Formation and prevention of light-struck taste white wine

Light-struck taste is a defect occurring white wines bottled in clear glass and exposed to light. It is manifested by a loss of color and aroma as a result of the presence of sulfur-like smells [1]. Its appearance is due to the reduction of riboflavin (RF), a high photosensitive compound, and the oxidation of methionine (Met) to give methional which is unstable under light and decomposes to acrolein and methanethiol. Two molecules of the latter compound can yield to dimethyl disulfide [1]. Methanethiol is highly volatile, has a low perception threshold (0.3 to 3 \ub5g/L in wine) and confers rotten eggs-like or cabbage-like aromas. Dimethyl disulfide is less volatile, but the olfactory perception threshold is still low (30 \ub5g/L) and it has an aroma impression of cooked cabbage or onion. Concentrations of RF lower than 80-100 \ub5g/L can decrease the risk of light-struck taste appearance [2]. The wine treatment with charcoal can lead to a depletion of RF in white wine [3], but it can have a detrimental effect on sensory properties of white wine. In order to limit the appearance of the light-struck taste, certain antioxidants (sulfur dioxide and glutathione) and wood tannins (oak, chestnut and galla) were tested in model wine containing RF and Met and exposed to light. The concentrations of these two compounds were monitored as well as the content of volatiles. The RF was completely degraded under light independently to the presence of Met. On the contrary, this amino acid underwent to photodegradation only in presence of RF. The sulfur dioxide limited the appearance of the defect maybe due to the formation of a complex riboflavin-sulfur dioxide making the vitamin less susceptible to the photo-degradation. The molar ratio degraded RF:degraded Met ranged from 1:8 to 1:20, much higher than one previously indicated in literature [1]. As expected, the increasing concentrations of RF led to major levels of sulfur compounds. Similarly, higher amounts of Met strongly affected the formation of volatiles which content increased as Met increased. The wood tannins could exert a protective effect, the galla tannins in particular. In fact, the lowest levels of volatiles, namely methanethiol and dimethyl disulfide, were found when the gallotannins were added. Nevertheless, the volatiles were lower in presence of both chestnut and oak tannins in comparison to the model solution. The content of oxidized phenols could be the main actor against the formation of the light-struck taste since it was the highest into the galla tannins. The oxidized phenols could bind the sulfur compounds and, consequently, they could be reduced back to phenols. The protection of white wine against the appearance of the light-struck taste can be achieved by adding the wood tannins, gallotannins in particular, before bottling. As this defect can appear for higher levels not only of RF, but also of Met, low concentrations of these compounds can also play a protective effect allowing the maintenance of the wine quality during the shelf-life

Application of UV-C light for preventing the light-struck taste in white wine

The light-struck taste is a fault occurring in white wine bottled in clear bottles and exposed to light. The defect is due to the formation of methanethiol and dimethyl sulphide responsible for like-cabbage aroma arising from the reaction between riboflavin (RF), a highly light-sensitive compound, and methionine (Met). The light-struck taste is limited for RF concentration lower than 50 \ub5g/L achieved through the choice of a Saccharomyces strain low RF-producer and the RF removal with charcoal and bentonite as fining agents [1]. Moreover, the protective effect of wood tannins has been recently showed, especially galla tannins [2]. Due to the RF sensibility to light, the UV-C light treatment was assayed. A synthetic wine solution spiked with RF (200 \ub5g/L) and Met (3 mg/L) was irradiated with UV-C light up to 2000 J/L and RF decay was monitored. A linear decrease as UV-C light intensity increase was observed. RF was lower than 50 \ub5g/L and 20 \ub5g/L for 1500 J/L and 2000 J/L treatments, respectively. The addition of tannins (40 mg/L) led to a limited RF decrease (73%) maybe due to their shading properties [3]. Even though the UV-C light treatment is not admitted by the International Organization of Vine and Wine, its application could represent a tool for avoid the risk of light-struck taste development in bottled wine. The light exposure when the redox potential is high and the combined use of tannins could limit the appearance of this fault after the wine bottling preserving the wine quality during the shelf-life

Characterisation of Vernaccia Nera (Vitis vinifera L.) grapes and wine

Vernaccia Nera (VN) is a minor Italian red grape cultivar whose oenological properties have not been investigated yet. Traditional winemaking procedures with VN can include grape drying and even triple sequential fermentations, but a rational vinification approach should be based on the grape composition. Since a comprehensive characterisation of the VN grape is still missing, the ripening of VN grapes was monitored by evaluating flavour compounds, proanthocyanidins and anthocyanins. The grapes were used to produce red wine whose chemical composition and sensory properties were assessed. Ripe VN grapes contained high amounts of extractable anthocyanins (0.88 g/kg). The most abundant anthocyanin was malvidin (56.6%), and high relative amounts of cumarate forms (11.3%) were also found. The grape skin showed a high concentration of proanthocyanidins (2 g/kg), whose degree of polymerisation was low (10.3). Epigallocatechin accounted for up to 39% of the flavan-3-ol units in the skin. Flavour compounds in the grapes included glycosylated norisoprenoids (mainly 3-oxo-alpha-ionol and vomifoliolo) and benzenoids. The VN red wine showed a high concentration of anthocyanins, but the level of proanthocyanidins (0.93 g/L) was lower than expected. The spicy flavours were the notes mostly recognised in the sensory evaluation. Our data highlight the VN grape as suitable for the production of ready-to-drink or shortly aged red wine due to its high acidity and low astringency

Oxygen Consumption in South African Sauvignon Blanc Wines: Role of Glutathione, Sulphur Dioxide and Certain Phenolics

The aim of this research was to investigate the interaction between sulphur dioxide, glutathione (GSH) andcertain phenols in the presence of oxygen in a synthetic wine and in clarified Sauvignon blanc wine. In thisstudy, the clarified wine, from which most of the phenols had been removed, was compared to syntheticwine solution, with both mediums being enriched with caffeic acid to investigate the effect of different levelsof sulphur dioxide and GSH on oxygen consumption. Moreover, thirteen young South African Sauvignonblanc wines with different levels of sulphur dioxide were oxygenated, and the oxygen consumption andphenolic and colour changes were monitored over time. The results show that oxygen consumption wasinfluenced greatly by the presence of sulphur dioxide and, to a lesser extent, by the presence of GSH,with both compounds decreasing during the course of the experiment. During oxidation, an increasewas observed in glutathionyl caffeic acid, as well as in oxidised glutathione (GSSG); however, this didnot coincide with the percentage decrease in GSH. Oxidation further led to an increase in absorbancemeasurements at 420 and 440 nm (yellow-orange colour), which were reduced by the presence of SO2. Alarge variation was also observed in the oxygen consumption of the young wines, with this rate increasingwith an increase in SO2 concentration. Positive correlations were also observed between oxygen, SO2, GSHand Cu concentrations, which were again negatively correlated with absorbance at 420 and 440 nm andGSSG concentrations

Chemical Characterization and Volatile Profile of Trebbiano di Lugana Wine: A Case Study

In this study, the volatile profile of Trebbiano di Lugana wine was determined and its chemical composition was considered to understand its potential longevity. Seven wine samples produced in different years (2005-2017) were collected by the same winery and analyzed up to 13 years after bottling. Color, total and polymeric phenols, glutathione, free volatiles and sensory characteristics were assessed. The color turned from yellow to an increased brownish hue as the aging time increased; nonetheless, it was stable up to five years from the production. Thirty-six aroma compounds were detected including higher alcohols, esters, and norisoprenoids (\u3b2-damascenone and \u3b2-oxo-ionone). While higher alcohols did not show a dependence on the different years of production, a decrease of esters was found over aging with the exception of wine produced in 2009, the latter showing higher levels of glutathione that could limit esters' hydrolysis. The perception of floral and fruity notes was dependent on the storage time with little differences up to five years after bottling. Trebbiano di Lugana wine could be suitable for aging and this aptitude might be further improved also through the proper choice of closure and packaging systems to encourage logistic and marketing strategies

Development of a HPLC method for the simultaneous analysis of riboflavin and other flavin compounds in liquid milk and milk products

A high-performance liquid chromatography method with fluorescence detection was developed for the quantification of riboflavin (RF), flavin mononucleotide (FMN), flavin adenine dinucleotide (FAD) and their photodegradation products, lumichrome (LC) and lumiflavin (LF), in liquid milk and milk products. Both sample preparation and chromatographic separation were studied to avoid acidic conditions that proved to affect flavin stability and degrade FAD into FMN. The sample preparation includes centrifugal skimming and ultrafiltration steps and is suitable for routine application. Linear response was obtained for individual flavins in the respective concentration ranges of interest and relative standard deviation (RSD) was lower than 5%, except for FAD (RSD 11%). The recovery ranged between 80\u2013100%. The proposed method proved to be suitable for assessing flavins in commercial liquid milk and fermented milk products, and for monitoring the degradation of FAD, FMN and RF and the formation of LF and LC in bottled milk exposed to light during shelf storage

Impact of Cooking on Bioactive Compounds and Antioxidant Activity of Pigmented Rice Cultivars

Pigmented rice cultivars, namely Venere and Artemide, are a source of bioactive molecules, in particular phenolics, including anthocyanins, exerting a positive effect on cardiovascular systems thanks also to their antioxidant capacity. This study aimed to determine the total phenol index (TPI), total flavonoids (TF), total anthocyanins (TA) and in vitro antioxidant capacity in 12 batches of Venere cultivar and two batches of Artemide cultivar. The rice was cooked using different methods (boiling, microwave, pressure cooker, water bath, rice cooker) with the purpose to individuate the procedure limiting the loss of bioactive compounds. TPI, TF and TA were spectrophotometrically determined in both raw and cooked rice samples. Rice samples of Artemide cultivars were richer in TPI (17.7-18.8 vs. 8.2-11.9 g gallic acid/kg in Venere rice), TF (13.1 vs. 5.0-7.1 g catechin/kg rice for Venere rice) and TA (3.2-3.4 vs. 1.8-2.9 g Cy-3glc/kg for Venere rice) in comparison to those of Venere cultivar; as well, they showed higher antioxidant capacity (46.6-47.8 vs. 14.4-31.9 mM Trolox/kg for Venere rice). Among the investigated cooking methods, the rice cooker and the water bath led to lower and comparable losses of phenolics. Interestingly, the cooking water remaining after cooking with the rice cooker was rich in phenolics. The consumption of a portion of rice (100 g) cooked with the rice cooker with its own cooking water can supply 240 mg catechin and 711 mg cyanidin 3-O-glucoside for Venere rice and 545 mg catechin and 614 mg cyanidin 3-O-glucoside for Artemide rice, with a potential positive effect on health

Effect of the grape must extraction steps on the content of varietal thiol precursors

The varietal thiols 3-sulfanyl-3-methylpentan-2-one, 3-sulfanylhexan-1-ol and its acetyl ester are the main responsible for boxwood, grapefruit and passion fruit notes of many white wines. These compounds occur in grape only as non-volatile precursors bound to S-glutathionyl- or S-cysteinyl- moieties but they are released by the yeast over the fermentation. However, the amount of these volatile compounds in wine is seldom related to the amount of their precursors in grape [1] because the lyase activity of yeast is a strain-dependent characteristic [2] and the probable contribution of hydrogen sulphide to the neoformation of the volatile thiols [3]. Fracassetti et al. [4, 5] reported massive loss of glutathione and glutathionyl- bounded varietal thiols as result of the grape juice extraction under production in industrial-scale conditions. Particularly, more than 60% of the precursors S-glutathionyl-3-sulfanylhexan-1-ol (GSH-3MH) and its aldehyde form (S-glutathionyl-3-sulfanylhexanal, GSH-3MHAl) got lost from Grillo and Catarratto bianco grape cultivars, the main Sicilian white grape cultivars, as result of the juice extraction. Such a behaviour can seriously detrimentally affect the flavouring properties of the final wine and it points out a further source of the lacking correlation between the amount of precursors in grape and volatile thiols in wine. The reasons for such behaviour were investigated in Grillo grape pressed under industrial-scale production. Must samples were collected after crashing, at draining, at pressing yield of 20%, 40%, 60% and 70%, during transfer in clarification tank, in the clarification tank and after clarification. The must was either air-exposed or air-free during the pre-fermentative steps. Thiol precursors were determined in SPE-purified must samples by UPLC-HRMS [5]. The concentration of thiol precursors detected following the crushing was comparable to the value found in grape, but it dramatically decreases (< 95%) in the must from the press loading. The concentration of thiol precursors increased as the must yield increased, and eventually equals the levels in the grape when a must yield of 60% was achieved. The final loss of thiol precursors was about 80% and 95% for GSH-3MH and GSH-3MHAl, respectively, in the must sampled at the clarification vat (the last juice fraction was excluded). Higher loss of thiol precursors was observed when the must was produced under air-free condition, whereas higher amounts were recorded in laboratory-made must, especially when sodium fluoride or EDTA were added prior the pressing. The results show that the contact of must with the grape skin leads to a loss of thiol precursors. Oxygen seems to be not involved in the oxidative loss of thiol precursor The protective behaviour of the cation-binding compounds suggests that the cations occurring on the grape skin can be responsible for the loss of thiol precursors during the pre-fermentative steps

NMR approach for monitoring the photo-degradation of riboflavin and methionine

The light exposure of white wine is responsible for several reactions leading to changes on colour, flavours and, consequently, affecting the sensory profile. These reactions can take place when the white wine is bottled in clear glass and their mechanisms are dependent on both light exposure and chemical composition of white wine. Particular attention has been given to the reaction involving riboflavin (RF), a photo-sensitizer compound, and methionine (Met), a sulfur-containing amino acid, that can cause the formation of volatile sulphur compounds (VSCs), namely methanethiol and dimethyl disulfide. These compounds are responsible for a defect known as light-struck taste. Previous studies showed that hydrolysable tannins, in particular those from nut galls, limited both the degradation of Met and the formation of VSCs. The effectiveness of hydrolysable tannins was also proved after light exposure and storage for 24 months. In order to better understand the role of tannins in the photo-degradative reactions, an NMR approach was carried out. A solution containing RF (0.2 mM) and Met (2 mM) acidified at pH 3.2 was exposed to light by using fluorescence light bulbs. The solution was exposed to light up to two hours sampling it every 15 minutes. The same experimental conditions were applied in presence of gallic acid (2 mM), a constitutive unit of nut gall tannins. The degradation of RF and Met was monitored and, as expected, their signals decreased as the light exposure increased. Results provided evidence that a new signal appeared at 2.64 ppm. This signal was assigned to the SOCH3 moiety of methionine sulfoxide through the addition of the standard solution and standard 2D-NMR assignment techniques. The formation kinetic of methionine sulfoxide was measured for increased duration of light exposure and its rate resulted two-folds lower with the addition of gallic acid. This result suggests that the limited degradation of Met in presence of tannins, also observed in previous studies, is due to their action as competitor with Met in reducing RF from its excited form. The NMR technique was suitable for monitoring the photo-degradative reaction of RF and Met. Further researches have been carried out in order to verify and prove the ability of tannins in quenching both singlet oxygen and RF

Why do grape-based fruit wines could be “super” magic?

In Europe, the global consumption of wine is decreasing and new alternatives of wine have been appearing on the market. The attractiveness of these products rely on the fact that they are inexpensive and easy to drink, with low alcohol content and obtained by mixing wines with fruit juices or flavoring wine. While fruit wines represent an ancient art [1], no studies have investigated the production of beverages that are obtained by the co-fermentation of grape and fruit. The formulation of new mixed-fruit wines could represent the basis for reducing post-harvest fruit losses and contribute to the economy of the existing wine industry. Moreover, throughout the selection of useful yeasts that drive the alcoholic fermentation, the final products could be enriched in novel active bio-functional compounds not found in traditional wines. The research activity has involved the setup of fermentation trials using grape must and fruit juices of strawberry, peach, cherry and kiwi. Must fermentations were carried out inoculating Saccharomyces cerevisiae and Torulaspora delbruekii species in four musts obtained by blending grape must (Chardonnay and Cabernet Sauvignon) and juices at 80:20 and 60:40 grape:fruit juice proportion. The aromatic profile was determined by GC-MS. S. cerevisiae was able to exhaust the available sugars in all trials. In particular, based on the proportion used, alcohol was 3-5% less in wines prepared with red grape and 6-7% (v/v) less in case of white grape. T. delbruekii showed a good fermentation performance as well, suggesting its potential use as starter yeast. Only negligible difference was found for the pH, while the total acidity was higher for mixed-fruit wines obtained with must from white grape and at the 60:40 proportion. In particular, the high level of citric acid detected (up to 8 g/L) in some products could exert a beneficial effect by protecting the wine components, bio-functional compounds included, against oxidation