AN INVESTIGATION OF THE EQUILIBRIA EXISTING IN GAS-WATER SYSTEMS FORMING ELECTROLYTES

ABSTRACTA gas chromatographic technique was used to determine sulfur dioxide and carbon dioxide in the headspace of packaged apples during storage. The headspace sulfur dioxide so determined decreased more rapidly and correlated better with nonenzymatic browning of the apples than free or total sulfur dioxide. The decrease in headspace sulfur dioxide, which was not accompanied by a comparable decrease in free sulfur dioxide, was attributed to the binding of sulfite to organic components of the apple. Free sulfur dioxide was found to measure not just the inorganic sulfite, which is commonly assumed, but also bound sulfite which was rapidly released under the acid conditions. Neither free nor total sulfur dioxide in a product could be quantitatively determined from headspace gas chromatographic techniques.

A simple and interference-free method for the determination of SO2 in wine based on removal of the analyte by pervaporation is proposed. The sulfur dioxide is formed in an acidic stream and removed from the liquid sample at the donor chamber of the pervaporation unit, then collected in an acceptor solution containing p-rosaniline and formaldehyde. The typical coloured compound thus formed is monitored photometrically at 578 nm on passage through a flow cell. The linear determination range is between 2.0 and 20 µg ml–1 with a precision, expressed as relative standard deviation, lower than 3.0%. The method has been successfully applied to the determination of free and total sulfur dioxide in red and white wines and compares well with the standard iodimetric method.

A voltammetric method for the determination of free and total sulfur dioxide in beer is described. First, volatile aldehydes (mainly acetaldehyde) are purged with nitrogen from a beer sample diluted in alkaline medium, collected in an appropriate electrolyte trapping solution and determined, after derivatization with hydrazine, by voltammetry using a hanging mercury drop electrode. Then, the remaining beer solution is strongly acidified and (total) sulfur dioxide is purged with nitrogen, collected in an appropriate electrolyte trapping solution and determined by voltammetry. The free sulfur dioxide concentration is calculated by difference between (total) sulfur dioxide and acetaldehyde concentrations. The proposed method has a relative standard deviation of about 2.1% and 4.4%, respectively for (total) sulfur dioxide and free sulfur dioxide concentrations normally found in beer, and results are in good agreement with those obtained by the p‐rosaniline reference method.

Analysis of free and total sulfur dioxide in wine by using a gas-diffusion analytical system with pH detection.

The effect of various levels of moisture content of dehydrated potato on the relationship of ‘total’ and ‘free’ sulphur dioxide contents has been studied and the influence of these relationships on the development of non‐enzymic browning has been noted. The use of ‘in‐package’ desiccants to reduce moisture contents reduces the rate of loss during storage of the total sulphite previously added to the potato. Free sulphur dioxide is also found to decrease during storage until the moisture content reaches a critical low value. At or below this moisture level, loss of ‘free’ sulphur dioxide is prevented, and in fact at moderate temperatures of storage it may actually increase. It is suggested that for potatoes of the variety and condition tested, the onset of non‐enzymic browning would be delayed beyond 52 weeks by ensuring that ‘free’ sulphur dioxide levels were maintained at not less than 250 p.p.m.

Studies have shown that the type of packaging can affect the quality and physico-chemical features of foods stored over a longer period of time. Important physico-chemical characteristics of wines that can change over a storage period are alcoholic strength, the amount of acidity or sulfur dioxide, relative density of wines or total dry extract. The aim of this paper was to determine and compare the physico-chemical properties of red wines (Cabernet sauvignon, Frankovka, Merlot and Pinot noir), stored over a period of one year in two different types of packaging (polyethylene terephthalate and bag-in-box). Relative density of wine, total dry extract, alcoholic strength, total acidity content, volatile acidity content, free and total sulfur dioxide content were determined after 3, 6 and 12 months of storage. The results showed that total and free sulfur dioxide content decreased over time in all wines. Volatile acidity and total acidity content increased over time. Alcoholic strength and total dry extract remained mostly stable. Relative density of wine decreased with time. There were no observed differences of these parameters in wines packed in polyethylene terephthalate and bag-in-box containers. Statistical multiple regression confirmed latter assertion.

Aim: This study aims at understanding the impact of the initial phenolic composition on the evolution of red wines after long bottle aging.Materials and results: three different red wines rich in tannins, Aglianico, Casavecchia and Pallagrello, bottled with the same amount of total sulfur dioxide and different amounts of free sulfur dioxide, were analysed after 5 years of bottle aging under controlled exposure to oxygen passing through the closure. Acetaldehyde and monomeric anthocyanins were determined by HPLC, the chromatic characteristics and the main phenolic classes by spectrophotometry, the saliva precipitation index (SPI) by CHIP electrophoresis, and the astringency subqualities by sensory analysis. The results confirmed that during aging there is an increase in polymerisation reactions. A higher amount of acetaldehyde was detected in wines which were bottled with a lower content of free SO2 and were less rich in anthocyanins and tannins; a significant closure effect was observed for these wines. Regarding the influence of closure on tannins, significant slight differences in vanilline reactive flavans and SPI content were observed for Pallagrello wines only, which were characterised by higher values for tannins at bottling. Astringency subqualities differed with closures for each wine.Conclusion: this study indicates that the amount of initial free and combined sulfur dioxide, as well as that of anthocyanins and tannins, are key factors in driving polymerisation reactions and the aging of red wines. After five years of bottle aging the influence of closure could still be observed.Significance of the study: this study provides new insights into the parameters that need to be evaluated before bottling in order to avoid the wrong evolution of red wines after long bottle aging.

Absorption of ultrasonic energy by solutions of sulphur dioxide ammonia and carbon dioxide in water, and in the case of the first gas in several other organic solvents, has been studied by the pulse technique. Aqueous sulphur dioxide solutions exhibit a relaxation phenomenon in the frequency range of 2 to 15 Mc/s. as evidenced by the absorption (α λ) showing a peak in this region when plotted against frequency. This peak occurs at higher frequencies for higher concentrations upto a limit after which the peak absorption frequency does not change with concentration. These observations, along with the fact that no such effect is observed in the case of other solvents, lead to the conclusion that the phenomenon is caused by a change in the dynamic equilibrium between H2SO3 molecules and H+ and HSO3− ions in the presence of the sound beam. The absence of a similar effect in the case of ammonia and carbon dioxide solutions which also involve a chemical reaction is explained on the basis of the widely differing relaxation times of the three gases.

A biosensor based on a glass electrode was developed to determine free sulfur dioxide in wine. The biosensor consists of a microbial membrane of Thiobacillus thiooxidans JCM7814 and a flat glass electrode. A porous gas-permeable membrane was incorporated in the biosensor system to separate free sulfur dioxide from bound sulfur dioxide and to avoid the buffer action of the sample solution. This biosensor gave a linear relationship between the pH decrease and concentration of sulfur dioxide up to 50 mg/liter with a response time of 20 min. The limit of detection for sulfur dioxide was 5.0 mg/liter, and the life-time of the microbial membrane was ca.30 days at 4°C. The biosensor could specifically determine free sulfur dioxide in wine, and was not influenced by temperature or oxygen concentration. The relative standard deviations were 7.41 % for red wine and 5.00% for white wine.

The Chemistry and Technology of the Pretreatment and Preservation of Fruit and Vegetable Products with Sulfur Dioxide and Sulfites

A time study was conducted on the relationship between oxygen and free sulfur dioxide stability in bottled red wine. Samples were obtained from one tank and classified into groups A, B, and C, with respective oxygen concentrations fixed at 1.5, 5.3, and 7.9 mg/L. The bottles were corked immediately after oxygen levels were fixed. Oxygen and free sulfur dioxide contents were measured periodically from a freshly opened bottle from each group for three months. Free sulfur dioxide dropped significantly under high initial oxygen. Loss of free sulfur dioxide in bottled red wine is proportional to the concentration of oxygen. Adjustment for this loss should be made to avoid total oxidation of sulfur and spoilage of wine.

In Republic of North Macedonia, the production of grapes and wine has been known since ancient times. Many grape varieties are grown in this region, but one of the most important and largest regions for wine production is the Tikves region. The aim of the research was to determine the presence of natural radionuclides, as well as total and free sulfur dioxide that are added as additives in wine during its production. The analyzes were performed by gamma spectrometry and the obtained spectra were analyzed by the GENIE 2000 program. The sulfites were determined using OIV accredited methods after prior validation and verification. The results show that 40K is present in all wine brands with a larger size than the other radionuclides observed. 40K levels ranged from low 24.15 ± 2.30 to 38.22 ± 1.50 Bq / L for white wines and 16.28 ± 3.20 to 22.80 ± 3.50 Bq / L for red. As for sulfites, differences can be noticed in terms of the content of total and free sulfur dioxide in all examined wines. Regarding red wines, the lowest value for the content of both total and free sulfur dioxide is observed in Merlot wine (free SO2 = 10.20 ± 0.54mg / L and total SO2 = 51.79 ± 0.55mg / L), and the highest in Traminec wine (free SO2 = 66.41 ± 3.53mg / L and total SO2 = 179.81 ± 1.92mg / L), both from different producers. In terms of white wines, the lowest content of total and free sulfur dioxide is observed in Muscat Ottonel wine (free SO2 = 6.84 ± 0.36mg / L and total SO2 = 40.24 ± 0.43mg / L).

A gas diffusion sequential injection system for the determination of sulphur dioxide in wines

Pervaporation has been coupled on-line to capillary electrophoresis (CE) by a simple interface consisting of a modified CE vial. The approach allows volatile analytes to be removed and injected into the capillary meanwhile the sample matrix remains in the pervaporator. By this approach volatile acidity and free sulfur dioxide have been simultaneously determined in wines. The detection limits (LODs) are 1.25 and 5.00 microg/mL, the quantification limits 4.12 and 16.50 microg/mL, and the linear dynamic ranges between LOD and 50 microg/mL and between 0.1 and 0.9 g/L for free sulfur dioxide and volatile acidity, respectively. The repeatability and within laboratory reproducibility, expressed as relative standard deviation (RSD), are 1.61% and 3.00% for free sulfur, and 3.35% and 4.58% for volatile acidity, respectively. The optimal pervaporation time and the time necessary for the individual separation-detection of the target analytes are 6 and 5 min, respectively. The analysis frequency is 7 h(-1) and the sample amount necessary is less than 7 mL. The proposed method and official methods for the analytes were applied to 32 wine samples. A two-tailed t-test was used to compare the methods, which yielded similar results. The errors, expressed as RSD for the two parameters, ranged between 1.3 and 4.1%.

The effects of wine closures on the sensory properties and aroma profiles of fresh Chardonnay wines were evaluated after four years of bottle storage. Natural cork closure, technical cork closure, Nomacorc light, Nomacorc classic and Nomacorc premium were investigated. Among these wines sealing with different closures, the physicochemical parameters of the wine samples showed no significant differences, except that of the free and total sulphur dioxide. Nomacorc light with the highest OTR (oxygen transition rate) had the least residual free sulphur dioxide. Most of volatiles were generally stable, and seven compounds (acetoin, 1-butanol, 2-phenylethanol, 1-pentanol, (Z)-3-hexen-1-ol, 2-nonanol and ethyl decanoate) were significantly affected by the wine closures. The sensory analysis revealed that cork closures preserved more fruity/flowery characters of the fresh wines after four years’ storage, as well as cork-tainted off-flavour. Two synthetic closures (Nomacorc light, Nomacorc classic) imparted some grilled attributes to the wines. Nomacorc premium highly reserved the fruity/flowery flavour without cork contamination or oxidised toasted characters.