Mango starch degradation. II. The binding of alpha-amylase and beta-amylase to the starch granule.

During mango ripening, soluble sugars that account for mango sweetening are accumulated through carbon supplied by both photosynthesis and starch degradation. The cultivar Keitt has a characteristic dependence on sugar accumulation during starch degradation, which takes place during ripening, only a few days after detachment from the tree. Most knowledge about starch degradation is based on seeds and leaves currently used as models. However, information about the mango fruit is scarce. This work presents the evaluation of alpha- and beta-amylases in the starch granule surface during fruit development and ripening. Extractable proteins were assayed for amylase activity and detected by immunofluorescence microscopy and correlated to gene expression. The results suggest that both amylases are involved in starch degradation during mango ripening, probably under the dependence of another signal triggered by the detachment from the mother-plant.

Mango starch degradation. I. A microscopic view of the granule during ripening.

The starch content of unripe mango Keitt is around 7% (FW), and it is converted to soluble sugars during the ripening of the detached fruit. Despite the importance of starch-to-soluble sugar metabolism for mango quality, little literature is found on this subject and none concerning the physical aspects of starch degradation. This manuscript presents some changes in the physical aspects of the starch granule during ripening, as analyzed by light microscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM). According to the analysis, unripe Keitt-mango-starch being spherical in shape and measuring around 15 microm, has A-type X-ray diffraction pattern with a degree of crystallinity around 21% with slight changes after 8 days of ripening. AFM images of the surface of the granules showed ultra microstructures, which are in agreement with a blocklet-based organization of the granules. The AFM-contrast image of growing layers covering the granule showed fibril-like structures, having 20 nm in diameter, transversally connecting the layer to the granule. The appearance of the partially degraded granules and the pattern of degradation were similar to those observed as a result of amylase activity, suggesting a hydrolytic pathway for the degradation of starch from mango cultivar Keitt. These results provide clues to a better understanding of starch degradation in fruits.

Estrutura do grânulo de amido de banana e sua relação com as enzimas que atuam no metabolismo amido-sacarose / Structure of the banana starch granule and its relation with the enzymes that attack in the metabolism starch-sucrose

A banana é considerada um bom modelo para o estudo da transformação amido-sacarose, já que acumula um alto teor de amido durante o desenvolvimento que é rapidamente degradado durante o amadurecimento. Várias enzimas e provavelmente mais de uma via metabólica estão envolvidas neste processo. Com isso, o objetivo deste trabalho foi estudar as características estruturais dos grânulos, bem como, a atuação das enzimas envolvidas em sua degradação. Os grânulos de amidos foram isolados de bananas controle (não tratadas) e submetidas a diferentes tratamentos: etileno, 1-MCP, frutos mantidos a 13'graus'C e frutos tratados com etileno e mantidos a 13'graus'C. Os resultados obtidos mostraram alta atividade de enzimas 'alfa' e 'beta'-amilases ligadas ao grânulo tanto por ensaios in vitro como por géis de eletroforese contendo amilopectina como substrato...