Abstract
Since ancient times, grape must and wine have been considered one of the most sophisticated matrices and, in the last few years, the continuous rise in volumes and prices of grapes and wine has encouraged fraud and adulteration in the oenological field. One of the most common adulterations is sugar addition to grape must in the form of cane or beet sugar or syrup coming from vegetable sources, such as cereals or fruits. Since 1990, the International Organisation of Vine and Wine (OIV) has issued specific official isotopic methods to fight against this practice, but they are not always effective. With the aim to develop a new method able to identify sugar addition, we compared the δ13C value of sugar extracted from grape must analyzed by elemental analyzer/isotope ratio mass spectrometry (EA-IRMS) to the δ13C value of proline analyzed by gas chromatography-combustion isotope ratio mass spectrometry (GC–C–IRMS), after extraction and derivatization. δ13C and δ15N of proline have also been tested as potential geographical markers. In addition, the carbon isotopic composition of two characteristic grape must sugars (myo- and scyllo-inositols) was measured by GC–C–IRMS, after derivatization, to identify the illegal correction of their concentration. On the basis of the obtained results we can conclude that the compound-specific isotope analysis represents a novel analytical tool to support and improve certification and control procedures.
Highlights
According to the International Organisation of Vine and Wine (OIV) definition wine is the beverage resulting exclusively from the partial or complete alcoholic fermentation of fresh grapes, whether crushed or not, or grape must that is the liquid product obtained naturally or by physical processes from fresh grapes.[1]
There is the suspect that fraudsters correct the concentration of these two polyalcohols, in particular myo-inositol, by adding commercially pure myoand scyllo-inositols to fake grape must concentrate originated from other fruits or from a mix of sugars
The instrumental data were corrected on the basis of the difference between the δ15N and δ13C values of the standard proline in GC−C−IRMS and Elemental Analysis Isotope Ratio Mass Spectrometry (EA−IRMS), which was in any case always lower than 0.5 and 1.6‰ for δ15N and δ13C, respectively
Summary
According to the International Organisation of Vine and Wine (OIV) definition wine is the beverage resulting exclusively from the partial or complete alcoholic fermentation of fresh grapes, whether crushed or not, or grape must that is the liquid product obtained naturally or by physical processes from fresh grapes.[1]. In the second study we tested two characteristic grape must sugars (myo- and scyllo-inositols) after derivatization to see if the analysis of their δ13C values could be useful in identifying the illegal correction of their concentration in concentrated and rectificated grape must (CRM) These polyalcohols originate in the grape berry and their quantification has already been proposed by Monetti et al to control the authenticity of the CRM because they are not retained by the resins used for the concentration process and are not present in other purified commercial sugars.[17] A minimum content of myo-inositol (750 mg/kg of sugar) and a myo- and scylloinositol ratio of 20 or less have been suggested as authenticity indexes.[17] In Regulation 479/2008 this proposal was only partially adopted and today official CRM controls focus on the presence of myo-inositol alone, without considering its commercial availability, its levels in musts, and the relationship between the two isomers.[18] There is the suspect that fraudsters correct the concentration of these two polyalcohols, in particular myo-inositol, by adding commercially pure myoand scyllo-inositols to fake grape must concentrate originated from other fruits (e.g., date or tapioca) or from a mix of sugars. The δ13C variability of authentic and fake polyalcohols has been explored in this study and tested on samples coming from the market, to verify their validity as fraud detectors
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