The fermentation process for elaboration of the beverage depends on the
performance of yeast to convert the sugars into alcohol, esters and other compounds.
Due to the differences in fruit composition, selected yeasts strains used for
fermentation have to adapt to different environments (e.g., sugar composition and
concentrations, presence of organic acids, etc.). Sixteen different yeasts (S.
cerevisiae and S. bayanus) were evaluated in the production of raspberry fruit wine.
Raspberry pulp was diluted with a sucrose solution to adjust the sugar concentration
to 16° Brix. CaCO3 was added to increase the pH value to 4.0. Batch fermentations
were carried out at 22 oC. Kinetic parameters, as conversion factors of substrate into
ethanol (Yp/s), biomass (Yx/s), glycerol (Yg/s), acetic acid (Yac/s) and efficiency (Ef) were
calculated. Volatile compounds (alcohols, esters, acetates and acids) were
determined by gas chromatography (GC-FID) after liquid-liquid extraction with
dichloromethane. The parameters Ef, Yp/s, Yg/s and Yx/s, were found in high levels when
yeasts commonly used in fuel ethanol industry (PE-2, BG, SA, CAT-1 e VR-1)
fermented raspberry pulp. Yeast UFLA FW 15, isolated from fruit, showed similar
results. Twenty-two volatile organic compounds (VOCs) were identified in raspberry
fruit wines. The highest total concentration of VOCs were found for the yeasts UFLA
FW 15 (87662.00 g L1)...
1. Our results show clearly that the Hofmeister series is not the correct expression of the relative effect of ions on the swelling of gelatin, and that it is not true that chlorides, bromides, and nitrates have "hydrating," and acetates, tartrates, citrates, and phosphates "dehydrating," effects. If the pH of the gelatin is taken into considertion, it is found that for the same pH the effect on swelling is the same for gelatin chloride, nitrate, trichloracetate, tartrate, succinate, oxalate, citrate, and phosphate, while the swelling is considerably less for gelatin sulfate. This is exactly what we should expect on the basis of the combining ratios of the corresponding acids with gelatin since the weak dibasic and tribasic acids combine with gelatin in molecular proportions while the strong dibasic acid H2SO4 combines with gelatin in equivalent proportions. In the case of the weak dibasic acids he anion in combination with gelatin is therefore monovalent and in the case of the strong H2SO4 it is bivalent. Hence it is only the valency and not the nature of the ion in combination with gelatin which affects the degree of swelling.
2. This is corroborated in the experiments with alkalies which show that LiOH, NaOH, KOH, and NH4OH cause the same degree of swelling at the same pH of the gelatin solution and that this swelling is considerably higher than that caused by Ca(OH)2 and Ba(OH)2 for the same pH. This agrees with the results of the titration experiments which prove that Ca(OH)2 and Ba(OH)2 combine with gelatin in equivalent proportions and that hence the cation in combination with the gelatin salt with these two latter bases is bivalent.
3. The fact that proteins combine with acids and alkalies on the basis of the forces of primary valency is therefore not only in full agreement with the influence of ions on the physical properties of proteins but allows us to predict this influence qualitatively and quantitatively.
4. What has been stated in regard to the influence of ions on the swelling of the different gelatin salts is also true in regard to the influence of ions on the relative solubility of gelatin in alcohol-water mixtures.
5. Conductivity measurements of solutions of gelatin salts do not support the theory that the drop in the curves for swelling...
In the present study, a simple and sensitive methodology based on dynamic headspace solid-phase microextraction (HS-SPME) followed by thermal desorption gas chromatography with quadrupole mass detection (GC–qMSD), was developed and optimized for the determination of volatile (VOCs) and semi-volatile (SVOCs) compounds from different alcoholic beverages: wine, beer and whisky. Key experimental factors influencing the equilibrium of the VOCs and SVOCs between the sample and the SPME fibre, as the type of fibre coating, extraction time and temperature, sample stirring and ionic strength, were optimized. The performance of five commercially available SPME fibres was evaluated and compared, namely polydimethylsiloxane (PDMS, 100 μm); polyacrylate (PA, 85 μm); polydimethylsiloxane/divinylbenzene (PDMS/DVB, 65 μm); carboxen™/polydimethylsiloxane (CAR/PDMS, 75 μm) and the divinylbenzene/carboxen on polydimethylsiloxane (DVB/CAR/PDMS, 50/30 μm) (StableFlex).
An objective comparison among different alcoholic beverages has been established in terms of qualitative and semi-quantitative differences on volatile and semi-volatile compounds. These compounds belong to several chemical families, including higher alcohols, ethyl esters, fatty acids...
A suitable analytical procedure based on static headspace solid-phase microextraction (SPME) followed by thermal desorption gas chromatography–ion trap mass spectrometry detection (GC–ITDMS), was developed and applied for the qualitative and semi-quantitative analysis of volatile components of Portuguese Terras Madeirenses red wines. The headspace SPME method was optimised in terms of fibre coating, extraction time, and extraction temperature. The performance of three commercially available SPME fibres, viz. 100 lm polydimethylsiloxane; 85 lm polyacrylate, PA; and 50/30 lm divinylbenzene/carboxen on polydimethylsiloxane, was evaluated and compared. The highest amounts extracted, in terms of the maximum signal recorded for the total volatile composition, were obtained with a PA coating fibre at 308C during an extraction time of 60 min with a constant stirring at 750 rpm, after saturation of the sample with NaCl (30%, w/v). More than sixty volatile compounds, belonging to different biosynthetic pathways, have been identified, including fatty acid ethyl esters, higher alcohols, fatty acids, higher alcohol acetates, isoamyl esters, carbonyl compounds, and monoterpenols/C13-norisoprenoids.
A stir bar sorptive extraction with liquid desorption followed by large volume injection coupled to gas chromatography–quadrupole mass spectrometry (SBSE-LD/LVI-GC–qMS) was evaluated for the simultaneous determination of higher alcohol acetates (HAA), isoamyl esters (IsoE) and ethyl esters (EE) of fatty acids. The method performance was assessed and compared with other solventless technique, the solid-phase microextraction (SPME) in headspace mode (HS). For both techniques, influential experimental parameters were optimised to provide sensitive and robust methods. The SBSE-LD/LVI methodology was previously optimised in terms of extraction time, influence of ethanol in the matrix, liquid desorption (LD) conditions and instrumental settings. Higher extraction efficiency was obtained using 60 min of extraction time, 10% ethanol content, n-pentane as desorption solvent, 15 min for the back-extraction period, 10 mL min−1 for the solvent vent flow rate and 10 °C for the inlet temperature. For HS-SPME, the fibre coated with 50/30 μm divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) afforded highest extraction efficiency, providing the best sensitivity for the target volatiles, particularly when the samples were extracted at 25 °C for 60 min under continuous stirring in the presence of sodium chloride (10% (w/v)). Both methodologies showed good linearity over the concentration range tested...