Foliar application of urea to Tempranillo vines increased the amino acid concentration of the must.

The aim of this study was to investigate the impact of fertilisation with foliar urea of Vitis vinifera var. Tempranillo on the concentration of amino acids in must and on their evolution during the final stage of grape ripening. Foliar urea fertilisation increased the concentration of amino nitrogen, ammonium nitrogen and yeast assimilable nitrogen (YAN) in Tempranillo must. In addition, fertilisation with foliar urea produced an increase in the concentration of many amino acids in the must. This increase was especially noticeable in the case of the most important amino acids for yeast metabolism throughout the alcoholic fermentation (arginine, glutamic acid, aspartic acid, histidine, serine and lysine). After comparing the results of this study with other ones, we may state that: in order to increase the amino acid concentration in must, it is important to apply the urea several times instead of making just one single application. Moreover, it is important to use a preparation of urea without biuret, which is a phytotoxic carbamyl urea formed as a condensation product arising from urea thermal decomposition.

Effects of reduced levels of sulfite in wine production using mixtures with lysozyme and dimethyl dicarbonate on levels of volatile and biogenic amines.

Sulphur dioxide (SO2) is an important preservative for wine, but its presence in foods can cause allergies and this has given impetus to the research for alternatives. The aim of this study was to reduce levels of sulfite in wine production using mixtures with lysozyme and dimethyl dicarbonate and examine the influence on levels of volatile and biogenic amines. To do so, vinifications were carried out using lysozyme, dimethyl dicarbonate (DMDC) and mixtures of these with SO2 in different concentrations (25 and 50 mg l-1). Results were compared with a control vinification with only SO2 (50 mg l-1). Mixing low concentrations of SO2 with lysozyme and DMDC reduced the concentration of biogenic amines (histamine, tyramine, putrescine, cadaverine, phenylethylamine + spermidine and spermine). In general, the total concentration of volatile amines (dimethylamine, isopropylamine, isobutylamine, pyrrolidine, ethylamine, diethylamine, amylamine and hexylamine) was higher in the sample fermented only with SO2. The concentrations of amines with secondary amino groups (dimethylamine, diethylamine, pyrrolidine) were higher in the sample only fermented with SO2 than those fermented with DMDC and lysozyme or with a mixture of preservatives. When SO2 was the only preservative in wine, total amine concentration (biogenic and volatile amines) was higher than for the rest of the treatments. Lysozyme by itself, and lysozyme mixed with SO2, both reduced the formation of biogenic amines but given the antioxidant activity of SO2 the use of the preservative mixture seems more advisable.

Improvement of wine aromatic quality using mixtures of lysozyme and dimethyl dicarbonate, with low SO2 concentration.

The use of sulphur dioxide (SO2) in the treatment of foodstuffs presents some problems as it could lead to pseudo-allergies in some people. The aim of this research work was to study the addition of different preservative mixtures and their influence on the concentration of volatile compounds and sensorial quality in wine. To do so, vinifications were carried out using Garnacha must to which lysozyme, dimethyl dicarbonate (DMDC) and mixtures of these with SO2 were added at different doses (25 and 50 mg l(-1)). The results were compared with a control sample to which only SO2 had been added (50 mg l(-1)). In general, mixtures of SO2 with lysozyme and DMDC favoured the formation of volatile compounds in the wines. Wines obtained from the mixtures of lysozyme and DMDC with 25 mg l(-1) of SO2 had better sensorial quality than the wines obtained with 50 mg l(-1) as the only preservative used.

Sorption of 4-ethylguaiacol and 4-ethylphenol on yeast cell walls, using a synthetic wine.

4-Ethylphenol (4-EP) and 4-ethylguaiacol (4-EG) are the identified volatile phenolic compounds associated with off-odour in wine. The aim of this work was to investigate the kinetics and thermodynamics of sorption of 4-EG and 4-EP by yeast cell walls, using a synthetic wine. Results showed that the sorption capacity by yeast cell walls for 4-EG was greater than that for 4-EP and that the kinetics of 4-EG were quicker, although the unions were weaker than in the case of 4-EP. The retention of these compounds was by means of specific chemical sorption. The process of sorption of these compounds to the yeast walls could be due to their binding to the residual lipids, as well as to interaction of 4-EP and 4-EG (positively charged compounds), with the functional groups of the mannoproteins and the free amino acids of the surface of the cell walls.

Effect of foliar urea fertilisation on volatile compounds in Tempranillo wine.

BACKGROUND: The impact of fertilisation with three doses of foliar urea (0, 2 and 4 kg N ha(-1)) on the concentration of volatile compounds in Tempranillo wine was studied. RESULTS: The total concentration of alcohols decreased with the application of urea. The concentrations of ethyl hexanoate, ethyl octanoate and ethyl decanoate were highest in the wine resulting from the 4 kg N ha(-1) urea treatment. Fatty acids showed different individual responses to the application of urea. Sensory analysis indicated that the wines from urea-treated grapevines had higher aroma intensity and a more fruity character than the control wine. CONCLUSION: It may be concluded that foliar urea fertilisation shows itself to be efficient in small doses as a complement to soil fertilisation to improve wine aroma.

SO(2) protects the amino nitrogen metabolism of Saccharomyces cerevisiae under thermal stress.

Thermal stress conditions during alcoholic fermentation modify yeasts' plasma membrane since they become more hyperfluid, which results in a loss of bilayer integrity. In this study, the influence of elevated temperatures on nitrogen metabolism of a Saccharomyces cerevisiae strain was studied, as well as the effect of different concentrations of SO(2) on nitrogen metabolism under thermal stress conditions. The results obtained revealed that amino nitrogen consumption was lower in the fermentation sample subjected to thermal stress than in the control, and differences in amino acid consumption preferences were also detected, especially at the beginning of the fermentation. Under thermal stress conditions, among the three doses of SO(2) studied (0, 35, 70 mg l(-1) SO(2) ), the highest dose was observed to favour amino acid utilization during the fermentative process, whereas sugar consumption presented higher rates at medium doses.