Abstract:

This study was a systematic investigation into the effects of pulping methods, extraction conditions and storage
conditions before analysis by liquid chromatography on the organic acid composition and contents of ‘Granny Smith’ apple
pulp. The results showed that manual grinding and mechanical homogenization were both effective means to crush apples,
and the selection depended on the test purpose and requirements and the specific circumstances. Extraction temperature and
oscillation time had no significant effects on extraction efficiency. We found extraction at 25 ℃ for 15 min with ultrasonic
oscillation to be optimal immediately followed by the liquid chromatographic analysis; otherwise, the crushed sample was
centrifuged before short-term storage at room temperature under light conditions. ‘Granny Smith’ apples were detected
to contain oxalic acid, quinic acid, malic acid, shikimic acid and citric acid. Their relative contents were in the following
descending order: malic acid > quinic acid > citric acid > oxalic acid > shikimic acid. Malic acid was the main organic
acid in all samples although there were tremendous differences in the content of each of the organic acids among
different apple fruits and among the contents of the organic acids in the same apple fruit. Thus, attention should be
paid to selection of the test material.

Key words: liquid chromatography, apple, organic acids, pretreatment technologies