Comparison of analytical methods for the determination of condensed tannins in grape skin

Background and Aims: Condensed tannins extracted from grapes are an important organoleptic component of wine. Assessing tannin level in grapes requires an effective analytical method. This study compared the efficacy of three analytical methods. Methods and Results: Condensed tannin levels were measured in 38 grape skin samples by protein and methylcellulose precipitation and by high‐performance liquid chromatography (HPLC)‐phloroglucinolysis. Total phenolics were determined by absorbance at 280 nm. Tannin levels by protein and methylcellulose precipitation were of similar magnitude, while levels determined by HPLC‐phloroglucinolysis were generally higher. No correlation was found between the level of phenolics and tannins by any of the methods employed. Neither was there a correlation between tannin levels determined by HPLC‐phloroglucinolysis and by precipitation, although previously a strong correlation had been reported between protein precipitation and HPLC‐phloroglucinolysis in wine. Conclusions: The ratio of tannin to non‐tannin phenolics is highly variable between cultivars. Each analytical method measures a different fraction of the tannin extracted from grape skin. Significance of the Study: The disparity between analytical methods requires that method selection reflect the decision‐making that will utilise the information produced. For example, protein precipitation of tannins by bovine serum albumin (BSA) has been correlated with perceived astringency; consequently this may be the best indicator of potential mouthfeel.     

Review: Condensed tannin and grape cell wall interactions and their impact on tannin extractability into wine

It has been suggested that tannin extraction from grape berries into wine is limited by tannin binding to cell walls. Here we review the current state of knowledge and identify gaps in research that would enable characterisation of these interactions. Such characterisation could improve tannin extraction management in winemaking. The work identified in this review supports the hypothesis that tannin–cell wall interactions are formed by hydrogen bonding and hydrophobic interactions with the binding capacity of the cell walls influenced by tannin and polysaccharide structure and composition. Cell wall changes during berry development may increase the tannin-binding capacity of cell walls, while tannin structure may also influence its affinity for cell wall material. This review also identifies the need to investigate cultural and environmental factors that affect tannin and polysaccharide composition, to characterise the tannin-binding capacity of cell walls and to develop methods for assessing tannin-binding capacity of fruit prior to harvest. It is envisaged that a detailed understanding of tannin interactions with other components in the grape would lead to a predictive model for extractability of condensed tannins into wine.     

Quantification of condensed tannins by precipitation with methyl cellulose: development and validation of an optimised tool for grape and wine analysis

A precipitation assay is presented that enables tannin measurement in matrices of red wine, 50% ethanol grape extract and aqueous tannin solutions. By exploiting the polysaccharide polymer methyl cellulose to precipitate tannins, the absorbance of phenolics at 280 nm before and after tannin precipitation (subtractive approach) can be obtained, thus enabling selective measurement of tannin only. This methyl cellulose precipitable (MCP) tannin assay allows complete precipitation of tannin from red wine and from grape homogenate extracts. The subtractive assay is both simple and robust, selective for condensed tannins and does not suffer interference from other 280 nm-absorbing phenolics such as anthocyanins or catechins. Matrix effects have only minimal impact on the assay performance and validation parameters indicate a robust performance. There was good correlation between tannin measured by reverse-phase HPLC and the MCP tannin assay for 121 Australian red wines ( r = 0.74) and also 54 grape extracts ( r = 0.79). We envisage that the technical simplicity of this tannin assay will enable widespread research and field applications. In addition, an alternative format that requires re-solubilisation of the tannin-polymer pellet in acetonitrile is reported, which is particularly suitable for measurement of smaller tannin concentrations. Notwithstanding that option, technical requirements of the re-solubilisation step lead us to suggest that the subtractive format would be simple for adoption by wine industry practitioners.     

Effect of the Prefermentative Addition of Five Enological Tannins on Anthocyanins and Color in Red Wines

Abstract: The effects of prefermentation addition of 5 exogenous tannins with different‐origin anthocyanins and color characteristics were investigated in “Cabernet Sauvignon wines” at the end of alcoholic fermentation and the end of malolactic fermentation, and after 6 mo and 9 mo of bottle aging, respectively. The results showed that the application of GSKT2 could significantly retard the degradation of most anthocyanins in the process of alcoholic fermentation and the decrease of some pyranoanthocyanins during the subsequent 3 stages, thus causing more yellowness of wine in comparison with the control. Three other condensed tannins, GSKT1, QUET, and GSET, had a positive impact only on several anthocyanin components. Four condensed tannins all contributed to more redness, suggesting that the action mechanism might be to protect wine against oxidation or contribute to form copigmented anthocyanidins, or polymeric pigments. The application of FOLT (hydrolysable tannin) did not produce any influence on wine redness even after 9 mo of bottle aging. This work provides some reasons for the reasonable application of tannin additives. Practical Application: The prefermentative application of condensed tannins overall could protect some pigment components from degradation and enhance wine redness. Tannin additives with different origins have different effectiveness. The tannin additive obtained from grape skins, like GSKT2, could produce significant promotion on both redness and yellowness in wine. The prefermentation addition of hydroxylase tannin like FOLT seems not to have a significant effect on wine color.     

Impact of Processing Parameters on the Phenolic Profile of Wines Produced from Hybrid Red Grapes Maréchal Foch,Corot noir,and Marquette

Phenolic extraction in hybrid and interspecific wine grape cultivars is poorly understood, especially in terms of the impact of fermentation and enological conditions on condensed tannins and anthocyanins. Following fractionation via solid‐phase extraction and high‐performance liquid chromatography, phenolic profiles of must and wine from red hybrid grape cultivars Maréchal Foch, Corot noir, and Marquette were examined to assess the impact of enzyme and tannin addition, cold soak, and hot press during vinification. Across cultivars, hot press treatments resulted in the greatest extraction of condensed tannin, anthocyanin, and other monomeric phenolic compounds in musts, and treatments that increased skin contact time or cellular degradation during fermentation produced higher concentrations of tannins, anthocyanins, and flavonols. However, these increases were transient, evincing incomplete carryover into finished wines. Depending on initial must extraction, diglucoside forms of anthocyanins were either selectively extracted or selectively retained throughout fermentation when compared to their monoglucoside counterparts. Typical of hybrid grapes, tannin concentrations across cultivars were low, even under hot press conditions. For condensed tannins and anthocyanins, a cultivar‐specific, stable‐state concentration and phenolic profile emerged regardless of fermentation conditions. Due to the high levels of diglucoside anthocyanins and low levels of condensed tannins, it is expected that the color development and profile in these wines produced from hybrid grape cultivars will be dictated by the monomeric anthocyanins and their potential role in copigmentation processes involving other monomeric phenolic species, as opposed to the formation of polymeric color pigments.     

Microwave Maceration of Pinot Noir Grape Must: Sanitation and Extraction Effects and Wine Phenolics Outcomes

Pinot noir grapes have a unique phenolic profile which can impinge on the extraction and stabilisation of compounds such as anthocyanins and tannins which contribute to the colour and mouthfeel of red wine. This study examined the concentration of phenolic compounds in Pinot noir grape must and wine following application of a novel microwave maceration treatment for red grape must. Microwave maceration was shown to be highly effective for extraction of phenolics from grape solids into grape juice. When juices were fermented to wine, ultraviolet–visible spectrophotometry showed microwave maceration was associated with significantly higher concentrations of total phenolics, anthocyanin, tannin and pigmented tannin in wine at 18 months bottle age, compared with control wine. Mean tannin concentration in microwave treatment wine was 0.60 gm/L at 18 months, compared with 0.14 gm/L in control wine. The microwave treatment was also associated with a substantial and rapid decrease in the grape-associated yeast population, compared with control maceration, and a shorter lag phase at the outset of alcoholic fermentation. Based on this study, microwave maceration warrants further investigation as a potential industrial-scale application in red winemaking.     

不同皮渣浸渍发酵时间对葡萄酒中缩合单宁构成及感官品质的影响

为明确不同皮渣浸渍时间对葡萄酒中缩合单宁的影响,以赤霞珠和西拉为材料,进行不同浸渍发酵时间处理,对葡萄皮和葡萄籽以及葡萄酒中缩合单宁的含量、组成、缩合单宁以及相关口感指标等进行了分析。结果表明,不同葡萄品种中缩合单宁的初始含量、聚合度及没食子酰化率都有显著差异（P<0.05）。葡萄皮中缩合单宁的平均聚合度显著高于葡萄籽（P<0.05）,而葡萄皮缩合单宁的没食子酰化率则显著低于葡萄籽缩合单宁（P<0.05）。葡萄皮和葡萄籽中缩合单宁组成的最大差异是葡萄籽缩合单宁中不含有（?）-表棓儿茶素亚单元,而且末端单元主要是由（+）-儿茶素、（?）-表儿茶素和（?）-表儿茶素没食子酸酯组成。皮渣浸渍时间对葡萄酒中缩合单宁的组成及含量都有明显影响。随着浸渍时间的延长,葡萄酒中缩合单宁的总含量呈上升趋势,而平均聚合度则呈下降趋势。不同品种的葡萄酒之间缩合单宁含量也存在显著差异（P<0.05）,这与不同葡萄品种中酚类物质的可浸提率有关。葡萄酒中葡萄皮缩合单宁的占比一直显著高于籽粒缩合单宁的占比（P<0.05）,说明葡萄皮中缩合单宁比葡萄籽缩合单宁更容易浸提到葡萄酒中。相对于苦味和酸味,不同浸渍时间处理对葡萄酒的涩味影响更为显著（P<0.05）,综合考虑酒体的丰满度和口感的平衡,皮渣浸渍时间选择14 d左右更好一些。     

添加葡萄籽单宁对橡木桶陈酿‘赤霞珠’和‘马瑟兰’干红葡萄酒香气的影响

采用气相色谱-质谱联用法和感官分析排序法,研究橡木桶陈酿前添加葡萄籽单宁（200 mg/L）对陈酿12 个月后‘赤霞珠’和‘马瑟兰’干红葡萄酒香气组分和感官特征的影响。结果表明：添加葡萄籽单宁对2 个品种葡萄酒香气的影响各异。葡萄籽单宁添加促进了橡木桶陈酿期间‘赤霞珠’葡萄酒中香草酸、香草醛、香草酸乙酯、糠醛、乙酰呋喃和糠醇等橡木来源香气物质的浸出,而抑制‘马瑟兰’干红葡萄酒中糠醛、乙酰呋喃、糠醇、5-甲基糠醛和5-羟甲基糠醛等橡木来源香气物质的浸出。添加葡萄籽单宁后,‘赤霞珠’葡萄酒的生青味和浆果香降低,烘烤味增强,‘马瑟兰’葡萄酒的生青味和花香略有增强,对陈酿型干红葡萄酒的生产具有重要指导作用。     

Impact of exogenous tannin additions on wine chemistry and wine sensory character

Tannins are an important part of wine quality and are frequently added during winemaking. Tannin additives and their impact on wine are poorly documented. This work sought to characterize a range of enological tannins and their contribution to wine quality. Enological tannins were analysed for protein precipitable tannins and iron reactive phenolics. One tannin product was added to a Merlot wine during barrel ageing, at a range of concentrations from 60 to 300 mg/l. Condensed and hydrolysable tannins were added to Cabernet Sauvignon wine post-pressing at a recommended and excessive rate. Wines were analysed for anthocyanin, small and large polymeric pigment, precipitable tannin, iron reactive phenolics and sensory character. Enological tannins contained 12-48% tannin and recommended additions had little impact on wine tannin. High tannin additions were readily measured in the wines and were discriminated in sensory analysis with lower intensities of most parameters except brown colour, bitterness and earthy character. Recommended addition rates are too low to impact the measured tannin concentration of Merlot and Cabernet Sauvignon wines from Washington (USA). High enological tannin additions had a measureable impact on final wine had a negative impact on sensory character. Tannins are added to wines for a range of reasons and represent one of many input costs in an industry increasingly seeking efficiencies in response to global economic circumstances, over-supply and an ongoing price point squeeze. This research suggests many tannin additions may be unjustified and have limited or negative impacts on quality.     

陕西泾阳赤霞珠葡萄冷冻处理酿酒特性研究

葡萄酒中多酚、单宁等功能性成分主要来源于葡萄果皮中,为提高葡萄酒中的酚类物质含量,改善葡萄酒的口感,试验以陕西泾阳赤霞珠葡萄浆果为原料,分别在-20℃和-35℃两种不同温度下进行冷冻处理葡萄浆果并进行小容器酿酒试验,研究了葡萄原料经冷冻处理后葡萄酒中理化指标的差异变化,以及冷冻处理对葡萄酒感官特性的影响。结果表明：赤霞珠葡萄原料经-20℃和-35℃两种不同温度冷冻处理后,葡萄酒中单宁和总酚物质的含量显著增高,且-20℃冷冻处理后含量最高,其中单宁含量为29.54mg/L,总酚含量为129.71mg/L;葡萄原料经-20℃冷冻处理后,葡萄酒的外观、口感和总体评定显著提高。     

Comparison of fining red wines with purified grape pomace versus commercial fining agents: effect on wine chromatic characteristics and phenolic content

The large quantity of grape pomace (seeds, skin, and peduncle) produced during the winemaking process can be a problem and the search for procedures which could permit their valorisation is considered an important issue. This study investigates the use of purified grape pomace as a fining agent for reducing the level of some wine phenolic compounds, especially tannins. For this, purified grape pomace was applied to three young red wines of different phenolic composition and the results were compared with the effect of some common commercial fining agents. The results demonstrated that grape pomace can be used to decrease the wine tannin content with similar results to those obtained with casein, while also reducing anthocyanin content although to a similar extent to when bentonite is used. The effect of purified Monastrell grapes pomace is similar in the three different studied wines although it affected the most to wines with high monomeric anthocyanin content.     

不同单宁提升赤霞珠干红葡萄酒品质的比较分析

本研究以新疆石河子产区所种植的赤霞珠葡萄为实验原料,通过在酒精发酵前分别以两种不同浓度（200 mg/L、400 mg/L）添加4种不同种类的单宁（橡木单宁、缩合单宁、葡萄单宁、鞣花单宁）,探究4种不同种类的单宁在不同添加量下对新疆产区红葡萄酒色泽及口感的影响。结果表明：当所有单宁的添加量在200 mg/L时,葡萄酒的色泽都有所提升,其中添加缩合单宁200 mg/L时,效果最为明显,色度值为21.52,该处理下葡萄酒的色度高出对照组27.25%,且随着陈酿进行到6个月时,添加缩合单宁200 mg/L的葡萄酒色度依然最高,色度值为24.38,且色泽稳定性较好,酒体呈现深宝石红色,香气较浓郁,带有甘草香。实验表明单宁的添加可以改善葡萄酒陈酿后的色泽稳定性,同时使得香气更加浓郁。该实验为新疆石河子产区的实际生产提供理论依据。     

Oenological tannins: a review

This review is a state‐of‐the‐art summary of current literature on the commercial oenological tannins that are often added to wine. These tannins can come from different origins, which affect their composition and characteristics. The two main sources of oenological tannins are grapes and oak wood. This review describes methods to quantify and characterise oenological tannins and indicates that these methods also need to be improved. These tannins have different interactions with proteins as well as with wine components such as anthocyanins and other phenolics in wine. The suppliers of commercial tannins often emphasise that these products can stabilise colour in red wine and influence the mouthfeel of the wine, among other things. The literature, however, suggests that the addition of these tannins often does not lead to large differences in the chemical profile of the wine and sometimes even leads to unwanted sensory characters being observed in the wine. More research clearly is needed regarding the role of oenological tannins in wine.     

葡萄酒中单宁含量调查与口感关系的分析

目的 通过测定不同产地、不同品种、不同类型的524支进出口葡萄酒中单宁的含量,进一步分析葡萄酒中的单宁与口感质量的关系。方法 将样品用蒸馏水稀释100倍,以没食子酸为标准物质,采用分光光度法对葡萄酒中的单宁进行定量分析。结果 该方法简单可靠,试剂用量少,操作方便,快速准确,仪器设备简单。在0 mg/L~5.0 mg/L范围内线性关系良好,相关系数为0.9999;单宁添加回收率在86.7%~120%之间,平均回收率达103.8%。产地方面,意大利的红葡萄酒中单宁含量最高,平均为2.70 g/L;品种方面,黑皮诺酿造的红葡萄酒中单宁含量较多,平均含量为3.15 g/L;国产葡萄酒方面,云南产区的葡萄酒中单宁含量相对较高,平均为2.51 g/L。结论 葡萄酒中单宁含量与葡萄品种、产地、酒类型有关;柔顺指数超过5.0的葡萄酒,口感与品质良好。     

干红树葡萄酒与干红葡萄酒功能成分及其抗氧化活性对比

分别测定干红树葡萄酒与2种干红葡萄酒(法国干红葡萄酒、国产干红葡萄酒)中的总多酚、总黄酮、白藜芦醇、单宁、酚酸、维生素、花青素及矿物质等功能性成分,采用DPPH法、ABTS法、邻二氮菲法和FRAP法分析3种酒的抗氧化能力,并对其差异进行分析比较。结果表明:干红树葡萄酒与2种干红葡萄酒功能成分种类及含量各有特点和优势。干红树葡萄酒中没食子酸、VA、VC、Mn与Zn含量均极显著高于国产干红葡萄酒和法国干红葡萄酒;法国干红葡萄酒中总多酚、总黄酮、白藜芦醇、儿茶素、咖啡酸、香豆酸、阿魏酸、矢车菊色素及Fe含量均极显著高于国产干红葡萄酒和干红树葡萄酒;国产干红葡萄酒中单宁、VD、飞燕草色素、矮牵牛色素、天竺葵色素、芍药色素、锦葵色素、Ca和Mg含量均极显著高于法国干红葡萄酒和干红树葡萄酒。3种酒抗氧化活性亦各具特色,树葡萄红酒对DPPH·的清除能力最强,法国干红葡萄酒对·OH的清除能力最强,国产干红葡萄酒对ABTS~+的清除能力及对铁离子的还原能力最强。     

Yeast and bacterial modulation of wine aroma and flavour

Wine is a highly complex mixture of compounds which largely define its appearance, aroma, flavour and mouth‐feel properties. The compounds responsible for those attributes have been derived in turn from three major sources, viz. grapes, microbes and, when used, wood (most commonly, oak). The grape‐derived compounds provide varietal distinction in addition to giving wine its basic structure. Thus, the floral monoterpenes largely define Muscat‐related wines and the fruity volatile thiols define Sauvignon‐related wines; the grape acids and tannins, together with alcohol, contribute the palate and mouth‐feel properties. Yeast fermentation of sugars not only produces ethanol and carbon dioxide but a range of minor but sensorially important volatile metabolites which gives wine its vinous character. These volatile metabolites, which comprise esters, higher alcohols, carbonyls, volatile fatty acids and sulfur compounds, are derived from sugar and amino acid metabolism. The malolactic fermentation, when needed, not only provides deacidification, but can enhance the flavour profile. The aroma and flavour profile of wine is the result of an almost infinite number of variations in production, whether in the vineyard or the winery. In addition to the obvious, such as the grapes selected, the winemaker employs a variety of techniques and tools to produce wines with specific flavour profiles. One of these tools is the choice of microorganism to conduct fermentation. During alcoholic fermentation, the wine yeast Saccharomyces cerevisiae brings forth the major changes between grape must and wine: modifying aroma, flavour, mouth‐feel, colour and chemical complexity. The wine bacterium Oenococcus oeni adds its contribution to wines that undergo malolactic fermentation. Thus flavour‐active yeasts and bacterial strains can produce desirable sensory results by helping to extract compounds from the solids in grape must, by modifying grape‐derived molecules and by producing flavour‐active metabolites. This article reviews some of the most important flavour compounds found in wine, and their microbiological origin.     

陕西合阳地区白色酿酒葡萄果实品质调研

以白色酿酒葡萄品种‘霞多丽’‘爱格丽’‘雷司令’‘小芒森’和‘贵人香’为试材,在陕西省合阳县气候条件下探讨葡萄成熟过程中浆果的还原糖、总酸的变化趋势,并测定成熟果实的可溶性固形物、果皮中总酚和单宁含量。结果表明‘爱格丽’在8月中、下旬成熟;‘雷司令’‘贵人香’和‘霞多丽’在9月上旬成熟;‘小芒森’在9月中旬成熟。成熟时‘小芒森’的含糖量最高,‘爱格丽’次之,‘雷司令’较低;含酸量‘小芒森’最高,‘霞多丽’最低,5个品种的糖酸比均大于20。‘贵人香’和‘霞多丽’的总酚和单宁含量较高。综合来看,‘爱格丽’与‘小芒森’可作为合阳地区白色酿酒葡萄的主推品种,‘贵人香’与‘霞多丽’为次要栽植品种,研究结果将为合阳地区酿酒葡萄的种植示范和推广提供参考和依据。     

Contributions of mass spectrometry in the Australian Wine Research Institute to advances in knowledge of grape and wine constituents

Since 1971 mass spectrometry (MS) has made a significant contribution to wine research at the Australian Wine Research Institute (AWRI). In the past decade (1995–2004), MS has been involved in an expanded range of studies and now accounts for approximately 40% of AWRI publications appearing in peer‐reviewed scientific journals. Studies involving MS include the analysis of grape‐derived and fermentation‐derived volatiles, oak volatiles, taint compounds, proteins, pigments and tannins. We discuss the contribution MS has made to wine research at the AWRI and the significant advances made by key scientists in this area. In particular, this review focuses on three main areas of analysis of compounds important to wine quality – volatile aroma and off‐flavour compounds, involatile larger molecules such as proteins and tannins, and investigations into taint problems.     

橡木中的鞣花单宁对葡萄酒质量的影响

鞣花单宁是橡木中的主要单宁，是影响橡木桶贮葡萄酒质量的重要因素之一。影响葡萄酒中鞣花单宁含量的因素有橡木来源、橡木桶的制桶工艺、橡木中鞣花单宁的可浸提比例和橡木桶贮存过程中鞣花单宁的化学变化。鞣花单宁可引起葡萄酒的感官特性、质量、蒸馏酒风味和葡萄酒中多酚含量的变化。(孙悟)     

Application of flow nephelometry to the analysis of the influence of carbohydrates on protein–tannin interactions

The flow nephelometric technique was recently introduced to study the interaction between tannins and proteins. This technique was employed here to study the ability of the polysaccharides xanthan, dextran and gum arabic to disrupt the interactions between condensed tannin fractions from grape seed and bovine serum albumin (BSA). Xanthan was shown to have a higher ability to inhibit the aggregate formation of tannins and BSA than the other polysaccharides. Xanthan's ability to inhibit protein‐tannin complex formation was higher for condensed tannin fractions of smaller size and lower complexity. Copyright © 2006 Society of Chemical Industry