Changes in chlorophyllase activity, chlorophyll and carotenoid content of Giant Cavendish banana fruit peel during ripening were measured at tropical temperatures (30-34°C) and at 20°C to relate them to the greenish and yellow colours of the fruit ripened at these temperatures. At 30-34°C bananas remained green on ripening due to incomplete chlorophyll degradation while at 20°C complete degreening occurred and fruits turned yellow. Peel total carotenoid content remained constant during ripening and did not change with temperature. Free xanthophylls decreased while xanthophyll esters increased on ripening. Chlorophyllase activity increased during ripening and paralleled the respiratory climacteric, although activity was not consistently related to the differential degradation of chlorophyll at these temperatures. Exogenous application of ethylene and ethrel accelerated ripening, but had no effect on chlorophyllase levels, chlorophyll degradation and carotenoid content of bananas ripened at either 30-34°C or at 20°C.
Synthesis and accumulation of carotenoids in the flesh of Alphonso mangoes on ripening was found to be maximal in fruits stored at tropical ambient temperatures (28-32°C). Gamma irradiation of preclimacteric fruits at 25 krad did not affect the formation of carotenoids. Storage of preclimacteric fruits either irradiated or unirradiated at 7-20°C for 16-43 days caused a substantial reduction in carotenoid formation even when these fruits were subsequently ripened under optimal conditions. Regardless of storage temperature, carotenes always exceeded xanthophylls in the ripe fruits and, in general, irradiated fruits showed higher levels of carotenes in comparison with unirradiated samples. Ascorbic acid loss during ripening was maximum at ambient temperatures while lengthy storage at low temperatures caused a net increase in ascorbic acid levels. Irradiation seemed to accentuate the loss in ascorbic acid during ripening.
A Gram-positive and catalase positive Staphylococcus strain was found to be associated with spongy tissue defect of Alphonso mango. The organism was identified to species level by physiological, morphological and biochemical characterization and fatty acid profile. The strain was identified as Staphylococcus xylosus (IMTECH, India, Accession No. MTCC 7441). The optimal growth of the organism was observed in the pH range of 5.0-9.0 and temperature range of 10-45°C. It was mannitol and arabinose-positive and able to produce acid from various sugars. The organism was able to grow in a medium containing 2-10% NaCl. It was further identified to species level by genomic sequencing of 1,387 base pairs of DNA (Gene Bank accession No. EU019195). Based on nucleotide homology and phylogenetic analysis, the microbe was found to be S. xylosus. The survey of Alphonso mango trees with a known history of producing spongy fruits showed that some of the twigs, leaves and flowers were coated with a honeydew-like sticky substance and mango hopper insects were observed over the inflorescence. The source of contamination of spongy fruits by S. xylosus was in the sticky mass. Gram staining, the catalase test and morphological features of the culture isolated from the sticky mass exhibited characteristics identical to the Staphylococcus strain isolated from the spongy pulp. Pathogenicity tests on different varieties of mangoes, apples and guavas indicated that the disease was experimentally transmitted from infected to healthy fruits. This observation suggested that this organism develops spongy symptoms in the fruits post-harvest and lacks specificity. In inoculated fruits, catalase and peroxidase enzymes were expressed as in naturally infected fruits. This report shows that the infection by S. xylosus could be a major initiating factor for spongy tissue development in Alphonso mangoes. Keywords Internal physiological disorder . Mangifera indica . Spongy tissue . Staphylococcus . X-ray imaging Abbreviations BHI brain heart infusion BPA Baird Parker agar NA nutrient agar PCA plate count agar PDA potato dextrose agar PMSF phenylmethanesulfonyl fluoride POX peroxidase Eur J Plant Pathol (2008) 122:335-348
Isoelectric focusing on thin layers of Sephadex G-75 superfine gel followed by the print technique was used to investigate the presence of polyphenol oxidase isoenzymes in banana fruits. The enzyme preparation from pulp tissues of unripe "Dwarf Cavendish" bananas, partially purified by (NH&SO, fractionation, revealed 14 isoenzymes having both monophenolase (p-cresol substrate) and diphenolase (dopamine or catechol substrate) functions with isoelectric points (~1) in the pH range 45.5.Similarly, two strains of the cv "Red Skin" showed 10 and 13 isoenzymes with pI in the pH range 4-5.8, most of which were capable of hydroxylation of monophenols. Individual isoenzymes exhibited variations in their activity towards mono and odiphenols.
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