Elisabete Coelho

Quantification approach for assessment of sparkling wine volatiles from different soils, ripening stages, and varieties by stir bar sorptive extraction with liquid desorption.

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 applied for the quantification of varietal and fermentative volatiles in sparkling wines. The analytical data were performed by using suitable standards of monoterpene hydrocarbons (alpha-pinene), monoterpenols (linalool), sesquiterpenoids (E,E-farnesol, Z-nerolidol, and guaiazulene), C(13) norisoprenoids (beta-ionone), aliphatic and aromatic alcohols (hexanol and 2-phenylethanol), and esters (hexyl acetate and ethyl decanoate) as model compounds. The wine volatiles were quantified using the structurally related standards. The methodology showed good linearity over the concentration range tested, with correlation coefficients ranging from 0.950 to 0.997, and a reproducibility of 9-18%. The SBSE-LD/LVI-GC-qMS methodology allowed, in a single run, the quantification of 71 wine volatiles that can be quantified accurately at levels lower than their respective olfactory thresholds. This methodology was used for assessment of sparkling wine volatiles from different soils, ripening stages, and varieties. The variety and soil influenced significantly the volatile composition of sparkling wines; lower effect was observed for the ripening stage of grapes picked up one week before or after the maturity state.

Optimisation of stir bar sorptive extraction and liquid desorption combined with large volume injection-gas chromatography–quadrupole mass spectrometry for the determination of volatile compounds in wines

Stir bar sorptive extraction and liquid desorption followed by large volume injection coupled to gas chromatography-quadrupole mass spectrometry (SBSE-LD/LVI-GC-qMS) had been applied for the determination of volatiles in wines. The methodology was optimised in terms of extraction time and influence of ethanol in the matrix; LD conditions, and instrumental settings. The optimisation was carried out by using 10 standards representative of the main chemical families of wine, i.e. guaiazulene, E,E-farnesol, beta-ionone, geranylacetone, ethyl decanoate, beta-citronellol, 2-phenylethanol, linalool, hexyl acetate and hexanol. The methodology shows good linearity over the concentration range tested, with correlation coefficients higher than 0.9821, a good reproducibility was attained (8.9-17.8%), and low detection limits were achieved for nine volatile compounds (0.05-9.09 microg L(-1)), with the exception of 2-phenylethanol due to low recovery by SBSE. The analytical ability of the SBSE-LD/LVI-GC-qMS methodology was tested in real matrices, such as sparkling and table wines using analytical curves prepared by using the 10 standards where each one was applied to quantify the structurally related compounds. This methodology allowed, in a single run, the quantification of 67 wine volatiles at levels lower than their respective olfactory thresholds. The proposed methodology demonstrated to be easy to work-up, reliable, sensitive and with low sample requirement to monitor the volatile fraction of wine.

PLL Structures for Utility Connected Systems under Distorted Utility Conditions

This work presents a phase detecting method applied to three-phase PLL (phase locked loop) systems for utility connected devices under distorted utility voltage conditions. PLL systems have been used in several equipment applications such as, UPS systems, active power filters, PWM rectifiers, etc, in which phase angle information of utility voltage is necessary. The presented three-phase PLL system is based on instantaneous power theory. The analysis is performed considering a three-phase stationary reference frame model, which use the instantaneous active power as the PLL references. The proposed PLL system uses the method of symmetrical coordinates to detect the positive sequence component of the voltages in an unbalance there-phase system. To validate the theoretical analysis, the model of the PLL system is presented and its dynamic response is discussed considering distorted utility voltage conditions. Mathematical analysis of the PLL system is made and a design procedure to determine the controller gains is presented. Both simulations and experimental results are presented to validate the theoretical analyses

Synergistic effect of high and low molecular weight molecules in the foamability and foam stability of sparkling wines.

The foam of sparkling wines is a key parameter of their quality. However, the compounds that are directly involved in foam formation and stabilization are not yet completely established. In this work, seven sparkling wines were produced in Bairrada appellation (Portugal) under different conditions and their foaming properties evaluated using a Mosalux-based device. Fractionation of the sparkling wines into four independent fractions, (1) high molecular weight material, with molecular weight higher than 12 kDa (HMW), (2) hydrophilic material with molecular weigh between 1 and 12 kDa (AqIMW), (3) hydrophobic material with molecular weigh between 1 and 12 kDa (MeIMW), and (4) hydrophobic material with a molecular weight lower than 1 kDa (MeLMW), allowed the observation that the wines presenting the lower foam stability were those that presented lower amounts of the MeLMW fraction. The fraction that presented the best foam stability was HMW. When HMW is combined with MeLMW fraction, the foam stability largely increased. This increase was even larger, approaching the foam stability of the sparkling wine, when HMW was combined with the less hydrophobic subfraction of MeLMW (fraction 3). Electrospray tandem mass spectrometry (ESI-MS/MS) of fraction 3 allowed the assignment of polyethylene glycol oligomers (n = 5-11) and diethylene glycol 8-hydroxytridecanoate glyceryl acetate. To observe if these molecules occur in sparkling wine foam, the MeLMW was recovered directly from the sparkling wine foam and was also analyzed by ESI-MS/MS. The presence of monoacylglycerols of palmitic and stearic acids, as well as four glycerylethylene glycol fatty acid derivatives, was observed. These surface active compounds are preferentially partitioned by the sparkling wine foam rather than the liquid phase, allowing the inference of their role as key components in the promotion and stabilization of sparkling wine foam.

Analysis and design of a three-phase PLL structure for utility connected systems under distorted utility conditions

This paper presents a new phase detecting method by using a digital three-phase PLL (phase locked loop) system for utility- connected devices under distorted utility conditions. The PLL systems have been used in several equipment applications such as, UPS systems, active filters, PWM rectifiers, etc, in which phase angle Information of utility voltage is necessary. The PLL system proposed in this work is based on instantaneous power theory. The analysis is performed considering a three-phase stationary reference frame model, which uses the instantaneous active power as the PLL reference. To detect the positive sequence component of the voltage in an unbalance there-phase system, the method of symmetrical coordinates is used. To validate the theoretical analysis a model of the PLL system is presented and its dynamic response, obtained from digital simulation, is discussed considering distorted voltage conditions. Mathematical analysis of the PLL system is made and a design procedure to determine the controller gains is presented.

Improved efficiency of brewer's spent grain arabinoxylans by ultrasound-assisted extraction.

Arabinoxylan (AX) rich extracts from brewers spent grain (BSG) were produced by the application of ultrasound-assisted extraction (UAE) and conventional alkaline extraction (AKE). UAE and AKE were optimised for the production of the highest yield of ethanol insoluble material using response surface methodology (RSM). The efficiency of UAE was established by the significant reduction of time (7h to 25 min) and energy when compared to AKE, to recover similar amounts of AX (60%) from BSG, leading to the production of starch-free AX-rich extracts.

Modifications of Saccharomyces pastorianus cell wall polysaccharides with brewing process

The cell wall polysaccharides of brewers spent yeast Saccharomyces pastorianus (BSY) and the inoculum yeast (IY) were studied in order to understand the changes induced by the brewing process. The hot water and alkali extractions performed solubilized mainly mannoproteins, more branched for BSY than those of IY. Also, (31)P solid state NMR showed that the BSY mannoproteins were 3 times more phosphorylated. By electron microscopy it was observed that the final residues of alkali sequential extraction until 4M KOH preserved the yeast three-dimensional structure. The final residues, composed mainly by glucans (92%), showed that the BSY, when compared with IY, contained higher amount of (1→4)-linked Glc (43% for BSY and 16% for IY) and lower (1→3)-linked Glc (17% for BSY and 42% for IY). The enzymatic treatment of final residue showed that both BSY and IY had (α1→4)-linked Glc and (β1→4)-linked Glc, in a 2:1 ratio, showing that S. pastorianus increases their cellulose-like linkages with the brewing process.

Valuation of brewers spent yeast polysaccharides: a structural characterization approach.

Brewers spent yeast (BSY) is a by-product from beer industry that can be exploited as source of glucans and mannoproteins, with potential biological activities. In order to solubilize these carbohydrate-rich polymeric materials, a sequential extraction with hot water and alkaline solutions (0.1-8 M KOH) was performed. Mannoproteins were mainly (85%) extracted with 4 M KOH whereas glucans were extracted with 8 M KOH and in an amount that accounted only for 34% of total glucose. Final residue still accounted for 34% of the initial glucans and contained 98% of glucose. Cellulase and α-amylase treatments showed the presence of both α- and β-(1→4)-Glc linkages. To promote total solubilization of these insoluble glucans, the final residue was submitted to a partial acid hydrolysis. This work is the first report showing that the most abundant polysaccharides in BSY are polymers that contain structural features similar to cellulose, thus justifying their resistance to alkaline extractions, acid hydrolysis, and insolubility in water.

Influence of grain particle sizes on the structure of arabinoxylans from brewer's spent grain.

BSG was milled and sieved and six different grain fractions of different particle sizes (PS) were obtained: PS ≤ 63 μm (PSA); 63 μm < PS ≤ 90 μm (PSB); 90 μm250 μm (PSF). SEM images showed that for the highest particle sizes, cells were still intact while for the smallest particles disruption of cells occurred. The sugar analysis of the grains showed the constant presence of arabinoxylans (AX) and the maximum amount was observed in PSC. AX rich extracts were obtained for all grain fractions presenting different estimate degrees of polymerisation (DP) and degrees of branching (DB). With the decreasing of grain PS, smallest and more branched polymers were extracted; the smallest AX in PSC, and the more branched AX in PSA and PSB. Residual arabinogalactans (AG) were extracted from PSD to PSA. Starch was present in all extracts accounting for 8-10% of the composition of the extract. AX rich extracts with different DP and DB were obtained from different grain PS.

Downscale fermentation for xylooligosaccharides production by recombinant Bacillus subtilis 3610

The global demand of prebiotics such as xylooligosaccharides (XOS) has been growing over the years, motivating the search for different production processes with increased efficiency. In this study, a cloned Bacillus subtilis 3610, containing the xylanase gene xyn2 of Trichoderma reesei coupled with an endogenous secretion tag, was selected for XOS production through direct fermentation of beechwood xylan. A mixture of XOS with a degree of polymerization ranging from 4 to 6 was obtained, presenting high stability after a static in vitro digestion (98.5 ± 0.2%). The maximum production yield expressed as total XOS per amount of xylan (306 ± 4 mg/g) was achieved after 8 h of fermentation operating under one-time impulse fed-batch. The optimal conditions found were pH 6.0 and 42.5 °C, using 2.5 g/L of initial concentration of xylan increased up to 5.0 g/L at 3 h. Xylopentaose was the major oligosaccharide produced, representing 47% of the total production yield.