# Color Mutations Alter the Biochemical Composition in the San Marzano Tomato Fruit
## 4 Discussion
### Biochemical Changes in Fruits of Yellow Flesh and of Its Combinations with \(y\) and \(gf\)
Differently, tomato \(r\) lines will probably show a lower score for the aroma, considering that some of the apocarotonoids providing floral or fruity notes are less represented in yellow fruits. Biochemical Changes in Fruits of Colorless Fruit Epidermis and of Its Combinations with \(r\) and \(g\)f  
Multivariate analysis of targeted P compounds tightly grouped lines carrying the \(y\) mutation, an expected result as \(y\) is characterized by substantial modifications of the class of phenylpropanoids, mainly due to the lack of yellow pigment naringenin chalcone [15]. As also observed in the case of the NP fraction, untargeted and targeted metabolomes did not perfectly matched, suggesting the existence of larger, still unexplored, metabolic changes. The decrease or absence of naringenins also characterized \(y\) and its two double mutants, leading to the conclusion that \(y\) is epistatic on \(g\)f and \(r\) for this class of compounds. Compared to red SM fruits, kaempfer-hexose-deoxyhexose-pentose was higher in \(y\) mutants, even if many other kaempferols showed no differences. Similarly, several quercetin showed higher levels in lines carrying \(y\). Variations in the PHE pathways could explain the reduced phosphocholine levels detected in the three \(y\) mutants, since increased activity of pathways generating cuticular lipids in tomato fruit peel precedes that of phenylpropanoid and flavonoid biosynthesis pathways [58]. No substantial differences in carotenoids were found between \(y\) and SM, except the higher all-trans-neoxanthin levels in \(y\_gf\) and \(y\_r\). Conversely, toochromanol metabolism was altered in \(y\) mutant berries as there was a decrease in tocopherools, mainly affecting \(y\) and \(y\_r\), confirming previous reports [15; 59]. Among VOCs, differences were found in compounds derived from phenylalanine, such as eugenol and 2-phenylethanol, in line with the known alterations of \(y\) in the phenylpropanol branch of phenylalanine catabolism [54]. Indeed, a significant number of VOCs derived from amino acids, are considered to have an influence on tomato flavor and liking, such as guaiacol and eugenol. In addition, 2-phenylethanol is a main contributor to tomato flavor, increasing floral aroma and the perception of sweetness [60; 61], it is plausible that increase of these class of volatiles exerts a positive effect on the aroma in lines carrying the \(y\) mutation. In addition, \(y\) mutants were characterized by higher production of many fatty acid derivatives, which are the most abundant volatiles produced in the tomato fruit [62]. These VOCs include several C\({}_{5}\) compounds such as 1-penten-3-one or (E)-2-pentenal, and C\({}_{6}\) volatiles such as 1-hexanol, (\(Z\))-3-hexenal, (\(E\))-2-hexenal, or hexanal, among others, that are classified as \"green leaf\" volatiles due to their 'green' characteristic, with a fresh aroma of cut grass. Although some studies suggested a reduced impact on tomato flavor and no effect on consumer preference of these compounds [63; 64], others claim their potential impact on overall flavor intensity and liking [37]. In addition to variation of the aroma, \(y\) mutants are endowed of higher kaempferol and quercetin levels, but also present the drawback of lower naringenin and tocopherools. Since all toochromanols are potent lipid-soluble antioxidants and are essential dietary nutrients for mammals as vitamin E [65], this aspect represents a negative trait in \(y\) tomato lines. Therefore, the \(y\) mutation is to be considered as a source of more aesthetic (color) and organoleptic (aroma) than nutritional novelty. Although no clear relationship between colorless epidermis and fruit shelf-life, peculiar mechanical properties of the \(y\) epicarp were manifested by the fact that the peel of the mutant fruit was richer of lignin [15; 66].