A “fingerprint” for fruit juices
Amongst the chemical methods of authentification, there are two different strategies. On the one hand, the employment of markers – chemical compounds that are ideally specific for or exclusive to each fruit and that can be rapidly, safely and cheaply measured and analysed.
This would be ideal. On many occasions, however, it is not possible to find markers that fulfil these requirements and, so, another approach to authentification methods is to measure and analyse a greater number of chemical compounds that make up the characteristic profile of each fruit or fruit juice. The complexity of this requires the employment of chemical analysis techniques and highly sophisticated statistical tools.
In order to confirm the authenticity of the fruit juices, researchers at the Department of Analytical Chemistry of the University of the Basque Country (EHU-UPV) are trying to identify their fingerprints, as it were, using a family of chemical compounds naturally present in all fruit and known as polyphenols. There are thousands of polyphenols amongst the various species in the vegetable kingdom, with differences both in the number of particular polyphenols present in each vegetable species as well as in the quantities found. Thus, different fruits have specific polyphenolic differences.
In order to analyse polyphenols present in each for each fruit, researchers at the EHU-UPV used a high-performance liquid chromatography technique (HPLC), through which they culled information about what particular polyphenols are present in each fruit and in what quantity. This enables the study of the differences in the polyphenols between one fruit and another.
In any case, to be more certain of these polyphenols profiles, the confirmation is needed of the identity of each one of the polyphenols appearing in these profiles. To this end, a mass spectroscopy (MS) analytical technique was employed.
Orange, mandarin, lemon …
A total of 16 fruits (Orange, mandarin, lemon, grapefruit, etc.), grown in Spain, were studied. In each case a study of the various varieties of each fruit was undertaken – up to 77 varieties, in order to know the common points of all fruits, and their differences.
Beatriz Abad has found, amongst other things in her PhD, a quite exclusive marker for lemon and three for grapefruit. She has also shown that using several markers instead of one increases the probability in detecting the food fraud. Moreover, she observed key differences in various “prints” and, using certain statistical tools, showed that such differences provide a quite reliable degree of accuracy in the detection of some mixtures of juices. For example, detecting the presence of grapefruit in orange juice is very sure and relatively easy; detecting the presence of lemon juice in orange juice is also quite accurate; but detecting the presence of mandarin oranges in orange juice is much more difficult and not very reliable, given that the mandarin and the orange are very similar in their “prints”.
To date they have defined the polyphenolic profiles or polyphenolic “fingerprints” of the various juices from genuine fruit. The next step is currently being carried out by researchers at the EHU-UPV – applying these “prints to existing commercial juices on the market in order to detect possible adulterations or frauds.
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