CIEL*a*b* parameters of white dehydrated grapes as quality markers according to chemical composition, volatile profile and mechanical properties

In the oenological sector, the withering process is of particular importance in the production of dry and sweet dessert wines due to the total or partial use of overripe and/or dehydrated grapes.This complex process leads to several changes in the chemical–physical characteristics of white grape berries affecting the wine quality and, at the end of the dehydration period, different visual attributes are usually present in the berry skins.The aim of this work, therefore, was to study the properties of Erbaluce dried grapes of varying external colors, classified into three groups based on reflectance colorimetry (green, gold and blue).The chemical composition, volatile profile and mechanical attributes were investigated, focusing on establishing relationships between CIEL*a*b* parameters of dehydrated grapes and their chemical–physical characteristics.The higher values of the glucose–fructose ratio, together with the higher content of sugars, gluconic acid and glycerol, but lower titratable acidity, suggests the presence of Botrytis cinerea Pers. infection in blue withered berries, which has been microbiologically confirmed.Regarding the instrumental mechanical properties, blue dehydrated grapes were characterized by a lower skin hardness and higher skin thickness in agreement with the higher weight loss experienced. Finally, the determination of free and bound volatile compounds showed that some of them were only found in blue withered berries, δ-lactones being considered the main chemical markers of the noble rot infection that are important for the odor character. C-10 alkyl massoia lactone was the most abundant volatile compound in blue botrytized grapes.

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► CIEL*a*b* parameters are chemical–physical markers of dehydrated grape.
► Blue color of berry skin is a marker of the noble rot infection.
► Blue grapes are characterized by a high content of gluconic acid and δ-lactones.
► Green and gold grapes are characterized by high values of skin hardness.