Calcium treatments promote the aroma volatiles emission of pear (Pyrus ussuriensis 'Nanguoli') fruit during post-harvest ripening process

- Ca treatment increased 'Nanguoli' pear fruit aroma mainly in three ways.
- Ca increased β-glucosidase activity and released more bound aroma compounds.
- Ca treatment significantly increased the activities of ADH, PDC and LOX in fruit, thereby promoting synthesis of ester compounds.
- Ca treatment increased amounts of metabolic substrates, especially of unsaturated fatty acids, providing more precursors for ester metabolic process needs.

Aroma is an important factor affecting pear fruit quality. This study was undertaken to assess whether pre-harvest calcium sprays (15 d before harvest, applications at 4%, w/v, 120 d after full bloom) could improve aroma of Pyrus ussuriensis 'Nanguoli' pear fruit at harvest and post-harvest, and analyse the mechanism of metabolic regulation.Most compounds contributing to overall flavor in ripe 'Nanguoli' fruit at harvest and post-harvest were enhanced in response to pre-harvest calcium applications. Ester, especially acetyl ester, content was enhanced by calcium treatment; however, contents of alcohols, aldehydes and hydrocarbons were little affected. These effects were consistent with higher pyruvate decarboxylase and alcohol dehydrogenase activities in treated fruit, suggesting that calcium treatment increased supply of alcohols and acyl CoAs for ester biosynthesis. We also found that activities of β-glucosidases (involved in the emission of bound volatile compounds) were improved and the contents of bound volatiles were reduced by calcium treatment. At the same time, relative contents of linoleic and linolenic acids were improved by calcium treatment, expression of genes encoding fatty acid desaturase involved in the biosynthesis of unsaturated fatty acid precursors (linoleic and linolenic acids) for volatile aroma were improved. Calcium treatment increased content of volatile aromatic substances, both because calcium promoted the decomposition of bound aroma substances to free aromatic forms, and also promoted the synthesis of volatile aromatic substances in pear fruit.