QUINIC ACID COMPOSITION IN ACTINIDIA

Quinic acid is a key intermediate for aromatic compound biosynthesis, and a major acid found in Actinidia deliciosa fruit. The fresh weight content of quinic acid in ‘Hayward’ fruit is at a maximum of about 2% between 28 and 42 days after anthesis and then declines to 0.8% at fruit harvest. The aim of this study was to compare these trends in Actinidia deliciosa with those of other kiwifruit species. Kiwifruit acids were analysed at different growth stages, and a study was conducted of the inheritance of quinic acid content in diploid Actinidia chinensis. There is a 3–26 fold difference in quinic acid content within seedling populations, and between different species of Actinidia. The quinic acid content of fruit shows a low level of inheritance and has a negative and moderate genetic correlation with citric acid concentration. In A. chinensis and A. deliciosa fruit, quinic acid accumulated rapidly and was around 4% of the fruit weight 75 days after anthesis (DAA), the amount of quinic acid thereafter declined rapidly until it was 0.8–1.0% of fruit weight at fruit harvest. In A. arguta, although similar trends were observed, the amount of quinic acid peaked at 1.5% total fruit weight. In contrast, citric acid content in all three cultivars increased slowly through fruit development and peaked at around 1.0% at fruit harvest. Quinic acid is a reservoir for onwards metabolism to many cyclic compounds, and the accumulation pattern indicated that quinic acid was stored in young fruit (<70 DAA) and utilised during subsequent fruit differentiation and development. Further studies of quinic acid metabolism are proposed as part of a wider view of fruit breeding in Actinidia species.