A Mathematical Model to Evaluate the Kinetics of D-glucose and D-fructose Fermentations by Saccharomyces bayanus at Increasing Ethanol Concentrations

In the cellar, slow and stuck fermentations occurring during winemaking are often successfully solved bythe addition of yeast strains like Saccharomyces bayanus. The kinetic behaviour shown by S. bayanus duringalcoholic fermentation was investigated using a mathematical model previously tested for S. cerevisiae, inorder to show which of the six functional parameters of the model differed significantly with the yeastpopulation. Although some parameters (hexose fractions converted to ethanol and glycerol) did not change,the kinetic constant related to the inactivation rate of the yeast population showed by S. cerevisiae assumeda value significantly higher (approximately 50-fold) than that observed for S. bayanus, while this latterpopulation was ten times less affected by ethanol than S. cerevisiae. Although no remarkable differencescould be found between the ability shown by the two yeast populations to convert hexoses (D-glucose andD-fructose), the tolerance for ethanol accumulation changed strongly. The conversion rate of these twohexoses by S. bayanus was affected less (about ten thousand-fold) by ethanol than that of S. cerevisiae

Evaluation of bread quality and volatile compounds of breads made by sourdoughs fermented by sediments of pulque (xaxtle) as starter culture

Sourdough is an important modern fermentation method of cereal flour and water. The fermentation process is carried out by lactic acid bacteria (LAB) and yeasts which confer specific flavor characteristics to the bread. The main aim of this research was to investigate the bread quality and volatile compounds of breads made by sourdoughs inoculated with sediments of pulque (xaxtle) used it as starter culture. Fifty five volatile compounds were found in the bread made with sourdoughs inoculated with xaxtle from three different regions of Mexico. Using gas chromatography-mass spectrometry, compounds as 3-hydroxy-2-butanone; 3-methyl-1-butanol; 2-methyl, 1-butanol; dimethyl disulfide; furfural, nonanal, phenyl ethyl alcohol and butanoic acid were presented in the flavor profile of the breads and having a positive response to sensory analysis made by evaluators. The xaxtle of Nanacamilpa (XN) and the xaxtle of Villa Alta (XV) were the best breads getting 8.3±0.03, 8.8±0.02, 6.2±0.08 and 8.2±0.01 scores in a scale from 0 to 10 in color, smell, texture and flavor attributes respectively which are positive attributes in favor of the quality bread. As a result of fermentation sourdough with LAB and yeasts from the xaxtle during 24 hours (30° C), the bread made with the sourdough inoculated with xaxtle of Milpa Alta (XM) showed the major acid flavor therefore its sample was less acceptable getting 8.1±0.01, 7.8±0.02, 5.3±0.01 and 7.9±0.01 in the same attributes evaluated. The xaxtle of Nanacamilpa, Tlaxcala (XN) run better than the others as starter fermentation culture for sourdoughs

The Kinetic Effect of Some Wine Components on the Enzymatic Hydrolysis of β-glucan

Enzymatic preparations containing β-glucanases are utilised extensively in winemaking to facilitate the filtration of musts and wines coming from grapes affected by Botrytis cinerea, and to induce the release of mannoproteins and oligosaccharides from the cell walls of yeasts. The aim of the present work was to investigate the possible inhibitory effect of some wine components, and in particular of ethanol, on β-glucanase activities. For this purpose, the kinetic activity of a commercial enzymatic preparation containing β-glucanases was tested utilising both model solutions (buffer solution having a pH value similar to a must/wine with or without 13% v/v of ethanol added) and a red wine. When ethanol was added to the model solution, both the kinetic constant k and glucose production suffered a decrease of about 50% compared to the values detected in the absence of ethanol. A further loss of activity (about 87%) was found using red wine as reaction medium, suggesting, as already reported in the literature, that phenols could add their inhibitory effect to that of ethanol. The results obtained provide useful suggestions that can be adopted during winemaking. To promote the hydrolysis of the possible excess of β-glucan coming from grapes affected by Botritis cinerea, it would be more convenient to add β-glucanases before a significant amount of ethanol accumulates in the must/wine, while it is not possible to avoid the negative impact of ethanol or other possible inhibitors (phenols) to promote yeast degradation in wine left on lees

A kinetic approach to describe the time evolution of red wine as a function of packaging and storage conditions

With the aim to determine the influence of packaging in preserving the quality of wine, in this research project the chemical and sensorial evolution of a red wine stored in different packaging materials (glass bottles vs multilayer Tetrabriks®) has been evaluated over a period of 12 months. Furthermore, two different temperature levels (4 and 20 °C) for each packaging solution were maintained throughout the storage period. The results show how the characteristics of packaging could deeply affect wine quality as a function of the storage conditions used, and suggest that with their rational optimization the quality of red wine during storage can be kept and its shelf life extended. In this context, the kinetic characterization of the time evolution of some chemical compounds that can be assumed as indexes of wine oxidation rate could enhance the consumer’s enjoyment during tasting. Under the adopted experimental conditions, the rate of wine aging was higher when the storage temperature increased. Furthermore, after 12 months of storage at room temperature, the glass bottles generally better preserved red wine from oxidation than multilayer Tetrabriks®

Un'innovazione nell'applicazione della frigoconservazione in atmosfera controllata degli alimenti: la cella intelligente

Premio Montana alla Ricerca Alimentare, II Edizion