59 research outputs found
Caratterizzazione di frazioni parietali di lievito sulla base delle forme cisteiniche ridotte
No full textLa presenza di forme tioliche cisteiniche ridotte (FTCR) nei preparati enologici da parete cellulare di lievito potrebbe contribuire a prevenire lo sviluppo di fenomeni ossidativi nel vino tramite la riduzione delle forme chinoniche derivate dall’ossidazione fenolica. Un approccio analitico innovativo basato sulla reattività dei guppi tiolici verso il p-benzochinone, è stato utilizzato per caratterizzare mannoproteine, scorze, lisati, estratti e fecce di lievito di origine commerciale. Molti di tali additivi enologici hanno mostrato una spiccata attività legante verso le molecole tioliche libere ed una generale povertà in FTCR sia libere che proteiche. Questi prodotti potrebbero impoverire il patrimonio aromatico del vino e favorire lo sviluppo di fenomeni ossidativi, ma possono anche promuovere la rimozione di precoci difetti di ridotto. Alcuni campioni di scorza o lisati cellulari sono risultati contenere oltre 4 mmol/100 g di Cys e GSH liberi ridotti oltre che quantità solo poco inferiori di tioli di diversa origine la cui ascrivibilità a forme di Cys proteica ridotta da lievito richiederebbe opportuna conferma. I preparati mannoproteici sono risultati ampiamente danneggiati da un’intensa reazione di Maillard, misurata come indice di furosina, e particolarmente poveri in FTCR. La metodica proposta potrebbe aiutare a isolare frazioni di parete, e soprattutto mannoproteine, con migliori proprietà antiossidanti, nonché a valutare ulteriori aspetti dell’attività enologica delle FTCR
Survey on indigenous Oenococcus oeni strains isolated from red wines of Valtellina, a cold climate wine-growing Italian area
No full textSpontaneous MLF in high acidity wines produced in cool-climate regions remains problematic though indispensable for the development of sensory characteristics. Genetic aspects and phenotypic traits of thirty-six Oenococcus oeni strains, most of them isolated from Valtellina wines over three consecutive years, were investigated. Molecular typing achieved by RAPD PCR and PFGE analyses allowed 27 different genotypes to be discriminated, whereas from the comparison of results arising by physiological tests (sugar fermentation, alcohol resistance, growth at low temperatures, biogenic ammines production) 28 different phenotypic profiles were obtained. Particularly, 69% of Valtellina isolates were able to develop at 5 degrees C in cultural broth. Micro-vinification experiments allowed the selection of strains with potential oenological performances and an interesting capability to grow in cold conditions was confirmed. Some O. oeni strains formed phenylethylamine (up to 47 mg/L) and tyramine (up to 36 mg/L) both in cultural broth and wine
Formation and prevention of light-struck taste white wine
No full textLight-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 μg/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 μg/L) and it has an aroma impression of cooked cabbage or onion. Concentrations of RF lower than 80-100 μg/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
Genetic diversity and physiological traits of Brettanomyces bruxellensis strainsnisolated from Tuscan Sangiovese wines
No full textEighty four isolates of Brettanomyces bruxellensis, were collected during fermentation of Sangiovese grapes in
several Tuscan wineries and characterized by restriction analysis of 5.8S-ITS and species-specific PCR. The
isolates were subsequently analysed, at strain level, by the combined use of the RAPD-PCR assay with primer
OPA-02 and the mtDNA restriction analysis with the HinfI endonuclease. This approach showed a high
degree of polymorphism and allowed to identify seven haplotypes, one of them being the most represented
and widely distributed (72 isolates, 85.7%). Physiological traits of the yeasts were investigated under a wine
model condition. Haplotypes clustered into two groups according to their growth rates and kinetics of
production of 4-ethylphenol and 4-ethylguaiacol. Hexylamine was the biogenic amine most produced (up to
3.92 mg l−1), followed by putrescine and phenylethylamine. Formation of octapamine was detected by some
haplotypes, for the first time
Light-struck taste in white wine : protective role of glutathione, sulfur dioxide and hydrolysable tannins
No full textLight exposure of white wine can cause a light-struck taste (LST), a fault induced by riboflavin (RF) and methionine (Met) leading to the formation of volatile sulfur compounds (VSCs), including methanethiol (MeSH) and dimethyl disulfide (DMDS). The study aimed to investigate the impact of different antioxidants, i.e., sulfur dioxide (SO2), glutathione (GSH) and chestnut tannins (CT), on preventing LST in model wine (MW) and white wine (WW), both containing RF and Met. Both MW and WW samples were added with the antioxidants, either individually or in different combinations, prior to 2-h light exposure and they were stored in the dark for 24 months. As expected, the light induced the degradation of RF in all the conditions assayed. Met also decreased depending on the antioxidants added. The presence of antioxidants limited the formation of LST as lower concentrations of VSCs were found in both MW and WW samples. In the latter matrix, neither MeSH nor DMDS were detected in the presence of CT, while only DMDS was found in WW+GSH, WW+SO2+GSH and WW+CT+SO2 samples at a concentration lower than the perception thresholds. Considering the antioxidants individually, the order of their effectiveness was CT > GSH > SO2 in WW under the adopted experimental conditions. The results indicate tannins as an effective enological tool for preventing LST in white wine and their use will be further investigated in different
white wines under industrial scale
Impact of Cooking on Bioactive Compounds and Antioxidant Activity of Pigmented Rice Cultivars
No full textPigmented 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
Application of UV-C light for preventing the light-struck taste in white wine
No full textThe 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 μg/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 μg/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 μg/L and 20 μg/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
NMR approach for monitoring the photo-degradation of riboflavin and methionine
No full textThe 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
Physiological and oenological traits of different Dekkera/Brettanomyces bruxellensis strains in wine-model conditions
No full textContamination of wine by Dekkera/Brettanomyces bruxellensis is mostly due to the production of off-flavours identified as vinyl- and especially ethyl-phenols, but these yeasts can also produce several other spoiling metabolites, such as acetic acid and biogenic amines. Little information is available about the correlation between growth, viability and off-flavour and biogenic amine production. In the present work, five strains of Dekkera bruxellensis isolated from wine were analysed over 3 months in wine-like environment for growth, cell survival, carbon source utilization and production of volatile phenols and biogenic amines. Our data indicate that the wine spoilage potential of D. bruxellensis is strain dependent, being strictly associated with the ability to grow under oenological conditions. 4-Ethyl-phenol and 4-ethyl-guaiacol production ranged between 0 and 2.7 and 2 mg L -1, respectively, depending on the growth conditions. Putrescine, cadaverine and spermidine were the biogenic amines found
Insight into the characterization of commercial oenological tannins
No full textThe characterization in terms of phenolics, antioxidant capacity and oxygen consumption rate (OCR) was carried out for 15 commercial oenological tannins of different origin. A NMR approach was used to evaluate their average molecular weight, and their glycosidic and aromatic moieties. The investigated oenological tannins showed wide differences in their chemical properties. Total phenol index (TPI) ranged from 461±28 and 1018±57 mg gallic acid/g for cherry tannin and nut gall tannin, respectively. The antioxidant capacity, positively correlated with TPI, was higher for hydrolysable tannins ranging 3.05±0.06 and 12.06±0.71 mM Trolox/g for ABTS assay, and from 3.70±0.23 and 10.94±1.28 mM Trolox/g for DPPH assay. Relevant differences in OCRs were found and chestnut tannin showed the highest OCR. Wide range of molecular weights were found with nut gall 1 tannin showing the highest one, ranging from 790 to 1900 Da. This study improves and expands the actual knowledge of tannins supporting the suitability of NMR for the characterization of oenological tannins
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