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In this paper, we investigate whether the analysis of stable isotope ratios D/H and ¹³C/¹²C in ethanol and acetic acid and of ¹⁸O/¹⁶O in water can be applied to the ingredients of "aceto balsamico di Modena IGP" (ABM) to evaluate their authenticity. We found that impurities in the extraction solution do not affect the ¹³C/¹²C of acetic acid and the D/H values of acetic acid are not affected under a composite NMR experiment. The standard deviation of repeatability and standard deviation of reproducibility are comparable in wine vinegar and ABM and generally lower than those quoted in the official methods. This means that the validation parameters quoted in the official methods can also be applied to the ingredients of ABM. In addition, we found no changes in the isotopic values from wine to vinegar and to ABM, and from the original must to the ABM must, providing experimental evidence that reference data from wine databanks can also be used to evaluate the authenticity of vinegar and ABM.

Stable isotope ratios (SIRs) of C, N, H and O have been exensively used in fruit juices quality control (ENV and AOAC methods) to detect added sugar and the watering down of concentrated juice, practices prohibited by European legislation (EU Directive 2012/12). The European Fruit Juice Association (AIJN) set some reference guidelines in order to allow the judging of the genuiness of a juice. Moreover, various studies have been carried out to determine the natural variability of SIRs in fruit juices, but none of these has investigated SIRs extensively in authentic citrus juices from Italy. In this work, about 500 citrus juice samples were officially collected in Italy by the Italian Ministry of Agricultural and Forestry Policies from 1998 onwards. (D/H)(I) and (D/H)(II) in ethanol and δ(13) C(ethanol), δ(13) C(pulp), δ(13) C(sugars), δ(18) O(vegetalwater), δ(15) N(pulp), and δ(18) O(pulp) were determined using Site-Specific Natural Isotope Fractionation-Nuclear Magnetic Resonance and Isotope Ratio Mass Spectrometry, respectively. The characteristic ranges of variability in SIRs in genuine Italian citrus juice samples are here presented as well as their relationships and compliance with the limits indicated by the AIJN and others proposed in the literature. In particular, the Italian range of values was found to be not completely in agreement with AIJN guidelines, with the risk that genuine juices could be judged as not genuine. Variety seems not to influence SIRs, whereas harvest year and region of origin have some influence on the different ratios, although their data distribution shows overlapping when principal component analysis is applied.

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This paper presents the results of a collaborative study involving seven laboratories and concerning two samples of wine vinegar, one of apple vinegar and four of balsamic vinegar. The aim of the study was to define standard deviations of repeatability (sr) and reproducibility (sR) for vinegar and balsamic vinegar stable isotope ratios of H (D/H), C (δ13C) and O (δ18O), in order to establish them as fully recognized official standards. Acetic acid was extracted and subjected to (D/H)CH3 and δ13C analysis. δ18O analysis was performed on whole samples. The grape must solution remained after distillation of balsamic vinegar was fermented and the resulting ethanol was subjected to (D/H)I, (D/H)II, R and δ13C analysis. The sr and sR were 0.6 ppm and 1.1 ppm for (D/H)CH3, 0.14‰ and 0.25‰ for δ13C of acetic acid, 0.1‰ and 0.17‰ for δ18O of water, 0.19 ppm and 0.64 ppm for ethanol (D/H)I, 1.14 and 1.31 ppm for (D/H)II, 0.09 and 0.11‰ for δ13C of ethanol. These data are in line with those in the literature or reported in corresponding official methods, and sr and sR of balsamic vinegar are in line with those of vinegar and must.

In this study we investigated the effect of the grape withering process occurring during the production of Italian passito wines on the variability of the (D/H)I, (D/H)II, δ(13)C, and δ(18)O of wine ethanol and the δ(18)O of wine water. The production of PDO Erbaluce di Caluso Passito in five different cellars in Piedmont (Italy) was considered in two successive years. Moreover, samples of 17 different traditional Italian passito wines taken at different stages of maturation were taken into account. We found that the δ(18)O of must and wine water and the δ(18)O of ethanol decrease in the case of passito wines produced in northern and central Italy using postharvest drying of the grapes in dedicated ventilated or unventilated fruit drying rooms (fruttaio), during autumn-winter. For passito wines produced in southern Italy, where the main technique involves withering on the plant (en plein air), δ(18)O tends to increase. The (DH)I of wine ethanol did not change during withering, whereas the (DH)II and δ(13)C values changed slightly, but without any clear trend. Particular attention must be therefore paid in the evaluation of the δ(18)O data of passito wines for fraud detection.

According to Organisation Internationale de la vigne et du vin (OIV) standards, when analysing the stable isotope ratio of deuterium to hydrogen D/H at the methyl (I) and methylene (II) site of ethanol from concentrated must, a dilution with tap water is needed in order to carry out the alcoholic fermentation. This dilution causes a partial transfer of water hydrogens to the sugar, and this affects the (D/H)I and (D/H)II isotopic values of ethanol, which need to be normalised through specific equations based on the analysis of water δ18O or δ2H. The aim of this study was to evaluate the effectiveness and correctness of these equations experimentally. Grape, cane, and beet sugar, as well as grape must were diluted with water with increasing H and O stable isotope ratios, fermented, and analysed. SNIF-NMR and IRMS techniques were applied following the respective OIV methods. The equations based on the δ2H analysis of the diluted sugar/must solutions proved to be reliable in all the cases, although it is not an OIV standard. When using the equations based on the values of δ18O of the diluted solution, data normalisation was reliable only in cases where the water used for dilution had not undergone isotopic fractionation due, for example, to evaporation. In these cases, δ2H should be analysed.

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