Abstract
Polyphenols have favorable antioxidant potential on human health suggesting that their high content is responsible for the beneficial effects of apple consumption. They control the quality of ciders as they predominantly account for astringency, bitterness, color and aroma. In this study, we identified QTLs controlling phenolic compound concentrations and the average polymerization degree of flavanols in a cider apple progeny. Thirty-two compounds belonging to five groups of phenolic compounds were identified and quantified by reversed phase liquid chromatography on both fruit extract and juice, over three years. The average polymerization degree of flavanols was estimated in fruit by phloroglucinolysis coupled to HPLC. Parental maps were built using SSR and SNP markers and used for the QTL analysis. Sixty-nine and 72 QTLs were detected on 14 and 11 linkage groups of the female and male maps, respectively. A majority of the QTLs identified in this study are specific to this population, while others are consistent with previous studies. This study presents for the first time in apple, QTLs for the mean polymerization degree of procyanidins, for which the mechanisms involved remains unknown to this day. Identification of candidate genes underlying major QTLs was then performed in silico and permitted the identification of 18 enzymes of the polyphenol pathway and six transcription factors involved in the apple anthocyanin regulation. New markers were designed from sequences of the most interesting candidate genes in order to confirm their co-localization with underlying QTLs by genetic mapping. Finally, the potential use of these QTLs in breeding programs is discussed.
Highlights
Apples can be separated in two main classes depending on their use: dessert and cider apples
The color is linked to the enzymatic oxidation of phenolic compounds, mainly chlorogenic acid, procyanidins, (+)-catechin and phloridzin, by polyphenoloxydase [2,3]
They were derived from a cross between the two hybrids X5210 and X8402 produced at the Institut National de la Recherche Agronomique (INRA) cider apple breeding program (Figure S1)
Summary
Apples can be separated in two main classes depending on their use: dessert and cider apples The latter are generally bitter and astringent, more rustic, and many cider varieties are more resistant to the major pathogens of apple. Phenolic compounds are responsible for bitterness, astringency, color and may partly contribute to aroma of cider. In relation to their tanning properties, procyanidins form aggregates with salivary proteins for astringency or receptors for bitterness, depending on their polymerization degree [1]. Apple consumption is inversely correlated with the development of diseases such as asthma, diabetes, cancer or cardiovascular diseases (for review see [5,6]) Their high phenolic content and antioxidant potential likely contribute to these protective effects. Interaction with other protective constituents such as dietary fibers plays a major role in the protection against these diseases [8,9]
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