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  • Author or Editor: Robert E. Paull x
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An invertase gene was isolated and its mRNA activity and protein levels were determined during papaya (Carica papaya L.) fruit development. A complete invertase cDNA (AF420223) and a partial sucrose synthase cDNA (AF420224) were isolated from papaya fruit cDNA libraries. The invertase cDNA encoded a predicted polypeptide of 582 residues (MW 65,537 Da), and was 68% and 45% identical with carrot apoplastic and vacuolar invertases, respectively. Key amino acids indicative of an apoplastic invertase were conserved. A full-length gene corresponding to the putative apoplastic invertase cDNA was isolated and was organized into seven exons and six introns. Exon 2 (9 bp long) encoded part of a highly conserved region (NDPNG/A). Invertase mRNA and activity levels increased during fruit maturation and sugar accumulation just before ripening. In contrast, sucrose synthase mRNA levels were high during early fruit growth and low during the fruit sugar accumulation stage. A 73-kDa cell wall extractable protein that cross-reacted with carrot apoplastic invertase antisera substantially increased during papaya fruit maturation and declined in full ripe fruit. The increase in invertase protein levels occurred 2 to 4 weeks before maturity and was markedly higher than the overall increase in enzyme activity at this stage. Subsequently, the increase in enzyme activity was higher than the increase in protein levels between 2 weeks before maturity and fully ripe. The results suggested that mRNA level and invertase activity were related to maturity. The data suggested that the invertase was apoplastic, and that post-translational control of enzyme activity occurred, in which a significant accumulation of invertase occurred before the peak of enzymes activity.

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Abstract

Compositional changes in ginger (Zingiber officinale Rosc.) rhizome stored at 22° or 12.5°C were studied. The rhizome surface Hunter “b” value increased from 9.2 to 18 in 4 weeks. Water loss did not become significant until 12 weeks of storage at 22°. There was little increase in dry matter of rhizomes stored at 12.5°. Rhizome crude fiber content, oil percentage, total phenols, and protein content did not change significantly. Rhizome total sugar increased significantly during storage at 12.5° for 32 weeks with pungency increasing 5-fold, as measured by gingerol content. No significant volatile flavor changes were noted, with rhizome variation being greater than storage effect. The changes in rhizome surface color did not lead to a significant loss in quality. The increase in pungency could be regarded as a favorable improvement in the fresh ginger market. The loss of water and increase in dry matter percentage significantly decrease overall appearance and quality of rhizomes stored at 22°.

Open Access

Breadfruit marketing is limited by its rapid ripening and deterioration after harvest; therefore, improved postharvest practices may facilitate breadfruit marketing. This study examined the effect of harvest maturity and 1-methylcyclopropene (1-MCP) on the postharvest quality of ‘Ma’afala’ breadfruit (Artocarpus altilis). Breadfruit was harvested at 13, 15, and 17 weeks after flowering, and half of each harvest was treated with 1 μL⋅L−1 of 1-MCP for 20 hours. During storage, the weight of the fruit, hand feeling, skin color, respiration rate, and ethylene production rate were evaluated every other day until the fruit deteriorated. Compared with untreated fruit, 1-MCP treatment delayed the climacteric respiratory peak by 6 days (65% delay), delayed complete softening by 7 days (63% delay), and increased uniformity in the number of days to the climacteric respiratory peak and complete softening. Skin discoloration was delayed during the earliest harvest period by 5 days (108% delay). Picking breadfruit at early harvest maturity may be useful for preventing discoloration, and 1-MCP may be useful for preventing softening.

Open Access