PubMed · 6034261
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P J Godin, T A King, E Stahl, J Pfeifle. 1967-04-15. "Pyrethrum" in peonies.. https://doi.org/10.1038/214319a0
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Low temperature alcoholic fermentations are becoming more frequent due to the wish to produce wines with more pronounced aromatic profiles. However, their biggest drawback is the high risk of stuck and sluggish fermentations. Changes in the plasma membrane composition may be an adaptive response to low temperature fermentations. The production of volatile compounds and the changes in the membrane fatty acids were determined by GC to show the degree of cell adaptation and performance at low temperatures (13 degrees C) taking 25 degrees C as reference. The tests were done in two strains of Saccharomyces cerevisiae and one strain of Saccharomyces bayanus. Low temperatures restricted yeast growth and lengthened the fermentations. The analysis of plasma membrane fatty acids showed that dry yeasts had similar levels of unsaturation, between 70% and 80%, with no medium-chain fatty acids (MCFA). Long-chain saturated fatty acids (SFA) were the most frequent membrane fatty acids throughout the fermentations. Lipid composition changed with the growth temperature. The optimal membrane fluidity at low temperatures was modulated by changes in the unsaturation degree in S. cerevisiae strains. In S. bayanus, however, this change in the unsaturated fatty acid (UFA) percentage was not observed at different growth temperatures but the concentration of MCFA at low fermentation temperatures was higher. Concentrations of volatile compounds were higher in wines produced at lower temperatures and depended on the strain.
A capillary zone electrophoresis (CZE) method, with UV detection and in the presence of dimethyl-beta-CD, was optimized by means of an experimental design for the separation and the simultaneous quantitation of ephedrine, pseudoephedrine, norephedrine (phenylpropanolamine) and norpseudoephedrine (cathine) in urine without any extraction. In this application, the optimization of the analytical conditions with an experimental design was preferred to a univariate study. Therefore, a central composite design was used and the following factors were investigated and varied simultaneously: buffer concentration, buffer pH and dimethyl-beta-CD concentration. In order to evaluate the influence of each experimental parameter on the analytical separation, the resolutions between the four compounds, as well as the separation time and generated current were observed and established as responses of the experimental design. A model was obtained for each response by linear multiple regression of a second-degree mathematical expression. After acceptance of the mathematical models, the most favorable conditions were determined by maximizing the resolutions between the four compounds and by setting the other responses at threshold values. Successful results were obtained with a 260 mM Tris-phosphate buffer at pH 3.5 in the presence of 13.3 mM dimethyl-beta-CD at 25 degrees C and with an applied voltage of 30 kV. Under these optimized conditions, a baseline separation of the four compounds was achieved in less than 6 min. The method was validated in terms of precision, linearity, accuracy and successfully applied for the determination of these compounds in urine samples without any extraction as well as in nutritional supplements.
The effect of ethanol content on the copigmentation of a Cencibel young red wine was studied, by means of ethanol elimination and reconstitution of the initial volume with different ethanol proportions. The reference wine (14.0% ethanol, 0.40 g/L volatile acidity) showed a bathochromic shift of 4 nm and a color enhancement (DeltaColor) of 41%, lower than that found for the reconstituted wine with the same ethanol content (53%). This discrepancy could be attributable to the loss of acetic acid during the ethanol elimination step. DeltaColor was 95% for the reconstituted wine without ethanol and decreased until 18% for the reconstituted wine with 22% ethanol. Copigmentation was important for reconstituted wines with ethanol contents typical for table red wine, showing DeltaColor between 53 and 57%. An increase in ethanol content in reconstituted wines was accompanied by an increase in the pH value. Perceivable changes in color (DeltaE > 1) followed every increase in ethanol content.