Abstract
Red wine grapes require a constant follow-up through analytical chemistry to assure the greatest wine quality. Wet chemical procedures are time-consuming and produce residues that are hard to eliminate. NIR (near infrared radiation) spectroscopy has been referred as an accurate, rapid, and cost-efficient technique to evaluate quality in many fruit species, both in field and in industry. The main objective of this study was to develop predictive models using NIR spectroscopy to quantify important quality attributes in wine grapes. Soluble solids content (SSC), titratable acidity (TA), total phenolic content, total flavonoids, total anthocyanins, and total tannins were quantified in four red wine grape varieties, ‘Aragonês’, ‘Trincadeira’, ‘Touriga Nacional’, and ‘Syrah’. Samples were collected during 2017 and 2018 along véraison. Prediction models were developed using a near-infrared portable device (Brimrose, Luminar 5030), and spectra were collected from entire grapes under near field conditions. Models were built using a partial least square regression (PLSR) algorithm and SSC, TA, total anthocyanins, and total tannins exhibited a determination coefficient of 0.89, 0.90, 0.87, and 0.88, respectively. The Residual Prediction Deviation (RPD) values of these models were higher than 2.3. The prediction models for SSC, TA, total anthocyanins, and total tannins have considerable potential to quantify these attributes in wine grapes. Total flavonoids and total phenolic content were predicted with a slightly lower capacity, with R2 = 0.72 and 0.71, respectively, and both with a RPD of 1.6, indicating a very low to borderline potential for quantitative predictions in flavonoids and phenols models.
Highlights
Introduction published maps and institutional affilIn modern viticulture, it is necessary to monitor the evolution of many quality parameters to adopt the best selective harvesting management and to produce high quality wines.Most of the phenolic compounds quantified in wine are derived primarily from the grape berry skin, and the most representative compounds in berry skin and seeds are flavonoids, anthocyanins, and tannins [1].Phenolic compounds in wine determine many of its sensory qualities, since they are related to colour, flavour, and taste, which make it essential to monitor these compounds in the vineyard during ripening
solids content (SSC) increased while titratable acidity (TA) decreased, and the evolution of both parameters was expected during this period
The results presented in this study have demonstrated the ability of NIR spectroscopy, in combination with a portable device, to quantify in entire grapes: SSC, TA, Total Phenolic Content, Total Flavonoids Content, Total Anthocyanins Content, and Total Tannins
Summary
Most of the phenolic compounds quantified in wine are derived primarily from the grape berry skin, and the most representative compounds in berry skin and seeds are flavonoids, anthocyanins, and tannins [1]. Phenolic compounds in wine determine many of its sensory qualities, since they are related to colour, flavour, and taste, which make it essential to monitor these compounds in the vineyard during ripening. In its constitution, a great part of phenolic compounds, which justifies the extreme importance of their determination during grape maturation [3]. Consumers are becoming even more demanding in terms of wine quality and curious about the product that they are consuming [4,5].
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