1-Aminocyclopropane-1-Carboxylic Acid Levels in Ripening Apple Fruits

1-Aminocyclopropane-1-carboxylic acid (ACC) in amino acid fractions of apple fruits was assayed by chemical conversion to ethylene. The specificity of the assay was checked with other amino acids; homocysteine was the only naturally occurring compound found to yield significant amounts of ethylene in the assay. Analysis of the thiol content of apples showed that homocysteine could not be a significant source of interference. Interference from an uncharacterized component of amino acid fractions was less than 20% of the ACC level in unripe fruit and insignificant in ripe fruit. Liquid chromatographic assay gave results in close agreement with the standard assay. Higher apparent ACC levels were measured in unfractionated apple juice than in the standard assay. Both of these methods and the liquid chromatographic assay were used on a number of apple samples during ripening. All three methods showed that ACC increased 30–40 fold whereas ethylene production increased by a factor of 104. In individual apples the ACC level increased about one day later than ethylene production.