SO2 In Wine Research Articles

A modified pararosaniline hydrochloride method for determination of total and bound sulfur dioxide in wine

An improved pararosaniline hydrochloride (PRA) method for rapid and accurate determination of total and bound sulfur dioxide (SO2) in wine was established. The determination conditions for total SO2 were optimized in model wine systems. The pH of the acidified PRA reagent had a significant effect on the color and the maximum absorption wavelength (λmax) of the reaction system, with its optimum pH 0.48 and a λmax at 549 nm. The addition of ethylene diamine tetraacetic acid (EDTA) could effectively shield the interference of coexisting metal ions present in wine, and a novel approach to double background subtraction was confirmed to remove the matrices interference of red wine color. Under the optimum conditions, the linear range for total SO2 in wine was within 1.00–8.00 mg L−1 (R = 0.9975), with the detection and quantification limits (MDL and MQL) found as 0.02 and 0.06 mg L−1, respectively. The recovery of SO2 ranged from 85.73 % to 105.70 % with the relative standard deviations (RSD) of 0.21 % - 7.78 %, suggesting high sensitivity and accuracy of the method. Combining with the optimized Monier-Williams method, the determination of bound SO2 in wine was also achieved. Sulfite determination can be performed in wine using the rapid, accurate and sensitive method without any pretreatment, and the results were comparable with those of the standard methods.

Assessment of the impact of chitosan treatment on microorganisms in enology

As part of the move to reduce SO2 in wines, the empirical use of chitosan to eliminate the spoilage yeast Brettanomyces bruxellensis is becoming a frequent alternative. Chitosan treatment has an effect on a number of microbial species, at least temporarily, but there is wide variability in response within strains of each species. In addition, the effectiveness of chitosan also depends on the physical and chemical parameters of the wine. However, when chitosan treatment is effective, it appears to be long-lasting.

Rapid determination of free sulfur dioxide in wine and cider by capillary electrophoresis

A novel method for the determination of “true” free sulfur dioxide (SO2) in wine and cider was developed using capillary electrophoresis with direct ultraviolet-visible spectrophotometric detection (CE-UV/vis). Free SO2 was measured in model solutions with different SO2-binding agents present (α-ketoglutarate, pyruvate, acetaldehyde, glucose, fructose, and malvidin-3-glucoside) as well as a variety of white and red wines and ciders. The CE method was compared to three conventional methods for measuring free SO2, the Ripper method, Aeration-Oxidation (AO), and pararosaniline by discrete analyzer (DA). While some statistically significant differences (p<0.05) were found between the four methods in unpigmented model solutions and samples, the values generally agreed. In the presence of anthocyanins in model solution and red wines, free SO2 values found by CE were significantly lower than the other three methods (p<0.05). The difference in values found by Ripper and CE correlated strongly with anthocyanin content (R2 = 0.8854) and even more strongly when accounting for polymeric pigments (R2 = 0.9251). The results in red ciders differed from those in red wines, while the CE measured significantly lower free SO2 values than the other three methods, the difference in free SO2 values measured by CE and Ripper correlated more closely with anthocyanin concentration (R2 = 0.8802) than absorbance due to bleachable pigment (R2 = 0.7770). The CE method was found to be rapid (4 min/injection), sensitive (LOD=0.5 mg/L, LOQ=1.6 mg/L free SO2 in wine, 0.8 and 2.8 mg/L, respectively, in cider), robust, and repeatable (average RSD = 4.9%) and did not suffer from the issue of over-reporting free SO2 in pigmented samples often observed with currently accepted methods.

Sulfur dioxide-free Verdejo wines through the use of a pure stilbene extract: exploring possible synergistic effect with glutathione.

The search for alternatives to sulfur dioxide (SO2 ) in white wine production is a tough challenge for the oenological industry. The current article investigates the effectiveness of several preservatives in protecting Verdejo white wines. The following wines were elaborated: without preservative (CT wines), with SO2 (SO2 wines), with stilbene-enriched extract (ST99 wines), with glutathione (GSH wines) and finally with the combination stilbene extract plus glutathione (ST99-GSH wines). ST99 extract preserved the wines from malolactic fermentation (MLF), maintained the quality parameters of the wines, but affected their color from the beginning of the process. Synergistic effects between ST99 and GSH were found for oxygen consumption rates, related to oxidation processes. The content of amino acids and biogenic amines was slightly affected by the treatments, but the quality or safety of the wines was not compromised. However, after 12 months of ageing in bottle, the SO2 wines showed the highest score in the sensory analysis. The reasons for the evolution of treated wines and the implications of this study for maintaining the quality of free SO2 white wines are discussed. ST99 may be proposed as an alternative to SO2 in wines to be consumed in the short term. Its combination with GSH does not prolong its shelf-life. © 2022 Society of Chemical Industry.

Electrochemical detection of food preservative SO2 in red wine using SiO2 coated CdS nanomaterials

Cadmium sulfide is an important chalcogenide semiconductor nanoparticle prepared by reverse micelle method using cetyltrimethylammonium bromide (CTAB), surfactant. Toxic CdS is coated with silica using tetraethyl orthosilicate (TEOS) precursor and are well characterized. SiO2 provides a sufficient contrast to show the core homogeneously surrounded by the silica shell. The coating can be made thicker by the addition of TEOS resulting in monodispersed silica spheres with CdS core. SO2 is the most important chemical (as preservative and antioxidant) used to prevent wine oxidation. CdS@SiO2 is serving as adsorbent for the detection of SO2 in wine. The detection mechanism and the sensitivity of the method were validated using limit of detection and the limit of quantification values which are determined from differential pulse voltammetric technique. This electrochemical sensing is found to be simple and reliable to detect the free SO2 present in the wine sample.

Premium price for natural preservatives in wine: a discrete choice experiment

The South African wine industry has recently launched the world’s first ‘no sulphite added’ wine made from indigenous Rooibos &amp; Honeybush toasted wood chips. This wood chip contains antioxidant properties known to protect wine from oxidation. On the other hand, SO2 as a preservative, is often perceived by wine consumers as causing headaches and migraines. Differentiated wines based on their SO2 content may be a profitable marketing avenue for the struggling industry. We interviewed more than 600 wine consumers to investigate their perceptions of wine preservatives and preference for several wine attributes. Specifically, we use discrete choice experiments to elicit willingness to pay for the innovative alternative based on Rooibos &amp; Honeybush wood chips. In addition to wine preservatives, we also examine consumers’ preferences for organic wine attributes and wine quality measured by a 100-point quality score and cost. Based on the results from the mixed logit model, we find that consumers are willing to pay an additional €3.53 (R56.48) per bottle of wine with natural Rooibos &amp; Honeybush wood chips, while they are ready to pay €1.22 (R19.52) more for organic wine and €0.10 (R1.60) for each point on the quality score. Consumer preferences are not statistically different between red and white wine but differ considerably across consumers. In particular, those who believe SO2 in wine causes headaches are willing to pay at least three times more for replacing sulphur-based preservatives with a natural one. Marketing implications are offered for the wine industry.

Total SO2 levels and risk assessment of wine and fruit wine consumed in South Korea

This study was conducted to determine the levels of total sulfur dioxide (SO2) in various fruit wines distributed across South Korea and to conduct risk assessment for SO2 exposure through wines. A total of 316 wines were analyzed in 2017, and the daily intake of wine was obtained from raw data provided in the Korea National Health and Nutrition Examination Survey conducted in 2016. In order to conduct risk assessments, we used a stochastic approach using the Monte Carlo method and presented the results in three scenarios to resolve uncertainty about SO2 non-detected (ND) data: the lower-bound scenario, which considers data below the limit of quantification (LOQ) to be 0 mg kg−1, the ½ LOQ scenario, which considers data below the LOQ as half of LOQ, and the upper-bound scenario, which considers data below the LOQ as LOQ value. During the monitoring of 316 wines, the detection range of total SO2 varied from ND to 340.06 mg kg−1, and there were no products exceeding 350 mg kg−1 total SO2, which is the regulated level in South Korea. Risk assessment revealed that most South Koreans were ingesting a safe level of SO2 through wine in terms of the acceptable daily intake (ADI, 0–0.7 mg kg−1 body weight day−1). Similar to the results of studies undertaken in other countries, only a limited percentage of South Korean individuals intake SO2 at a reasonably high amount. The regular monitoring of high levels of SO2 in wine should be a national concern, although this percentage is minimal, and we recommend that the standard be reset as appropriate.

Development and characterization of a pure stilbene extract from grapevine shoots for use as a preservative in wine

Grapevine shoots, known to be a source of bioactive stilbenes, are considered one of the most important and abundant waste products from the vineyard. The objective of this study was to obtain a pure stilbene extract from grapevine shoots and test its properties, mainly antimicrobial ones, as a preservative in wine. A new extract with a purity of 99% in stilbenes was obtained by centrifugal partition chromatography. The extract was characterized by HPLC-MS, the main compounds being E-ε-viniferin (70%) and E-resveratrol (18%). The stability conditions for the extract solution were low temperature (4 °C) and darkness for a maximum of 21 days. Data regarding to the stability of E-ϵ-viniferin, ω-viniferin and r-viniferin are reported first.The antimicrobial activity of the extract was higher against yeast (Brettanomyces bruxellensis, Zygosaccharomyces bailli, Haseniaspora uvarum, Candida zemplinina) than against bacteria (Lactobacillus hilgardii, Oenococcus oeni, Pediococcus pentasaceus). The best antimicrobial activity was found on Brettanomyces bruxellensis and Zygossaccharomyces bailli. The aromatic characterization of the extract allows us to establish that it does not affect the sensory properties of wine, and thus wine quality is not compromised with the addition of the extract. All of the above allow us to propose ST99 as a promising alternative to SO2 in wines, including rose and white wines.

Reducing SO2 Doses in Red Wines by Using Grape Stem Extracts as Antioxidants.

SO2 is a very important wine preservative. However, there are several drawbacks associated with the use of SO2 in wine. The aim of this work is to evaluate the effect of the partial substitution of SO2 in the Tempranillo wine by a Mazuelo grape stem extract and by a commercial vine wood extract (Vinetan®). The results were compared with a control sample (with no addition of any extract). After 12 months of storage in a bottle, total anthocyanin content, together with total polyphenol and flavonoid content were slightly higher for control wines than for those treated with extracts. These differences were of little relevance, as no differences in antioxidant activity were found between any of the wines at the end of the study. The sensory analysis revealed that the use of both extracts as partial substitutes of SO2 could lead to wines with good organoleptic properties, similar or even better to the control ones.

1,1,6-Trimethyl-1,2-dihydronaphthalene (TDN) Sensory Thresholds in Riesling Wine.

1,1,6-Trimethyl-1,2-dihydronaphthalene (TDN) is an aroma compound responsible for the kerosene/petrol notes in Riesling wines. In the current article, three sensory thresholds for TDN were determined in young Riesling wine: detection threshold (about 4 µg/L), recognition threshold (10–12 µg/L), and rejection threshold (71–82 µg/L). It was demonstrated that an elevated content of free SO2 in wine may have a certain masking effect on the TDN aroma perception. In addition, the influence of wine serving temperature on the recognition of kerosene/petrol notes was studied. It was found, that a lower wine serving temperature (about 11 °C) facilitated identification of the TDN aroma compared to the same wine samples at room temperature.

Direct quantification of sulfur dioxide in wine by Surface Enhanced Raman Spectroscopy

A rapid Surface Enhanced Raman Spectroscopy (SERS) method to detect SO2 in wine is presented, exploiting the preferential binding of silver nanoparticles (AgNPs) with sulfur-containing species. This interaction promotes the agglomeration of the AgNPs and inducing the formation of SERS “hot spots” responsible for SO2 signals enhancement. For increasing SO2 concentrations from 0 to100 mg/l in wine simulant, SERS intensity showed an increasing trend, following a Langmuir absorption function (R2 = 0.94). Due to the wine matrix variability, a standard additions method was then employed for quantitative analysis in red and white wines. This method does not require the SO2 separation but only a matrix pre-cleaning by solid phase extraction. The limit of detection (LOD) was defined for each wine tested, ranging from 0.6 mg/l to 9.6 mg/l. The results obtained were validated by comparison with the International Organization of Vine and Wine method (OIV-MA-AS323-04A).

Determination of Molecular and “Truly” Free Sulfur Dioxide in Wine: A Comparison of Headspace and Conventional Methods

Conventional methods such as Ripper titration and aeration-oxidation (A-O) are widely used for the analysis of sulfur dioxide (SO2) in wine. However, the free SO2 reported by these procedures is overestimated due to dissociation of weakly bound SO2 forms during the analysis, particularly from anthocyanin-bisulfite complexes. “Truly” free SO2 in wine can be determined from the headspace SO2 concentration of an equilibrated wine sample. A headspace SO2 method based on gas detection tubes (HS-GDT) was recently described but is not readily automated. While solid phase microextraction (SPME) yielded poor precision in our experiments, our new method, based on static headspace gas chromatography and sulfur chemiluminescence detection (HS-GC-SCD), is readily automated and achieves high precision (

Alternative Methods to SO2 for Microbiological Stabilization of Wine.

The use of sulfur dioxide (SO2 ) as wine additive is able to ensure both antioxidant protection and microbiological stability. In spite of these undeniable advantages, in the last two decades the presence of SO2 in wine has raised concerns about potential adverse clinical effects in sensitive individuals. The winemaking industry has followed the general trend towards the reduction of SO2 concentrations in food, by expressing at the same time the need for alternative control methods allowing reduction or even elimination of SO2. In the light of this, research has been strongly oriented toward the study of alternatives to the use of SO2 in wine. Most of the studies have focused on methods able to replace the antimicrobial activity of SO2 . This review article gives a comprehensive overview of the current state-of-the-art about the chemical additives and the innovative physical techniques that have been proposed for this purpose. After a focus on the chemistry and properties of SO2 in wine, as well as on wine spoilage and on the conventional methods used for the microbiological stabilization of wine, recent advances on alternative methods proposed to replace the antimicrobial activity of SO2 in winemaking are presented and discussed. Even though many of the alternatives to SO2 showed good efficacy, nowadays no other physical technique or additive can deliver the efficacy and broad spectrum of action as SO2 (both antioxidant and antimicrobial), therefore the alternative methods should be considered a complement to SO2 in low-sulfite winemaking, rather than being seen as its substitutes.

Conductometric Determination of Sulfur Dioxide in Wine Using a Multipumping System Coupled to a Gas-Diffusion cell

A conductometric system with a multipumping module and a gas-diffusion cell has been developed to determine free and total sulfur dioxide (SO2) in wine. The developed method has two protocols to determine both types of SO2 using the same system. For free SO2, sulfite is converted to H2SO4 by acidification and diffusion with H2O2 in an acceptor channel. The sample was previously hydrolyzed by mixing the sample with NaOH and heated at 70 °C prior making the determination of total SO2 in order to break the bonds of the combined SO2. Free and total SO2 were determined in the ranges of 2.5–25.4 and 10.2–76.2 mg L−1 with a sample throughput of 13 and 12 h−1, respectively. The calibration curves of free and total SO2 were in the range of ΔG (mS cm−1) = (–1.0242 ± 0.2871) + (0.6613 ± 0.0201) [SO2, mg L−1], r2 of 0.997 and ΔG (mS cm−1) = (–0.5850 ± 0.1678) + (0.1236 ± 0.0033) [SO2, mg L−1], r2 of 0.997. The proposed automated method is simple and easy to apply for the determination of SO2 in wine using simple reagents.

Headspace-Sampling Paper-Based Analytical Device for Colorimetric/Surface-Enhanced Raman Scattering Dual Sensing of Sulfur Dioxide in Wine.

This study demonstrates a novel strategy for colorimetric/surface-enhanced Raman scattering (SERS) dual-mode sensing of sulfur dioxide (SO2) by coupling headspace sampling (HS) with paper-based analytical device (PAD). The smart and multifunctional PAD is fabricated with a vacuum filtration method in which 4-mercaptopyridine (Mpy)-modified gold nanorods (GNRs)-reduced graphene oxide (rGO) hybrids (rGO/MPy-GNRs), anhydrous methanol, and starch-iodine complex are immobilized into cellulose-based filter papers. The resultant PAD exhibits a deep-blue color with a strong absorption peak at 600 nm due to the formation of an intermolecular charge-transfer complex between starch and iodine. However, the addition of SO2 induces the Karl Fischer reaction, resulting in the decrease of color and increase of SERS signals. Therefore, the PAD can be used not only as a naked-eye indicator of SO2 changed from blue to colorless but also as a highly sensitive SERS substrates because of the SO2-triggered conversion of Mpy to pyridine methyl sulfate on the GNRs. A distinguishable change in the color was observed at a SO2 concentration of 5 μM by the naked eye, and a detection limit as low as 1.45 μM was obtained by virtue of UV-vis spectroscopy. The PAD-based SERS method is effective over a wide range of concentrations (1 μM to 2000 μM) for SO2, and the detection limit for SO2 is found to be 1 μM. The HS-PAD based colorimetric/SERS method is applied for the determination of SO2 in wine, and the detection results match well with those obtained from the traditional Monier-Williams method. This study not only offers a new method for on-site monitoring of SO2 but also provides a new strategy for designing of paper-based sensing platform for a wide range of field-test applications.

Formation and Accumulation of Acetaldehyde and Strecker Aldehydes during Red Wine Oxidation.

The main aim of the present work is to study the accumulation of acetaldehyde and Strecker aldehydes (isobutyraldehyde, 2-methylbutanal, isovaleraldehyde, methional, phenylacetaldehyde) during the oxidation of red wines, and to relate the patterns of accumulation to the wine chemical composition. For that, eight different wines, extensively chemically characterized, were subjected at 25°C to three different controlled O2 exposure conditions: low (10 mg L−1) and medium or high (the stoichiometrically required amount to oxidize all wine total SO2 plus 18 or 32 mg L−1, respectively). Levels of volatile aldehydes and carbonyls were then determined and processed by different statistical techniques. Results showed that young wines (<2 years-old bottled wines) hardly accumulate any acetaldehyde regardless of the O2 consumed. In contrast, aged wines (>3 years-old bottled wines) accumulated acetaldehyde while their content in SO2 was not null, and the aged wine containing lowest polyphenols accumulated it throughout the whole process. Models suggest that the ability of a wine to accumulate acetaldehyde is positively related to its content in combined SO2, in epigallocatechin and to the mean degree of polymerization, and negatively to its content in Aldehyde Reactive Polyphenols (ARPs) which, attending to our models, are anthocyanins and small tannins. The accumulation of Strecker aldehydes is directly proportional to the wine content in the amino acid precursor, being the proportionality factor much higher for aged wines, except for phenylacetaldehyde, for which the opposite pattern was observed. Models suggest that non-aromatic Strecker aldehydes share with acetaldehyde a strong affinity toward ARPs and that the specific pattern of phenylacetaldehyde is likely due to a much reduced reactivity toward ARPs, to the possibility that diacetyl induces Strecker degradation of phenyl alanine and to the potential higher reactivity of this amino acid to some quinones derived from catechin. All this makes that this aldehyde accumulates with intensity, particularly in young wines, shortly after wine SO2 is depleted.

Effect of grape juice composition and nutrient supplementation on the production of sulfur dioxide and carboxylic compounds bySaccharomyces cerevisiae

Background and Aims For health‐related reasons, it is crucial to reduce or even eliminate the use of SO2 in wines. The aim of this work was to assess and compare the influence of different Saccharomyces cerevisiae strains, and composition and nutritive supplementation of musts, on the production of SO2 and carboxylic compounds during alcoholic fermentation. Methods and Results Tempranillo and Albarino musts, supplemented with nitrogen and nutrients, from the 2013 to 2015 vintages, were fermented with several S. cerevisiae strains. The SO2 concentration in wines was more influenced by the yeast strain than by the addition of nitrogen. The addition of diammonium phosphate in combination with thiamine reduced the concentration of α‐ketoglutarate. The SO2 production by high and low sulfite‐forming strains depended on the composition of the musts. High sugar concentration and low nitrogen concentration in musts favoured the production of SO2 in wines. Conclusions The opportunity to produce SO2‐free wines from Albarino and Tempranillo by commercial and indigenous S. cerevisiae yeast strains has been shown. The composition of musts can greatly influence the SO2 produced. Moreover, the addition of nitrogen and nutrients can also influence the concentration of carboxylic compounds of wines. Significance of the Study This work contributes to an improved understanding of how to produce SO2‐free wines and may assist decision‐making during winemaking to obtain wines with a low potential to generate allergic reactions in consumers.

Headspace thin-film microextraction coupled with surface-enhanced Raman scattering as a facile method for reproducible and specific detection of sulfur dioxide in wine.

By coupling thin-film microextraction (TFME) with surface-enhanced Raman scattering (SERS), a facile method was developed for the determination of sulfur dioxide (SO2), the most effective food additive in winemaking technology. The TFME substrate was made by free settling of sea urchin-like ZnO nanomaterials on a glass sheet. The headspace sampling (HS) procedure for SO2 was performed in a simple homemade device, and then the SO2 was determined using SERS after uniformly dropping or spraying a SERS-active substrate (gold nanoparticles, AuNPs) onto the surface of the TFME substrate. A reproducible and strong SERS response of the SO2 absorbed onto the ZnO substrate was obtained. After condition optimization, the SERS signal intensity at a shift of 600 cm(-1) and the SO2 concentration showed a good linearity in the range of 1-200 μg/mL, and the linear correlation coefficient was 0.992. The detection limit for SO2 was found to be 0.1 μg/mL. The HS-TFME-SERS method was applied for the determination of SO2 in wine, and the results obtained agreed very well with those obtained using the traditional distillation and titration method. Analysis of variance and Student t test show that there is no significant difference between the two methods, indicating that the newly developed method is fast, convenient, sensitive and has selective characteristics in the determination of SO2 in wine.

Sensing Free Sulfur Dioxide in Wine

Sulfur dioxide (SO2) is important in the winemaking process as it aids in preventing microbial growth and the oxidation of wine. These processes and others consume the SO2 over time, resulting in wines with little SO2 protection. Furthermore, SO2 and sulfiting agents are known to be allergens to many individuals and for that reason their levels need to be monitored and regulated in final wine products. Many of the current techniques for monitoring SO2 in wine require the SO2 to be separated from the wine prior to analysis. This investigation demonstrates a technique capable of measuring free sulfite concentrations in low volume liquid samples in white wine. This approach adapts a known colorimetric reaction to a suspended core optical fiber sensing platform, and exploits the interaction between guided light located within the fiber voids and a mixture of the wine sample and a colorimetric analyte. We have shown that this technique enables measurements to be made without dilution of the wine samples, thus paving the way towards real time in situ wine monitoring.

Surviving in the presence of sulphur dioxide: strategies developed by wine yeasts

Sulphur dioxide has been used as a common preservative in wine since at least the nineteenth century. Its use has even become essential to the making of quality wines because of its antioxidant, antioxidasic and antiseptic properties. The chemistry of SO₂ in wine is fairly complex due to its dissociation into different species and its binding to other compounds produced by yeasts and bacteria during fermentation. The only antiseptic species is the minute part remaining as molecular SO₂. The latter concentration is both dependent on pH and concentration of free bisulphite. However, certain yeast species have developed cellular and molecular mechanisms as a response to SO₂ exposure. Some of these mechanisms are fairly complex and have only been investigated recently, at least for the molecular mechanisms. They include sulphite reduction, sulphite oxidation, acetaldehyde production, sulphite efflux and the entry into viable but not culturable state, as the ultimate response. In this review, the chemistry of SO₂ in wine is explained together with the impact of SO₂ on yeast cells. The different defence mechanisms are described and discussed, mostly based on current knowledge available for Saccharomyces cerevisiae.