Elsevier

Tetrahedron

Volume 71, Issue 20, 20 May 2015, Pages 3095-3099
Tetrahedron

Grape and wine sensory attributes correlate with pattern-based discrimination of Cabernet Sauvignon wines by a peptidic sensor array

https://doi.org/10.1016/j.tet.2014.09.062Get rights and content

Abstract

A major factor that contributes to the characteristic taste of red wine is its composition of a class of polyphenols known as tannins. Extended ripening times of grapes are known to influence the sugar and acid content of the fruit, but their effect on tannin composition is less understood. In this study, we demonstrate that a differential, cross reactive peptide-based sensing array can discriminate Cabernet Sauvignon wines made from grapes that were harvested at different stages of maturation. Linear discriminant analysis shows a clear discrimination of the wines based on their tannin content, which is in strong correlation with the harvest time. A partial least square regression model using the mouth-feel and taste descriptive sensory attributes of wine revealed a strong correlation of the sensing array to perceived astringency and bitterness, which is also well known to correlate with tannin concentration.

Introduction

There is a high demand in the winemaking industry for developing reliable and cost-efficient methods for quality and authentication assessment. Multiple analytical methods have been used for analysis of wine such as atomic absorption and inductively coupled plasma Mass Spectrometry for metal analysis,1 high performance liquid chromatography for phenolic compounds,2 and more recently multidimensional gas chromatography for aroma composition.3 However, descriptive sensory analysis using trained sensory panels has been the most reliable approach for the assessment of wine quality and flavor. Currently, there are emerging efforts to use electronic tongues based on differential sensing for multicomponent analysis and assessment of food products.4 For example, an electronic tongue composed of receptors for cations and anions, among other constituents, was recently developed for the identification and classification of beer with a success rate of 81.9%.5 Wine contains a large number of compounds that contribute to its taste and aroma. Correlation between wine descriptive sensory attributes and the cross reactivity of synthetic receptors is our approach for the development of multicomponent sensors suitable for grape and wine classification and the prediction of taste characteristics.

Grape ripening induces a series of biochemical reactions that influence the chemical composition of the fruit, and hence, the wine. Extended ripening time is known to result in wines with higher sugar content and lower acidity level, which in turn affects the sensory attributes of wine.6, 7, 8, 9, 10, 11, 12, 13, 14, 15 However, the effect of ripening time on the grape and wine tannin composition is more complex. In addition, there are methods used to create wines with enhanced flavors, which include blending of varietals, utilizing different yeasts for fermentation, and harvesting grapes at different times during the ripening period.16 The unique properties of a wine are made from a combination of the factors mentioned above among others.17 Recently, the ‘hang time’ approach in harvesting grapes has sparked a debate between the wineries and grape growers over best practices for determining the optimum harvest time.18 Hang time involves leaving grapes on the vine for extended time post ripening before harvesting, which leads to higher sugar concentration and lower acidity levels. The effect of extended grape ripening on Cabernet Sauvignon wine sensory attributes was recently investigated.19

We have developed peptide-based multicomponent sensing ensembles for fingerprinting red wine varietals.20 This approach utilizes arrays of cross reactive sensors that differentially bind tannins in wine. Tannins are a group of flavonoids that are found in the skin and seeds of grapes. Their structure is dictated by the grape's genome, and therefore, tannin composition is a diagnostic measure of wine varietals.21 The sensing ensembles function via Indicator Displacement Assay (IDA), a technique that has been routinely used to monitor the binding of analytes to receptors.22 Inspired by the senses of taste and smell, differential array sensing has increasingly gained interest over the traditional single analyte chemical sensing.23 In this investigation, we describe the application of an array of peptide-based receptors to fingerprint samples of Cabernet Sauvignon wines made using grapes harvested at different maturation times. Our array is composed of a combinatorial library of colorimetric pH indicators, divalent metals ions, and histidine-containing, metal-binding short peptides. Displacement of the indicator by the wine tannins causes a spectral change, which is monitored using UV–vis spectroscopy. In addition, we have sought to correlate the responses of our sensing array to the taste and mouth-feel sensory attributes of red wine.

Section snippets

General

The colorimetric indicators Chrome Azurol S (CAS) (65%), Bromopyrogallol Red (BPR), and Pyrocatechol Violet (PCV) (purity 100%) were purchased from Sigma–Aldrich. Nickel chloride hexahydrate (99.70%), copper (II) sulfate (purity 99.20%), and HEPES buffer were purchased from Fisher Scientific. All solid phase peptide synthesis materials were purchased from Novabiochem. Cabernet Sauvignon wines samples were provided by Dr. Heymann's research group at the University of California–Davis. Detailed

Results and discussion

Our group has previously utilized arrays of peptide based cross reactive receptors to discriminate red wine varietals based on their tannin composition.20 Herein, we describe the application of an array made of nine multicomponent sensing ensembles to differentiate samples of Cabernet Sauvignon wine made from grapes harvested at different post véraison maturation levels. Extended maturation times are known to increase the sugar content of grapes, lower the acidity, and increase the pH. Wine

Conclusions

In summary, we have shown that an array of supramolecular sensing ensembles composed of short peptides, divalent metal ions, and colorimetric indicators, can produce a unique pattern for Cabernet Sauvignon wines made from grapes harvested at different post-ripening times. Our findings clearly indicate that the peptide-based receptors are sensitive to subtle differences in the total tannin content of the same wine varietal. The variability among the ensembles shows that differential sensing is

Acknowledgements

We gratefully acknowledge the Freshman Research Initiative of the College of Natural Sciences at UT Austin. We also acknowledge the financial support of the National Science Foundation (Grant CHE-0716049), the Howard Hughes Medical Institute (Grant 52006985), and the Welch Foundation (Grant F-1151).

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