Abstract
The chemical composition of wine grapes changes qualitatively and quantitatively during the ripening process. In addition to the sugar content, which determines the alcohol content of the wine, it is necessary to consider the phenolic composition of the grape skins and seeds to obtain quality red wines. In this work, some imaging techniques have been used for the comprehensive characterisation of the chemical composition of red grapes (cv. Tempranillo and cv. Syrah) grown in a warm-climate region during two seasons. In addition, and for the first time, mathematical models trained with laboratory images have been extrapolated for using in field images, obtaining interesting results. Determination coefficients of 0.90 for sugars, 0.73 for total phenols, and 0.73 for individual anthocyanins in grape skins have been achieved with a portable hyperspectral camera between 400 and 1000 nm, and 0.83 for total and individual phenols in grape seeds with a desktop hyperspectral camera between 900 and 1700 nm.
Highlights
Progress has been made in the use of different imaging techniques for the evaluation of wine grapes and wine grape seeds
In the case of whole grapes, it was possible to measure very accurately the sugar content and to estimate families and some individual phenolic compounds from their spectra between 400 and 1000 nm
For the first time, it has been possible to transfer mathematical models trained on laboratory samples to field samples
Summary
At the same time, these components vary qualitatively and quantitatively throughout the maturation of the berries During this maturation, the phenomenon of veraison occurs, which leads to the loss of chlorophyll and the appearance of anthocyanin pigments in the skin. These anthocyanins will give the characteristic colour of red wine Both in the skin and seeds, other uncoloured phenols are synthesised and develop through polymerisation reactions that modulate the astringency of tannins in the berries and improve the taste quality of grapes. These uncoloured polyphenols play an essential role in the stabilisation of the colour of red wine, as they interact with anthocyanins and protect their structure through the phenomenon known as co-pigmentation [1]
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