Precipitation of salivary proteins after the interaction with wine: the effect of ethanol, pH, fructose, and mannoproteins

Astringency is a complex sensation mainly caused by the precipitation of salivary proteins with polyphenols. In wine it can be enhanced or reduced depending on the composition of the medium. In order to investigate the effect of ethanol, tartaric acid, fructose, and commercial mannoproteins (MPs) addition on the precipitation of salivary proteins, the saliva precipitation index (SPI) was determined by means of the sodium dodecyl sulphate polyacrylamide gel electrophoresis of human saliva after the reaction with Merlot wines and model solutions. Gelatin index, ethanol index, and Folin-Ciocalteu index were also determined. As resulted by Pearson's correlation, data on SPI were well correlated with the sensory analysis performed on the same samples. In a second experiment, increasing the ethanol (11%-13%-17%), MPs (0-2-8 g/L), fructose (0-2-6 g/L) level, and pH values (2.9-3.0-3.6), a decrease in the precipitation of salivary proteins was observed. A difference in the SPI between model solution and red wine stated that an influence of wine matrix on the precipitation of salivary proteins occurred. PRACTICAL APPLICATION: Results provide interesting suggestions for enologists, which could modulate the astringency of red wine by: (i) leaving some residual reducing sugars (such as fructose) in red wine during winemaking of grapes rich in tannins; (ii) avoiding the lowering of pH; (iii) adding commercial mannoproteins or promoting a "sur lie" aging; and (iv) harvesting grapes at high technological maturity in order to obtain wines with a satisfactory alcoholic content when possible.     

Evaluation of the astringency of commercial tannins by means of the SDS–PAGE-based method

The astringency of wines enriched with commercial tannins (CTs) was evaluated by a method based on the SDS–PAGE electrophoresis of salivary proteins after the reaction of saliva with wine. Nineteen CTs tested in synthetic wine at the same pH (3.6) and concentration (1 g/l) gave different values of saliva precipitation index (SPI). The effect of CTs addition was investigated in four wines. Results showed that the wine matrix influenced the astringent capacity of CTs and that became less pronounced as wine polyphenolic complexity increased. For some types of wine, astringency was not affected, indicating that the effect of CTs utilisation is not easily predictable by classical methods. The ability to objectively evaluate the astringency provided by CTs with the SDS–PAGE-based method would supply producers and winemakers with a useful tool to manage the processing conditions and thus to improve the quality of wine.     

An assessment of the effects of wine volatiles on the perception of taste and astringency in wine

The objective of this work is measuring the effect of different volatile extract compositions on the perception of taste, astringency, global intensity and persistence of wine. Six Spanish wines, two from Chardonnay and four from Tempranillo grapes, all of them showing different chemical and sensory characteristics, were selected. Wines were separated into volatile and non-volatile fractions by solid phase extraction and lyophilisation and further liquid extraction, respectively. Eighteen “reconstituted wines” were prepared, combining different volatile extracts and different non-volatile matrices and adjusting ethanol content to 12% (v/v), and were further described by a specifically trained sensory panel. Taste attributes (sweetness, acidity, bitterness), astringency, aroma intensity, global intensity and persistence were assessed in both, original and “reconstituted” wines by using a numerical category scale. The sensory properties of the original wines were retained by their corresponding “reconstituted samples”. The sensory assessment of the “reconstituted wines” showed that the addition of volatile fruity extracts from white wines brought about a decrease in astringency and bitterness and an increase in sweet perception in all cases. While global intensity and persistence of white wine matrices were also increased, they did not change in red wine matrices, which suggests that the volatile fraction plays only a secondary role in these attributes of red wines. Similarly, the effects of replacing the volatile fraction of a red wine by volatile extracts from other red wines were small and inconsistent, which confirms that taste and astringency are primarily driven by non-volatile molecules in these wines.     

Applications of an oak extract on Petit Verdot grapevines. Influence on grape and wine volatile compounds

Petit Verdot vineyards were treated at veraison with a commercial aqueous French oak extract in order to determine if the extract’s volatile components can be transferred to grapes and then to wines. Three different formulations (25% (one application), 25% (four applications) and 100%) were tested, together with an eugenol and guaiacol standard solution to better follow their behaviour. The volatile compounds of treated grapes and their wines after alcoholic and malolactic fermentation and after 8 months were analysed by stir bar sorptive extraction and gas chromatography mass spectrometry (SBSE-GC–MS). The results showed that the grapes stored the volatile compounds mainly as non-volatile precursors, and some of these were released after winemaking. In the case of wines, it was possible to distinguish the control versus the ones from vineyard treatments. The different oak extract applications were evident only after alcoholic fermentation sampling, making it very interesting for young wines.     

Enological tannins affect acetaldehyde evolution,colour stability and tannin reactivity during forced oxidation of red wine

The addition of enological tannins is a practice admitted and widely used to improve wine phenolic compositions. Although wine ageing is an oxidative process involving phenolic compounds and acetaldehyde production and consumption, the effect of enological tannins on the acetaldehyde and chromatic and phenolic changes of a red wine during oxidation is still not known. In this study, three enological tannins preparations containing gallotannins GT, ellagitannins ET and condensed tannins CT were added to a young commercial Lambrusco red wine in order to obtain wines with three different phenolic compositions. Samples were then treated with hydrogen peroxide to trigger oxidation. All added tannins have determined a production of acetaldehyde greater than control. Acetaldehyde was then consumed in 30 days. The samples treated with CT and ET showed, after oxidation, an increase in colour intensity, determined as the sum of 420, 520 and 620 nm absorbances. A simultaneously increase in polymeric pigments was detected. No significant variation of the Saliva Precipitation Index (SPI), an index useful to give an indirect measure of wine astringency, was observed after 30 days of treatment of CT and ET samples. Results highlight that the addition of CT and ET can help to stabilise colour without affecting wine reactivity towards salivary proteins. A significant role of acetaldehyde has been even detected. These are the first data showing the effect of different enological tannins on the production and consumption of acetaldehyde formation during an oxidation process.     

Beer aroma recovery and dealcoholisation by a two-step pervaporation process

Pervaporation with a polydimethylsiloxane membrane (PDMS) has previously been used for the recovery of aroma compounds or to dealcoholise beer. This work considers two PDMS pervaporation processes and associated operating conditions. In addition to ethanol, two esters and one higher alcohol were chosen as key beer aroma compounds. The effects of feed flow rate and temperature on aroma recovery were studied, with feed temperature and permeate pressure evaluated with regard to beer dealcoholisation. The required membrane areas for a given alcoholic beer flow rate were simulated by mass balance to achieve a non-alcoholic product. With aroma recovery, no concentration polarisation was observed with Reynolds numbers above 1520 and the optimal temperature was 10°C. For alcohol removal, the best operation conditions were 65°C and 1400 Pa. With such conditions, the required membrane surface to recover 50% of ethyl acetate from the original beer was 13.8 m² in the first pervaporation unit, whereas 4.4 m² was needed in the second one to achieve an alcohol content of 0.05% (v/v). The mixed final product was defined as an alcohol-free beer with significant aroma compounds, showing the feasibility of pervaporation for both beer aroma recovery and dealcoholisation. © 2019 The Institute of Brewing & Distilling     

Comparison of analytical methods for measuring proanthocyanidins in wines and their relationship with perceived astringency

The concentration of proanthocyanidins from twenty red wines from cv. Cabernet Sauvignon, five rosé wines from cv. Cabernet Sauvignon and five white wines from cv. Sauvignon Blanc was quantified using four analytical methodologies, and their relationship with the perceived astringency was investigated. Proanthocyanidin concentrations were determined by a methylcellulose precipitation assay, a protein precipitation assay and two colourimetric methods (Bate‐Smith and vanillin assay). The four methodologies showed high repeatability but differed widely in proanthocyanidin concentrations. The methylcellulose and protein precipitation assays could not quantify proanthocyanidins in rosé and white wines. The protein precipitation assay gave the lowest concentration of proanthocyanidins in all of the red wines. The methylcellulose precipitation assay (r = 0.7725; r² = 0.59) and the protein precipitation assay (r = 0.6828; r² = 0.47) showed a strong correlation with the perceived astringency compared with the colourimetric methods. The strong correlation of the methylcellulose precipitation method with the perceived astringency could be a useful tool to estimate red wine astringency.     

Sensory attribute evolution in bottled young red wines from Rioja Alavesa

The evolution of 19 bottled young red wines from Rioja Alavesa was studied through 9 months. Twenty-four sensory attributes (including appearance, aroma, flavor, taste and mouth-feel) were evaluated at four times (at 1, 3, 5 and 9 months after bottling) by a ten-member panel. Fifteen physicochemical parameters were also analyzed at these four times. Effect of winemaking process (carbonic maceration vs. destemming), and grape variety (only Tempranillo vs. Tempranillo with a white variety) on wine evolution was considered too. Data were analyzed by analysis of variance. Nine sensory attributes changed significantly through the time: red berry aroma and flavor, body, balance, purple hue and color intensity increased, whereas alcoholic aroma and flavor, and astringency decreased. Almost all the physicochemical parameters changed significantly through the time. The winemaking process and the addition of white grapes did not influence sensory and physicochemical evolution.     

Intensity of taste and astringency sensations elicited by red wines is associated with sensitivity to PROP (6-n-propylthiouracil)

The relationship between sensitivity to 6-n-propylthiouracil (PROP) and taste and astringency perception elicited by red wines was examined. Twenty-five subjects were classified into three PROP sensitivity groups (non-tasters, tasters and super-tasters) based on their bitterness ratings of a 0.32 mM PROP solution as measured on a Labeled Magnitude Scale (LMS). In a completely randomized block design, subjects used the LMS to rate the bitterness, astringency and acidity intensities of three commercial red wines. Contrary to the findings of previous studies with wine, bitterness, astringency and acidity intensities were all correlated with individual PROP taster status. PROP non-tasters gave significantly lower intensity ratings for the bitterness, astringency and acidity of the red wines than did PROP tasters and super-tasters. Individual differences among taster groups may be related to preference and consumption behavior of consumers of wine and other alcoholic beverages.     

Sensory and chemical effects of two alternatives of prefermentative cold soak in Malbec wines during winemaking and bottle ageing

Two alternatives of cold soak (CS), traditional external refrigeration (CS‐T) and use of solid CO₂ (CS‐DI), were evaluated in Malbec wines and contrasted against a control (C) during winemaking and up to 24 months of bottle ageing. Sugar consumption up to 5 g L day^‐1 was observed in CS‐T during the CS period. Both the viability of the population of Saccharomyces and non‐Saccharomyces were maintained during CS. CS‐T was detrimental for the anthocyanin and phenolic content and caused a reduction of absorbance in the visible spectrum of the wines relative to C and CS‐DI. CS‐DI had an early positive effect in the anthocyanin content and chromatic properties, but this effect subsided after 6 months of bottle ageing relative to C. From a sensory standpoint, CS‐T had the lowest colour saturation and a marked acetaldehyde character. CS‐DI wines were the most saturated in colour at press and early ageing, whereas a balsamic‐like aroma developed during bottle ageing. C wines were characterised by red fruits aroma, reduction and astringency early during winemaking, but a decrease in astringency and the reduction character occurred during bottle ageing.     

Characterisation of wines and distilled spirits from melon (Cucumis melo L.)

Melon fermentation and distillation was studied with a view to produce melon spirits. Three different substrates were obtained from melon (Cucumis melo L.). Sugar concentration was around 60–70 g L^?1 and the pH between 4.6 and 5.2. The substrates were clarified and then fermented at one of two pH levels at 20 °C. A commercial Saccharomyces cerevisiae starter culture was used to obtain melon wines with an alcohol concentration of 3.8–5.8% (v/v). The melon wines were distilled in a distillation column to yield distillates with an alcohol content of 33–60% (v/v). The major volatiles in the melon wines and in the distillates were analysed by gas chromatography (GC). The results demonstrated that melon could be a good substrate of fermentation and distillation but also yielded significant differences in the volatiles analysed in the different melon wines and distillates obtained from the different substrates in the different conditions of the experiment. Fermentation pH greatly affected the methanol, acetaldehyde, and butanol contents and thus the final quality of the spirits produced.     

Effects of ultrasound on structural and physical properties of soy protein isolate (SPI) dispersions

The effects of low-frequency (20 kHz) ultrasonication at varying power (200, 400 or 600 W) and time (15 or 30 min) on functional and structural properties of reconstituted soy protein isolate (SPI) dispersions were examined. Ultrasonic treatments reduced both the storage modulus and loss modulus of SPI dispersions and formed more viscous SPI dispersions (fluid character). Moreover, ultrasound treatment significantly decreased the consistency coefficients and increased the flow behaviour index of SPI dispersions. Scanning electron microscopy of lyophilized ultrasonicated SPI showed different microstructure with larger aggregates compared to non-treated SPI. No significant change was observed in the protein electrophoretic patterns by SDS-PAGE. However, free sulfhydryl content, surface hydrophobicity and protein solubility of SPI dispersions were all increased with ultrasonic treatment. Differences in solubility profiles in the presence versus absence of denaturing (0.5% sodium dodecyl sulphate and 6 M urea) and reducing (mercaptoethanol) agents suggested a decrease in non-covalent interactions of SPI in dispersion after ultrasonic treatment. Secondary structure analysis by circular dichroism indicated lower α-helix and random coil in SPI treated at lower power, in contrast to higher α-helix and lower β-sheet in SPI treated with higher power (600 W). In conclusion, under the conditions investigated in this study, ultrasonic treatment resulted in partial unfolding and reduction of intermolecular interactions as demonstrated by increases in free sulfhydryl groups and surface hydrophobicity, leading to improved solubility and fluid character of SPI dispersions, while larger aggregates of ultrasonic-treated SPI in the dry state were formed after lyophilization.     

Effect of a pulsed electric field treatment on the anthocyanins composition and other quality parameters of Cabernet Sauvignon freshly fermented model wines obtained after different maceration times

The influence of the application of a pulsed electric field (PEF) treatment (5 kV/cm, 2.1 kJ/kg) to the grape pomace on different quality parameters and anthocyanins content of Cabernet Sauvignon wines obtained after different maceration times (48, 72, 96 and 248 h) has been investigated.Regardless of the maceration time, the application of a PEF treatment led to freshly fermented model wines that were richer in colour intensity, total polyphenols index (TPI), tannins and showed better visual characteristics. It was observed that the concentration of anthocyanins compounds in the freshly fermented model wines obtained from PEF-treated pomace was higher, as compared to the control wine. The HPLC anthocyanic profiles of freshly fermented model wines obtained from PEF-treated pomace were similar to those of control wine indicating that the permeabilization of the cell membranes of pomace did not produce a selective effect on any anthocyanin. Malvidin-3-glucoside and Malvidin-3-glucoside acetate were the predominant anthocyanins in both control and PEF wine.According to the results obtained in this investigation the application of a PEF treatment permitted to reduce the maceration time during vinification of Cabernet Sauvignon grapes from 268 to 72 h.     

Evaluation of the potential of high pressure technology as an enological practice for red wines

The impact of high hydrostatic pressure (HHP) treatments on the phenolic compounds composition of a red wine was studied after storage in order to evaluate the potential of this technology as an enological practice. Red wines pressurized at 500 and 600 MPa at 20 °C for 5 and 20 min, respectively, showed a lower content of monomeric anthocyanins (13 to 14%), phenolic acids (8 to 11%), and flavonols (14 to 19%) after 5 months of storage, when compared to the unpressurized wine. These results, together with the different degree of tannin polymerization and flavan-3-ol content in the pressurized wines led to propose an effect of HHP in the increase of polymerization and cleavage reactions of proanthocyanidins. The sensorial analysis of pressurized wines showed lower astringency, a higher intensity of cooked fruit aroma and lower intensity of fruity notes, when compared with the unpressurized wine. These effects are associated to those observed during wine aging.Industrial relevanceDuring the last decade, the use of high hydrostatic pressure (HHP) as a non-thermal technology for food preservation and modification has increased substantially. Recently, pressure treatments have shown to influence long term red wine physicochemical and sensorial characteristics, leading to aged wine-like characteristics. Therefore, the use of HHP technology to modify wine composition could benefit the wine industry, especially to improve wines with low aging potential. This work shows that HHP can be potentially used as enological practice, modulating the organoleptic properties of wine by decreasing astringency and increasing pleasant aromas. It seems possible to exploit commercially the production of young red wines with distinct characteristics using this technology, addressing the market and consumer demand.     

Astringency,bitterness and color changes in dry red wines before and during oak barrel aging: An updated phenolic perspective review

To understand effects of using oak barrels on the astringency, bitterness and color of dry red wines, phenolic reactions in wines before and after barrel aging are reviewed in this paper, which has been divided into three sections. The first section includes an introduction to chemical reactivities of grape-derived phenolic compounds, a summary of the phenolic reactions that occur in dry red wines before barrel aging, and a discussion of the effects of these reactions on wine astringency, bitterness and color. The second section introduces barrel types that determine the oak barrel constituents in wines (primarily oak aldehydes and ellagitannins) and presents reactions between the oak constituents and grape-derived phenolic compounds that may modulate wine astringency, bitterness and color. The final section illustrates the chemical differences between basic oxidation and over-oxidation in wines, discusses oxygen consumption kinetics in wines during barrel aging by comparing different oxygen consumption kinetics observed previously by others, and speculates on the possible preliminary phenolic reactions that occur in dry red wines during oak barrel aging that soften tannins and stabilize pigments via basic oxidation. Additionally, sulfur dioxide (SO₂) addition during barrel aging and suitability of adopting oak barrels for aging wines are briefly discussed.     

Effect of the prefermentative addition of copigments on the polyphenolic composition of Tempranillo wines after malolactic fermentation

The influence of the prefermentative addition of copigments and different winemaking technologies on the polyphenolic composition of Tempranillo red wines after malolactic fermentation was studied. Six experiments dealing with the prefermentative addition of caffeic acid, rutin, (+) catechin, white grape skin tannin, white grape seed tannin and control wines were realised. Three different winemaking technologies (traditional vinification, prefermentative cold maceration at 6–8 °C and cold soak at 0–2 °C with dry ice) were studied. Prefermentative addition of copigments increases anthocyanin copigmentation reactions and produces wines with a greater colour, a higher anthocyanin concentration, a superior contribution of anthocyanins to the colour of the wine, a superior percentage of tannins polymerised with polysaccharides and less astringency. Cold prefermentative maceration increases the extraction of polyphenols, the anthocyanin copigmentation reactions and the polymerisation reactions between tannins and polysaccharides. The effectiveness of the combination of copigments and prefermentative maceration treatments was demonstrated by the increase of the concentration of the polyphenolic compounds.     

Preparation and optimization of soy protein isolate–high methoxy pectin microcapsules loaded with Lactobacillus delbrueckii

This study was aimed to use soy protein isolate (SPI) and high methoxy pectin (HMP) as encapsulating materials for probiotic bacterial (Lactobacillus delbrueckii) delivery systems. The encapsulation conditions were optimised, and scanning electron microscopy (SEM) was used to characterise the microstructural changes of the microcapsule. The results showed that the optimal conditions for microcapsule preparation were 90 mg mL^?1 SPI and 1 mg mL^?1 HMP, with a SPI/HMP ratio of 7:1 (v/v), and a L. delbrueckii suspension to SPI–HMP complex ratio of 1:1 (v/v). The viability of the probiotics in the microcapsules reaching the small intestine was 3 log CFU mL^?1 higher than that of naked bacteria. SEM showed that the surface of the SPI–HMP compound microcapsules was smooth and that a large number of L. delbrueckii could be seen in cross‐sections of the microcapsules.