Month: August 2019

Organic and biodynamic wines quality and characteristics: the scientific point of view

By Maria Carla Cravero

Nowadays the wine market proposes organic wines, biodynamic wines and a wide range of wines with different labels or claims without any law or regulation - natural wine, sustainable wines, wines with low environmental impact, vegan and vegetarian wines, wines without suphites – which can confuse the consumers. Biodynamic wines are not regulated by law, but by private associations or by a self-declaration of one producer.
The organic wines represent the 2.4% of the wine global market and their trend is increasing. Their production is regulated by law, but it has not the same meaning in different countries. For example, in Europe organic wine is a wine made using organically grown grapes, but it can contain added sulfites, in the USA organic wine is a product without sulphites.
Jones and Grandjean (2017) evidence that the law differences among countries are a problem for the wine operators. The authors consider the organic wines “a case study of failed category creation.” They studied the evolution of the organic wines from the 1970s and they observed that this wine class did not have the same success than other organic food and drinks, like tea. They also mark the great differences in consumption of organic wines in the world, for example in Sweden is really higher than in the USA, considering the number of inhabitants.


The scientific studies on this subject are still restricted and it is difficult to define the real quality of organic and biodynamic wines. A recent review examines the different aspects related to organic and biodynamic wines:
Cravero M.C., 2019 Organic and biodynamic wines quality and characteristics: A review. Food Chemistry, 295, 15 October 2019, Pages 334-340.
Several methods of analysis experimented in Italy, Spain, Australia Czech Republic did not evidence great differences between organic and non-organic wines.
Other aspects of the organic wines concern the content of compounds potentially toxic to human health: pesticides and metals, such as copper, deriving from treatments in the vineyard, or ochratoxin A - a mycotoxin produced by several fungal species - and biogenic amines.
Pesticides were not detected in organic juices and wines in Brazil. Their content was significantly lower in concentration and number in organic wines than conventional ones produced in different regions of Croatia. Generally even copper concentration in grapes and wines is within the legal limits. The same for the levels of minerals and trace elements (Al, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Ni, P, Pb, S, Se, Sn, V, Zn) in wines produced in Italy, Slovakia, Croatia and Brazil. Fluoride content was not different in organic and non-organic Spanish wines and it did not exceed the health limit.
The content of biogenic amines (BA) were analyzed in Turkish wines and Chilean organic and non-organic wines, and some differences in the content of different ammines were pointed out. Sometimes, the wines produced with traditionally grapes had greater concentrations of some BA than the wines produced with organically grapes.
The studies did not point out significant differences in the content of ochratoxin A (OTA) between organic and conventional Croatian and Italian wines, in most cases the OTA levels were below the legal limits (2 ng/mL).
A study (Comuzzo et al., 2013) surveyed a high number of samples, of vintages 1999-2007. They were about 1000 organic wines (634 red, 303 white and 34 rosé), produced in Italy, France, Germany, Austria, Spain and Switzerland. Several analytical parameters were determined, including SO2, which was lower than 110–120 mg/L, in compliance with the current European legislation. The OTA levels were quantified in 199 wines and in the 95% of the samples they were within the legally-permitted limits. The BA concentration was determined in 105 samples, and a high content of BA was found in a certain number of wines, attributed to the difficulties in ending the malolactic fermentation.
Phenols and antioxidant activity in organic wines sometimes resulted higher in some Italian organic wines and in some Croatian organic wines than in conventional products, not in other studies carried out in Italy and Spain.
At last, organic wines, in which, unlike non-organic wines, the SO2 must be lower or absent, may undergo premature ageing and present high levels of oxidation compounds. The use of selected indigenous yeasts to reduce the production of these molecules and allow the production of wines with high organoleptic quality.
Studies carried out in Germany did not show important variances in soils in response to biodynamic management in comparison to organic or integrated management approaches. Some differences were evidenced in the soil microbial diversity.


Some papers report the results of the comparison between biodynamic and organic wines. Sometimes, the biodynamic grapes had a better composition (significantly higher sugar content, higher levels of total polyphenols and anthocyanins) and the wines better sensory aspects than the control fruit and the corresponding organic products. Other results show that the type of agricultural and winemaking practice had no impact.
Some authors evidenced that biodynamic and organic wine characteristics tend to be similar after the first year of conversion, implying that high-quality wines can be produced by biodynamic management.
The grape management - organic or biodynamic - affects the yeast population of wines, but the wine composition is associated with the winemaking process, followed by the grape management.
Some specific analysis - proton nuclear magnetic resonance (1H-NMR) and crystallographic analysis - have been experimented to discriminate organic and biodynamic wines.
Some aspects of the biodynamic wine and vineyard management are based upon philosophical tenants, not established science. It is important to test experimentally biodynamic practices that are based on anecdotal evidence.
In conclusion, the published scientific papers report the results obtained on a limited number of grape varieties and wines in a specific area. It is difficult to define the real quality of organic and biodynamic wines and more studies on the subject are warmly welcome.


Maria Carla Cravero
CREA Council for Agricultural Research and Economics, Research Centre for Viticulture and Enology, Via P. Micca 35, 14100 Asti, Italy

Web of Science ResearcherID H-8091-2019
ORCID 0000-0002-6919-4697

Graduate degree in Agriculture and post-graduate degree in Viticulture and Enology (University of Turin –Italy).
Researcher of CREA Council for Agricultural Research and Economics, Research Centre for Viticulture and Enology, Asti (Italy). Research experience in grape and wine physical-chemical analysis from 1988 to 1997 and from 1997 in sensory analysis of grape, wine and alcoholic beverages. Experience of collaboration for the sensory analysis in projects concerning viticulture, chemical grape composition (polyphenols and aromatic compounds), wine technology and microbiology. Organization of many workshops about wine sensory analysis.
From 2005 to 2015 she was member of Italian delegation to the International Organization of Vine and Wine (OIV) and she contributed to the document:
In possession of the professional qualification of Sensory Project Manager issued by the SISS (Italian Sensory Science Society) of Florence (Italian law 4/2013) and ordinary member of the SISS.
She is the author of more than 200 publications.
Guest Editor for the Special Issue Wine traceability per Beverages (ISSN 2306-5710) in 2018.
Reviewer of international Journals (
She contributed to translate the “Traité d’oenologie” of P. Ribéreau-Gayon, D. Dubourdieu, B. Donèche, A. Lonvaud, form the French to Italian: II edition (2003), III edition (2007) and IV edition (2018).


Comuzzo, P., Rauhut, D., Werner, M., Lagazio, C., Zironi, R. (2013). A survey on wines from organic viticulture from different European countries. Food Control, 34(2), 274-282.

Jones, G., and Grandjean, E. (2017). Creating the Market for Organic Wine: Sulfites, Certification, And Green Values. Harvard Business School General Management Unit, Working Paper 18-048: 1–59.

Posted by in Enology, Viticulture

Exploring the diversity of a collection of native non-Saccharomyces yeasts to develop co-starter cultures for winemaking

By Renato L. Binati and Sandra Torriani

The variety of the microbiota naturally present in the vineyards is affected by several parameters, such as grape variety, location, climate, vintage, vineyard treatments, pruning techniques, growing stage and ripening (Varela & Borneman, 2017). In the spontaneous fermentation of wine, the process is carried out by a succession of that myriad of different species, together with the microbes colonizing the winery equipment. Yet, the inoculation of Saccharomyces cerevisiae starter cultures in grape musts became a common practice worldwide, due to its tolerance to the harsh conditions found in fermenting musts, excellent fermentation performance, and satisfactory aroma-related metabolism (Padilla et al., 2016). However, some critics of the extensive use of this approach claim that it could result in wines lacking complexity, typicity and distinction, which could presumably be augmented with native non-Saccharomyces yeasts as co-starters, due to their relevant enzymatic activities and production of metabolites of oenological significance (Jolly et al., 2006).
This study, graphically represented in Figure 1, used culture-dependent methods to set up a vast culture collection gathered from a wide range of Italian viti-vinicultural regions and assess the non-conventional yeast diversity, focusing on oenologically interesting species. The screening integrated genomic and technological features aiming to exploit the huge untapped potential of native microorganisms.

Figure 1: Graphical abstract of the screening program carried out.

A high diversity of non-Saccharomyces yeasts was found after mining more than 400 isolates in 167 samples of grapes, grape musts and other high-sugar matrices, such as honey, overripe and dried fruits. Careful observation of yeast colony and cell morphology, combined with molecular methods, such as RAPD-PCR analysis with primer M13, and ITS 5.8S rRNA sequencing, demonstrated to be a powerful strategy for the unblemished identification of the commonly encountered and also unusual species associated with the studied samples, summarized in Figure 2.
An in-depth genotypic and phenotypic characterization was then carried out with a large number of native yeast isolates belonging to the genera Starmerella, Metschnikowia and Lachancea, considering the fact that they were found in higher quantity and higher distribution among the samples. In addition, these yeasts display several interesting oenological features, such as the reduction of ethanol and acetic acid levels, and the increase of glycerol content in wine (Englezos et al., 2015; Benito et al., 2016; Varela et al., 2017).
The genotyping consisted of using Rep-PCR [with primer (GTG)5; Pfliegler et al., 2014] and SAU-PCR [with primer SAG; Corich et al., 2005] techniques to identify the different strains among the isolates of those three groups.
The phenotypic characterization considered stress tolerance assays, enzymatic activity trials and single inoculum fermentations. The tolerance of the yeast strains was tested against ethanol, glucose, sulfur dioxide, copper and gluconic acid; in microtiter plates containing concentrations that could be encountered in grape must or wine and hinder the yeasts development. Six enzymatic activities relevant for wine quality were tested by spot assay on Petri dishes: sulfite reductase, β-glucosidase, glycosidase, esterase, pectinase and protease. Finally, natural must from Trebbiano grapes was inoculated with each isolate of Lachancea thermotolerans and Starmerella bacillaris; while Metschnikowia spp. isolates were not tested in single fermentation trials, since the stress tolerance assays demonstrated their poor ethanol resistance.
Isolates of S. bacillaris showed the highest tolerance to ethanol and Metschnikowia spp. the lowest. All three groups of isolates were dramatically sensitive to SO2 (100 ppm); while all were tolerant to glucose and copper (except some L. thermotolerans completely inhibited), but a slower proliferation of yeast cells was observed as the concentrations increased. Metschnikowia spp. were the only isolates exhibiting remarkable aroma-related enzymatic activities (protease, β-glucosidase, and esterase) and showed a much higher potential to metabolize gluconic acid, which are all prized features in winemaking.

Figure 2: Differential distribution of main oenological species divided by the type of sample.

At the end of fermentation, the main chemical parameters of the wines were measured and reported in Table 1, as the mean values for all isolates of each species, compared to the control with the commercial strain S. cerevisiae EC 1118. None of the tested non-Saccharomyces was able to complete the alcoholic fermentation, whereas EC 1118 fermented almost to dryness. Nevertheless, the proposed strategy to exploit non-Saccharomyces yeasts is through mixed fermentation with S. cerevisiae, as it is generally recognized that these species would not be able to conclude the alcoholic fermentation on their own.
The glycerol yield was 3.4 times higher for S. bacillaris than S. cerevisiae and almost two times higher than L. thermotolerans. The production of acetic acid varied among the isolates of non-Saccharomyces, but S. bacillaris showed a mean value and a production yield higher than L. thermotolerans. As regarding the production of L(+)-lactic acid, which results in a natural acidification of wines and consequent improved stability, higher freshness and lower need of SO2 (Morata et al., 2018), a significant diversity was found among the L. thermotolerans isolates. Moreover, only the control with S. cerevisiae was able to consume part of the malic acid present in the must.
None strict correspondence was verified between intraspecies grouping by the genotypic and phenotypic clusters, but these methods appear complementary in separating strains with technologically important properties useful for winemaking applications. Since most of the characteristics analyzed were species- and strain-dependent, the obtained results highlight the success of an efficient selection program aiming to exalt the quality of regional wine by characterizing a large number of native isolates. The selection of a new generation of co-starters has the objective of finding the best strains within determined species that are able to maximize the strengths and minimize the weaknesses, with the ultimate goal to be integrated in innovative and rational mixed fermentation strategies. The technological suitability and aromatic contribution of the distinct selected strains have to be further investigated in combination with S. cerevisiae.


The PhD scholarship of R.L.B. was funded by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq, Brazil). This research was supported by the University of Verona and the company Bioenologia 2.0 S.r.l. (Oderzo, Italy) in the framework of Joint Projects 2015, and it was carried out by Renato L. Binati, Giada Innocente, Veronica Gatto, Alessandro Celebrin, Maurizio Polo, Giovanna E. Felis and Sandra Torriani. The complete article is available at


Table 1: Analysis of wines obtained from single yeast cultures, shown as average amounts and standard deviation for all isolates belonging to each species.

Renato Binati is Postdoctoral Research Fellow in the Food Microbiology Laboratory in the Department of Biotechnology at the University of Verona, Italy. PhD in Biotechnology by the University of Verona, Italy, with a 6-month research visit at the Stellenbosch University, South Africa. Master of Science in Biotechnology & Biosciences by the Federal University of the State of Santa Catarina, Brazil. Bioprocess Engineer & Biotechnologist by the Federal University of the State of Paraná, Brazil. His research interests are mainly focused on oenological microbiology. He has experience with isolation, characterization, selection and technological application of yeast and bacterial strains related with alcoholic and malolactic fermentation in wines. The research activity included publications in scientific peer-reviewed journals, participation in international conferences with poster and oral presentation, co-supervision of master and bachelor students, assistance in practical lessons and seminars. He has also accomplished the WSET Level 3 Award in Wines, and is currently enrolled as WSET Diploma student.

Sandra Torriani is full Professor in Agro-Food Microbiology in the Department of Biotechnology at the University of Verona. (Italy). Head of Food Microbiology Laboratory. Her research interests lie in the field of molecular food microbiology. Attention is given to the molecular analysis and detection of microorganisms involved in food fermentation, the selection of suitable strains of microorganisms to be used as starters in the food and wine industries and the development of new functional food products. She has experience as scientific responsible of national and international research projects. In 2011, she founded the company Microbion Ltd., a spin-off of the Verona University. Member of the Editorial Board of Food Microbiology; Associate Editor of Frontiers in Microbiology (Food Microbiology) and she acted as Topic Editors for the Research Topic “Microbiota of grapes: positive and negative role on wine quality”. Reviewer of many scientific journals, research projects and PhD theses. Member of the SIMTREA, and of the Working Group “Wine Microbiology” of AIVV. The research activity is documented by the publication of over 160 articles in international peer review journals. She also contributed to 15 chapters in national or international books, and participated to numerous national and international conferences with posters or oral presentations. The h-index is equal to 42, and the total citations are 5,069 (23/07/2019).


Benito, Á., Calderón, F., Palomero, F., & Benito, S. (2016). Quality and composition of Airén wines fermented by sequential inoculation of Lachancea thermotolerans and Saccharomyces cerevisiae. Food technology and biotechnology, 54, 135-144.

Corich, V., Mattiazzi, A., Soldati, E., Carraro, A., & Giacomini, A. (2005). Sau-PCR, a novel amplification technique for genetic fingerprinting of microorganisms. Applied and Environmental Microbiology, 71, 6401–6406.

Englezos, V., Rantsiou, K., Torchio, F., Rolle, L., Gerbi, V., Cocolin, L. (2015). Exploitation of the non-Saccharomyces yeast Starmerella bacillaris (synonym Candida zemplinina) in wine fermentation: physiological and molecular characterizations. International Journal of Food Microbiology, 199, 33–40.

Jolly, N. P., Augustyn, O. P. H., & Pretorius, I. S. (2006). The role and use of non-Saccharomyces yeasts in wine production. South African Journal of Enology & Viticulture, 27, 15–38.

Morata, A., Loira, I., Tesfaye, W., Bañuelos, M. A., González, C., Suárez-Lepe, J. A. (2018) Lachancea thermotolerans applications in wine technology. Fermentation, 4, e53.

Padilla, B., Gil, J. V., & Manzanares, P. (2016). Past and future of non-Saccharomyces yeasts: from spoilage microorganisms to biotechnological tools for improving wine aroma complexity. Frontiers in microbiology, 7, e00411.

Pfliegler, W. P., Horváth, E., Kállai, Z., & Sipiczki, M. (2014). Diversity of Candida zemplinina isolates inferred from RAPD, micro/minisatellite and physiological analysis. Microbiological Research, 169, 402–410.

Varela, C., & Borneman, A. R. (2017). Yeasts found in vineyards and wineries. Yeast, 34, 111–128.

Varela, C., Barker, A., Tran, T., Borneman, A., & Curtin, C. (2017). Sensory profile and volatile aroma composition of reduced alcohol Merlot wines fermented with Metschnikowia pulcherrima and Saccharomyces uvarum. International Journal of Food Microbiology, 252, 1–9.

Posted by in Enology, Food Science and Technology

How to increase the tannin content of cold-hardy interspecific hybrid grape wines cultivated in cold climate?

By Pamela Nicolle and Karine Pedneault

Cold-hardy interspecific hybrid grape (CIHG) cultivars are crosses between the European Vitis specie V. vinifera and North American Vitis species, such as V. labrusca and V. riparia (Pedneault and Provost, 2016). CIHG cultivars have contributed extensively to the expansion of northern wine production areas, such as the Province of Quebec (Canada) that typically have harsh winters and short growing seasons (Pedneault et al., 2013). Despite the real advantage they present from a viticulture standpoint, including high tolerance to fungal diseases and frost, CIHG are challenging to work with in the winery, due to their unique biochemical composition (Pedneault and Provost, 2016). For instance, CIHG cultivars produce wines with high anthocyanin but low tannin concentrations (Manns et al., 2013), making their tannin/anthocyanin ratio unsuitable for tannin polymerisation during winemaking (Ribéreau-Gayon et al., 2006). Thus, young red CIHG wines typically exhibit a low mean degree of polymerisation (≤ 4) (Manns et al., 2013) that lead to low mouthfeel wines. However, consumers associate higher mouthfeel to higher quality in wine (Kassara and Kennedy, 2011).
Red wine astringency positively relates to the concentration of tannins and to their degree of polymerisation, as well as their degree of galloylation. Appropriate winemaking processes, mainly based on duration and temperature of maceration (e.g. pre-fermentative heat treatment, must freezing, extended maceration), contribute to optimising the extraction of phenolic compounds in wine, including tannins (Sacchi et al., 2005). The use of additives, either in the form of natural grape additives (e.g. pomace) (Nicolle et al., 2018) or as commercial enological tannins (Kyraleou and al., 2016), is another common practice to compensate for tannin deficiency and improve wine structure. But grape composition may also significantly impact tannin extractability and retention in wine, eventually leading to conflicting results. For example, practices such as tannin addition, cold pre-fermentative maceration and thermovinification, showed little to no effect on both tannin concentration and mouthfeel of red wines made from the CIHG varieties Marechal Foch, Corot noir, and Marquette (Manns et al., 2013).
High molecular tannins are known to interact with proteins and polysaccharides from the grape cell wall, which eventually removes them from must (Bindon, Kassara, and Smith, 2017). The pulp of CIHG varieties contains high concentration of pathogenesis-related proteins compared to typical wine grape varieties (V. vinifera) (Springer and Sacks, 2014). Pathogenesis-related proteins contribute to limit the extraction and retention of high molecular weight tannins in CHIG red wines (Springer et al., 2016).
Recently, our research group explored the impact of different treatments aiming at reducing the concentration of proteins in CHIG must on tannin retention in CHIG wine. Thus the impact of (1) must protein treatment, bentonite and heat; (2) pomace, fermented with and without; (3) tannin addition, 0-9 g/L; (4) and time of maceration, 0-11 days on tannin and protein extraction/retention in red CHIG wine were tested using a factorial experimental design (Figure 1). The CHIG variety used for this experiment was Frontenac, a cold-hardy variety developed at the University of Minnesota. Results were published in the journal Food chemistry (Nicolle et al., 2019)

Figure 1: Factorial experimental design used to produce experimental Frontenac wines, including the following factors: must protein treatment (untreated, bentonite-treated, and heat-treated must), pomace (must fermented with and without pomace), tannin addition (0, 1, 3, and 9 g/L), and time of maceration (0, 4, and 11 days after the end of alcoholic fermentation).

One of the most relevant finding was that protein removal from must prior to alcoholic fermentation, using bentonite addition or heat treatment, did not significantly improve tannin retention in CHIG Frontenac wines. On the contrary, conducting fermentation without pomace significantly increased tannin retention in wine, when exogenous tannins were used. In this case, concentrations of exogeneous tannins comprised between 5-15 times the recommended dose were necessary to obtain a significant increase in wine tannin concentration.

Figure 2: Tannin content (m/L epicatechin equivalent) in experimental Frontenac wines made from untreated, bentonite-treated and heat-treated must, related to the dose of tannin addition (0, 1, 3, and 9 g/L) at the end of alcoholic fermentation, in wines fermented with and without pomace. Different letter (lower case: oligomeric tannins; capital: polymeric tannin) indicate significant differences between wines at the 0.05 probability level.

In the light of these results, thermovinication has been proposed to the winemakers of Quebec wine industry as a suitable method to increase tannin retention in CHIG wines. Heating must and pomace prior to alcoholic fermentation (60-80°C) remove proteins from CHIG wines but, most importantly, limit any interaction between the cell wall components of the pomace and therefore maximises the retention of the exogeneous tannins required. Moreover, this winemaking approach has proved to be efficient for maximising the colour and improving its stabilisation. Work on sensory acceptability of this practise coupled with high exogeneous tannins addition need to be evaluated in terms of wine colour and stability as well as wine astringency and aroma profile.

Pamela Nicolle is a Ph.D. student at Laval University. She has been studying the compounds involved in tannin retention of red interspecific hybrid grape wines cultivated in cold climate. She has over 10 years of experience in fermented beverage in France and Canada. She has an expertise in winemaking as well as in chemical and sensory analysis.

Karine Pedneault is an assistant professor at the Department of Sciences of Sainte-Anne University (Nova Scotia, Canada) and an associated research scientist in Institut de Recherche en Biologie Végétale (IRBV; Montreal, Canada). Karine Pedneault's research focuses on factors affecting the quality of ciders and wines produced in cold climate. She is interested in the relations between the growing conditions of horticultural fruit plants (vine, apple), the quality of fruits (sugars, acidity, aromas, tannins) and the quality of wines.


Kassara, S., Kennedy, J.A., 2011. Relationship between Red Wine Grade and Phenolics. 2. Tannin Composition and Size. J. Agric. Food Chem. 59, 8409–8412. doi:10.1021/jf201054p

Kyraleou, M., Tzanakouli, E., Kotseridis, Y., Chira, K., Ligas, I., Kallithraka, S., & Teissedre, P.-L., 2016. Addition of wood chips in red wine during and after alcoholic fermentation: Differences in color parameters, phenolic content and volatile composition. OENO One, 50, doi : 10.20870/oeno-one.2016.50.4.885.

Manns, D.C., Coquard Lenerz, C.T.M., Mansfield, A.K., 2013. Impact of processing parameters on the phenolic profile of wines produced from hybrid red grapes Maréchal Foch, Corot noir, and Marquette. J Food Sci 78, C696–702. doi:10.1111/1750-3841.12108

Nicolle, P., Marcotte, C., Angers, P., Pedneault, K., 2019. Pomace limits tannin retention in Frontenac wines. Food Chem 277, 438–447. doi:10.1016/j.foodchem.2018.10.116

Nicolle, P., Marcotte, C., Angers, P., Pedneault, K., 2018. Co-fermentation of red grapes and white pomace: A natural and economical process to modulate hybrid wine composition. Food Chem 242, 481–490. doi:10.1016/j.foodchem.2017.09.053

Pedneault, K., Dorais, M., Angers, P., 2013. Flavor of cold-hardy grapes: impact of berry maturity and environmental conditions. J. Agric. Food Chem. 61, 10418–10438. doi:10.1021/jf402473u

Pedneault, K., Provost, C., 2016. Fungus resistant grape varieties as a suitable alternative for organic wine production: Benefits, limits, and challenges. Scientia Horticulturae 208, 57–77. doi:10.1016/j.scienta.2016.03.016

Ribéreau-Gayon, P., Glories, Y., Maujean, A., Dubourdieu, D., 2006. Handbook of Enology, 2nd ed. Wiley.

Sacchi, K.L., Bisson, L.F., Adams, D.O., 2005. A Review of the Effect of Winemaking Techniques on Phenolic Extraction in Red Wines. Am J Enol Vitic 56, 197–206.

Springer, L.F., Sacks, G.L., 2014. Protein-Precipitable Tannin in Wines from Vitis vinifera and Interspecific Hybrid Grapes ( Vitisssp.): Differences in Concentration, Extractability, and Cell Wall Binding. J. Agric. Food Chem. 62, 7515–7523. doi:10.1021/jf5023274

Springer, L.F., Sherwood, R.W., Sacks, G.L., 2016. Pathogenesis-Related Proteins Limit the Retention of Condensed Tannin Additions to Red Wines. J. Agric. Food Chem. 64, acs.jafc.5b04906–1317. doi:10.1021/acs.jafc.5b04906


Posted by in Viticulture

Red grape pomace: a wine by-product with potential health benefits

By Letizia Bresciani

Epidemiological evidence has associated phenolic-rich foods with the prevention of several chronic pathologies, including cardiovascular diseases, diabetes, neurodegenerative diseases and some types of cancer (Zanotti et al,. 2015, Tresserra-Rimbau et al,. 2014, Liu et al,. 2014, Rothwell et al,. 2017). Due to these claimed, but not well clarified effects, the interest of consumers in polyphenol-rich foods increased exponentially in the last decades, with the consequent injection into the global market of several new products rich in phenolic compounds. Obviously, the claimed effects of any given product must be unequivocally demonstrated, and the potential benefits are strictly related to absorption, bioavailability and metabolism of the putatively bioactive compounds contained in it (Del Rio et al,. 2013, Rodriguez-Mateos et al,. 2014). Red wine production generates an important amount of grape by-products. Recent European policies encourage the re-utilization of these industry by-products, which may represent a readily available, low cost, innovative functional ingredients, exploitable to increase the bioactive fraction of a wide range of food products or beverages. Grape pomace is the major by-product of wine and grape juice industry and it represents a rich source of polyphenols, including anthocyanins and flavan-3-ols, in the form of monomers and oligomers (commonly known as tannins), together with flavonols, flavanones, phenolic acids and their derivatives, stilbenes and lignans. In the papers here discussed, a red grape pomace drink rich in polyphenols has been characterized and comprehensive pharmacokinetic and excretive profiles of phenolic metabolites after the acute administration of the drink (Castello et al,. 2018) have been performed. Moreover, the acute effects of the drink on glucose/insulin and triglyceride responses to a standard meal in healthy individuals and the relationship between plasma levels of phenolic metabolites and metabolic parameters (Costabile et al,. 2018) have been investigated.

In the first work, a total of 28 phenolic metabolites were quantified in the blood plasma of ten volunteers who consumed the red grape pomace drink. Phenyl-γ-valerolactones (VL) were the most abundant class of phenolic metabolites in circulation (63%) (Figure 1A). Additionally, 35 polyphenol metabolites were quantified in urine collected within 48 h after drink consumption. As reported for plasma, phenyl-γ-valerolactones (VL) were the main class of excreted phenolic metabolites (59%), followed by simple phenols and hydroxybenzoic acids (HB), hydroxyphenylpropionic and hydroxycinnamic acids (HPP) and (epi)catechins (CAT) (Figure 1B). Both in plasma and in urine, the phase II conjugates of 5-(3′,4′-dihydroxyphenyl)-γ-valerolactone were the highest contributors.




Figure 1: A) Relative plasma area under the plasma concentration-time curve (AUC0-24) calculated for phenolic metabolites after red grape pomace consumption. B) 48 h-excretion in urine of phenolic metabolites. VL: phenyl-γ-valerolactones (including phenyl-valeric acid-sulphate-glucuronide); HB: simple phenols and hydroxybenzoic acids; HPP: hydroxyphenylpropionic acids and hydroxycinnamic acids; CAT: (epi)catechins.

Figure 2: A) Cumulative urinary excretion of phenolic metabolites at 48 h. B) Relative contribution of each class of phenolic compounds to the total urinary excretion at 48 h. Phenyl-γ-valerolactones (VL, including phenyl-valeric acid-sulphate-glucuronide), simple phenols and hydroxybenzoic acids (HB), hydroxyphenylpropionic acids and hydroxycinnamic acids (HPP), and (epi)catechins (CAT). Subject #3 was excluded from these calculations because of a lack of compliance with the study protocol during the period 24–48 h.

A high inter-individual variability was demonstrated, both in plasma and in urine samples, and different patterns of circulating metabolites were unraveled. The variance (CV%) for each urinary excreted metabolite ranged from 20 to 167%, with a mean CV of 52%. Considering all the metabolite classes, the excreted phenolic metabolites varied between 348 and 844 μmol in 48h (Fig. 4A-B).
The potential health benefits of drink intake was evaluated on 12 healthy men in a second study. All participants consumed a drink rich in polyphenols or a control drink (no polyphenols), followed, after 3h, by a standard meal (960 kcal, 18% protein, 30% fat, 52% carbohydrate). Glycemic and triglyceride post-meal responses were similar between the test and the control drink. In contrast, postprandial insulin levels, and, consistently, the incremental area (iAUC0-5h) were significantly lower after red grape pomace drink than after control drink consumption (Figure 3).

Figure 3: Postprandial plasma insulin concentration and corresponding incremental area under the curve (iAUC) (means ± SEM) after the intake of the Red Grape Pomace Drink (RGPD) and Control Drink (CD) in young volunteers. § p < 0.05 for drink effect by Repeated Measures ANOVA; *p < 0.05 Different from Control (Paired sample t-test).

Insulin secretion index, calculated over 5h after the standard meal, was significantly lower (-18%), and insulin sensitivity (SI) index, significantly higher (36%) after red grape pomace drink consumption (Figure 4) with respect to control. Finally, a linear correlation analysis showed that, among the many circulating phenolic metabolites, gallic acid inversely correlated with insulin response and, quite expectedly, positively with insulin sensitivity, indicating gallic acid as the best predictor of the insulin sensitivity index, followed by epicatechin-glucuronide and dihydrocaffeic acid-sulphate. No other correlation reached the statistical significance.

Figure 4: Insulin Secretion (A) and Insulin Sensitivity (B) Indices (meas±SEM) after the intake of the Red Grape Pomace Drink (RGPD) and Control Drink (CD) in young volunteers. *p < 0.05 Different from Control (Paired sample t-test).

Figure 5: Correlation between plasma gallic acid concentration (iAUC0e8h) and Postprandial Insulin Response (iAUC0e5h) and Insulin Sensitivity Index (SI).

In conclusion, these two works demonstrate that the intake of a drink based on red grape pomace can deliver significant amounts of different phenolic metabolites to the human system. However, more attention should be addressed to inter-individual variability, regarding both the production of gut microbial-derived metabolites and the phase II metabolic step. Moreover, besides the acute nature and the small sample size of the second study, polyphenols from red grape pomace drink have been shown to improve insulin sensitivity, an effect likely mediated by the increase in plasma levels of gallic acid. The use of by-products originating from food production as potentially beneficial ingredients represents a very wise strategy both in terms of public health and circular economy.

Dr. Letizia Bresciani: Master’s degree in food science and Technology (2011) and PhD in Food Science (2016) at the University of Parma. Currently, she is a Post-Doctoral Research Fellow at The Laboratory of Phytochemicals in Physiology, Human Nutrition Unit, Department of Veterinary Science of the University of Parma (Italy), led by Prof. Daniele Del Rio. Her expertise includes characterization of phenolic compounds from vegetables and investigation of pharmacokinetics, absorption, metabolism, bioavailability and bioactivity of human and microbial phenolic metabolites, using principally in vivo models.

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