10.1111/1541-4337.12551​​

“Botanical origin authentication of dietary supplements by DNA‐based approaches.”​

Authors: Liliana Grazina, Joana S, Amaral Isabel Mafra.