Skin Color in Apples—Influence of Copigmentation and Plastid Pigments on Shade and Darkness of Red Color in Five Genotypes

Abstract

<jats:p>The biochemical and cytological mechanisms responsible for the differences in red color quality of apples <jats:italic>(Malus domestics</jats:italic> Borkh.) were investigated. Copigmentation, the increase in absorbance maxima (λ max) from anthocyanin and flavonoid interactions, is known to be a mechanism for producing variation in shade of red in flowers. In intact apple skin cells, the mean λ max was 550 nm, with no significant difference between genotypes. Furthermore, the ratio of flavonols and proanthocyanidins to anthocyanins was similar for all genotypes. Therefore, copigmentation is not a mechanism producing different shades of red in apples. Darkness of red skin was positively related to the proportion of red cells in the skin and the size of the vacuoles containing anthocyanins. Measurements of plastid pigments, chlorophyll, and carotenoids, compared with L<jats:sup>*</jats:sup>, a<jats:sup>*</jats:sup>, b<jats:sup>*</jats:sup> measurements, indicated that the visual blending of plastid pigments and anthocyanins has an important influence on red coloration of apple skin.</jats:p>

Non‐destructive evaluation of ripening and quality traits in apples using a multiparametric fluorescence sensor

“…Therefore, according to its definition (Equation 1), the ANTH index increased proportionally with the anthocyanins content. On the other hand, the optimal localisation of anthocyanins in the epidermis and outer hypodermal cells of apple peel10, 50 enables them to efficiently filter part of the green excitation light travelling towards the chlorophyll molecules in the inner hypodermal layers. This anatomical characteristic makes it possible to quantify anthocyanins in the epidermis by means of chlorophyll fluorescence measurements.…”

“…The colourless flavonols located in the peel epidermis of apples8 absorb ultraviolet (UV) radiation and can then protect the underlying tissues against UV‐induced damage 9. Flavonoids also help to stabilise peel colour by means of co‐pigmentation,10 defend against pathogen attacks,11 and act as scavengers of reactive oxygen species 12…”

Apple flavonols during fruit adaptation to solar radiation: spectral features and technique for non-destructive assessment

“…In addition to the concentration-dependent effect of Flv on spectral reflectance, the changes observed could be related with their intermolecular interactions such as copigmentation and aggregation of vacuolar Flv resulting in a considerable bathochromic shift of their absorption band as suggested for explanation of yellow coloration exhibited by flower petals of certain plant species (Smith and Markham, 1998;Markham et al, 2001). This mechanism is quite possible since local concentration of Flv in vacuoles of apple peel cells is extremely high, reaching 1.7 Â 10 À2 M (Lancaster et al, 1994). As a result of accumulation of high amounts of Flv the spectral features of Chl a in the Soret band were masked by Flv absorption both in whole apple fruit reflectance (Figs.…”

Comparative study of phenolic profile of fruit and juice samples of a progeny of ‘Meana’ × ‘Florina’ from an Asturian cider apple breeding program

“…Flavonols are minor compounds essentially located in apple peel, being partially responsible for the peel color of some varieties [33]. Quercetin glycosides are main apple flavonols, although several isorhamnetin derivates have been also quantified for the first time in apple fruit in the present work However, apple juice samples present very low levels of quercetin glycosides (isorhamnetin glycosides found in apples were not detected in juice samples), due to the fact that they are mainly located in the peel.…”