Methods used to detect juice adulteration

Over the past 30 years, extensive research has been carried out to find ways to detect the adulteration of fruit juices. The approaches have developed from simple procedures, such as measuring the potassium and nitrogen contents of juices, to the use of highly sophisticated and expensive equipment to detect the most recent approaches that unscrupulous suppliers may be using to extend their products. Such adulteration often involves the substitution of some of the fruit juice solids by sugars derived from beet, cane, com or inulin, or the addition of cheaper juices or second extracts of the fruit. 

The methods used to detect adulteration of juices have been reviewed by a number of authors and two examples are given here (Fry el al., 1995 Hammond, 1996). With the changing methods of unscrupulous suppliers it is now common to use a battery of tests to ensure that a product is authentic. Although this is costly, it is the only way to ensure the authenticity of a product and protect company reputations. The array of tests will often include a number of the procedures described above, such as sugar and acid profiles, along with other methods such as stable isotopic and fingerprinting procedures. 

All the compositional guidelines - RSK, AFNOR and AIJN - define ranges for a number of analytes within which a sample s data should fall. These are valuable approaches but they should not be used to the exclusion of other, newer procedures, which are sometimes more sensitive to the more sophisticated approaches that adulterators now have to use to extend their products with any hope that they will not to be detected. 

Fingerprinting methods such as the anthocyanin methods and the Kirksey method for polyphenols (Kirksey el al., 1995) offer good ways to check for the addition of other fruits in a product. As the adulterators have become more sophisticated in the approaches that they use to extend juices, there has been a need for more complex methods of analysis. This means that it is now not uncommon to have to use fingerprinting techniques and isotopic methods to detect the most sophisticated forms of adulteration. These sophisticated analytical methods can even involve detection of the isotope ratios within a class of compounds such as sugars (Hammond el al., 1998). Using the RSSL 13C-IRIS approach, which was developed with financial support from the UK Food Standards Agency, it was possible to reduce the detection limit for the addition of C4-derived sugars to juices by about a factor of two. 

Sometimes it is even important to look at the internal isotope ratios seen within a molecule such as malic acid in apple juice. Two groups, Isolab in Germany and Eurofms in France, found it was useful to look at the carbon isotope ratios at the Q and C4 positions of malic acid extracted from apple juice. This allowed them to detect the addition of synthetic L-malic acid to apple juice at much lower levels than would be possible by other means (Jamin el al., 2000). 

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