Thursday, June 27, 2013

Freshly squeezed Barcodes

Almost a year ago I posted about a technology that could provide fast, robust and reliable identifications of a handful of species that are not easy to distinguish based on morphology. A Scottish researcher used High Resolution Melt (HRM - see box below for details) to help with the identification of a handful of closely related fish species. The result was a HRM protocol that represented a quick and cost effective method of genetic screening and an alternative to DNA sequencing between the four genetically very similar species.

Today I came across a new publication from Portugal that described a proof of concept study utilizing HRM for fruit juices authentication. Fruit juices labeled as 100% fruit are a growing market world wide. In the European Union alone their sales represent approximately two-thirds or 7 billion liters of total EU juice sales in 2011. The increased consumer demand for premium juices has also led to a dramatic rise in the  requirement for freshly squeezed juices. Those are usually higher priced and therefore favorite targets for adulteration. Adulteration of fruit-based products is mostly performed by blending original products with cheaper and more available fruits.

The researchers from the University of Porto picked a marker that had been proposed and discussed for plant DNA Barcoding: the trnL intron. This choice was mainly an opportunistic one as at the time of the study GenBank contained sequences for most of the fruit species in question. The tests were conducted using fresh fruits from the species Citrus sinensis (orange); Mangifera indica (mango); Prunus persica (peach); Pyrus communis (pear); and Ananas comosus (pineapple) purchased at local markets and immediately processed to juices in a home fruit processor. Pulp was removed and 3 different extraction methods applied to determine the most efficient one. In order to test the effect of blended fruit juices on the melt profile assignment different mixtures of juices in different ratios were tested. Not only could all species be correctly identified but also the individual quantities. 

These are very promising results and consider this:
The method consisted of a single step closed tube procedure, took approximately 3 h to complete and costed approximately €2.00 per sample (including DNA extraction and HRM reagents). Now that sounds affordable to me even when it comes to larger quantities. I guess industry and inspection agencies are left with not many excuses when it comes to more rigorous testing for consumer protection.

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