A degradação do amido da banana depende da ação combinada de α-amilase e ß-amilase em regiões de diferentes graus de cristalinidade do grânulo / The banana starch degradation depends on the combined action of α-amylase and ß-amylase in regions of different degrees of crystallinity of the granules

A banana é considerada um bom modelo de estudo para a transformação amido-sacarose, já que acumula um teor alto de amido durante o desenvolvimento, que é degradado durante o amadurecimento. Já foram detectadas em polpa de banana atividade e proteína relativa a várias enzimas supostamente envolvidas no processo de degradação do amido. Entre elas, a α-amilase, a ß-amilase, a amido fosforilase e as glucano-água-diquinases (GWD). Estas enzimas estão envolvidas em dois processos distintos de degradação de amido em plantas: o dependente da ação inicial da α-amilase e o dependente da fosforilação do grânulo pela GWD e PWD e posterior ação da ß-amilase. A dificuldade do estabelecimento da participação efetiva de cada enzima no processo de degradação do amido está associada a muitos fatores, entre eles a não-correlação entre atividade e real envolvimento em um processo, e a acessibilidade da enzima ao seu substrato. Aliado ao estudo da morfologia do grânulo de amido e suas modificações sofridas durante o processo de degradação que ocorre durante o amadurecimento do fruto, estudos in vitro que simulem a ação da enzima sobre o seu substrato poderiam ser mais efetivos no estabelecimento da real ação de dada enzima sobre o suposto substrato. Tentativas no sentido de obter as proteínas relativa à degradação não foram bem sucedidas. Assim, os ensaios de grânulos de amido isolados versus enzimas foram feitos com α-amilase e ß-amilase comerciais. O grau de fosforilação da amilopectina nas posições Glic-6 e Glic-3 foi determinado, condição necessária para o início da degradação do grânulo pela ß-amilase. Os resultados mostraram que os grânulos de amido isolados de bananas recém colhidas, ou verdes, já estão fosforilados e as enzimas responsáveis por esta fosforilação estão associadas aos grânulos. Após 72 h de incubação dos grânulos de amido com as enzimas hidrolítica, os grânulos foram separados do tampão contendo as enzimas e os produtos de hidrólise. Os sobrenadantes foram analisados por cromatografia líquida acoplada a detector amperométrico e os grânulos por Microscopia Eletrônica de Varredura (MEV) e microscopia de força atômica (MFA). Os resultados mostraram que a α-amilase hidrolisa preferencialmente regiões amorfas dos grânulos, com predominância de amilose, expondo as regiões mais cristalinas dos anéis de crescimento, enquanto que a ß-amilase parece atuar preferencialmente nas regiões cristalinas dos grânulos, degradando os bloquetes, que são formados por amilopectina. Pode-se concluir que ambas as enzimas parecem ser importantes no processo de degradação do amido da banana, com diferentes especificidades

Banana is considered a good model to study the starch-sucrose metabolism, since it accumulates a high starch content during development, which is degraded during fruit ripening. It have been detected in banana pulp some proteins and activities of several enzymes supposedly involved in starch degradation process. Among them, α-amylase, ß-amylase, starch phosphorylase and glucan-water-diquinases (GWD). These enzymes are involved in two separate processes of starch degradation in plants: the initial action of α-amylase dependent, and the starch granule phosphorylation by GWD and PWD enzymes and subsequent action of ß-amylase. The difficulty of establishing the effective participation of each enzyme in the starch degradation process is associated with many factors, including the lack of correlation between real activity and involvement in the process, and accessibility of the enzyme to its substrate. Allied to study the morphology of the starch granule and its modifications suffered during the process of degradation, which occurs during the fruit ripening, in vitro studies that simulate the action of the enzyme on its substrate could be more effective in establishing the real action of a given enzyme on the argued substrate. However, attempts to obtain the proteins related to the degradation process were unsuccessful. Thus, assays of isolated starch granules versus enzymes were made with commercial α-amylase and ß-amylase enzymes. The degree of phosphorylation of amylopectin in the Gluc-6 and Gluc-3 positions was determined, a necessary condition for the start of degradation by ß-amylase enzyme. The results showed that the starch granules isolated from freshly harvested bananas, or green, are already phosphorylated and the enzymes responsible for this phosphorylation is associated with the starch granules surface. After 72 h incubation of the starch granules with the hydrolytic enzymes, the granules were separated from the buffer containing the enzymes and the hydrolysis products. The supernatants were analyzed by liquid chromatography coupled with amperometric detector and the granules were visualized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The results showed that the α-amylase preferentially hydrolyzes amorphous regions of the granule, especially amylose, exposing more crystalline regions of the growth rings, whereas ß-amylase appears to act preferentially on crystalline regions of the granule, degrading blocklets that consist of amylopectin. It can be concluded that both enzymes appear to be important in the banana starch degradation process, with different specificities

Black leaf streak disease affects starch metabolism in banana fruit.

Black leaf streak disease (BLSD), also known as black sigatoka, represents the main foliar disease in Brazilian banana plantations. In addition to photosynthetic leaf area losses and yield losses, this disease causes an alteration in the pre- and postharvest behavior of the fruit. The aim of this work was to investigate the starch metabolism of fruits during fruit ripening from plants infected with BLSD by evaluating carbohydrate content (i.e., starch, soluble sugars, oligosaccharides, amylose), phenolic compound content, phytohormones, enzymatic activities (i.e., starch phosphorylases, α- and ß-amylase), and starch granules. The results indicated that the starch metabolism in banana fruit ripening is affected by BLSD infection. Fruit from infested plots contained unusual amounts of soluble sugars in the green stage and smaller starch granules and showed a different pattern of superficial degradation. Enzymatic activities linked to starch degradation were also altered by the disease. Moreover, the levels of indole-acetic acid and phenolic compounds indicated an advanced fruit physiological age for fruits from infested plots.

Plantain and banana starches: granule structural characteristics explain the differences in their starch degradation patterns.

Different banana cultivars were used to investigate the influences of starch granule structure and hydrolases on degradation. The highest degrees of starch degradation were observed in dessert bananas during ripening. Scanning electron microscopy images revealed smooth granule surface in the green stage in all cultivars, except for Mysore. The small and round granules were preferentially degraded in all of the cultivars. Terra demonstrated a higher degree of crystallinity and a short amylopectin chain length distribution, resulting in high starch content in the ripe stage. Amylose content and the crystallinity index were more strongly correlated than the distribution of amylopectin branch chain lengths in banana starches. α- and ß-amylase activities were found in both forms, soluble in the pulp and associated with the starch granule. Starch-phosphorylase was not found in Mysore. On the basis of the profile of α-amylase in vitro digestion and the structural characteristics, it could be concluded that the starch of plantains has an arrangement of granules more resistant to enzymes than the starch of dessert bananas.