Abstract
The kinetics and activity of pyruvate decarboxylase of ‘Golden Delicious’ apples under different storage conditions were investigated. The capability of a partially purified enzyme preparation from preclimacteric apples to decarboxylate pyruvate and to synthesize acetoin in vitro was tested by removing and adding co-factors (thiamine pyrophosphate (TPP), Mg 2+). The results show the presence of a TPP- and Mg 2+-dependent enzyme in the partially purified enzyme preparation which catalyses the synthesis of acetoin. There was an increase of pyruvate decarboxylase activity in crude extracts of ‘Golden Delicious’ apples in cold storage (+4°C), low pressure (LPS), LPS + O 2, LPS + C 2H 4 and controlled atmosphere (CA). The highest increase was found in apples from LPS and LPS + C 2H 4. However, no ethanol or acetoin accumulated in these apples. Ethanol and acetoin accumulation was detected in ripe apples during cold storage and LPS + O 2. The significance of in vitro pyruvate decarboxylase activity as an indicator of a metabolic shift towards fermentation in stored apples is discussed.
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