Abstract:

Ripe kiwi fruits were peeled, cut into crescent pieces and ground with aqueous metaphosphoric acid at a solid to
water ratio of 1:4 manually or by mechanical homogenization, and then the mash was ultrasonically extracted, centrifuged
and stored until being analyzed for the ascorbic acid content by liquid chromatography. The pretreatment conditions
including manual or mechanical grinding, extractant type and concentration, extraction temperature and time, and storage
conditions were optimized. Significant difference analyses were carried out among various processed samples. The results
showed that both manual grinding and mechanical homogenization were effective means of mashing the fruit, and the latter
method was superior to the former. Extraction temperature and time were identified as main factors influencing extraction
efficiency. An extraction temperature of 0 ℃ and 10 min extraction proved optimal. Accurate results were obtained when
the analysis was carried out immediately after sample preparation, significantly different from those reported for the stored
samples. Extractant type and concentration, separation of the mash, storage temperature, and light condition were main
factors affecting the accuracy of the determination of ascorbic acid using the stored samples. The samples prepared by
extraction using higher concentrations of acid and centrifugation should be stored at low temperatures in darkness if analysis
cannot be performed immediately. Though no significant difference in ascorbic acid content existed among three kiwifruits,
much attention should be paid to selection of the test material.

Key words: liquid chromatography, kiwi fruit, ascorbic acid, pretreatment technologies