Month: January 2019

From grape to wine: a focus on seed tannins

By Pauline Rousserie, Amélie Rabot and Laurence Geny-denis
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Tannins, also called condensed tannins or proanthocyanidins (PAs) are polyphenolic compounds widely found in the plant kingdom. They are essentially secondary metabolites produced by plant for their adaptation and protection to biotic and abiotic stresses. In wine, they are among the most important quality factors due to their contribution to the organoleptic characteristics such as colour, astringency and bitterness 1–3. Although tannins found in wine can come from microbial and oak sources, the main sources of polyphenols are grape skins and seeds 4. Since the 1960s, this subject has been widely studied by a large number of researchers covering different types of wine, climate conditions, growing practices, and grape varieties. As these works have been conducted under different conditions, the data collected can be conflicting. This is why the question remains: what factors influence the biosynthesis, the quantity and the distribution of tannins in grape seeds and how can winemaking processes impact the extractability of seed tannins in wine?
Tannins result from the polymerisation of flavanols, also named flavan-3-ols which are the most reduced form of flavonoids. Tannins structure depend on the flavan-3-ols starter and extension units, the position and the stereochemistry of the linkage to the lower units, the degree of polymerization, and the presence of absence of modifications of the 3-hydroxyl group 5. The most commonly found monomeric units in PAs are (+)-catechin and (-)-epicatechin (table 1).

Table 1. Chemical Structure of the Principal Flavan-3-ols Monomers.

PAs are broadly distributed inside grapes and depending on the grape tissue location and the developmental stage of the berry, the quantity, the structure and the degree of polymerisation and galloylation of grape PAs differ. Indeed, at harvest time, the total of extractable phenolics in grape are distributed as follow: 10% or less in pulp, 28 to 35% in the skins and 60 to 70% in the seeds 6. Additionally, although differences are observed across varieties and vintages, it seems that at maturity, skin PAs present a significantly higher degree of polymerisation (from 2.1 to 85.7) than those of seeds (from 2.3 to 30.3). In terms of galloylation, differences between skin PAs and seed PAs at maturity have also been observed: seed PAs seem to present a higher percentage of galloylation (G%) (from 13.1 to 32.2%) than skin PAs (from 1.4 to 19%) 7.

Even though it is generally accepted that PA seeds are accumulated during the first berry growth phase, and decrease during the second growth phase, opinion on the evolution of the amount of seed tannins during ripening is divided. On one side, some authors report a significant decrease in the amount of PAs during the berry development, in some cases reaching 60% of the start amount. On the other side, a minority of authors have not found significant differences in PA seed content all along berry development. In cases where differences in polyphenol content are observed during berry maturation, observations show the same pattern consisting of two distinct periods, one of accumulation (from pea sized stage to veraison) and one of decline (from veraison to maturity) 8 (figure 1).

 

Figure 1 : Accumulation pattern of polyphenols in grape seed 8

Furthermore, viticultural practices such as pruning, thinning, leaf removal and irrigation can impact the PAs seed biosynthesis and content 7.
Because of the significant influence of tannins on red wine quality, many winemaking techniques have been developed as an alternative to the traditional elaboration of red wines. Some of this techniques such as fermentative maceration, cold maceration, enzyme addition, post fermentative maceration, high fermentation temperature, thermovinifcation, flash release and pulsed electric field are known improve the extraction of seed tannins (figure 2) 7.

 

Figure 2 : Global pattern of grape seed metabolism and how winemaking processes impact the extractability of seed tannins (1: Berry integrity, 2: Maceration time, 3: PEF, 4: Cold soak, 5: Maceration enzyme, 6: High fermentation temperature, 7: Thermovinification and Flash release) 7

To conclude, due to a lack of knowledge, it remains difficult to estimate the seed phenolic maturity, even though the winemaker will take into account this maturity to determine the best harvest date. Indeed, no reliable, simple tool exists to determine the phenolic maturity of the seed, which is why winemakers often delay harvest time until the seeds turn uniformly brown. The consequence of this delay is an increase in the Brix level, leading to undesirably high ethanol levels during maceration. To get a better idea of the phenolic maturity of grape seeds and its impact on the sensory properties of wine, a robust study of the phenolic metabolism of seeds should be conducted. Knowledge of how tannins are metabolised by the grape seed will lead to the discovery of strong maturity markers which can be used to create a reliable tool to determine the phenolic maturity of seeds.
Those interested in a longer length report can download the working paper at:
https://pubs.acs.org/doi/abs/10.1021/acs.jafc.8b05768

 

 

Pauline Rousserie
PhD student working in oenology research unit of ISVV (Institut des Sciences de la Vigne et du Vin) at University of Bordeaux. Doctorate research project focused on the grape seed metabolism in various Vitis species to give no insight about tannins biosynthesis in seed, seed phenolic maturity and seed tannins extractability potential.

Amélie Rabot
Post graduate in plant physiology and PhD in Agronomy and Molecular Biology. Currently she is associate professor in Vine and Wine Sciences Institute in Bordeaux (France). Her main area of research is about the developmental process of grapeseeds. She focuses especially on biomolecules biosynthesis evolution during seeds ripening which could impact winemaking.

Laurence GENY-DENIS 
Professor of grapevine physiology and viticulture at the Institut des Sciences de la Vigne et du Vin (ISVV) of Bordeaux University. Her research is focused on ripening process and impact of grape maturity on wine quality. She is co-authors of more 47 papers in international scientifics journals and had supervised 10 phD. She is coordinator of several research projects on grape quality in relation with technical practices as pruning and climate change. She supervises three diploma (a professional bachelor of winetourism, an international master of winetourism and a diploma of pruning (DUTE)) and coordinates the professional training at the ISVV.

References:

  1. Ma, W., Guo, A., Zhang, Y., Wang, H., Liu, Y. & Li, H. A review on astringency and bitterness perception of tannins in wine. Trends Food Sci. Technol. 40, 6–19 (2014).
  2. Soares, S., Brandão, E., Mateus, N. & de Freitas, V. Sensorial properties of red wine polyphenols: astringency and bitterness. Crit. Rev. Food Sci. Nutr. 57, 937–948 (2017).
  3. Teissedre, P.-L. & Jourdes, M. Tannins and anthocyanins of wine: phytochemistry and organoleptic properties. in Natural Products (eds. Ramawat, K. G. & Mérillon, J.-M.) 2255–2274 (Springer Berlin Heidelberg, 2013).
  4. Kennedy, J. A. Grape and wine phenolics: observations and recent findings. Cienc. E Investig. Agrar. 35, 107–120 (2008).
  5. Waterhouse, A. L. Wine Phenolics. Ann. N. Y. Acad. Sci. 957, 21–36 (2002).
  6. Shi, J., Yu, J., Pohorly, J. E. & Kakuda, Y. Polyphenolics in grape seeds—biochemistry and functionality. J. Med. Food 6, 291–299 (2003).
  7. Rousserie, P., Rabot, A. & Geny-Denis, L. From flavanols biosynthesis to wine tannins: what place for grape seeds? J. Agric. Food Chem. (2019).
  8. Kennedy, J. A., Troup, G. J., Pilbrow, J. R., Hutton, D. R., Hewitt, D., Hunter, C. R., Ristic, R., Iland, P. G. & Jones, G. P. Development of seed polyphenols in berries from Vitis vinifera L. cv. Shiraz. Aust. J. Grape Wine Res. 6, 244–254 (2000).
  9. Petrussa, E., Braidot, E., Zancani, M., Peresson, C., Bertolini, A., Patui, S. & Vianello, A. Plant flavonoids: biosynthesis, transport and involvement in stress responses. Int. J. Mol. Sci. 14, 14950–14973 (2013).
  10. Xia, E.-Q., Deng, G.-F., Guo, Y.-J. & Li, H.-B. Biological activities of polyphenols from grapes. Int. J. Mol. Sci. 11, 622–646 (2010).
  11. Quideau, S., Deffieux, D., Douat-Casassus, C. & Pouységu, L. Plant polyphenols: chemical properties, biological activities, and synthesis. Angew. Chem. Int. Ed. 50, 586–621 (2011).
Posted by in Chemistry, Viticulture

Combining rootstocks and deficit irrigation techniques to maintain vineyard sustainability under semiarid and water limiting conditions

By Pascual Romero

The threat of climate change (CC) will make it necessary to combine different adaptation measures, especially those related to irrigation and water management and availability, in order to maintain the sustainability of vineyards (Iglesias y Garrote et al., 2015) - especially in the semiarid, warm, and more vulnerable winegrowing regions of Southern Europe (such as SE Spain). In a recent study, we combined the use of different rootstocks and deficit irrigation (DI) techniques (RDI and PRI) with a low amount of water (Table 1), to increase WUE and improve vine performance and sustainability, as a long-term adaptation to CC in semiarid and water limiting areas. The results show that the rootstock had a significant impact on the ability to extract water from the soil and, in consequence, on the vine water status, leaf photosynthesis, vigor, productivity, WUE, and berry quality of Monastrell vines (Romero et al., 2018).

Table 1. Deficit irrigation strategy and water volume applied for each irrigation method (PRI and RDI) in each phenological period and the total for every year of the experiment (2012-2016).

Table 2. Berry technological quality index (QI technological berry), berry phenolic quality index (QI phenolic berry), and overall berry quality index (QI overall berry) calculated for Monastrell grapes at harvest, for five different rootstocks (140Ru, 1103P, 41B, 110R, and 161-49C) and two different irrigation methods (PRI and RDI), from 2012 to 2016.

Our study showed, that vines grafted on invigorating rootstocks - such as 1103P or 140Ru, both classified as rootstocks with high or very high drought tolerance, maintained greater water uptake capacity during the growing season and were able to exploit soil water resources more efficiently, increasing the irrigation efficiency under DI. This greater soil water uptake was also reflected in higher leaf nutrient content and vigor, superior accumulation of water and dry matter in plant organs, higher yield and WUE response (especially in 140Ru: yield: > 16,000 kg/ha, WUE: 18 kg grape/m3). But this was offset by poorer final berry quality and color, lower polyphenolic and nutraceutical concentrations in the must, and lower QI scores (Table 2), compared to rootstocks of medium-low vigor due, among other factors, to a greater dilution effect (bigger berry size and greater water content in the pulp and in the whole berry). In addition, vines grafted on either of the invigorating rootstocks had sink-source ratios such as yield/pruning weight and leaf area/yield, that were well outside the optimal agronomic ranges proposed for improving polyphenolic berry quality in DI Monastrell grapevines (Romero et al., 2016), suggesting that these vines were unbalanced. Besides, these vines had more closed canopies (higher proportion of shaded and internal leaves within the canopy) and decreased PAR in the cluster zone, which can also negatively affect berry quality.

Interestingly, the results revealed that Monastrell vines grafted on the least productive and least vigorous rootstocks - 161-49C, followed by 110R showed a significant improvement in long-term vine performance and berry quality under DI. Low yield/vigor rootstocks (especially 161-49C) stimulated the accumulation of polyphenolics (stilbenes, anthocyanins) and amino acids and some improvements in technological parameters (higher tartaric/malic ratio and TSS, lower pH), giving the highest berry QI scores (Table 2). Besides, they showed several other positive features, which may also have contributed to higher berry quality: lower berry weight, lower cluster compactness, lower % of big clusters, higher % of small clusters and a higher degree of homogeneity in the clusters. These vines were also better balanced, with significantly lower yield/pruning weight ratios, a higher leaf area/yield ratio, a high exposed leaf area/total leaf area ratio (more open canopies and exposed clusters), and had a greater water stress level during ripening (around -1.3 MPa, Figure 1) as maintained in vines grafted on 161-49C, close to or within the optimum physiological and agronomic thresholds and ranges proposed for Monastrell grapevines (Romero et al., 2010). All these features improved Monastrell berry quality (phenolic and technological) and nutraceutical potential.

Figure 1. Seasonal evolution of midday stem water potential, Ψs in 2012, 2013, and 2015 for each rootstock. The green dashed lines indicate the optimum range of Ψs (-1.25/-1.35 MPa, moderate water stress) that improves Monastrell berry quality. The red dashed line represents the dangerous threshold of Ψs and severe water stress.

Our results also show that, berry quality parameters and nutraceutical potential were significantly improved by the PRI method, relative to RDI. Depending on the specific rootstock-scion interaction, PRI can also be beneficial for Monastrell yield or berry quality, even with low irrigation water volumes, decreased θv availability in the wet root zone and lower root water uptake compared to RDI. Thus, compared to RDI, the application of PRI with low water volumes improved substantially Monastrell yield response (110R) and berry quality (polyphenols, amino acids) and nutraceutical potential - especially for low vigor rootstocks (161-49C, 110R) and two invigorating rootstocks (140Ru, 1103P). Our results also reflected intrinsic changes in vine physiology and berry metabolism caused specifically by PRI and altered endogenous hormonal status of the berries (e.g. abscisic acid, ABA).

The effects of PRI differed clearly between the two low vigor rootstocks, 110R and 161-49C. Thus, PRI vines grafted on 110R showed enhanced pruning weight, yield (+ 1400 kg ha-1), total amino acids, and resveratrol and a similar QI score compared to RDI vines grafted on 110R. In contrast, 161-49C vines under PRI maintained similar vigor and lower berry weight, yield (-1700 kg ha-1), and WUEyield, compared to RDI vines, but had the highest QItecnological berry, QIphenolic berry, and QIoverall berry scores and nutraceutical potential of all the combinations (Table 2). This rootstock-scion-irrigation method combination, under DI with low water volumes, would give low yields of berries of highest quality and nutraceutical potential for the production of premium red wine with a high added value.

 

Figure 2. Application of conventional regulated deficit irrigation (RDI) and partial root zone drying irrigation (PRI) techniques in field–grown Monastrell grapevines grafted onto different rootstocks in SE Spain.

In conclusion, the application of low irrigation volumes (85-90 mm year-1), in combination with low fertilizer inputs, low vigor rootstocks (161-49C and 110R), and well-designed DI strategies (PRI and RDI, Table 1) it could be an adaptation to CC in order to guarantee the sustainability of the Monastrell vineyards under semiarid conditions of SE Spain. Besides, for the invigorating, drought tolerant rootstocks (especially 140Ru), our results show that irrigation could be reduced even more under optimized DI strategies in order to control the excess vigor and yield.
Those interested in a longer length report can download the working paper at:
https://www.sciencedirect.com/science/article/pii/S0378377418302622

 

Pascual Romero

Grupo de Riego y Fisiología del Estrés. Departamento de Bioeconomía, agua y medio ambiente. Instituto Murciano de Investigación y Desarrollo Agrario y Alimentario (IMIDA), c/ Mayor s/n, 30150, La Alberca, Murcia, Spain.

Pascual Romero
Telephone: +34 968 366739
Fax: +34 968 366792
e-mail: pascual.romero@carm.es

Biologist, PhD. Agrarian researcher at the Instituto Murciano de Investigación y Desarrollo Agrario y Alimentario (IMIDA), Ministry of Water and Agriculture, Region of Murcia, Spain. Main head of several national search projects focused in topics related to the physiology of water stress, plant-soil water relations, water use efficiency and the application of different deficit irrigation techniques and new irrigation technologies in different species such as: almond, peach, citrus and vine.

 

References:

Iglesias, A., Garrote, L. 2015. Adaptation strategies for agricultural water management under climate change in Europe. Agr. Water Manag. 155, 113-124.
Romero, P., Fernández-Fernández, JI, Martínez-Cutillas, A. 2010. Physiological thresholds for efficient regulated deficit irrigation management in winegrapes grown under semiarid conditions. Am. J. Enol. Vitic. 61 (3), 300-310.
Romero, P., Fernández-Fernández, J.I., Gil-Muñoz, R., Botía, P. 2016. Vigour-yield-quality relationships in long-term deficit-irrigated wine grapes grown under semiarid conditions. Theor. Exp. Plant Physiol. 28, 23-51.
Romero, P., Botía, P., Navarro, J.M. 2018. Selecting rootstocks to improve vine performance and vineyard sustainability in deficit irrigated Monastrell grapevines under semiarid conditions. Agr. Water Manag. 209, 73-93.

Posted by in Viticulture

What percentage of cork should a cork-based stopper have from a mechanical perspective?

By Mariola Sánchez-González and David Pérez-Terrazas

Most bottles of wine consumed in the world are sealed with cylindrical stoppers which can be classified into three types: natural cork stoppers, made from a single piece of natural cork; cork-based stoppers (also known as technical cork stoppers) obtained from agglomerated or micro-agglomerated cork and comprising one or several pieces; and synthetic stoppers, which can be molded by injection or extrusion. In cork-based stoppers cork is mixed with other materials, mainly binder, so it would be interesting to determine the minimum cork content required to achieve a cork-like behaviour. In this study we compared natural cork stoppers, micro-agglomerated cork stoppers and co-extruded synthetic closures through different tests which simulate the bottling process, the beginning of the sealing period and the extraction process (Sánchez-González and Perez-Terrazas, 2018a; Sánchez-González and Pérez-Terrazas, 2018b). We tested micro-agglomerated cork stoppers with different percentages of cork tin their formulation allowing us to determine the percentage of cork that should be present in a cork-based stopper to achieve a cork-like behavior from a mechanical perspective.

Figure 1. Schematic representation of the experimental design and main results. Taken from Sánchez-González and Pérez-Terrazas (2018).

The micro-agglomerated cork stoppers tested in this study are composed of cork granulate and binder alone, with no other auxiliary products so that the effect of cork percentage on the mechanical behaviour of the stoppers can be assessed correctly. As regards the percentage of cork which should be present in a cork-based stopper, our results suggest that to clarify this question, the stopper density should be taken into account. Accordingly, cork percentage together with stopper density, provide a better indicator of the mechanical behaviour of a micro-agglomerated cork stopper. Furthermore, the binder content is not as decisive as cork content with regard to the mechanical behavior of micro-agglomerated cork stoppers. These results highlight the versatility of cork-based stoppers from a mechanical perspective. It is possible to design micro-agglomerated cork stoppers with certain formulations capable of improving, equalling or diminishing the mechanical characteristics of natural cork stoppers.
However, if our results are to be extrapolated to other cork-based stoppers, the specific characteristics of the stoppers tested in our study should be taken into account, as should the characteristics of the mechanical tests. The size of the cork particles and the presence of micro-spheres or other additives in the composition of stoppers are variables that could affect their mechanical behaviour (Motte et al., 2017). The duration of the sealing period is another influential factor. In this study we tested the evolution of the relaxation force over the first 24h after corking, although it would be of interest to extend this period. Another important factor to consider is hydration (Lagorce-Tachon et al., 2015, 2016), in this study all stoppers were tested previous acclimatization at 20°C and 65% of relative humidity, however is important to point out that mechanical properties of wine stoppers can change under different relative humidity environments. Hence, further research is needed in order to provide a specific answer to the question posed with regard to mechanical behaviour.

In addition, other aspects such as sensorial and chemical factors must also be considered. A suitable closure for wine should scarcely interact with the wine and should correctly regulate the gaseous exchange with the external atmosphere, which insures excellent conservation and gradual evolution of the wine in the bottle (Karbowiak et al., 2010; Lopes et al., 2012). The stopper must also be sufficiently elastic to guarantee the maintenance of liquid tightness for prolonged periods of time, while at the same time facilitating easy extraction from the bottle by the consumer (Chatonnet and Labadie, 2003). Therefore, the comparative performance of the different types of stoppers can be assessed from chemical, sensorial, mechanical and physical perspectives. However, there are other considerations that must be taken into account when choosing a stopper, namely, ecological, environmental and socioeconomic aspects. Cork is considered among the most important forest products and the associated economic activities form part of the Bioeconomy. Cork is a natural, renewable and sustainable raw material with low environmental impact and which possesses unique properties that make it ideal for the bottling of wine (Pereira, 2007). The use of cork contributes to the conservation of cork oak (Quercus suber L.) woodlands, a Mediterranean ecosystem with high biodiversity which acts as a carbon sink and also fulfils a fundamental ecological function of protection against advancing desertification and erosion. Furthermore, cork oaks contribute significantly to rural development in the areas where they are found.

Those interested in a longer length report can download the working paper at:
https://www.sciencedirect.com/science/article/pii/S2352340918314446

Mariola Sánchez-González, PhD, is researcher at the Forest Research Centre (CIFOR) of the Spanish National Institute for Agricultural and Food Research and Technology (INIA) and is the head of the INIA-CIFOR Cork Laboratory. Her research is focused in generating scientific and technological information for the integrated management of cork value chain from the forest to the industry. She is co-author of more than 40 papers in international scientific journals. She engages in the application of science to real world problems by collaborating with non-academic partners. Besides, she participates as an expert in the Spanish Standards Technical Committee about cork (CTN56) and in the International Organization for Standardization Technical Committee about cork (ISO/TC87).

 

David Pérez-Terrazas is PhD candidate in Doctorate in Engineering and Management of the Natural Environment at Polytechnic University of Madrid, funded by the Spanish Ministry of Education and Vocational Training (FPU Grant reference FPU17/03295). Doctorate research project focused on characterization of cork granulate for the manufacture of cork-based stopper.

 

References:

Chatonnet, P., Labadie, D., 2003. Contrôle de la conformité des bouchons: objectifs et paramètres à l'usage des professionnels. (Conformity assessment of stoppers: objectives and parameters for professional use). Revue Française D'Œnologie 198, 20-29.
Karbowiak, T., Gougeon, R.D., Alinc, J.-B., Brachais, L., Debeaufort, F., Voilley, A., Chassagne, D., 2010. Wine Oxidation and the Role of Cork. Crit. Rev. Food Sci. Nutr. 50, 20-52.
Lagorce-Tachon, A., Karbowiak, T., Champion, D., Gougeon, R.D., Bellat, J.P., 2015. Mechanical properties of cork: Effect of hydration. Mater. Des. 82, 148-154.
Lagorce-Tachon, A., Karbowiak, T., Champion, D., Gougeon, R.D., Bellat, J.P., 2016. How does hydration affect the mechanical properties of wine stoppers? Journal of Materials Science 51, 4227–4237.
Lopes, P., Roseira, I., Cabral, M., Saucier, C., Darriet, P., Teissedre, P.-L., Dubourdieu, D., 2012. Impact of different closures on intrinsic sensory wine quality and consumer preferences. Wine & Viticulture Journal 27, 34-41.
Motte, J.-C., Delenne, J.-Y., Barron, C., Dubreucq, É., Mayer-Laigle, C., 2017. Elastic properties of packing of granulated cork: Effect of particle size. Industrial Crops and Products 99, 126-134.
Pereira, H., 2007. Cork: Biology, Production and Uses. Elsevier, Amsterdan.
Sánchez-González, M., Perez-Terrazas, D., 2018a. Assessing the percentage of cork that a stopper should have from a mechanical perspective. Food Packaging and Shelf Life 18, 212-220.
Sánchez-González, M., Pérez-Terrazas, D., 2018b. Dataset of mechanical properties from different types of wine stopper: micro-agglomerated cork, natural cork and synthetic closures. Data in brief 21, 2103-2109.

Posted by in Enology

Pulsed electric fields accelerate release of mannoproteins from Saccharomyces cerevisiae during aging on the lees of Chardonnay wine

By Juan Manuel Martínez and Javier Raso


Mannoproteins are highly glycosylated proteins which constitute the major component of the cell wall in yeast. Their presence in wine produces positive effects such as reduction of haze formation, prevention of tartaric salt precipitation, diminution of astringency, and the improvement of mouthfeel, aroma intensity, and color stability (Pérez-Serradilla & De Castro 2008).
Traditionally, the mannoprotein enrichment of certain types of wines occurs during yeast autolysis in the “aging on lees” step. In this practice, the wine is deliberately left in contact with the lees sediment (mainly composed of yeast). Autolysis causes disorganization of membranous systems and thus permits the release of enzymes such as glucanase and proteinase, thereby leading to the degradation of the cell wall and the subsequent release of mannoproteins into the wine. This process, associated with yeast death, is very slow – lasting from a few months to years (Alexandre & Guilloux-Benatier 2006).

Figure 1. Mechanism involved in the triggering of manoprotein release by Pulsed Electric Fields.

Aging on the lees is a technique that requires considerable investment on the part of wineries in equipment (tanks, barrels), entails elevated labor costs (periodic stirring – bâtonnage – and sensorial analyses), and implies immobilization of winery stocks. Furthermore, this practice may negatively affect wine quality increasing the risk of wine oxidation and microbial contamination with bacteria and Brettanomyces. Different strategies have been suggested for the acceleration of yeast autolysis, including enzymes capable of hydrolyzing β-glucans from yeast cell walls, thermolysis, or mechanical methods for large-scale disruption of microbial cells (such as ultrasound, microwaves, and high pressure homogenization) (Martínez et al., 2016).
Pulsed Electric Fields (PEF) is a technology that provokes the increment of the permeability of cytoplasmic membrane of cells (electroporation) via the application of pulses of high electric field strength (kV/cm) and short duration (μs-ms). It has been recently proven that PEF triggers the autolysis of Saccharomyces cerevisiae  and accelerates the release of mannoproteins (Martínez et al. 2016). It is thought that the mechanism involved is related with the fact, the electroporation of the cytoplasmic membrane by PEF could facilitate the contact of endogenous lytic enzymes with the yeast cell wall were the mannoproteins are located (Figure 1).
The present study investigated the potential of PEF for triggering autolysis of Saccharomyces cerevisiae  and accelerating the release of mannoproteins during aging on the lees of Chardonnay wine.
Release of mannoproteins from untreated (control) and PEF-treated (5 and 10 kV/cm, 75 μs) yeast of Saccharomyces cerevisiae was monitored along the aging-on-lees storage period.

Figure 2. Effect of Pulsed Electric Fields on the release of mannoproteins during aging on the lees of Chardonnay wine.

Release of mannoproteins in Chardonnay wine increased drastically in samples containing PEF-treated (5 and 10 kV/cm, 75 μs) yeasts (Figure 2). No mannoprotein release was observed in the first ten days of aging on the lees in wine containing untreated yeast; however, after the same time interval, the concentration of those compounds increased by 40 and 60 % in wines containing yeast treated by PEF at 5 and 10 kV/cm, respectively. After 30 days of incubation, the mannoprotein concentration in wines containing yeast treated under the most intense PEF conditions reached the maximum value. Control cells, on the other hand, required six months to reach that maximum level.

Chromatic characteristics, total polyphenol index, total volatile acidity, pH, ethanol, and CIELAB parameters of the wine were not affected during aging on the lees with PEF-treated yeast. On the other hand, mannoproteins released from yeast treated by PEF decreased wine turbidity and showed foaming properties as mannoproteins released during the traditional “aging on the lees” (Figure 2).


The gentle PEF treatment required to induce autolysis open up the possibility of processing large volumes of lees in continuous flow with low energy consumption using the most economical PEF devices in the market.
Those interested in a longer length report can download the working paper at:
https://www.sciencedirect.com/science/article/pii/S0963996918307348

 

Juan Manuel Martínez is a PhD student from vew technologies of food processing group at University of Zaragoza (Spain). He studied his Bachelor degree in Veterinary and then he completed a Master in Food Science and Technology Research. Later on he studied a Master in Research and Development Management in Companies. In addition to the University of Zaragoza education, he has performed two trimester internships in the University of Natural Resources and Life Science in Vienna (Austria) and in Umea University in Sweden. All his investigations are focused on the extraction of interest compounds from different microorganisms utilizing Pulsed Electric Field (PEF) technology. He has been involved in the study of autolysis of yeast induced by PEF, the release of mannoproteins and its application to aging on lees step in winemaking. But also he has studied the PEF-assisted extraction of high-valuable compounds from different microorganism such as yeast and microalgae. Co-author of 10 scientific papers, a book chapter and 13 congress communications.

 

Javier Raso received his PhD in 1995 at the University of Zaragoza (Spain) where he is currently professor of Food Technology and former Director of the Pilot Plant of Food Science and Technology. He has been visiting researcher of the Microbiology Department at Unilever Research in Bedford (UK), of the Department of Food Biotechnology and Food Process Engineering at Technical University of Berlin (Germany) and of the Biological Systems Engineering Department at Washington State University (USA). His areas of research are in the field of food preservation and processing by thermal and non-thermal technologies such as ultrasound, high hydrostatic pressure, pulsed electric fields and combined processing. Research interest is focused in critical factors affecting efficacy of technologies, kinetics and mathematical modeling, process optimization and mechanisms of action. He has been involved in a number of EU and national funded projects in these topics and he is the author of more than 120 peer-review papers. He is co-author of the book “Pulsed Electric Fields Technology for the Food Industry” and he is serving in the editorial board of the “Innovative Food Science and Emerging Technologies” journal. He was Vice-Chair of the COST Action TD1104 “European network for development of electroporation-based technologies and treatments (EP4Bio2Med) and coordinator of the project FieldFOOD of the Horizon2020 Framework Program of the European Union

 

References:

Pérez-Serradilla, J. A., & De Castro, M. L. (2008). Role of lees in wine production: areview. Food Chemistry, 111(2), 447–456.
Alexandre, H., & Guilloux-Benatier, M. (2006). Yeast autolysis in sparkling wine-a review. Australian Journal of Grape and Wine Research, 12, 119–127.
Martínez, J. M., Cebrián, G., Álvarez, I., & Raso, J. (2016). Release of mannoproteins during Saccharomyces cerevisiae autolysis induced by pulsed electric field. Frontiers in Microbiology, 7, 1435.
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