Abstract
Significant variation in organic acid components was detected in mature fruits of 101 apple accessions using high-performance liquid chromatography. The Malus species predominantly accumulated malic acid and citric acid, whereas wild fruits exhibited significantly higher levels of organic acid content than that in cultivated fruits. Differential accumulation patterns during fruit developmental stages was detected between malic acid and citric acid, thus suggesting a complex genetic regulation mechanism of organic acid metabolism in apple fruit. A highly positive correlation was detected between fruit total organic acid content with malic acid and citric acid content, thus suggesting that malic acid and citric acid are the principal determinants of apple fruit acidity. In contrast to malic acid, citric acid was predominantly detected in partial wild apples, while extremely low to undetectable concentrations of citric acid were observed in cultivated apple fruits; this is likely due to the genetic effects of parental characters. Our results provide vital information that could be useful for future studies on genetic analysis and improvement of organic acid accumulation in apple fruits.
Highlights
Fruit taste is an important trait majorly controlled by organic acids and, together with aromatic volatile compounds and soluble sugars, they strongly facilitate overall organoleptic quality and fruit stability [1,2]
To determine the components of organic acids in apple fruits, an artificial mixture containing six acids was prepared according to previous reports [6,10,25], including malic acid, citric acid, tartaric acid, quininic acid, lactic acid, and succinic acid
Organic acid components were characterized by high-performance liquid chromatography (HPLC), and our results revealed that malic acid and citric acid are the two predominant organic acids in Malus species, which is inconsistent with previous findings that malic acid is the major organic acid [6,14,15]
Summary
Fruit taste is an important trait majorly controlled by organic acids and, together with aromatic volatile compounds and soluble sugars, they strongly facilitate overall organoleptic quality and fruit stability [1,2]. Three major organic acids that accumulate in most fruits include malic, citric, and tartaric acid, and their final concentration in ripening fruits depends on the balance between the biosynthesis of organic acid, their degradation, and their vacuolar storage [3,4]. Organic acids are the main soluble constituents which influence important fruit qualities such as fruit coloration, the shelf life of fresh fruits, and ripeness; they can be used as an index of consumer acceptability [8].
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