Simão Renata Antoun, Silva Ana Paula Fioravante Bernardes, Peroni Fernanda Helena Gonçalves, do Nascimento João Roberto Oliveira, Louro Ricardo Pereira, Lajolo Franco Maria, Cordenunsi Beatriz Rosana
Programa de Engenharia Metalurgica e de Materiais, COPPE, Universidade Federal do Rio de Janeiro, CT-F 209, Cidade Universitaria, Ilha do Fundao, Caixa Postal 68.505, 21945-970, Rio de Janeiro, RJ, Brazil.
J Agric Food Chem. 2008 Aug 27;56(16):7410-5. doi: 10.1021/jf800467v. Epub 2008 Jul 26.
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.
未成熟的凯特芒果淀粉含量约为7%（鲜重），在离体果实成熟过程中会转化为可溶性糖。尽管淀粉向可溶性糖的代谢对芒果品质很重要，但关于这一主题的文献很少，且没有关于淀粉降解物理方面的研究。本手稿介绍了通过光学显微镜、扫描电子显微镜（SEM）和原子力显微镜（AFM）分析，淀粉颗粒在成熟过程中的一些物理变化。分析表明，未成熟的凯特芒果淀粉呈球形，直径约15微米，具有A型X射线衍射图谱，结晶度约为21%，成熟8天后略有变化。颗粒表面的AFM图像显示出超微结构，这与基于微晶块的颗粒组织一致。覆盖颗粒的生长层的AFM对比图像显示出直径为20纳米的纤维状结构，横向连接层与颗粒。部分降解颗粒的外观和降解模式与淀粉酶活性导致的观察结果相似，表明凯特芒果品种淀粉降解存在水解途径。这些结果为更好地理解果实中的淀粉降解提供了线索。
