Effect of nitrogen fertilisation on the free amino acid composition of kiwifruit during development and postharvest storage

Abstract

Total fruit-nitrogen (N) and free amino acids were measured in fruit from mature field-grown kiwifruit ( Actinidia deliciosa var. deliciosa) vines during fruit development (25 weeks) and postharvest storage (20 weeks at 0°C) to determine the nature of compositional changes in these compounds, and the effect of fertiliser N on their concentration. Vines used in this study ranged from those which had never received applied N, to those receiving 1420 kg N ha −1 prior to commencement. Concentrations of total-N declined sharply during the first 12 weeks of growth, while free amino-N increased to a maximum at 9 weeks after fruit set. Free amino-N and fruit-N concentrations were both constant during the remainder of fruit development and storage. Free amino acids comprised as little as 13% and as much as 28–40% of total fruit-N during fruit development. About 26% of total-N was present as free amino-N during storage. Arginine, asparagine, glutamine and γ-aminobutyrate were the principal free acids, accounting for 67–85% of the total amino acid composition and 82–92% of the total amino-N at all stages of development and postharvest storage. Fruit-N concentrations generally increased with increasing N application and were highly correlated with arginine concentrations, but not consistently with those of any other amino acid. The relative distribution of amino acids in fruit was largely unaffected by N treatment, except in fruit from unfertilised vines, where smaller percentages of arginine and asparagine were compensated for by increased percentages of aspartate, glutamate and γ-aminobutyrate. During storage, the concentrations of a number of amino acids increased, including glutamine, leucine, isoleucine, serine, threonine and valine. Concentrations of the other major species were essentially stable, while those of alanine and aspartate declined during the latter stages of storage.