Gli enzimi pectolitici del mosto

Nel mosto d'uva esiste una pectinmetilesterasi aspecifica, la quale determina la demetossilazione sia delle pectine del mosto, sia di pectine di altra origine aggiunte al mosto.L'andamento della demetossilazione è quello di una reazione monomolecolare con coefficiente di temperatura Q10<2.Il fatto che la demetossilazione enzimatica delle pectine segua l'andamento di una reazione del primo ordine permette una semplice e significativa valutazione dell'attività della PME nel mosto.Il mosto contiene inoltre una poligalatturonasi specifica che attacca le pectine naturali del mosto stesso, ma è incapace di idrolizzare pectine di origine diversa.I dati sperimentali avvalorano ancora l'esistenza di una protopectinasi nel mosto; tuttavia, specie a causa delle piccole concentrazioni in gioco, l'attività protopectinasica non appare sicuramente dimostrata

Brettanomyces bruxellensis yeasts: impact on wine and winemaking

Yeasts belonging to the Brettanomyces/Dekkera genus are non-conventional yeasts, which affect winemaking by causing wine spoilage all over the world. This mini-review focuses on recent results concerning the presence of Brettanomyces bruxellensis throughout the wine processing chain. Here, culture-dependent and independent methods to detect this yeast on grapes and at the very early stage of wine production are encompassed. Chemical, physical and biological tools, devised for the prevention and control of such a detrimental species during winemaking are also presented. Finally, the mini-review identifies future research areas relevant to the improvement of wine safety and sensory profiles

Les colloïdes glucidiques solubles des moûts et des vins (*)

Les colloïdes des moûts et des vins, obtenus par précipitation par l'alcool, peuvent être divisés en deux groupes : les pectines, d'une part, essentiellement constituées d'acide galacturonique, un autre groupe de colloïdes, d'autre part, contenant encore de l'acide galacturonique, pouvant être ultérieurement fractionné par électrophorèse. Six monomères entrent dans la structure des colloïdes : le galactose, le mannose, l'arabinose, le rhamnose, l'acide galacturonique et l'acide glucuronique. Les taux en divers monomères sont très variables selon les poids moléculaires ; ceci milite en faveur d'un, mélange d'espèces colloïdales. On note, dans les vins, une structure de poids moléculaire défini, constituée d'acide galacturonique, de rhamnose et d'arabinose, stable dans le temps. Les levures forment des colloïdes de nature glucidique, constitués essentiellement de mannanes et d'une faible quantité de polymères de glucose. Le poids moléculaire des colloïdes des moûts et des vins est, pour 60 à 70 p. 100, compris entre 20.000 et 200.00 ; moins de 5 p. 100 dépassent la valeur de 500.000 ou sont inférieurs à 6.500. Les colloïdes produits par les levures ont des poids moléculaires plus élevés : 74 p. 100 dépassent la valeur de 50.000 et 24 p. 100 le poids moléculaire de 500.000. +++ Musts and wines colloïds prepared by precipitation with alcohol can be divided between two groups : pectins, mainly including galacturonic acid and an another group containing galacturonic acid which can be fractionnated by electrophoresis. Colloïds are composed with six monomers galactose, mannose, arabinose, rhamnose, galacturonic and glucuronic acids. Ratios of different monomers are very different in connection with molecular weights ; that proves a mixture of colloïds. In wines a stable, define molecular weighted structure was identified ; it contains galacturonic acid, rhamnose and arabinose. Yeasts are producing glucidic colloïds mainly constituted by mannanes with small quantities of glucose polymers. Molecular weight of colloïds extracted from musts and wines is included, for 60 to 70 per cent, between 20 000 and 200 000 ; less than 5 per cent overweigh 500 000 or underweigh 6 500. Molecular weight of colloïds produced by yeasts is higher : 74 per cent overweigh 50 000 and 24 per cent overweigh 500 000.   (*) Conférence donnée à l'Institut d'OEnologie de Bordeaux, le 22 septembre 1975

O carbonato de cálcio na desacidificação do vinho Isabel The calcium carbonate in the desacidification of Isabella wine

A uva Isabel (Vitis labrusca) é a cultivar de videira mais difundida na Região Vitícola da Serra Gaúcha. Entre outras finalidades, é utilizada para a elaboração de vinho tinto de mesa, o qual, geralmente, apresenta acidez elevada, devido ao teor de ácido tartárico livre. O objetivo do presente trabalho foi avaliar a influência de diferentes doses de carbonato de cálcio (0,0; 0,5; 1,0; 1,5; 2,0; 2,5 e 3,0 g L-1) na correção da acidez e na composição do vinho Isabel da Serra Gaúcha. O estudo foi realizado na Embrapa Uva e Vinho, em Bento Gonçalves - RS, na safra de 2002. O delineamento experimental utilizado foi o de blocos casualizados, com sete tratamentos e quatro repetições. As análises dos vinhos, realizadas dez dias após o tratamento, constaram da densidade, álcool, acidez total, acidez volátil, pH, açúcares redutores, extrato seco, extrato seco reduzido, cinzas, densidade ótica a 420, 520 e 620 nm, intensidade de cor e coloração, efetuadas através de métodos físico-químicos. O ácido tartárico foi determinado através da cromatografia líquida de alta eficiência (CLAE). O potássio e o cálcio foram analisados por espectrofotometria de absorção atômica. Além da redução da acidez do vinho Isabel, o carbonato de cálcio interferiu na cor, no extrato seco, nas cinzas e no teor de elementos minerais do vinho Isabel.<br>Isabel grape (Vitis labrusca) is the variety mostly spread in the Serra Gaúcha Region which is used, among other purposes, to elaborate red table wines. This wine usually presents high acidity, due to the level of free tartaric acid. The purpose of this work was to evaluate the effect of different doses of calcium carbonate in acidity and in the Isabel wine composition of the Serra Gaúcha region. The study carried out at Embrapa Uva e Vinho consisted of application in Isabel wine, from the 2002 vintage, different concentrations of calcium carbonate (0,0; 0,5; 1,0; 1,5; 2,0; 2,5 and 3,0 g L-1). The experimental design was a randomized block with seven treatments and four replications. The wines were analyzed ten days after treatment. The determinations were accomplished by physical-chemical methods: density, alcohol, total titratable acidity, pH, reducing sugar, dry extract, reduced dry extract, ashes, optical density at 420, 520 and 620 nm, color intensity and coloration. The tartaric acid was measured by liquid chromatography. The potassium and calcium were analyzed by atomic absorption spectrometry. Results showed that besides the reduction of acidity, the calcium carbonate interfered in color, dry extract, ashes and in the mineral elements of the Isabel wine

Quantitative analysis of geraniol, nerol, linalool, and a-terpineol in wine

A mixture of [²H₇]-geraniol, [²H₇]-nerol, [²H₇]-linalool and [²H₇]-f-terpineol was prepared for use as internal standards in a rapid and accurate analytical method, employing gas chromatography-mass spectrometry (GC/MS), to determine the concentration of geraniol, nerol, linalool and f-terpineol in wine. The method avoids the possible formation, degradation and interconversion of these compounds during their analysis

Impact of sulphur dioxide on the viability, culturability, and volatile phenol production of Dekkera bruxellensis in wine

Viability and culturability of eight Dekkera bruxellensis strains in wine along with the accumulation of volatile phenols in response to increasing concentrations of molecular sulphur dioxide (mSO2) were investigated. mSO2 concentrations up to 1 mg/L induced the non-culturable state of a portion of the population in all the strains to a different extent for each strain, although the cells were still viable. At 1.4 mg/L mSO2, cells were non-culturable, though 0.38–29.01 % of cells retained their viability. When exposed to 2.1 mg/L mSO2, viable cells were not detected. Up to 0.24 mg/L 4-vinylguaiacol and up to 0.73 mg/L 4-ethylphenol were accumulated by non-culturable and dead Dekkera bruxellensis strains, respectively. The concentration of mSO2 needed for the transition from viable to non-culturable state of D. bruxellensis strains was higher in wine than in synthetic wine medium. The volatile phenols accumulated in wine were different from those produced in synthetic wine medium, although their accumulation kinetics were similar