Relationship between the blend of grapes of Bonarda D.O.C. red wine from Oltrepò Pavese and red color

Several parameters contribute to the definition of food quality and nowadays consumers’ demand regards high food safety, absence of defects, good sensorial properties, attractive appearance, authenticity and product traceability. As regards red wine, the color is one of the key sensorial characteristic. Red wine color is due to anthocyanins that occur naturally in grapes in the form of glycosides. Anthocyanins can be classified into many types based on chemical structure modifications, such as substituent groups on the B ring, type and number of conjugated sugar, and the presence or absence of an acyl group. In grapes and red wine there are all the six main types of anthocyanins: pelargonidins, cyanidins, delphinidins, peonidins, petunidins, and malvidins. The hue of anthocyanins may vary according to different substituent groups present on the B ring, and color saturation increases with increasing number of hydroxyl groups and decreases with the addition of methoxyl groups. Under highly acidic conditions, anthocyanins assume the form of a flavylium ion, exhibit a red color, and are relatively stable. The hue of anthocyanins may vary also according to the occurrence of sulfur dioxide and interaction with metals, such as iron. Of particular interest is the reaction with sulfur dioxide in which the carbons in positions 2 and 4 have a partial positive charge and therefore can attract nucleophilic groups such as the HS03-sulphonic acids. The subsequent loss of charge on the flavylium system leads to loss of color. As far as metals are concerned, the role of metals in wine is very important because metals affect the organoleptic characteristics of wine, including color. Because of the reductive conditions in wine, metals are mainly present in their lower oxidation states. They may exist as free ions and complexes with organic acids, amino acids, polysaccharides, peptides, proteins, and polyphenols. Especially condensed tannins and anthocyanins are the most important metal ligands, since these species have numerous coordination sites capable of binding metal cations (e.g., cyanidin-3-glucoside anthocyanin with two -OH groups in the ortho position can complex Cu and Zn and Fe at the ratio 2:1). In the present paper the color evaluation (performed both spectrophotometrically and with sensorial analysis) of Bonarda DOC red wine, a typical red wine produced in Oltrepò Pavese, was correlated to the chemical composition, and metal content. Furthermeore, the relationship between red wine color and blend of grapes is established