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Yong-Soo Hwang, D.J. Huber and L.G. Albrigo

Cell wall composition and structure were examined in visually normal (N), granulated (G), and collapsed (VC) juice vesicles of `Marsh Seedless' grapefruit (Citrus paradisi) Macf.). According to gel-filtration data, VC appeared to be associated with a modification of water-soluble (WSP) and chelate-soluble (CSP) pectin molecular weight (Mr); small-Mr pectins increased, whereas large-J4. pectins decreased. The difference in M = of pectins did not appear to be mediated by polygalacturonases. Molecular weight of hemicelluloses did not differ. Granulated vesicles contained about two times more structural polysaccharides (pectins, hemicelhdose, and cellulose) than N vesicles, although hemicellulose and pectin M = modification were absent. Ion-exchange profiles of WSP, CSP, and hemicelhrlose fractions of VC and G vesicles were not different from those of N vesicles. Individual cells in vesicles with G and these vesicles themselves were much larger than those of N vesicles, whereas cells in VC were partially or completely collapsed.

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Yong-Soo Hwang, Jong-Pil Chun and Jae-Chang Lee

Physiological disorder occurred in a recently developed oriental melon cultivar, `Gumssaragi-Bunchun' (Cucumis melo var. makuwa), is involved with the appearance of water soaking area in placenta and can be extended to the pulp when severely affected. Physiological changes between normal and disordered fruits were compared. Ethanol soluble sugars were significantly decreased in both pulp and placenta tissue of disordered fruits whereas acidity was increased. Ethanol and acetaldehyde accumulation were confirmed in juice from disordered fruits, which were net detectable in normal ones. The contents of boron and calcium, especially water and HCl soluble calcium, were fairly low in disordered pulp. Also, there was a great difference in pectin content between both fruit tissue and severe hydrolysis of water soluble pectins isolated from disordered placenta was found by gel chromatography. However, the hydrolysis of pectins seemed not to be associated with the increase of wall hydrolase activities such as polygalacturonase and β-galactosidase.

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Jong-Pil Chun, Jae-Chang Lee and Yong-Soo Hwang

Pectins isolated from three cultivars with different maturity were compared to find a potential role of pectin modification on the fruit softening during fruit development and ripening. There was an increase of total pectins in developing fruit and no significant decrease of pectins was confirmed even after storage in `Tusgaru' (30 days) and `Fuji' (120 days), whereas soluble pectins, except NaOH-soluble ones, gradually increased in all cultivars. Gel-filtration profile and ion exchange chromatographic evidence of soluble pectins revealed that pectin degradation in apple fruit may not be associated with softening. However, a degree of esterification probably has an important role on softening of fruits. Further results will be discussed in the presentation.