QUALITY AND SAFETY OF ITALIAN WINE VINEGAR

Abstract

The aim of this work was to investigate the most common frauds in the production of wine vinegar in Italy. By means of isotopic analyses (SNIF-NMR and IRMS techniques), 100 samples of commercial wine vinegars and 100 samples of red and white wines used for vinegar production were analysed to detect any illegal practices such as watering, sugaring, addition of synthetic acetic acid or table grapes. For further investigations, samples were also submitted to chemical, physical, microbiological and sensorial analyses. The results show that the addition of synthetic acetic acid is still a very common fraud. [PUBLICATION ABSTRACT]

Headnote

ABSTRACT

The aim of this work was to investigate the most common frauds in the production of wine vinegar in Italy. By means of isotopic analyses (SNIF-NMR and IRMS techniques), 100 samples of commercial wine vinegars and 100 samples of red and white wines used for vinegar production were analysed to detect any illegal practices such as watering, sugaring, addition of synthetic acetic acid or table grapes. For further investigations, samples were also submitted to chemical, physical, microbiological and sensorial analyses. The results show that the addition of synthetic acetic acid is still a very common fraud.

- Keywords: frauds, isotopic, quality, safety, vinegar, wine -

INTRODUCTION

Vinegar is an acidic liquid derived from the oxidation of ethanol (CH3CH2OH), which has previously been fermented from sugar. The result is the production of acetic acid (CH3COOH), the main component of vinegar. This process was first explained by PASTEUR. In 1864, he made an important contribution to the scientific study of this substance, by demonstrating that the oxidation of ethanol by means of acetic acid bacteria led to the formation of acetic acid.

Vinegar has long been known and appreciated. It was employed as a culinary ingrethent and preservative as well as a medicament and disinfectant in ancient Greece, Roman times and the Middle Ages. The Italian term "aceto" derives from the Latin acetum (acid and sour liquid obtained from wine) whereas the English term "vinegar" comes from the Old French vin aigre meaning "sour wine". Both words link vinegar with sourness and wine, but this important by-product can be made also from malt, apple cider, fruit, rice, coconut, cane, beer, honey, etc. However, the most common type is wine vinegar. The aim of this study was to investigate the most common frauds relating to Italian wine vinegars, pointing out the infringements of legal limits and quality standards or the risks to human health. These are very important of food quality and safety issues, as vinegar is still widely used in cooking and food preservation.

In Italy, the 20 February 2006 No. 82 Law incorporated the EU Directive for the Common Market Organization (CMO) that regulates wine and also vinegar production. As for commercial wine vinegars, it fixes legal limits for the following parameters: total acidity, alcoholic degree, ashes, sulfur dioxide, zinc, copper, lead, boric acid, bromine and sorbitol. According to Italian legislation, wines used to produce wine vinegars can only be affected by sourness. The Italian Ministry of Agriculture controls food products in order to detect frauds or non-conformities to the law. The term "fraud" generally indicates an intentional deception made to secure unfair advantage or unlawful gain. Our laboratory is involved in this prevention effort, the aim of which is to secure quality and safety for consumers. We carry out analyses on irregular samples of wines, musts, spirits and wine vinegars, already examined by other agencies, in order to confirm or refute the previous results (Review Analysis).

In this work, 1 00 samples of commercial wine vinegars and 100 samples of red and white wines used in vinegar production were analysed. The results were compared with standards set out in current legislation in order to evaluate the incidence of the most common frauds.

With regard to vinegars, we first need to investigate the addition of synthetic acid, a very common illegal practice. Until the introduction of radiocarbon analytical method, this addition was very difficult to detect (RESMINI and VOLONTERIO, 1974; MATTA and GIANNESSI, 1987). Vinegar containing synthetic acetic acid can be assessed by the content of 14C. The amounts of 14C in natural wine vinegars are determined by the year of production. Other adulterations such as watering and sugaring are today easily detectable by means of isotopie analyses (SNIF-NMR and IRMS techniques).

Isotopie techniques were first introduced in France in the 1980s and soon became widely applied in oenology (MARTIN et ed., 1986; FORSTEL et ed., 1996; JAMIN et ed., 2004; THOMAS and JAMIN, 2009). They are based on the fact that a particular molecule may have different isotope contents, depending on the biochemical processes involved in its synthesis. These analyses also made it possible to control mislabelling, a practice concerning both wines and primary products like grapes. As for wines used for vinegar production, it is now easily to verify much of the data or statements reported on their labels. By means of isotopie analyses, we detected the use of table grapes, such as Pergolone, instead of wine grapes. Table grapes and wine grapes have similar isotopie parameters but a different potential alcohol degree. Unscrupulous producers take advantage of the availability of table grapes which cost less, and due to their use on a massive production scale they can make greater profits. As the potential amount of alcohol is lower in table grapes than in wine grapes, a solution of water and sugar is usually added to increase it.

MATERIALS AND METHODS

Materials

Red and white wine vinegars

In this work, 100 commercial samples of white and red wine vinegars originating from the most important Italian production areas were analysed anonymously and indicated by progressive numbers. The samples were collected in the following regions: Piemonte, Lombardia, Veneto, Emilia Romagna, Campania, Sicilia.

Red and white wines used in vinegar production

Other 100 red and white wines employed in vinegar production were also analysed anonymously and indicated by progressive numbers. The samples were collected in the following regions: Piemonte, Lombardia, Veneto, Friuli, Emilia Romagna, Lazio, Puglia, Sicilia, Campania.

Methods

Red and white wine vinegars

The chemical and physical analyses covered the following legal parameters: total acidity, ethanol, copper, zinc and lead content, presence of synthetic acetic acid. They were carried out according to the standards established by the resolution of the International Organisation of Vine and Wine (OIV): "Oenology 2000 - Methods of analysis of vinegars".

- Total acidity was determined by titration with sodium hydroxide 0. 1 N. (Phenolphthalein indicator).

- Ethanol was determined after distillation by titration with the addition of an excess of potassium dichromate and then back titrated with a solution of ferrous sulfate and ammonium.

- Heavy metals were determined in vinegars using a Zeeman 5100 atomic absorption spectrometer (Perkin Elmer). Copper was determined by flame ionization spectroscopy. In the case of very low concentrations, we used the method of a standard addition. Zinc was also determined by flame ionization spectroscopy. Lead was determined by ashing.

- Synthetic acetic acid was quantified by the amount of 14C detected. Natural wine vinegars have amounts of 14C which relate to their year of production. The addition of synthetic acid causes a noticeable reduction in 14C values. Measurements were carried out by means of a 14C liquid scintillation spectrometer. As a reference, we used our data-base of radioactivity values for natural vinegar.

Red and white wines used for vinegar production

All the samples of wines were submitted to chemical, physical and isotopie analyses, according to the resolutions established by the OIV methods. The chemical and physical analyses covered the following legal parameters: total sulfur dioxide, copper, zinc, lead, methanol, isotopie parameters. Organoleptic faults were ascertained through a series of sensory analyses. Italian laws states that all the values detected in wines used for vinegar production must be within the legal ranges. Only the volatile acidity can be over the legal limit.

- Total sulfur dioxide. It was oxidized by sulfuric acid with oxygenated water and measured by titration with 0. 1 N sodium hydroxide using the mixed indicator Methyl Red-Methylene Blue - alcoholic solution.

- Heavy metals. These were directly determined in wines using a Zeeman 5 1 00 atomic absorption spectrometer (Perkin Elmer). Lead was determined by furnace whereas copper was determined by flame ionization spectroscopy.

- Methanol. It was quantified according to the OIV gas chromatographic method and extracted from wine by distillation and then quantified using a Carlo Erba model 5300 gas Chromatograph and an Innowax column equipped with a flame ionization detector, according to the OIV reference method.

- Isotopie parameters. These were determined by applying the following methods: SNIF-NMR Isotopie Ratio (D /H)I determinations were performed on a Bruker Avance 300 (Cryomagnet 300/52) NMR spectroscope. The analysis was carried out on distilled wine (Fig. 1).

13C /12C isotopie ratios were determined by isotopie ratio mass spectrometry, using a Fisons, Optima model. The variation from a standard value attributed to a reference substance by the International Atomic Energy Agency of Vienna (IAEA) was measured. The analyses were carried out on distilled wine (Fig. 2).

18O/ 16O isotopie ratio measurements were performed on the same mass spectrometer. These values represent the % variation from the standard value attributed to ocean water, the Vienna Standard Mean Ocean Water (V-SMOW). The analyses were carried out directly on wine without any distillation.

- Organoleptic faults. These were detected through a series of sensorial analyses carried out by the CRA-ENO wine tasting panel, formed by five wine tasters trained to detect wine faults.

RESULTS

Red and white wine vinegar

For red and white wine vinegars, we detected the addition of synthetic acid and dried currants.

Addition of synthetic acetic acid radiocarbon

In the past, the addition of pyroligneous acid or "wood vinegar" to vinegars was a very common practice. This synthetic acid was very difficult to detect, because it has the same chemical structure as vinegar. In the detenriination of 14C in our vinegar samples, we recorded a minimum value of 1 1 .29 dpm/g C and a maximum value of 14 dpm/g C. The reference value of 14 dpm/g for authentic vinegars was determined in our laboratory. Values that are 5% or more under the reference value are considered to be irregular because of the addition of acetic acid. In our investigation, 20 samples were found to be irregular. Although the incidence of this fraud has diminished, it still remains one of the most widespread.

Addition of dried currants

The use of dried currants in vinification is another common practice. Their presence in wine is exposed by the variation in isotopie parameters. In vinegars, this addition is very difficult to detect, if water is added to dilute the wines used for vinegar production. This is a legal oenological practice but it changes the isotopie parameters of the wines. We found 3 irregular samples.

Red and white wines used for vinegar production

For the red and white wines used for vinegar production, we detected the following isotopie parameters.

The detenriination of the isotopie parameter (D /H)I produced values ranging from a minimum of 94 ppm to a maximum of 108 ppm. Reference values were obtained from the National Annual Data Bank on Authentic Wines: the range established was from 98 to 1 08 ppm. We found 10 irregular samples because of sugaring. Values from 94 to 98 ppm are due to the addition of sugar beet to wine, whereas values over 110 ppm are due to the addition of sugar cane.

The detenriination of the 13CV12C isotopie parameter showed values ranging from a miriimum of -19 d% to a maximum of -28 d%. The range established from the National Data Bank is from -24 to -28 d%. Values below -24 d% indicates the addition of exogenous sugars made from sugar cane or maize. We found 5 nregular samples.

The determination of the 18O/ 16O isotopie parameter 18O/ 16O showed values ranging from a minimum of -5 d% (V-SMOW) to positive values (Fig. 3). Reference values are determined yearly and were positive for the year concerning our samples. In general, negative values of this parameter indicate watering of the wine employed for vinegar production. This dilution increases the total volume of wines. We found 15 irregular samples.

We also found 5 samples for which all three isotopie parameters did not correspond to the reference values. This indicated the use of table grapes, e.g. Pergolone, instead of wine grapes (mislabelling). The two types of grapes have similar isotopie parameters but different potential alcohol degrees. When table grapes are illegally used in wine production, water and sugar are added to increase the alcohol content. This addition can be now identified by carrying out the isotopie analyses described.

Subsequently, we investigated the possible presence of heavy metals in our samples.

Copper

Copper sulfate pentahydrate is a fungicide. Mixed with calcium oxide it forms the so-called "Bordeaux Mixture" which is used to control fungus on grapes. In wines, this compound is usually below 1 mg/L, because it is partially eliminated during fermentation in the form of insoluble salts absorbed by lees. Thus the presence of copper in wines may be due to other causes: releases from the winery equipment or wine treatments with copper sulfpbate to eliminate bad odours. In the analysed samples, we found a minimum content of 0,3 mg/L and a maximum of 3 mg/L. Wine legislation establishes a limit for copper of 1 mg/L. We found 12 samples with a content over the legal limit.

Zinc

Although zinc is an essential requirement for our health, an excess of zinc can be harmful. Its presence in wine may be due to its release from the storage containers. Zinc alloys have been used for thousands of years: brass is doubtless the most ancient. It was widely employed because of its resistance and the large availability of its component materials. The introduction of steel in wineries limited the use of zinc and its alloys. The content in zinc of our samples varied from a minimum of 2 mg/L and a maximum of 6 mg/L. The legal limit is 5 mg/L. We found 1 sample over the legal limit.

Lead

Lead is very dangerous to human health because it is highly toxic and may cause saturnism. The lead content in wines has been object of many studies carried out by OIV and E.U. experts. The legal limit of 0.2 µg/L is very low. The values determined for the analysed samples ranged from a minimum of 0. 1 µg/mL to a maximum of 0.6 µg/mL. We found 2 irregular samples. A higher lead content may be due to traffic pollution near vineyards (fuel contains tetraethyl lead), vineyard treatments with copper salts contaminated by lead, releases by the storage container, winery machinery, or from the screw caps of wine bottles.

Methanol

This is a very noxious compound. Today its content in wines is generally low. Higher contents can be found in the so-called "hard-pressed wines" because of the natural degradation of pectins, during fermentation. This occurs when pomace is overpressed in orderte extract the juice that it still contains. The values determined in our samples varied from a minimum of 0. 1 mL % of alcohol anhydride (a.a.) to a maximum of 0.45 mL % a.a. The legal limit for alcohol anhydride is 0.20 mL % mL a.a., for white wines, and 0.25 mL % a.a. for red wines. We found 5 irregular samples.

Sulfur dioxide

High contents of sulfur dioxide are toxic. Nowadays wine quality is better than in the past, but current sulfur dioxide legal limits are still high, especially for sweet wines. The values determined in our samples varied from a minimum of 50 mg/L to a maximum of 360 mg/ L. The legal limit established by E.U. laws is 200 mg/L for white wines and 150 mg/L for red wines. We found 3 irregular samples.

To complete our survey, we investigated the possible presence of organoleptic faults or microbiological contamination.

Organoleptic faults

Some organoleptic faults were detected in 35 samples. Well-known wine defects such as (oxidation, casse, flowers of wine or mould) were the most common ones. Organoleptic faults cannot be considered "frauds" in a strict sense and are generally related to wine storage problems.

Microbiological contamination

Lactic bacteria and re-fermentation were detected in 2 samples.

CONCLUSIONS

The quality of Italian wine vinegars has generally improved. Today, the availability of modern technologies and the use of good oenological products are more widespread. However, some infringements of the law are still committed (Fig. 4). To detect the slightest amount of an illegal or noxious compound, more reliable analytical methods, such as isotopie analyses, are now applied. The introduction of a restrictive legislation and effective measures to prevent frauds has produced good results. Therefore, it is very important to continue to assess the number and variety of these infringements in order to further improve food quality and safety.

ACKNOWLEDGEMENTS

We would like to thank Mr. Angelo Barrocu for collaborating on the analyses and Mrs. Annamaria Di Franco for her help with the English text.

References

REFERENCES

Forstel H., Martin G.J. Olschimke D. and Wittkowski R. 1996. Détermination du rapport isotopique 180/160 de l'eau des vins, Office International de la Vigne et du Vin FV N° 1035 2366/190396.

Giannessi P. and Matta M. 1987. Trattato di scienza e di Enologia, Vol. I1 p. 122-137.

Jamin. E., Martin. F. and Martin G.G. 2004. Determination of the 13C /12C ratio of Ethanol derived from fruit juices and maple syrup by Isotopie Ratio Mass Spectrometry. Journal of AOAC International, 87 (3): 621-630.

Martin G.J., Guillou C, Naulet N., Brun S., Tep Y., Cabanis J.C. and Sudraud P. 1986. Control of origin and enrichment of wine by Specific Isotope Analyses. Sciences des Aliments, 6: 385-405.

OIV 1995. Cahier scientifique et technique: le plomb. Bulletin OIV.

Resmini P. and Volonterio G. 1974. Determinazione del livello naturale di 14C nell'alcool etilico mediante scintillazione liquida: ottimizzazione delle condizioni di conteggio. Rivista di Viticoltura e di Enologia di Conegliano, 10: 420-430.

Thomas F. and Jamin E. 2009. 2H NMR and 13C-IRMS Analyses of acetic acid from vinegar, 18O-IRMS analysis of water in vinegar (International Collaborative Report), Analytica Chimica Acta, 649: 98-105.

Paper received September 27, 2011 Accepted October 27, 2011